Merge branch 'master' into interfaceFixes

src/compiler/binder.ts

@@ -518,7 +518,6 @@ namespace ts {
                 hasExplicitReturn = false;
                 bindChildren(node);
                 // Reset all reachability check related flags on node (for incremental scenarios)
-                // Reset all emit helper flags on node (for incremental scenarios)
                 node.flags &= ~NodeFlags.ReachabilityAndEmitFlags;
                 if (!(currentFlow.flags & FlowFlags.Unreachable) && containerFlags & ContainerFlags.IsFunctionLike && nodeIsPresent((<FunctionLikeDeclaration>node).body)) {
                     node.flags |= NodeFlags.HasImplicitReturn;
@@ -1950,9 +1949,6 @@ namespace ts {
                     return bindParameter(<ParameterDeclaration>node);
                 case SyntaxKind.VariableDeclaration:
                 case SyntaxKind.BindingElement:
-                    if ((node as BindingElement).dotDotDotToken && node.parent.kind === SyntaxKind.ObjectBindingPattern) {
-                        emitFlags |= NodeFlags.HasRestAttribute;
-                    }
                     return bindVariableDeclarationOrBindingElement(<VariableDeclaration | BindingElement>node);
                 case SyntaxKind.PropertyDeclaration:
                 case SyntaxKind.PropertySignature:
@@ -1980,7 +1976,6 @@ namespace ts {
                         }
                         root = root.parent;
                     }
-                    emitFlags |= hasRest ? NodeFlags.HasRestAttribute : NodeFlags.HasSpreadAttribute;
                     return;
 
                 case SyntaxKind.CallSignature:
@@ -2236,15 +2231,6 @@ namespace ts {
         }
 
         function bindClassLikeDeclaration(node: ClassLikeDeclaration) {
-            if (!isDeclarationFile(file) && !isInAmbientContext(node)) {
-                if (getClassExtendsHeritageClauseElement(node) !== undefined) {
-                    emitFlags |= NodeFlags.HasClassExtends;
-                }
-                if (nodeIsDecorated(node)) {
-                    emitFlags |= NodeFlags.HasDecorators;
-                }
-            }
-
             if (node.kind === SyntaxKind.ClassDeclaration) {
                 bindBlockScopedDeclaration(node, SymbolFlags.Class, SymbolFlags.ClassExcludes);
             }
@@ -2314,12 +2300,6 @@ namespace ts {
         }
 
         function bindParameter(node: ParameterDeclaration) {
-            if (!isDeclarationFile(file) &&
-                !isInAmbientContext(node) &&
-                nodeIsDecorated(node)) {
-                emitFlags |= (NodeFlags.HasDecorators | NodeFlags.HasParamDecorators);
-            }
-
             if (inStrictMode) {
                 // It is a SyntaxError if the identifier eval or arguments appears within a FormalParameterList of a
                 // strict mode FunctionLikeDeclaration or FunctionExpression(13.1)
@@ -2377,9 +2357,6 @@ namespace ts {
                 if (isAsyncFunctionLike(node)) {
                     emitFlags |= NodeFlags.HasAsyncFunctions;
                 }
-                if (nodeIsDecorated(node)) {
-                    emitFlags |= NodeFlags.HasDecorators;
-                }
             }
 
             if (currentFlow && isObjectLiteralOrClassExpressionMethod(node)) {

src/compiler/checker.ts

@@ -38,6 +38,8 @@ namespace ts {
         // is because diagnostics can be quite expensive, and we want to allow hosts to bail out if
         // they no longer need the information (for example, if the user started editing again).
         let cancellationToken: CancellationToken;
+        let requestedExternalEmitHelpers: ExternalEmitHelpers;
+        let externalHelpersModule: Symbol;
 
         const Symbol = objectAllocator.getSymbolConstructor();
         const Type = objectAllocator.getTypeConstructor();
@@ -3064,7 +3066,15 @@ namespace ts {
         }
 
         function getRestType(source: Type, properties: PropertyName[], symbol: Symbol): Type {
-            Debug.assert(!!(source.flags & TypeFlags.Object), "Rest types only support object types right now.");
+            source = filterType(source, t => !(t.flags & TypeFlags.Nullable));
+            if (source.flags & TypeFlags.Never) {
+                return emptyObjectType;
+            }
+
+            if (source.flags & TypeFlags.Union) {
+                return mapType(source, t => getRestType(t, properties, symbol));
+            }
+
             const members = createMap<Symbol>();
             const names = createMap<true>();
             for (const name of properties) {
@@ -3105,7 +3115,7 @@ namespace ts {
             let type: Type;
             if (pattern.kind === SyntaxKind.ObjectBindingPattern) {
                 if (declaration.dotDotDotToken) {
-                    if (!(parentType.flags & TypeFlags.Object)) {
+                    if (!isValidSpreadType(parentType)) {
                         error(declaration, Diagnostics.Rest_types_may_only_be_created_from_object_types);
                         return unknownType;
                     }
@@ -3319,14 +3329,19 @@ namespace ts {
         // Return the type implied by an object binding pattern
         function getTypeFromObjectBindingPattern(pattern: ObjectBindingPattern, includePatternInType: boolean, reportErrors: boolean): Type {
             const members = createMap<Symbol>();
+            let stringIndexInfo: IndexInfo;
             let hasComputedProperties = false;
             forEach(pattern.elements, e => {
                 const name = e.propertyName || <Identifier>e.name;
-                if (isComputedNonLiteralName(name) || e.dotDotDotToken) {
-                    // do not include computed properties or rests in the implied type
+                if (isComputedNonLiteralName(name)) {
+                    // do not include computed properties in the implied type
                     hasComputedProperties = true;
                     return;
                 }
+                if (e.dotDotDotToken) {
+                    stringIndexInfo = createIndexInfo(anyType, /*isReadonly*/ false);
+                    return;
+                }
 
                 const text = getTextOfPropertyName(name);
                 const flags = SymbolFlags.Property | SymbolFlags.Transient | (e.initializer ? SymbolFlags.Optional : 0);
@@ -3335,7 +3350,7 @@ namespace ts {
                 symbol.bindingElement = e;
                 members[symbol.name] = symbol;
             });
-            const result = createAnonymousType(undefined, members, emptyArray, emptyArray, undefined, undefined);
+            const result = createAnonymousType(undefined, members, emptyArray, emptyArray, stringIndexInfo, undefined);
             if (includePatternInType) {
                 result.pattern = pattern;
             }
@@ -4509,20 +4524,21 @@ namespace ts {
         function resolveMappedTypeMembers(type: MappedType) {
             const members: SymbolTable = createMap<Symbol>();
             let stringIndexInfo: IndexInfo;
-            let numberIndexInfo: IndexInfo;
             // Resolve upfront such that recursive references see an empty object type.
             setStructuredTypeMembers(type, emptySymbols, emptyArray, emptyArray, undefined, undefined);
             // In { [P in K]: T }, we refer to P as the type parameter type, K as the constraint type,
-            // and T as the template type.
+            // and T as the template type. If K is of the form 'keyof S', the mapped type and S are
+            // homomorphic and we copy property modifiers from corresponding properties in S.
             const typeParameter = getTypeParameterFromMappedType(type);
             const constraintType = getConstraintTypeFromMappedType(type);
+            const homomorphicType = getHomomorphicTypeFromMappedType(type);
             const templateType = getTemplateTypeFromMappedType(type);
-            const isReadonly = !!type.declaration.readonlyToken;
-            const isOptional = !!type.declaration.questionToken;
+            const templateReadonly = !!type.declaration.readonlyToken;
+            const templateOptional = !!type.declaration.questionToken;
             // First, if the constraint type is a type parameter, obtain the base constraint. Then,
             // if the key type is a 'keyof X', obtain 'keyof C' where C is the base constraint of X.
             // Finally, iterate over the constituents of the resulting iteration type.
-            const keyType = constraintType.flags & TypeFlags.TypeParameter ? getApparentType(constraintType) : constraintType;
+            const keyType = constraintType.flags & TypeFlags.TypeVariable ? getApparentType(constraintType) : constraintType;
             const iterationType = keyType.flags & TypeFlags.Index ? getIndexType(getApparentType((<IndexType>keyType).type)) : keyType;
             forEachType(iterationType, t => {
                 // Create a mapper from T to the current iteration type constituent. Then, if the
@@ -4531,29 +4547,22 @@ namespace ts {
                 const iterationMapper = createUnaryTypeMapper(typeParameter, t);
                 const templateMapper = type.mapper ? combineTypeMappers(type.mapper, iterationMapper) : iterationMapper;
                 const propType = instantiateType(templateType, templateMapper);
-                // If the current iteration type constituent is a literal type, create a property.
-                // Otherwise, for type string create a string index signature and for type number
-                // create a numeric index signature.
-                if (t.flags & (TypeFlags.StringLiteral | TypeFlags.NumberLiteral | TypeFlags.EnumLiteral)) {
+                // If the current iteration type constituent is a string literal type, create a property.
+                // Otherwise, for type string create a string index signature.
+                if (t.flags & TypeFlags.StringLiteral) {
                     const propName = (<LiteralType>t).text;
+                    const homomorphicProp = homomorphicType && getPropertyOfType(homomorphicType, propName);
+                    const isOptional = templateOptional || !!(homomorphicProp && homomorphicProp.flags & SymbolFlags.Optional);
                     const prop = <TransientSymbol>createSymbol(SymbolFlags.Property | SymbolFlags.Transient | (isOptional ? SymbolFlags.Optional : 0), propName);
-                    prop.type = addOptionality(propType, isOptional);
-                    prop.isReadonly = isReadonly;
+                    prop.type = propType;
+                    prop.isReadonly = templateReadonly || homomorphicProp && isReadonlySymbol(homomorphicProp);
                     members[propName] = prop;
                 }
                 else if (t.flags & TypeFlags.String) {
-                    stringIndexInfo = createIndexInfo(propType, isReadonly);
-                }
-                else if (t.flags & TypeFlags.Number) {
-                    numberIndexInfo = createIndexInfo(propType, isReadonly);
+                    stringIndexInfo = createIndexInfo(propType, templateReadonly);
                 }
             });
-            // If we created both a string and a numeric string index signature, and if the two index
-            // signatures have identical types, discard the redundant numeric index signature.
-            if (stringIndexInfo && numberIndexInfo && isTypeIdenticalTo(stringIndexInfo.type, numberIndexInfo.type)) {
-                numberIndexInfo = undefined;
-            }
-            setStructuredTypeMembers(type, members, emptyArray, emptyArray, stringIndexInfo, numberIndexInfo);
+            setStructuredTypeMembers(type, members, emptyArray, emptyArray, stringIndexInfo, undefined);
         }
 
         function getTypeParameterFromMappedType(type: MappedType) {
@@ -4569,10 +4578,15 @@ namespace ts {
         function getTemplateTypeFromMappedType(type: MappedType) {
             return type.templateType ||
                 (type.templateType = type.declaration.type ?
-                    instantiateType(getTypeFromTypeNode(type.declaration.type), type.mapper || identityMapper) :
+                    instantiateType(addOptionality(getTypeFromTypeNode(type.declaration.type), !!type.declaration.questionToken), type.mapper || identityMapper) :
                     unknownType);
         }
 
+        function getHomomorphicTypeFromMappedType(type: MappedType) {
+            const constraint = getConstraintDeclaration(getTypeParameterFromMappedType(type));
+            return constraint.kind === SyntaxKind.TypeOperator ? instantiateType(getTypeFromTypeNode((<TypeOperatorNode>constraint).type), type.mapper || identityMapper) : undefined;
+        }
+
         function getErasedTemplateTypeFromMappedType(type: MappedType) {
             return instantiateType(getTemplateTypeFromMappedType(type), createUnaryTypeMapper(getTypeParameterFromMappedType(type), anyType));
         }
@@ -4580,7 +4594,7 @@ namespace ts {
         function isGenericMappedType(type: Type) {
             if (getObjectFlags(type) & ObjectFlags.Mapped) {
                 const constraintType = getConstraintTypeFromMappedType(<MappedType>type);
-                return !!(constraintType.flags & (TypeFlags.TypeParameter | TypeFlags.Index));
+                return maybeTypeOfKind(constraintType, TypeFlags.TypeVariable | TypeFlags.Index);
             }
             return false;
         }
@@ -5652,6 +5666,7 @@ namespace ts {
             containsString?: boolean;
             containsNumber?: boolean;
             containsStringOrNumberLiteral?: boolean;
+            unionIndex?: number;
         }
 
         function binarySearchTypes(types: Type[], type: Type): number {
@@ -5846,6 +5861,9 @@ namespace ts {
                 typeSet.containsAny = true;
             }
             else if (!(type.flags & TypeFlags.Never) && (strictNullChecks || !(type.flags & TypeFlags.Nullable)) && !contains(typeSet, type)) {
+                if (type.flags & TypeFlags.Union && typeSet.unionIndex === undefined) {
+                    typeSet.unionIndex = typeSet.length;
+                }
                 typeSet.push(type);
             }
         }
@@ -5872,15 +5890,6 @@ namespace ts {
             if (types.length === 0) {
                 return emptyObjectType;
             }
-            for (let i = 0; i < types.length; i++) {
-                const type = types[i];
-                if (type.flags & TypeFlags.Union) {
-                    // We are attempting to construct a type of the form X & (A | B) & Y. Transform this into a type of
-                    // the form X & A & Y | X & B & Y and recursively reduce until no union type constituents remain.
-                    return getUnionType(map((<UnionType>type).types, t => getIntersectionType(replaceElement(types, i, t))),
-                        /*subtypeReduction*/ false, aliasSymbol, aliasTypeArguments);
-                }
-            }
             const typeSet = [] as TypeSet;
             addTypesToIntersection(typeSet, types);
             if (typeSet.containsAny) {
@@ -5889,6 +5898,14 @@ namespace ts {
             if (typeSet.length === 1) {
                 return typeSet[0];
             }
+            const unionIndex = typeSet.unionIndex;
+            if (unionIndex !== undefined) {
+                // We are attempting to construct a type of the form X & (A | B) & Y. Transform this into a type of
+                // the form X & A & Y | X & B & Y and recursively reduce until no union type constituents remain.
+                const unionType = <UnionType>typeSet[unionIndex];
+                return getUnionType(map(unionType.types, t => getIntersectionType(replaceElement(typeSet, unionIndex, t))),
+                    /*subtypeReduction*/ false, aliasSymbol, aliasTypeArguments);
+            }
             const id = getTypeListId(typeSet);
             let type = intersectionTypes[id];
             if (!type) {
@@ -5910,7 +5927,7 @@ namespace ts {
             return links.resolvedType;
         }
 
-        function getIndexTypeForTypeParameter(type: TypeParameter) {
+        function getIndexTypeForGenericType(type: TypeVariable | UnionOrIntersectionType) {
             if (!type.resolvedIndexType) {
                 type.resolvedIndexType = <IndexType>createType(TypeFlags.Index);
                 type.resolvedIndexType.type = type;
@@ -5929,7 +5946,7 @@ namespace ts {
         }
 
         function getIndexType(type: Type): Type {
-            return type.flags & TypeFlags.TypeParameter ? getIndexTypeForTypeParameter(<TypeParameter>type) :
+            return maybeTypeOfKind(type, TypeFlags.TypeVariable) ? getIndexTypeForGenericType(<TypeVariable | UnionOrIntersectionType>type) :
                 getObjectFlags(type) & ObjectFlags.Mapped ? getConstraintTypeFromMappedType(<MappedType>type) :
                 type.flags & TypeFlags.Any || getIndexInfoOfType(type, IndexKind.String) ? stringType :
                 getLiteralTypeFromPropertyNames(type);
@@ -6026,17 +6043,18 @@ namespace ts {
             }
             const mapper = createUnaryTypeMapper(getTypeParameterFromMappedType(type), indexType);
             const templateMapper = type.mapper ? combineTypeMappers(type.mapper, mapper) : mapper;
-            return addOptionality(instantiateType(getTemplateTypeFromMappedType(type), templateMapper), !!type.declaration.questionToken);
+            return instantiateType(getTemplateTypeFromMappedType(type), templateMapper);
         }
 
         function getIndexedAccessType(objectType: Type, indexType: Type, accessNode?: ElementAccessExpression | IndexedAccessTypeNode) {
-            if (indexType.flags & TypeFlags.TypeParameter ||
-                objectType.flags & TypeFlags.TypeParameter && indexType.flags & TypeFlags.Index ||
-                isGenericMappedType(objectType)) {
-                // If either the object type or the index type are type parameters, or if the object type is a mapped
-                // type with a generic constraint, we are performing a higher-order index access where we cannot
-                // meaningfully access the properties of the object type. In those cases, we first check that the
-                // index type is assignable to 'keyof T' for the object type.
+            if (maybeTypeOfKind(indexType, TypeFlags.TypeVariable | TypeFlags.Index) || isGenericMappedType(objectType)) {
+                if (objectType.flags & TypeFlags.Any) {
+                    return objectType;
+                }
+                // If the index type is generic or if the object type is a mapped type with a generic constraint,
+                // we are performing a higher-order index access where we cannot meaningfully access the properties
+                // of the object type. In those cases, we first check that the index type is assignable to 'keyof T'
+                // for the object type.
                 if (accessNode) {
                     if (!isTypeAssignableTo(indexType, getIndexType(objectType))) {
                         error(accessNode, Diagnostics.Type_0_cannot_be_used_to_index_type_1, typeToString(indexType), typeToString(objectType));
@@ -6123,11 +6141,25 @@ namespace ts {
          * this function should be called in a left folding style, with left = previous result of getSpreadType
          * and right = the new element to be spread.
          */
-        function getSpreadType(left: Type, right: Type, isFromObjectLiteral: boolean): ResolvedType | IntrinsicType {
-            Debug.assert(!!(left.flags & (TypeFlags.Object | TypeFlags.Any)) && !!(right.flags & (TypeFlags.Object | TypeFlags.Any)), "Only object types may be spread.");
+        function getSpreadType(left: Type, right: Type, isFromObjectLiteral: boolean): Type  {
             if (left.flags & TypeFlags.Any || right.flags & TypeFlags.Any) {
                 return anyType;
             }
+            left = filterType(left, t => !(t.flags & TypeFlags.Nullable));
+            if (left.flags & TypeFlags.Never) {
+                return right;
+            }
+            right = filterType(right, t => !(t.flags & TypeFlags.Nullable));
+            if (right.flags & TypeFlags.Never) {
+                return left;
+            }
+            if (left.flags & TypeFlags.Union) {
+                return mapType(left, t => getSpreadType(t, right, isFromObjectLiteral));
+            }
+            if (right.flags & TypeFlags.Union) {
+                return mapType(right, t => getSpreadType(left, t, isFromObjectLiteral));
+            }
+
             const members = createMap<Symbol>();
             const skippedPrivateMembers = createMap<boolean>();
             let stringIndexInfo: IndexInfo;
@@ -6515,19 +6547,19 @@ namespace ts {
         }
 
         function instantiateMappedType(type: MappedType, mapper: TypeMapper): Type {
-            // Check if we have an isomorphic mapped type, i.e. a type of the form { [P in keyof T]: X } for some
-            // type parameter T. If so, the mapped type is distributive over a union type and when T is instantiated
+            // Check if we have a homomorphic mapped type, i.e. a type of the form { [P in keyof T]: X } for some
+            // type variable T. If so, the mapped type is distributive over a union type and when T is instantiated
             // to a union type A | B, we produce { [P in keyof A]: X } | { [P in keyof B]: X }. Furthermore, for
-            // isomorphic mapped types we leave primitive types alone. For example, when T is instantiated to a
+            // homomorphic mapped types we leave primitive types alone. For example, when T is instantiated to a
             // union type A | undefined, we produce { [P in keyof A]: X } | undefined.
             const constraintType = getConstraintTypeFromMappedType(type);
             if (constraintType.flags & TypeFlags.Index) {
-                const typeParameter = (<IndexType>constraintType).type;
-                const mappedTypeParameter = mapper(typeParameter);
-                if (typeParameter !== mappedTypeParameter) {
-                    return mapType(mappedTypeParameter, t => {
+                const typeVariable = (<IndexType>constraintType).type;
+                const mappedTypeVariable = instantiateType(typeVariable, mapper);
+                if (typeVariable !== mappedTypeVariable) {
+                    return mapType(mappedTypeVariable, t => {
                         if (isMappableType(t)) {
-                            const replacementMapper = createUnaryTypeMapper(typeParameter, t);
+                            const replacementMapper = createUnaryTypeMapper(typeVariable, t);
                             const combinedMapper = mapper.mappedTypes && mapper.mappedTypes.length === 1 ? replacementMapper : combineTypeMappers(replacementMapper, mapper);
                             combinedMapper.mappedTypes = mapper.mappedTypes;
                             return instantiateMappedObjectType(type, combinedMapper);
@@ -7260,10 +7292,12 @@ namespace ts {
                     }
                     // Given a type parameter T with a constraint C, a type S is assignable to
                     // keyof T if S is assignable to keyof C.
-                    const constraint = getConstraintOfTypeParameter((<IndexType>target).type);
-                    if (constraint) {
-                        if (result = isRelatedTo(source, getIndexType(constraint), reportErrors)) {
-                            return result;
+                    if ((<IndexType>target).type.flags & TypeFlags.TypeParameter) {
+                        const constraint = getConstraintOfTypeParameter(<TypeParameter>(<IndexType>target).type);
+                        if (constraint) {
+                            if (result = isRelatedTo(source, getIndexType(constraint), reportErrors)) {
+                                return result;
+                            }
                         }
                     }
                 }
@@ -8444,28 +8478,78 @@ namespace ts {
         // Return true if the given type could possibly reference a type parameter for which
         // we perform type inference (i.e. a type parameter of a generic function). We cache
         // results for union and intersection types for performance reasons.
-        function couldContainTypeParameters(type: Type): boolean {
+        function couldContainTypeVariables(type: Type): boolean {
             const objectFlags = getObjectFlags(type);
-            return !!(type.flags & TypeFlags.TypeParameter ||
-                objectFlags & ObjectFlags.Reference && forEach((<TypeReference>type).typeArguments, couldContainTypeParameters) ||
+            return !!(type.flags & TypeFlags.TypeVariable ||
+                objectFlags & ObjectFlags.Reference && forEach((<TypeReference>type).typeArguments, couldContainTypeVariables) ||
                 objectFlags & ObjectFlags.Anonymous && type.symbol && type.symbol.flags & (SymbolFlags.Method | SymbolFlags.TypeLiteral | SymbolFlags.Class) ||
                 objectFlags & ObjectFlags.Mapped ||
-                type.flags & TypeFlags.UnionOrIntersection && couldUnionOrIntersectionContainTypeParameters(<UnionOrIntersectionType>type));
+                type.flags & TypeFlags.UnionOrIntersection && couldUnionOrIntersectionContainTypeVariables(<UnionOrIntersectionType>type));
         }
 
-        function couldUnionOrIntersectionContainTypeParameters(type: UnionOrIntersectionType): boolean {
-            if (type.couldContainTypeParameters === undefined) {
-                type.couldContainTypeParameters = forEach(type.types, couldContainTypeParameters);
+        function couldUnionOrIntersectionContainTypeVariables(type: UnionOrIntersectionType): boolean {
+            if (type.couldContainTypeVariables === undefined) {
+                type.couldContainTypeVariables = forEach(type.types, couldContainTypeVariables);
             }
-            return type.couldContainTypeParameters;
+            return type.couldContainTypeVariables;
         }
 
         function isTypeParameterAtTopLevel(type: Type, typeParameter: TypeParameter): boolean {
             return type === typeParameter || type.flags & TypeFlags.UnionOrIntersection && forEach((<UnionOrIntersectionType>type).types, t => isTypeParameterAtTopLevel(t, typeParameter));
         }
 
-        function inferTypes(context: InferenceContext, originalSource: Type, originalTarget: Type) {
-            const typeParameters = context.signature.typeParameters;
+        // Infer a suitable input type for a homomorphic mapped type { [P in keyof T]: X }. We construct
+        // an object type with the same set of properties as the source type, where the type of each
+        // property is computed by inferring from the source property type to X for the type
+        // variable T[P] (i.e. we treat the type T[P] as the type variable we're inferring for).
+        function inferTypeForHomomorphicMappedType(source: Type, target: MappedType): Type {
+            const properties = getPropertiesOfType(source);
+            let indexInfo = getIndexInfoOfType(source, IndexKind.String);
+            if (properties.length === 0 && !indexInfo) {
+                return undefined;
+            }
+            const typeVariable = <TypeVariable>getIndexedAccessType((<IndexType>getConstraintTypeFromMappedType(target)).type, getTypeParameterFromMappedType(target));
+            const typeVariableArray = [typeVariable];
+            const typeInferences = createTypeInferencesObject();
+            const typeInferencesArray = [typeInferences];
+            const templateType = getTemplateTypeFromMappedType(target);
+            const readonlyMask = target.declaration.readonlyToken ? false : true;
+            const optionalMask = target.declaration.questionToken ? 0 : SymbolFlags.Optional;
+            const members = createSymbolTable(properties);
+            for (const prop of properties) {
+                const inferredPropType = inferTargetType(getTypeOfSymbol(prop));
+                if (!inferredPropType) {
+                    return undefined;
+                }
+                const inferredProp = <TransientSymbol>createSymbol(SymbolFlags.Property | SymbolFlags.Transient | prop.flags & optionalMask, prop.name);
+                inferredProp.declarations = prop.declarations;
+                inferredProp.type = inferredPropType;
+                inferredProp.isReadonly = readonlyMask && isReadonlySymbol(prop);
+                members[prop.name] = inferredProp;
+            }
+            if (indexInfo) {
+                const inferredIndexType = inferTargetType(indexInfo.type);
+                if (!inferredIndexType) {
+                    return undefined;
+                }
+                indexInfo = createIndexInfo(inferredIndexType, readonlyMask && indexInfo.isReadonly);
+            }
+            return createAnonymousType(undefined, members, emptyArray, emptyArray, indexInfo, undefined);
+
+            function inferTargetType(sourceType: Type): Type {
+                typeInferences.primary = undefined;
+                typeInferences.secondary = undefined;
+                inferTypes(typeVariableArray, typeInferencesArray, sourceType, templateType);
+                const inferences = typeInferences.primary || typeInferences.secondary;
+                return inferences && getUnionType(inferences, /*subtypeReduction*/ true);
+            }
+        }
+
+        function inferTypesWithContext(context: InferenceContext, originalSource: Type, originalTarget: Type) {
+            inferTypes(context.signature.typeParameters, context.inferences, originalSource, originalTarget);
+        }
+
+        function inferTypes(typeVariables: TypeVariable[], typeInferences: TypeInferences[], originalSource: Type, originalTarget: Type) {
             let sourceStack: Type[];
             let targetStack: Type[];
             let depth = 0;
@@ -8483,7 +8567,7 @@ namespace ts {
             }
 
             function inferFromTypes(source: Type, target: Type) {
-                if (!couldContainTypeParameters(target)) {
+                if (!couldContainTypeVariables(target)) {
                     return;
                 }
                 if (source.aliasSymbol && source.aliasTypeArguments && source.aliasSymbol === target.aliasSymbol) {
@@ -8533,7 +8617,7 @@ namespace ts {
                         target = removeTypesFromUnionOrIntersection(<UnionOrIntersectionType>target, matchingTypes);
                     }
                 }
-                if (target.flags & TypeFlags.TypeParameter) {
+                if (target.flags & TypeFlags.TypeVariable) {
                     // If target is a type parameter, make an inference, unless the source type contains
                     // the anyFunctionType (the wildcard type that's used to avoid contextually typing functions).
                     // Because the anyFunctionType is internal, it should not be exposed to the user by adding
@@ -8543,9 +8627,9 @@ namespace ts {
                     if (source.flags & TypeFlags.ContainsAnyFunctionType) {
                         return;
                     }
-                    for (let i = 0; i < typeParameters.length; i++) {
-                        if (target === typeParameters[i]) {
-                            const inferences = context.inferences[i];
+                    for (let i = 0; i < typeVariables.length; i++) {
+                        if (target === typeVariables[i]) {
+                            const inferences = typeInferences[i];
                             if (!inferences.isFixed) {
                                 // Any inferences that are made to a type parameter in a union type are inferior
                                 // to inferences made to a flat (non-union) type. This is because if we infer to
@@ -8559,7 +8643,7 @@ namespace ts {
                                 if (!contains(candidates, source)) {
                                     candidates.push(source);
                                 }
-                                if (!isTypeParameterAtTopLevel(originalTarget, <TypeParameter>target)) {
+                                if (target.flags & TypeFlags.TypeParameter && !isTypeParameterAtTopLevel(originalTarget, <TypeParameter>target)) {
                                     inferences.topLevel = false;
                                 }
                             }
@@ -8578,24 +8662,24 @@ namespace ts {
                 }
                 else if (target.flags & TypeFlags.UnionOrIntersection) {
                     const targetTypes = (<UnionOrIntersectionType>target).types;
-                    let typeParameterCount = 0;
-                    let typeParameter: TypeParameter;
-                    // First infer to each type in union or intersection that isn't a type parameter
+                    let typeVariableCount = 0;
+                    let typeVariable: TypeVariable;
+                    // First infer to each type in union or intersection that isn't a type variable
                     for (const t of targetTypes) {
-                        if (t.flags & TypeFlags.TypeParameter && contains(typeParameters, t)) {
-                            typeParameter = <TypeParameter>t;
-                            typeParameterCount++;
+                        if (t.flags & TypeFlags.TypeVariable && contains(typeVariables, t)) {
+                            typeVariable = <TypeVariable>t;
+                            typeVariableCount++;
                         }
                         else {
                             inferFromTypes(source, t);
                         }
                     }
-                    // Next, if target containings a single naked type parameter, make a secondary inference to that type
-                    // parameter. This gives meaningful results for union types in co-variant positions and intersection
+                    // Next, if target containings a single naked type variable, make a secondary inference to that type
+                    // variable. This gives meaningful results for union types in co-variant positions and intersection
                     // types in contra-variant positions (such as callback parameters).
-                    if (typeParameterCount === 1) {
+                    if (typeVariableCount === 1) {
                         inferiority++;
-                        inferFromTypes(source, typeParameter);
+                        inferFromTypes(source, typeVariable);
                         inferiority--;
                     }
                 }
@@ -8636,12 +8720,25 @@ namespace ts {
             function inferFromObjectTypes(source: Type, target: Type) {
                 if (getObjectFlags(target) & ObjectFlags.Mapped) {
                     const constraintType = getConstraintTypeFromMappedType(<MappedType>target);
-                    if (getObjectFlags(source) & ObjectFlags.Mapped) {
-                        inferFromTypes(getConstraintTypeFromMappedType(<MappedType>source), constraintType);
-                        inferFromTypes(getTemplateTypeFromMappedType(<MappedType>source), getTemplateTypeFromMappedType(<MappedType>target));
+                    if (constraintType.flags & TypeFlags.Index) {
+                        // We're inferring from some source type S to a homomorphic mapped type { [P in keyof T]: X },
+                        // where T is a type variable. Use inferTypeForHomomorphicMappedType to infer a suitable source
+                        // type and then make a secondary inference from that type to T. We make a secondary inference
+                        // such that direct inferences to T get priority over inferences to Partial<T>, for example.
+                        const index = indexOf(typeVariables, (<IndexType>constraintType).type);
+                        if (index >= 0 && !typeInferences[index].isFixed) {
+                            const inferredType = inferTypeForHomomorphicMappedType(source, <MappedType>target);
+                            if (inferredType) {
+                                inferiority++;
+                                inferFromTypes(inferredType, typeVariables[index]);
+                                inferiority--;
+                            }
+                        }
                         return;
                     }
                     if (constraintType.flags & TypeFlags.TypeParameter) {
+                        // We're inferring from some source type S to a mapped type { [P in T]: X }, where T is a type
+                        // parameter. Infer from 'keyof S' to T and infer from a union of each property type in S to X.
                         inferFromTypes(getIndexType(source), constraintType);
                         inferFromTypes(getUnionType(map(getPropertiesOfType(source), getTypeOfSymbol)), getTemplateTypeFromMappedType(<MappedType>target));
                         return;
@@ -11380,7 +11477,8 @@ namespace ts {
                         if (impliedProp) {
                             prop.flags |= impliedProp.flags & SymbolFlags.Optional;
                         }
-                        else if (!compilerOptions.suppressExcessPropertyErrors) {
+
+                        else if (!compilerOptions.suppressExcessPropertyErrors && !getIndexInfoOfType(contextualType, IndexKind.String)) {
                             error(memberDecl.name, Diagnostics.Object_literal_may_only_specify_known_properties_and_0_does_not_exist_in_type_1,
                                 symbolToString(member), typeToString(contextualType));
                         }
@@ -11396,6 +11494,9 @@ namespace ts {
                     member = prop;
                 }
                 else if (memberDecl.kind === SyntaxKind.SpreadAssignment) {
+                    if (languageVersion < ScriptTarget.ESNext) {
+                        checkExternalEmitHelpers(memberDecl, ExternalEmitHelpers.Assign);
+                    }
                     if (propertiesArray.length > 0) {
                         spread = getSpreadType(spread, createObjectLiteralType(), /*isFromObjectLiteral*/ true);
                         propertiesArray = [];
@@ -11405,7 +11506,7 @@ namespace ts {
                         typeFlags = 0;
                     }
                     const type = checkExpression((memberDecl as SpreadAssignment).expression);
-                    if (!(type.flags & (TypeFlags.Object | TypeFlags.Any))) {
+                    if (!isValidSpreadType(type)) {
                         error(memberDecl, Diagnostics.Spread_types_may_only_be_created_from_object_types);
                         return unknownType;
                     }
@@ -11483,6 +11584,12 @@ namespace ts {
             }
        }
 
+        function isValidSpreadType(type: Type): boolean {
+            return !!(type.flags & (TypeFlags.Any | TypeFlags.Null | TypeFlags.Undefined) ||
+                type.flags & TypeFlags.Object && !isGenericMappedType(type) ||
+                type.flags & TypeFlags.UnionOrIntersection && !forEach((<UnionOrIntersectionType>type).types, t => !isValidSpreadType(t)));
+        }
+
         function checkJsxSelfClosingElement(node: JsxSelfClosingElement) {
             checkJsxOpeningLikeElement(node);
             return jsxElementType || anyType;
@@ -11583,6 +11690,9 @@ namespace ts {
         }
 
         function checkJsxSpreadAttribute(node: JsxSpreadAttribute, elementAttributesType: Type, nameTable: Map<boolean>) {
+            if (compilerOptions.jsx === JsxEmit.React) {
+                checkExternalEmitHelpers(node, ExternalEmitHelpers.Assign);
+            }
             const type = checkExpression(node.expression);
             const props = getPropertiesOfType(type);
             for (const prop of props) {
@@ -12483,7 +12593,7 @@ namespace ts {
             const context = createInferenceContext(signature, /*inferUnionTypes*/ true);
             forEachMatchingParameterType(contextualSignature, signature, (source, target) => {
                 // Type parameters from outer context referenced by source type are fixed by instantiation of the source type
-                inferTypes(context, instantiateType(source, contextualMapper), target);
+                inferTypesWithContext(context, instantiateType(source, contextualMapper), target);
             });
             return getSignatureInstantiation(signature, getInferredTypes(context));
         }
@@ -12518,7 +12628,7 @@ namespace ts {
             if (thisType) {
                 const thisArgumentNode = getThisArgumentOfCall(node);
                 const thisArgumentType = thisArgumentNode ? checkExpression(thisArgumentNode) : voidType;
-                inferTypes(context, thisArgumentType, thisType);
+                inferTypesWithContext(context, thisArgumentType, thisType);
             }
 
             // We perform two passes over the arguments. In the first pass we infer from all arguments, but use
@@ -12540,7 +12650,7 @@ namespace ts {
                         argType = checkExpressionWithContextualType(arg, paramType, mapper);
                     }
 
-                    inferTypes(context, argType, paramType);
+                    inferTypesWithContext(context, argType, paramType);
                 }
             }
 
@@ -12555,7 +12665,7 @@ namespace ts {
                     if (excludeArgument[i] === false) {
                         const arg = args[i];
                         const paramType = getTypeAtPosition(signature, i);
-                        inferTypes(context, checkExpressionWithContextualType(arg, paramType, inferenceMapper), paramType);
+                        inferTypesWithContext(context, checkExpressionWithContextualType(arg, paramType, inferenceMapper), paramType);
                     }
                 }
             }
@@ -13642,7 +13752,7 @@ namespace ts {
                 for (let i = 0; i < len; i++) {
                     const declaration = <ParameterDeclaration>signature.parameters[i].valueDeclaration;
                     if (declaration.type) {
-                        inferTypes(mapper.context, getTypeFromTypeNode(declaration.type), getTypeAtPosition(context, i));
+                        inferTypesWithContext(mapper.context, getTypeFromTypeNode(declaration.type), getTypeAtPosition(context, i));
                     }
                 }
             }
@@ -13728,7 +13838,7 @@ namespace ts {
                 // T in the second overload so that we do not infer Base as a candidate for T
                 // (inferring Base would make type argument inference inconsistent between the two
                 // overloads).
-                inferTypes(mapper.context, links.type, instantiateType(contextualType, mapper));
+                inferTypesWithContext(mapper.context, links.type, instantiateType(contextualType, mapper));
             }
         }
 
@@ -13864,7 +13974,7 @@ namespace ts {
             if (!switchTypes.length) {
                 return false;
             }
-            return eachTypeContainedIn(type, switchTypes);
+            return eachTypeContainedIn(mapType(type, getRegularTypeOfLiteralType), switchTypes);
         }
 
         function functionHasImplicitReturn(func: FunctionLikeDeclaration) {
@@ -14303,7 +14413,7 @@ namespace ts {
             if (!(isTypeComparableTo(leftType, stringType) || isTypeOfKind(leftType, TypeFlags.NumberLike | TypeFlags.ESSymbol))) {
                 error(left, Diagnostics.The_left_hand_side_of_an_in_expression_must_be_of_type_any_string_number_or_symbol);
             }
-            if (!isTypeAnyOrAllConstituentTypesHaveKind(rightType, TypeFlags.Object | TypeFlags.TypeParameter | TypeFlags.IndexedAccess)) {
+            if (!isTypeAnyOrAllConstituentTypesHaveKind(rightType, TypeFlags.Object | TypeFlags.TypeVariable)) {
                 error(right, Diagnostics.The_right_hand_side_of_an_in_expression_must_be_of_type_any_an_object_type_or_a_type_parameter);
             }
             return booleanType;
@@ -14348,6 +14458,9 @@ namespace ts {
                 }
             }
             else if (property.kind === SyntaxKind.SpreadAssignment) {
+                if (languageVersion < ScriptTarget.ESNext) {
+                    checkExternalEmitHelpers(property, ExternalEmitHelpers.Rest);
+                }
                 const nonRestNames: PropertyName[] = [];
                 if (allProperties) {
                     for (let i = 0; i < allProperties.length - 1; i++) {
@@ -15260,6 +15373,13 @@ namespace ts {
                 checkGrammarFunctionLikeDeclaration(<FunctionLikeDeclaration>node);
             }
 
+            if (isAsyncFunctionLike(node) && languageVersion < ScriptTarget.ES2017) {
+                checkExternalEmitHelpers(node, ExternalEmitHelpers.Awaiter);
+                if (languageVersion < ScriptTarget.ES2015) {
+                    checkExternalEmitHelpers(node, ExternalEmitHelpers.Generator);
+                }
+            }
+
             checkTypeParameters(node.typeParameters);
 
             forEach(node.parameters, checkParameter);
@@ -16395,7 +16515,15 @@ namespace ts {
                 error(node, Diagnostics.Experimental_support_for_decorators_is_a_feature_that_is_subject_to_change_in_a_future_release_Set_the_experimentalDecorators_option_to_remove_this_warning);
             }
 
+            const firstDecorator = node.decorators[0];
+            checkExternalEmitHelpers(firstDecorator, ExternalEmitHelpers.Decorate);
+            if (node.kind === SyntaxKind.Parameter) {
+                checkExternalEmitHelpers(firstDecorator, ExternalEmitHelpers.Param);
+            }
+
             if (compilerOptions.emitDecoratorMetadata) {
+                checkExternalEmitHelpers(firstDecorator, ExternalEmitHelpers.Metadata);
+
                 // we only need to perform these checks if we are emitting serialized type metadata for the target of a decorator.
                 switch (node.kind) {
                     case SyntaxKind.ClassDeclaration:
@@ -16782,7 +16910,7 @@ namespace ts {
         }
 
         function checkCollisionWithGlobalPromiseInGeneratedCode(node: Node, name: Identifier): void {
-            if (!needCollisionCheckForIdentifier(node, name, "Promise")) {
+            if (languageVersion >= ScriptTarget.ES2017 || !needCollisionCheckForIdentifier(node, name, "Promise")) {
                 return;
             }
 
@@ -16959,6 +17087,9 @@ namespace ts {
             }
 
             if (node.kind === SyntaxKind.BindingElement) {
+                if (node.parent.kind === SyntaxKind.ObjectBindingPattern && languageVersion < ScriptTarget.ESNext) {
+                    checkExternalEmitHelpers(node, ExternalEmitHelpers.Rest);
+                }
                 // check computed properties inside property names of binding elements
                 if (node.propertyName && node.propertyName.kind === SyntaxKind.ComputedPropertyName) {
                     checkComputedPropertyName(<ComputedPropertyName>node.propertyName);
@@ -17225,7 +17356,7 @@ namespace ts {
 
             // unknownType is returned i.e. if node.expression is identifier whose name cannot be resolved
             // in this case error about missing name is already reported - do not report extra one
-            if (!isTypeAnyOrAllConstituentTypesHaveKind(rightType, TypeFlags.Object | TypeFlags.TypeParameter | TypeFlags.IndexedAccess)) {
+            if (!isTypeAnyOrAllConstituentTypesHaveKind(rightType, TypeFlags.Object | TypeFlags.TypeVariable)) {
                 error(node.expression, Diagnostics.The_right_hand_side_of_a_for_in_statement_must_be_of_type_any_an_object_type_or_a_type_parameter);
             }
 
@@ -17876,6 +18007,10 @@ namespace ts {
 
             const baseTypeNode = getClassExtendsHeritageClauseElement(node);
             if (baseTypeNode) {
+                if (languageVersion < ScriptTarget.ES2015) {
+                    checkExternalEmitHelpers(baseTypeNode.parent, ExternalEmitHelpers.Extends);
+                }
+
                 const baseTypes = getBaseTypes(type);
                 if (baseTypes.length && produceDiagnostics) {
                     const baseType = baseTypes[0];
@@ -20316,8 +20451,6 @@ namespace ts {
 
             // Initialize global symbol table
             let augmentations: LiteralExpression[][];
-            let requestedExternalEmitHelpers: NodeFlags = 0;
-            let firstFileRequestingExternalHelpers: SourceFile;
             for (const file of host.getSourceFiles()) {
                 if (!isExternalOrCommonJsModule(file)) {
                     mergeSymbolTable(globals, file.locals);
@@ -20337,15 +20470,6 @@ namespace ts {
                         }
                     }
                 }
-                if ((compilerOptions.isolatedModules || isExternalModule(file)) && !file.isDeclarationFile) {
-                    const fileRequestedExternalEmitHelpers = file.flags & NodeFlags.EmitHelperFlags;
-                    if (fileRequestedExternalEmitHelpers) {
-                        requestedExternalEmitHelpers |= fileRequestedExternalEmitHelpers;
-                        if (firstFileRequestingExternalHelpers === undefined) {
-                            firstFileRequestingExternalHelpers = file;
-                        }
-                    }
-                }
             }
 
             if (augmentations) {
@@ -20411,57 +20535,51 @@ namespace ts {
             const symbol = getGlobalSymbol("ReadonlyArray", SymbolFlags.Type, /*diagnostic*/ undefined);
             globalReadonlyArrayType = symbol && <GenericType>getTypeOfGlobalSymbol(symbol, /*arity*/ 1);
             anyReadonlyArrayType = globalReadonlyArrayType ? createTypeFromGenericGlobalType(globalReadonlyArrayType, [anyType]) : anyArrayType;
+        }
 
-            // If we have specified that we are importing helpers, we should report global
-            // errors if we cannot resolve the helpers external module, or if it does not have
-            // the necessary helpers exported.
-            if (compilerOptions.importHelpers && firstFileRequestingExternalHelpers) {
-                // Find the first reference to the helpers module.
-                const helpersModule = resolveExternalModule(
-                    firstFileRequestingExternalHelpers,
-                    externalHelpersModuleNameText,
-                    Diagnostics.Cannot_find_module_0,
-                    /*errorNode*/ undefined);
-
-                // If we found the module, report errors if it does not have the necessary exports.
-                if (helpersModule) {
-                    const exports = helpersModule.exports;
-                    if (requestedExternalEmitHelpers & NodeFlags.HasClassExtends && languageVersion < ScriptTarget.ES2015) {
-                        verifyHelperSymbol(exports, "__extends", SymbolFlags.Value);
-                    }
-                    if (requestedExternalEmitHelpers & NodeFlags.HasSpreadAttribute &&
-                        (languageVersion < ScriptTarget.ESNext || compilerOptions.jsx === JsxEmit.React)) {
-                        verifyHelperSymbol(exports, "__assign", SymbolFlags.Value);
-                    }
-                    if (languageVersion < ScriptTarget.ESNext && requestedExternalEmitHelpers & NodeFlags.HasRestAttribute) {
-                        verifyHelperSymbol(exports, "__rest", SymbolFlags.Value);
-                    }
-                    if (requestedExternalEmitHelpers & NodeFlags.HasDecorators) {
-                        verifyHelperSymbol(exports, "__decorate", SymbolFlags.Value);
-                        if (compilerOptions.emitDecoratorMetadata) {
-                            verifyHelperSymbol(exports, "__metadata", SymbolFlags.Value);
-                        }
-                    }
-                    if (requestedExternalEmitHelpers & NodeFlags.HasParamDecorators) {
-                        verifyHelperSymbol(exports, "__param", SymbolFlags.Value);
-                    }
-                    if (requestedExternalEmitHelpers & NodeFlags.HasAsyncFunctions) {
-                        verifyHelperSymbol(exports, "__awaiter", SymbolFlags.Value);
-                        if (languageVersion < ScriptTarget.ES2015) {
-                            verifyHelperSymbol(exports, "__generator", SymbolFlags.Value);
+        function checkExternalEmitHelpers(location: Node, helpers: ExternalEmitHelpers) {
+            if ((requestedExternalEmitHelpers & helpers) !== helpers && compilerOptions.importHelpers) {
+                const sourceFile = getSourceFileOfNode(location);
+                if (isEffectiveExternalModule(sourceFile, compilerOptions)) {
+                    const helpersModule = resolveHelpersModule(sourceFile, location);
+                    if (helpersModule !== unknownSymbol) {
+                        const uncheckedHelpers = helpers & ~requestedExternalEmitHelpers;
+                        for (let helper = ExternalEmitHelpers.FirstEmitHelper; helper <= ExternalEmitHelpers.LastEmitHelper; helper <<= 1) {
+                            if (uncheckedHelpers & helper) {
+                                const name = getHelperName(helper);
+                                const symbol = getSymbol(helpersModule.exports, escapeIdentifier(name), SymbolFlags.Value);
+                                if (!symbol) {
+                                    error(location, Diagnostics.This_syntax_requires_an_imported_helper_named_1_but_module_0_has_no_exported_member_1, externalHelpersModuleNameText, name);
+                                }
+                            }
                         }
                     }
+                    requestedExternalEmitHelpers |= helpers;
                 }
             }
         }
 
-        function verifyHelperSymbol(symbols: SymbolTable, name: string, meaning: SymbolFlags) {
-            const symbol = getSymbol(symbols, escapeIdentifier(name), meaning);
-            if (!symbol) {
-                error(/*location*/ undefined, Diagnostics.Module_0_has_no_exported_member_1, externalHelpersModuleNameText, name);
+        function getHelperName(helper: ExternalEmitHelpers) {
+            switch (helper) {
+                case ExternalEmitHelpers.Extends: return "__extends";
+                case ExternalEmitHelpers.Assign: return "__assign";
+                case ExternalEmitHelpers.Rest: return "__rest";
+                case ExternalEmitHelpers.Decorate: return "__decorate";
+                case ExternalEmitHelpers.Metadata: return "__metadata";
+                case ExternalEmitHelpers.Param: return "__param";
+                case ExternalEmitHelpers.Awaiter: return "__awaiter";
+                case ExternalEmitHelpers.Generator: return "__generator";
             }
         }
 
+        function resolveHelpersModule(node: SourceFile, errorNode: Node) {
+            if (!externalHelpersModule) {
+                externalHelpersModule = resolveExternalModule(node, externalHelpersModuleNameText, Diagnostics.This_syntax_requires_an_imported_helper_but_module_0_cannot_be_found, errorNode) || unknownSymbol;
+            }
+            return externalHelpersModule;
+        }
+
+
         function createInstantiatedPromiseLikeType(): ObjectType {
             const promiseLikeType = getGlobalPromiseLikeType();
             if (promiseLikeType !== emptyGenericType) {
@@ -21206,6 +21324,9 @@ namespace ts {
             else if (accessor.body === undefined && !(getModifierFlags(accessor) & ModifierFlags.Abstract)) {
                 return grammarErrorAtPos(getSourceFileOfNode(accessor), accessor.end - 1, ";".length, Diagnostics._0_expected, "{");
             }
+            else if (accessor.body && getModifierFlags(accessor) & ModifierFlags.Abstract) {
+                return grammarErrorOnNode(accessor, Diagnostics.An_abstract_accessor_cannot_have_an_implementation);
+            }
             else if (accessor.typeParameters) {
                 return grammarErrorOnNode(accessor.name, Diagnostics.An_accessor_cannot_have_type_parameters);
             }

src/compiler/commandLineParser.ts

@@ -272,7 +272,7 @@ namespace ts {
                 "es2017": ScriptTarget.ES2017,
                 "esnext": ScriptTarget.ESNext,
             }),
-            description: Diagnostics.Specify_ECMAScript_target_version_Colon_ES3_default_ES5_or_ES2015,
+            description: Diagnostics.Specify_ECMAScript_target_version_Colon_ES3_default_ES5_ES2015_ES2016_ES2017_or_ESNEXT,
             paramType: Diagnostics.VERSION,
         },
         {

src/compiler/declarationEmitter.ts

@@ -1625,6 +1625,12 @@ namespace ts {
                             Diagnostics.Parameter_0_of_call_signature_from_exported_interface_has_or_is_using_name_1_from_private_module_2 :
                             Diagnostics.Parameter_0_of_call_signature_from_exported_interface_has_or_is_using_private_name_1;
 
+                    case SyntaxKind.IndexSignature:
+                        // Interfaces cannot have parameter types that cannot be named
+                        return symbolAccessibilityResult.errorModuleName ?
+                            Diagnostics.Parameter_0_of_index_signature_from_exported_interface_has_or_is_using_name_1_from_private_module_2 :
+                            Diagnostics.Parameter_0_of_index_signature_from_exported_interface_has_or_is_using_private_name_1;
+
                     case SyntaxKind.MethodDeclaration:
                     case SyntaxKind.MethodSignature:
                         if (hasModifier(node.parent, ModifierFlags.Static)) {

src/compiler/diagnosticMessages.json

@@ -851,6 +851,10 @@
         "category": "Error",
         "code": 1317
     },
+    "An abstract accessor cannot have an implementation.": {
+        "category": "Error",
+        "code": 1318
+    },
     "Duplicate identifier '{0}'.": {
         "category": "Error",
         "code": 2300
@@ -1023,6 +1027,10 @@
         "category": "Error",
         "code": 2342
     },
+    "This syntax requires an imported helper named '{1}', but module '{0}' has no exported member '{1}'.": {
+        "category": "Error",
+        "code": 2343
+    },
     "Type '{0}' does not satisfy the constraint '{1}'.": {
         "category": "Error",
         "code": 2344
@@ -1063,6 +1071,10 @@
         "category": "Error",
         "code": 2353
     },
+    "This syntax requires an imported helper but module '{0}' cannot be found.": {
+        "category": "Error",
+        "code": 2354
+    },
     "A function whose declared type is neither 'void' nor 'any' must return a value.": {
         "category": "Error",
         "code": 2355
@@ -2288,6 +2300,14 @@
         "category": "Message",
         "code": 4090
     },
+    "Parameter '{0}' of index signature from exported interface has or is using name '{1}' from private module '{2}'.": {
+        "category": "Error",
+        "code": 4091
+    },
+    "Parameter '{0}' of index signature from exported interface has or is using private name '{1}'.": {
+        "category": "Error",
+        "code": 4092
+    },
 
     "The current host does not support the '{0}' option.": {
         "category": "Error",
@@ -2453,7 +2473,7 @@
         "category": "Message",
         "code": 6012
     },
-    "Specify ECMAScript target version: 'ES3' (default), 'ES5', or 'ES2015'": {
+    "Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', or 'ESNEXT'": {
         "category": "Message",
         "code": 6015
     },

src/compiler/parser.ts

@@ -2558,6 +2558,8 @@ namespace ts {
                 case SyntaxKind.OpenBraceToken:
                 case SyntaxKind.OpenBracketToken:
                 case SyntaxKind.LessThanToken:
+                case SyntaxKind.BarToken:
+                case SyntaxKind.AmpersandToken:
                 case SyntaxKind.NewKeyword:
                 case SyntaxKind.StringLiteral:
                 case SyntaxKind.NumericLiteral:
@@ -2617,6 +2619,7 @@ namespace ts {
         }
 
         function parseUnionOrIntersectionType(kind: SyntaxKind, parseConstituentType: () => TypeNode, operator: SyntaxKind): TypeNode {
+            parseOptional(operator);
             let type = parseConstituentType();
             if (token() === operator) {
                 const types = createNodeArray<TypeNode>([type], type.pos);

src/compiler/transformers/destructuring.ts

@@ -459,7 +459,7 @@ namespace ts {
                 var t = {};
                 for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p) && e.indexOf(p) < 0)
                     t[p] = s[p];
-                if (typeof Object.getOwnPropertySymbols === "function")
+                if (s != null && typeof Object.getOwnPropertySymbols === "function")
                     for (var i = 0, p = Object.getOwnPropertySymbols(s); i < p.length; i++) if (e.indexOf(p[i]) < 0)
                         t[p[i]] = s[p[i]];
                 return t;

src/compiler/transformers/ts.ts

@@ -345,6 +345,7 @@ namespace ts {
 
                 case SyntaxKind.PropertyDeclaration:
                     // TypeScript property declarations are elided.
+                    return undefined;
 
                 case SyntaxKind.Constructor:
                     return visitConstructor(<ConstructorDeclaration>node);
@@ -1905,7 +1906,7 @@ namespace ts {
                     : (<ComputedPropertyName>name).expression;
             }
             else if (isIdentifier(name)) {
-                return createLiteral(name.text);
+                return createLiteral(unescapeIdentifier(name.text));
             }
             else {
                 return getSynthesizedClone(name);

src/compiler/types.ts

@@ -418,26 +418,20 @@ namespace ts {
         HasImplicitReturn =  1 << 7,  // If function implicitly returns on one of codepaths (initialized by binding)
         HasExplicitReturn =  1 << 8,  // If function has explicit reachable return on one of codepaths (initialized by binding)
         GlobalAugmentation = 1 << 9,  // Set if module declaration is an augmentation for the global scope
-        HasClassExtends =    1 << 10, // If the file has a non-ambient class with an extends clause in ES5 or lower (initialized by binding)
-        HasDecorators =      1 << 11, // If the file has decorators (initialized by binding)
-        HasParamDecorators = 1 << 12, // If the file has parameter decorators (initialized by binding)
-        HasAsyncFunctions =  1 << 13, // If the file has async functions (initialized by binding)
-        HasSpreadAttribute = 1 << 14, // If the file as JSX spread attributes (initialized by binding)
-        HasRestAttribute =   1 << 15, // If the file has object destructure elements
-        DisallowInContext =  1 << 16, // If node was parsed in a context where 'in-expressions' are not allowed
-        YieldContext =       1 << 17, // If node was parsed in the 'yield' context created when parsing a generator
-        DecoratorContext =   1 << 18, // If node was parsed as part of a decorator
-        AwaitContext =       1 << 19, // If node was parsed in the 'await' context created when parsing an async function
-        ThisNodeHasError =   1 << 20, // If the parser encountered an error when parsing the code that created this node
-        JavaScriptFile =     1 << 21, // If node was parsed in a JavaScript
-        ThisNodeOrAnySubNodesHasError = 1 << 22, // If this node or any of its children had an error
-        HasAggregatedChildData = 1 << 23, // If we've computed data from children and cached it in this node
+        HasAsyncFunctions =  1 << 10, // If the file has async functions (initialized by binding)
+        DisallowInContext =  1 << 11, // If node was parsed in a context where 'in-expressions' are not allowed
+        YieldContext =       1 << 12, // If node was parsed in the 'yield' context created when parsing a generator
+        DecoratorContext =   1 << 13, // If node was parsed as part of a decorator
+        AwaitContext =       1 << 14, // If node was parsed in the 'await' context created when parsing an async function
+        ThisNodeHasError =   1 << 15, // If the parser encountered an error when parsing the code that created this node
+        JavaScriptFile =     1 << 16, // If node was parsed in a JavaScript
+        ThisNodeOrAnySubNodesHasError = 1 << 17, // If this node or any of its children had an error
+        HasAggregatedChildData = 1 << 18, // If we've computed data from children and cached it in this node
 
         BlockScoped = Let | Const,
 
         ReachabilityCheckFlags = HasImplicitReturn | HasExplicitReturn,
-        EmitHelperFlags = HasClassExtends | HasDecorators | HasParamDecorators | HasAsyncFunctions | HasSpreadAttribute | HasRestAttribute,
-        ReachabilityAndEmitFlags = ReachabilityCheckFlags | EmitHelperFlags,
+        ReachabilityAndEmitFlags = ReachabilityCheckFlags | HasAsyncFunctions,
 
         // Parsing context flags
         ContextFlags = DisallowInContext | YieldContext | DecoratorContext | AwaitContext | JavaScriptFile,
@@ -2808,6 +2802,7 @@ namespace ts {
         UnionOrIntersection = Union | Intersection,
         StructuredType = Object | Union | Intersection,
         StructuredOrTypeParameter = StructuredType | TypeParameter | Index,
+        TypeVariable = TypeParameter | IndexedAccess,
 
         // 'Narrowable' types are types where narrowing actually narrows.
         // This *should* be every type other than null, undefined, void, and never
@@ -2920,7 +2915,9 @@ namespace ts {
         /* @internal */
         resolvedProperties: SymbolTable;  // Cache of resolved properties
         /* @internal */
-        couldContainTypeParameters: boolean;
+        resolvedIndexType: IndexType;
+        /* @internal */
+        couldContainTypeVariables: boolean;
     }
 
     export interface UnionType extends UnionOrIntersectionType { }
@@ -2976,8 +2973,13 @@ namespace ts {
         iteratorElementType?: Type;
     }
 
+    export interface TypeVariable extends Type {
+        /* @internal */
+        resolvedIndexType: IndexType;
+    }
+
     // Type parameters (TypeFlags.TypeParameter)
-    export interface TypeParameter extends Type {
+    export interface TypeParameter extends TypeVariable {
         constraint: Type;        // Constraint
         /* @internal */
         target?: TypeParameter;  // Instantiation target
@@ -2986,20 +2988,21 @@ namespace ts {
         /* @internal */
         resolvedApparentType: Type;
         /* @internal */
-        resolvedIndexType: IndexType;
-        /* @internal */
         isThisType?: boolean;
     }
 
-    export interface IndexType extends Type {
-        type: TypeParameter;
-    }
-
-    export interface IndexedAccessType extends Type {
+    // Indexed access types (TypeFlags.IndexedAccess)
+    // Possible forms are T[xxx], xxx[T], or xxx[keyof T], where T is a type variable
+    export interface IndexedAccessType extends TypeVariable {
         objectType: Type;
         indexType: Type;
     }
 
+    // keyof T types (TypeFlags.Index)
+    export interface IndexType extends Type {
+        type: TypeVariable | UnionOrIntersectionType;
+    }
+
     export const enum SignatureKind {
         Call,
         Construct,
@@ -3705,6 +3708,25 @@ namespace ts {
         readonly priority?: number; // Helpers with a higher priority are emitted earlier than other helpers on the node.
     }
 
+    /**
+     * Used by the checker, this enum keeps track of external emit helpers that should be type
+     * checked.
+     */
+    /* @internal */
+    export const enum ExternalEmitHelpers {
+        Extends = 1 << 0,           // __extends (used by the ES2015 class transformation)
+        Assign = 1 << 1,            // __assign (used by Jsx and ESNext object spread transformations)
+        Rest = 1 << 2,              // __rest (used by ESNext object rest transformation)
+        Decorate = 1 << 3,          // __decorate (used by TypeScript decorators transformation)
+        Metadata = 1 << 4,          // __metadata (used by TypeScript decorators transformation)
+        Param = 1 << 5,             // __param (used by TypeScript decorators transformation)
+        Awaiter = 1 << 6,           // __awaiter (used by ES2017 async functions transformation)
+        Generator = 1 << 7,         // __generator (used by ES2015 generator transformation)
+
+        FirstEmitHelper = Extends,
+        LastEmitHelper = Generator
+    }
+
     /* @internal */
     export const enum EmitContext {
         SourceFile,         // Emitting a SourceFile

src/compiler/utilities.ts

@@ -423,6 +423,10 @@ namespace ts {
         return false;
     }
 
+    export function isEffectiveExternalModule(node: SourceFile, compilerOptions: CompilerOptions) {
+        return isExternalModule(node) || compilerOptions.isolatedModules;
+    }
+
     export function isBlockScope(node: Node, parentNode: Node) {
         switch (node.kind) {
             case SyntaxKind.SourceFile:

src/harness/unittests/tsserverProjectSystem.ts

@@ -51,9 +51,8 @@ namespace ts.projectSystem {
             throttleLimit: number,
             installTypingHost: server.ServerHost,
             readonly typesRegistry = createMap<void>(),
-            telemetryEnabled?: boolean,
             log?: TI.Log) {
-            super(installTypingHost, globalTypingsCacheLocation, safeList.path, throttleLimit, telemetryEnabled, log);
+            super(installTypingHost, globalTypingsCacheLocation, safeList.path, throttleLimit, log);
         }
 
         safeFileList = safeList.path;
@@ -2729,6 +2728,65 @@ namespace ts.projectSystem {
                 arguments: { projectFileName: projectName }
             }).response;
             assert.isTrue(diags.length === 0);
+
+            session.executeCommand(<server.protocol.SetCompilerOptionsForInferredProjectsRequest>{
+                type: "request",
+                command: server.CommandNames.CompilerOptionsForInferredProjects,
+                seq: 3,
+                arguments: { options: { module: ModuleKind.CommonJS } }
+            });
+            const diagsAfterUpdate = session.executeCommand(<server.protocol.CompilerOptionsDiagnosticsRequest>{
+                type: "request",
+                command: server.CommandNames.CompilerOptionsDiagnosticsFull,
+                seq: 4,
+                arguments: { projectFileName: projectName }
+            }).response;
+            assert.isTrue(diagsAfterUpdate.length === 0);
+        });
+
+        it("for external project", () => {
+            const f1 = {
+                path: "/a/b/f1.js",
+                content: "function test1() { }"
+            };
+            const host = createServerHost([f1, libFile]);
+            const session = createSession(host);
+            const projectService = session.getProjectService();
+            const projectFileName = "/a/b/project.csproj";
+            const externalFiles = toExternalFiles([f1.path]);
+            projectService.openExternalProject(<protocol.ExternalProject>{
+                projectFileName,
+                rootFiles: externalFiles,
+                options: {}
+            });
+
+            checkNumberOfProjects(projectService, { externalProjects: 1 });
+
+            const diags = session.executeCommand(<server.protocol.CompilerOptionsDiagnosticsRequest>{
+                type: "request",
+                command: server.CommandNames.CompilerOptionsDiagnosticsFull,
+                seq: 2,
+                arguments: { projectFileName }
+            }).response;
+            assert.isTrue(diags.length === 0);
+
+            session.executeCommand(<server.protocol.OpenExternalProjectRequest>{
+                type: "request",
+                command: server.CommandNames.OpenExternalProject,
+                seq: 3,
+                arguments: {
+                    projectFileName,
+                    rootFiles: externalFiles,
+                    options: { module: ModuleKind.CommonJS }
+                }
+            });
+            const diagsAfterUpdate = session.executeCommand(<server.protocol.CompilerOptionsDiagnosticsRequest>{
+                type: "request",
+                command: server.CommandNames.CompilerOptionsDiagnosticsFull,
+                seq: 4,
+                arguments: { projectFileName }
+            }).response;
+            assert.isTrue(diagsAfterUpdate.length === 0);
         });
     });
 

src/harness/unittests/typingsInstaller.ts

@@ -20,13 +20,12 @@ namespace ts.projectSystem {
     }
 
     class Installer extends TestTypingsInstaller {
-        constructor(host: server.ServerHost, p?: InstallerParams, telemetryEnabled?: boolean, log?: TI.Log) {
+        constructor(host: server.ServerHost, p?: InstallerParams, log?: TI.Log) {
             super(
                 (p && p.globalTypingsCacheLocation) || "/a/data",
                 (p && p.throttleLimit) || 5,
                 host,
                 (p && p.typesRegistry),
-                telemetryEnabled,
                 log);
         }
 
@@ -36,7 +35,7 @@ namespace ts.projectSystem {
         }
     }
 
-    function executeCommand(self: Installer, host: TestServerHost, installedTypings: string[], typingFiles: FileOrFolder[], cb: TI.RequestCompletedAction): void {
+    function executeCommand(self: Installer, host: TestServerHost, installedTypings: string[] | string, typingFiles: FileOrFolder[], cb: TI.RequestCompletedAction): void {
         self.addPostExecAction(installedTypings, success => {
             for (const file of typingFiles) {
                 host.createFileOrFolder(file, /*createParentDirectory*/ true);
@@ -907,7 +906,7 @@ namespace ts.projectSystem {
             const host = createServerHost([f1, packageJson]);
             const installer = new (class extends Installer {
                 constructor() {
-                    super(host, { globalTypingsCacheLocation: "/tmp" }, /*telemetryEnabled*/ false, { isEnabled: () => true, writeLine: msg => messages.push(msg) });
+                    super(host, { globalTypingsCacheLocation: "/tmp" }, { isEnabled: () => true, writeLine: msg => messages.push(msg) });
                 }
                 installWorker(_requestId: number, _args: string[], _cwd: string, _cb: server.typingsInstaller.RequestCompletedAction) {
                     assert(false, "runCommand should not be invoked");
@@ -971,15 +970,18 @@ namespace ts.projectSystem {
             let seenTelemetryEvent = false;
             const installer = new (class extends Installer {
                 constructor() {
-                    super(host, { globalTypingsCacheLocation: cachePath, typesRegistry: createTypesRegistry("commander") }, /*telemetryEnabled*/ true);
+                    super(host, { globalTypingsCacheLocation: cachePath, typesRegistry: createTypesRegistry("commander") });
                 }
                 installWorker(_requestId: number, _args: string[], _cwd: string, cb: server.typingsInstaller.RequestCompletedAction) {
                     const installedTypings = ["@types/commander"];
                     const typingFiles = [commander];
                     executeCommand(this, host, installedTypings, typingFiles, cb);
                 }
-                sendResponse(response: server.SetTypings | server.InvalidateCachedTypings | server.TypingsInstallEvent) {
-                    if (response.kind === server.EventInstall) {
+                sendResponse(response: server.SetTypings | server.InvalidateCachedTypings | server.BeginInstallTypes | server.EndInstallTypes) {
+                    if (response.kind === server.EventBeginInstallTypes) {
+                        return;
+                    }
+                    if (response.kind === server.EventEndInstallTypes) {
                         assert.deepEqual(response.packagesToInstall, ["@types/commander"]);
                         seenTelemetryEvent = true;
                         return;
@@ -997,4 +999,102 @@ namespace ts.projectSystem {
             checkProjectActualFiles(projectService.inferredProjects[0], [f1.path, commander.path]);
         });
     });
+
+    describe("progress notifications", () => {
+        it ("should be sent for success", () => {
+            const f1 = {
+                path: "/a/app.js",
+                content: ""
+            };
+            const package = {
+                path: "/a/package.json",
+                content: JSON.stringify({ dependencies: { "commander": "1.0.0" } })
+            };
+            const cachePath = "/a/cache/";
+            const commander = {
+                path: cachePath + "node_modules/@types/commander/index.d.ts",
+                content: "export let x: number"
+            };
+            const host = createServerHost([f1, package]);
+            let beginEvent: server.BeginInstallTypes;
+            let endEvent: server.EndInstallTypes;
+            const installer = new (class extends Installer {
+                constructor() {
+                    super(host, { globalTypingsCacheLocation: cachePath, typesRegistry: createTypesRegistry("commander") });
+                }
+                installWorker(_requestId: number, _args: string[], _cwd: string, cb: server.typingsInstaller.RequestCompletedAction) {
+                    const installedTypings = ["@types/commander"];
+                    const typingFiles = [commander];
+                    executeCommand(this, host, installedTypings, typingFiles, cb);
+                }
+                sendResponse(response: server.SetTypings | server.InvalidateCachedTypings | server.BeginInstallTypes | server.EndInstallTypes) {
+                    if (response.kind === server.EventBeginInstallTypes) {
+                        beginEvent = response;
+                        return;
+                    }
+                    if (response.kind === server.EventEndInstallTypes) {
+                        endEvent = response;
+                        return;
+                    }
+                    super.sendResponse(response);
+                }
+            })();
+            const projectService = createProjectService(host, { typingsInstaller: installer });
+            projectService.openClientFile(f1.path);
+
+            installer.installAll(/*expectedCount*/ 1);
+
+            assert.isTrue(!!beginEvent);
+            assert.isTrue(!!endEvent);
+            assert.isTrue(beginEvent.eventId === endEvent.eventId);
+            assert.isTrue(endEvent.installSuccess);
+            checkNumberOfProjects(projectService, { inferredProjects: 1 });
+            checkProjectActualFiles(projectService.inferredProjects[0], [f1.path, commander.path]);
+        });
+
+        it ("should be sent for error", () => {
+            const f1 = {
+                path: "/a/app.js",
+                content: ""
+            };
+            const package = {
+                path: "/a/package.json",
+                content: JSON.stringify({ dependencies: { "commander": "1.0.0" } })
+            };
+            const cachePath = "/a/cache/";
+            const host = createServerHost([f1, package]);
+            let beginEvent: server.BeginInstallTypes;
+            let endEvent: server.EndInstallTypes;
+            const installer = new (class extends Installer {
+                constructor() {
+                    super(host, { globalTypingsCacheLocation: cachePath, typesRegistry: createTypesRegistry("commander") });
+                }
+                installWorker(_requestId: number, _args: string[], _cwd: string, cb: server.typingsInstaller.RequestCompletedAction) {
+                    executeCommand(this, host, "", [], cb);
+                }
+                sendResponse(response: server.SetTypings | server.InvalidateCachedTypings | server.BeginInstallTypes | server.EndInstallTypes) {
+                    if (response.kind === server.EventBeginInstallTypes) {
+                        beginEvent = response;
+                        return;
+                    }
+                    if (response.kind === server.EventEndInstallTypes) {
+                        endEvent = response;
+                        return;
+                    }
+                    super.sendResponse(response);
+                }
+            })();
+            const projectService = createProjectService(host, { typingsInstaller: installer });
+            projectService.openClientFile(f1.path);
+
+            installer.installAll(/*expectedCount*/ 1);
+
+            assert.isTrue(!!beginEvent);
+            assert.isTrue(!!endEvent);
+            assert.isTrue(beginEvent.eventId === endEvent.eventId);
+            assert.isFalse(endEvent.installSuccess);
+            checkNumberOfProjects(projectService, { inferredProjects: 1 });
+            checkProjectActualFiles(projectService.inferredProjects[0], [f1.path]);
+        });
+    });
 }

src/lib/es2017.object.d.ts

@@ -4,11 +4,22 @@ interface ObjectConstructor {
       * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
       */
     values<T>(o: { [s: string]: T }): T[];
+
+    /**
+      * Returns an array of values of the enumerable properties of an object
+      * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
+      */
     values(o: any): any[];
+
+    /**
+      * Returns an array of key/values of the enumerable properties of an object
+      * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
+      */
+    entries<T>(o: { [s: string]: T }): [string, T][];
+
     /**
       * Returns an array of key/values of the enumerable properties of an object
       * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
       */
-    entries<T extends { [key: string]: any }, K extends keyof T>(o: T): [keyof T, T[K]][];
     entries(o: any): [string, any][];
 }

src/server/project.ts

@@ -248,9 +248,7 @@ namespace ts.server {
                 this.compilerOptions.allowNonTsExtensions = true;
             }
 
-            if (this.projectKind === ProjectKind.Inferred || this.projectKind === ProjectKind.External) {
-                this.compilerOptions.noEmitForJsFiles = true;
-            }
+            this.setInternalCompilerOptionsForEmittingJsFiles();
 
             this.lsHost = new LSHost(this.projectService.host, this, this.projectService.cancellationToken);
             this.lsHost.setCompilationSettings(this.compilerOptions);
@@ -266,6 +264,12 @@ namespace ts.server {
             this.markAsDirty();
         }
 
+        private setInternalCompilerOptionsForEmittingJsFiles() {
+            if (this.projectKind === ProjectKind.Inferred || this.projectKind === ProjectKind.External) {
+                this.compilerOptions.noEmitForJsFiles = true;
+            }
+        }
+
         getProjectErrors() {
             return this.projectErrors;
         }
@@ -637,6 +641,7 @@ namespace ts.server {
                     this.lastCachedUnresolvedImportsList = undefined;
                 }
                 this.compilerOptions = compilerOptions;
+                this.setInternalCompilerOptionsForEmittingJsFiles();
                 this.lsHost.setCompilationSettings(compilerOptions);
 
                 this.markAsDirty();

src/server/protocol.ts

@@ -2117,6 +2117,40 @@ namespace ts.server.protocol {
         typingsInstallerVersion: string;
     }
 
+    export type BeginInstallTypesEventName = "beginInstallTypes";
+    export type EndInstallTypesEventName = "endInstallTypes";
+
+    export interface BeginInstallTypesEvent extends Event {
+        event: BeginInstallTypesEventName;
+        body: BeginInstallTypesEventBody;
+    }
+
+    export interface EndInstallTypesEvent extends Event {
+        event: EndInstallTypesEventName;
+        body: EndInstallTypesEventBody;
+    }
+
+    export interface InstallTypesEventBody {
+        /**
+         * correlation id to match begin and end events
+         */
+        eventId: number;
+        /**
+         * list of packages to install
+         */
+        packages: ReadonlyArray<string>;
+    }
+
+    export interface BeginInstallTypesEventBody extends InstallTypesEventBody {
+    }
+
+    export interface EndInstallTypesEventBody extends InstallTypesEventBody {
+        /**
+         * true if installation succeeded, otherwise false
+         */
+        success: boolean;
+    }
+
     export interface NavBarResponse extends Response {
         body?: NavigationBarItem[];
     }

src/server/server.ts

@@ -20,34 +20,41 @@ namespace ts.server {
     } = require("os");
 
     function getGlobalTypingsCacheLocation() {
-        let basePath: string;
         switch (process.platform) {
-            case "win32":
-                basePath = process.env.LOCALAPPDATA ||
+            case "win32": {
+                const basePath = process.env.LOCALAPPDATA ||
                     process.env.APPDATA ||
                     (os.homedir && os.homedir()) ||
                     process.env.USERPROFILE ||
                     (process.env.HOMEDRIVE && process.env.HOMEPATH && normalizeSlashes(process.env.HOMEDRIVE + process.env.HOMEPATH)) ||
                     os.tmpdir();
-                break;
-            case "linux":
-            case "android":
-                basePath = (os.homedir && os.homedir()) ||
-                    process.env.HOME ||
-                    ((process.env.LOGNAME || process.env.USER) && `/home/${process.env.LOGNAME || process.env.USER}`) ||
-                    os.tmpdir();
-                break;
+                return combinePaths(normalizeSlashes(basePath), "Microsoft/TypeScript");
+            }
             case "darwin":
-                const homeDir = (os.homedir && os.homedir()) ||
-                        process.env.HOME ||
-                        ((process.env.LOGNAME || process.env.USER) && `/Users/${process.env.LOGNAME || process.env.USER}`) ||
-                        os.tmpdir();
-                basePath = combinePaths(homeDir, "Library/Application Support/");
-                break;
+            case "linux":
+            case "android": {
+                const cacheLocation = getNonWindowsCacheLocation(process.platform === "darwin");
+                return combinePaths(cacheLocation, "typescript");
+            }
+            default:
+                Debug.fail(`unsupported platform '${process.platform}'`);
+                return;
         }
+    }
 
-        Debug.assert(basePath !== undefined);
-        return combinePaths(normalizeSlashes(basePath), "Microsoft/TypeScript");
+    function getNonWindowsCacheLocation(platformIsDarwin: boolean) {
+        if (process.env.XDG_CACHE_HOME) {
+            return process.env.XDG_CACHE_HOME;
+        }
+        const usersDir = platformIsDarwin ? "Users" : "home"
+        const homePath = (os.homedir && os.homedir()) ||
+            process.env.HOME ||
+            ((process.env.LOGNAME || process.env.USER) && `/${usersDir}/${process.env.LOGNAME || process.env.USER}`) ||
+            os.tmpdir();
+        const cacheFolder = platformIsDarwin
+            ? "Library/Caches"
+            : ".cache"
+        return combinePaths(normalizeSlashes(homePath), cacheFolder);
     }
 
     interface NodeChildProcess {
@@ -198,7 +205,7 @@ namespace ts.server {
         private socket: NodeSocket;
         private projectService: ProjectService;
         private throttledOperations: ThrottledOperations;
-        private telemetrySender: EventSender;
+        private eventSender: EventSender;
 
         constructor(
             private readonly telemetryEnabled: boolean,
@@ -231,7 +238,7 @@ namespace ts.server {
         }
 
         setTelemetrySender(telemetrySender: EventSender) {
-            this.telemetrySender = telemetrySender;
+            this.eventSender = telemetrySender;
         }
 
         attach(projectService: ProjectService) {
@@ -291,12 +298,30 @@ namespace ts.server {
             });
         }
 
-        private handleMessage(response: SetTypings | InvalidateCachedTypings | TypingsInstallEvent) {
+        private handleMessage(response: SetTypings | InvalidateCachedTypings | BeginInstallTypes | EndInstallTypes) {
             if (this.logger.hasLevel(LogLevel.verbose)) {
                 this.logger.info(`Received response: ${JSON.stringify(response)}`);
             }
-            if (response.kind === EventInstall) {
-                if (this.telemetrySender) {
+
+            if (response.kind === EventBeginInstallTypes) {
+                if (!this.eventSender) {
+                    return;
+                }
+                const body: protocol.BeginInstallTypesEventBody = {
+                    eventId: response.eventId,
+                    packages: response.packagesToInstall,
+                };
+                const eventName: protocol.BeginInstallTypesEventName = "beginInstallTypes";
+                this.eventSender.event(body, eventName);
+
+                return;
+            }
+
+            if (response.kind === EventEndInstallTypes) {
+                if (!this.eventSender) {
+                    return;
+                }
+                if (this.telemetryEnabled) {
                     const body: protocol.TypingsInstalledTelemetryEventBody = {
                         telemetryEventName: "typingsInstalled",
                         payload: {
@@ -306,10 +331,19 @@ namespace ts.server {
                         }
                     };
                     const eventName: protocol.TelemetryEventName = "telemetry";
-                    this.telemetrySender.event(body, eventName);
+                    this.eventSender.event(body, eventName);
                 }
+
+                const body: protocol.EndInstallTypesEventBody = {
+                    eventId: response.eventId,
+                    packages: response.packagesToInstall,
+                    success: response.installSuccess,
+                };
+                const eventName: protocol.EndInstallTypesEventName = "endInstallTypes";
+                this.eventSender.event(body, eventName);
                 return;
             }
+
             this.projectService.updateTypingsForProject(response);
             if (response.kind == ActionSet && this.socket) {
                 this.sendEvent(0, "setTypings", response);

src/server/shared.ts

@@ -3,7 +3,8 @@
 namespace ts.server {
     export const ActionSet: ActionSet = "action::set";
     export const ActionInvalidate: ActionInvalidate = "action::invalidate";
-    export const EventInstall: EventInstall = "event::install";
+    export const EventBeginInstallTypes: EventBeginInstallTypes = "event::beginInstallTypes";
+    export const EventEndInstallTypes: EventEndInstallTypes = "event::endInstallTypes";
 
     export namespace Arguments {
         export const GlobalCacheLocation = "--globalTypingsCacheLocation";

src/server/types.d.ts

@@ -43,10 +43,11 @@ declare namespace ts.server {
 
     export type ActionSet = "action::set";
     export type ActionInvalidate = "action::invalidate";
-    export type EventInstall = "event::install";
+    export type EventBeginInstallTypes = "event::beginInstallTypes";
+    export type EventEndInstallTypes = "event::endInstallTypes";
 
     export interface TypingInstallerResponse {
-        readonly kind: ActionSet | ActionInvalidate | EventInstall;
+        readonly kind: ActionSet | ActionInvalidate | EventBeginInstallTypes | EventEndInstallTypes;
     }
 
     export interface ProjectResponse extends TypingInstallerResponse {
@@ -65,11 +66,20 @@ declare namespace ts.server {
         readonly kind: ActionInvalidate;
     }
 
-    export interface TypingsInstallEvent extends TypingInstallerResponse {
-        readonly packagesToInstall: ReadonlyArray<string>;
-        readonly kind: EventInstall;
-        readonly installSuccess: boolean;
+    export interface InstallTypes extends ProjectResponse {
+        readonly kind: EventBeginInstallTypes | EventEndInstallTypes;
+        readonly eventId: number;
         readonly typingsInstallerVersion: string;
+        readonly packagesToInstall: ReadonlyArray<string>;
+    }
+
+    export interface BeginInstallTypes extends InstallTypes {
+        readonly kind: EventBeginInstallTypes;
+    }
+
+    export interface EndInstallTypes extends InstallTypes {
+        readonly kind: EventEndInstallTypes;
+        readonly installSuccess: boolean;
     }
 
     export interface InstallTypingHost extends JsTyping.TypingResolutionHost {

src/server/typingsInstaller/nodeTypingsInstaller.ts

@@ -70,13 +70,12 @@ namespace ts.server.typingsInstaller {
         private readonly npmPath: string;
         readonly typesRegistry: Map<void>;
 
-        constructor(globalTypingsCacheLocation: string, throttleLimit: number, telemetryEnabled: boolean, log: Log) {
+        constructor(globalTypingsCacheLocation: string, throttleLimit: number, log: Log) {
             super(
                 sys,
                 globalTypingsCacheLocation,
                 toPath("typingSafeList.json", __dirname, createGetCanonicalFileName(sys.useCaseSensitiveFileNames)),
                 throttleLimit,
-                telemetryEnabled,
                 log);
             if (this.log.isEnabled()) {
                 this.log.writeLine(`Process id: ${process.pid}`);
@@ -113,7 +112,7 @@ namespace ts.server.typingsInstaller {
             });
         }
 
-        protected sendResponse(response: SetTypings | InvalidateCachedTypings) {
+        protected sendResponse(response: SetTypings | InvalidateCachedTypings | BeginInstallTypes | EndInstallTypes) {
             if (this.log.isEnabled()) {
                 this.log.writeLine(`Sending response: ${JSON.stringify(response)}`);
             }
@@ -149,7 +148,6 @@ namespace ts.server.typingsInstaller {
 
     const logFilePath = findArgument(server.Arguments.LogFile);
     const globalTypingsCacheLocation = findArgument(server.Arguments.GlobalCacheLocation);
-    const telemetryEnabled = hasArgument(server.Arguments.EnableTelemetry);
 
     const log = new FileLog(logFilePath);
     if (log.isEnabled()) {
@@ -163,6 +161,6 @@ namespace ts.server.typingsInstaller {
         }
         process.exit(0);
     });
-    const installer = new NodeTypingsInstaller(globalTypingsCacheLocation, /*throttleLimit*/5, telemetryEnabled, log);
+    const installer = new NodeTypingsInstaller(globalTypingsCacheLocation, /*throttleLimit*/5, log);
     installer.listen();
 }

src/server/typingsInstaller/typingsInstaller.ts

@@ -97,7 +97,6 @@ namespace ts.server.typingsInstaller {
             readonly globalCachePath: string,
             readonly safeListPath: Path,
             readonly throttleLimit: number,
-            readonly telemetryEnabled: boolean,
             protected readonly log = nullLog) {
             if (this.log.isEnabled()) {
                 this.log.writeLine(`Global cache location '${globalCachePath}', safe file path '${safeListPath}'`);
@@ -309,47 +308,58 @@ namespace ts.server.typingsInstaller {
             const requestId = this.installRunCount;
             this.installRunCount++;
 
+            // send progress event
+            this.sendResponse(<BeginInstallTypes>{
+                kind: EventBeginInstallTypes,
+                eventId: requestId,
+                typingsInstallerVersion: ts.version, // qualified explicitly to prevent occasional shadowing
+                projectName: req.projectName
+            });
+
             this.installTypingsAsync(requestId, scopedTypings, cachePath, ok => {
-                if (this.telemetryEnabled) {
-                    this.sendResponse(<TypingsInstallEvent>{
-                        kind: EventInstall,
+                try {
+                    if (!ok) {
+                        if (this.log.isEnabled()) {
+                            this.log.writeLine(`install request failed, marking packages as missing to prevent repeated requests: ${JSON.stringify(filteredTypings)}`);
+                        }
+                        for (const typing of filteredTypings) {
+                            this.missingTypingsSet[typing] = true;
+                        }
+                        return;
+                    }
+
+                    // TODO: watch project directory
+                    if (this.log.isEnabled()) {
+                        this.log.writeLine(`Installed typings ${JSON.stringify(scopedTypings)}`);
+                    }
+                    const installedTypingFiles: string[] = [];
+                    for (const packageName of filteredTypings) {
+                        const typingFile = typingToFileName(cachePath, packageName, this.installTypingHost, this.log);
+                        if (!typingFile) {
+                            this.missingTypingsSet[packageName] = true;
+                            continue;
+                        }
+                        if (!this.packageNameToTypingLocation[packageName]) {
+                            this.packageNameToTypingLocation[packageName] = typingFile;
+                        }
+                        installedTypingFiles.push(typingFile);
+                    }
+                    if (this.log.isEnabled()) {
+                        this.log.writeLine(`Installed typing files ${JSON.stringify(installedTypingFiles)}`);
+                    }
+
+                    this.sendResponse(this.createSetTypings(req, currentlyCachedTypings.concat(installedTypingFiles)));
+                }
+                finally {
+                    this.sendResponse(<EndInstallTypes>{
+                        kind: EventEndInstallTypes,
+                        eventId: requestId,
+                        projectName: req.projectName,
                         packagesToInstall: scopedTypings,
                         installSuccess: ok,
                         typingsInstallerVersion: ts.version // qualified explicitly to prevent occasional shadowing
                     });
                 }
-
-                if (!ok) {
-                    if (this.log.isEnabled()) {
-                        this.log.writeLine(`install request failed, marking packages as missing to prevent repeated requests: ${JSON.stringify(filteredTypings)}`);
-                    }
-                    for (const typing of filteredTypings) {
-                        this.missingTypingsSet[typing] = true;
-                    }
-                    return;
-                }
-
-                // TODO: watch project directory
-                if (this.log.isEnabled()) {
-                    this.log.writeLine(`Installed typings ${JSON.stringify(scopedTypings)}`);
-                }
-                const installedTypingFiles: string[] = [];
-                for (const packageName of filteredTypings) {
-                    const typingFile = typingToFileName(cachePath, packageName, this.installTypingHost, this.log);
-                    if (!typingFile) {
-                        this.missingTypingsSet[packageName] = true;
-                        continue;
-                    }
-                    if (!this.packageNameToTypingLocation[packageName]) {
-                        this.packageNameToTypingLocation[packageName] = typingFile;
-                    }
-                    installedTypingFiles.push(typingFile);
-                }
-                if (this.log.isEnabled()) {
-                    this.log.writeLine(`Installed typing files ${JSON.stringify(installedTypingFiles)}`);
-                }
-
-                this.sendResponse(this.createSetTypings(req, currentlyCachedTypings.concat(installedTypingFiles)));
             });
         }
 
@@ -417,6 +427,6 @@ namespace ts.server.typingsInstaller {
         }
 
         protected abstract installWorker(requestId: number, args: string[], cwd: string, onRequestCompleted: RequestCompletedAction): void;
-        protected abstract sendResponse(response: SetTypings | InvalidateCachedTypings | TypingsInstallEvent): void;
+        protected abstract sendResponse(response: SetTypings | InvalidateCachedTypings | BeginInstallTypes | EndInstallTypes): void;
     }
 }

tests/baselines/reference/classAbstractAccessor.errors.txt

@@ -0,0 +1,17 @@
+tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractAccessor.ts(4,17): error TS1318: An abstract accessor cannot have an implementation.
+tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractAccessor.ts(6,17): error TS1318: An abstract accessor cannot have an implementation.
+
+
+==== tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractAccessor.ts (2 errors) ====
+    
+    abstract class A {
+       abstract get a();
+       abstract get aa() { return 1; } // error
+                    ~~
+!!! error TS1318: An abstract accessor cannot have an implementation.
+       abstract set b(x: string);
+       abstract set bb(x: string) {} // error
+                    ~~
+!!! error TS1318: An abstract accessor cannot have an implementation.
+    }
+    

tests/baselines/reference/classAbstractAccessor.js

@@ -0,0 +1,28 @@
+//// [classAbstractAccessor.ts]
+
+abstract class A {
+   abstract get a();
+   abstract get aa() { return 1; } // error
+   abstract set b(x: string);
+   abstract set bb(x: string) {} // error
+}
+
+
+//// [classAbstractAccessor.js]
+var A = (function () {
+    function A() {
+    }
+    Object.defineProperty(A.prototype, "aa", {
+        get: function () { return 1; } // error
+        ,
+        enumerable: true,
+        configurable: true
+    });
+    Object.defineProperty(A.prototype, "bb", {
+        set: function (x) { } // error
+        ,
+        enumerable: true,
+        configurable: true
+    });
+    return A;
+}());

tests/baselines/reference/declarationEmitIndexTypeNotFound.errors.txt

@@ -0,0 +1,17 @@
+tests/cases/compiler/declarationEmitIndexTypeNotFound.ts(3,6): error TS1023: An index signature parameter type must be 'string' or 'number'.
+tests/cases/compiler/declarationEmitIndexTypeNotFound.ts(3,13): error TS2304: Cannot find name 'TypeNotFound'.
+tests/cases/compiler/declarationEmitIndexTypeNotFound.ts(3,13): error TS4092: Parameter 'index' of index signature from exported interface has or is using private name 'TypeNotFound'.
+
+
+==== tests/cases/compiler/declarationEmitIndexTypeNotFound.ts (3 errors) ====
+    
+    export interface Test {
+        [index: TypeNotFound]: any;
+         ~~~~~
+!!! error TS1023: An index signature parameter type must be 'string' or 'number'.
+                ~~~~~~~~~~~~
+!!! error TS2304: Cannot find name 'TypeNotFound'.
+                ~~~~~~~~~~~~
+!!! error TS4092: Parameter 'index' of index signature from exported interface has or is using private name 'TypeNotFound'.
+    }
+    

tests/baselines/reference/declarationEmitIndexTypeNotFound.js

@@ -0,0 +1,9 @@
+//// [declarationEmitIndexTypeNotFound.ts]
+
+export interface Test {
+    [index: TypeNotFound]: any;
+}
+
+
+//// [declarationEmitIndexTypeNotFound.js]
+"use strict";

tests/baselines/reference/decoratorWithUnderscoreMethod.js

@@ -0,0 +1,37 @@
+//// [decoratorWithUnderscoreMethod.ts]
+
+declare var console : { log(arg: string): void };
+function dec(): Function {
+    return function (target: any, propKey: string, descr: PropertyDescriptor): void {
+        console.log(target[propKey]);
+        //logs undefined
+        //propKey has three underscores as prefix, but the method has only two underscores
+    };
+}
+
+class A {
+    @dec()
+    private __foo(bar: string): void {
+        // do something with bar
+    }
+}
+
+//// [decoratorWithUnderscoreMethod.js]
+function dec() {
+    return function (target, propKey, descr) {
+        console.log(target[propKey]);
+        //logs undefined
+        //propKey has three underscores as prefix, but the method has only two underscores
+    };
+}
+var A = (function () {
+    function A() {
+    }
+    A.prototype.__foo = function (bar) {
+        // do something with bar
+    };
+    return A;
+}());
+__decorate([
+    dec()
+], A.prototype, "__foo");

tests/baselines/reference/decoratorWithUnderscoreMethod.symbols

@@ -0,0 +1,42 @@
+=== tests/cases/compiler/decoratorWithUnderscoreMethod.ts ===
+
+declare var console : { log(arg: string): void };
+>console : Symbol(console, Decl(decoratorWithUnderscoreMethod.ts, 1, 11))
+>log : Symbol(log, Decl(decoratorWithUnderscoreMethod.ts, 1, 23))
+>arg : Symbol(arg, Decl(decoratorWithUnderscoreMethod.ts, 1, 28))
+
+function dec(): Function {
+>dec : Symbol(dec, Decl(decoratorWithUnderscoreMethod.ts, 1, 49))
+>Function : Symbol(Function, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+
+    return function (target: any, propKey: string, descr: PropertyDescriptor): void {
+>target : Symbol(target, Decl(decoratorWithUnderscoreMethod.ts, 3, 21))
+>propKey : Symbol(propKey, Decl(decoratorWithUnderscoreMethod.ts, 3, 33))
+>descr : Symbol(descr, Decl(decoratorWithUnderscoreMethod.ts, 3, 50))
+>PropertyDescriptor : Symbol(PropertyDescriptor, Decl(lib.d.ts, --, --))
+
+        console.log(target[propKey]);
+>console.log : Symbol(log, Decl(decoratorWithUnderscoreMethod.ts, 1, 23))
+>console : Symbol(console, Decl(decoratorWithUnderscoreMethod.ts, 1, 11))
+>log : Symbol(log, Decl(decoratorWithUnderscoreMethod.ts, 1, 23))
+>target : Symbol(target, Decl(decoratorWithUnderscoreMethod.ts, 3, 21))
+>propKey : Symbol(propKey, Decl(decoratorWithUnderscoreMethod.ts, 3, 33))
+
+        //logs undefined
+        //propKey has three underscores as prefix, but the method has only two underscores
+    };
+}
+
+class A {
+>A : Symbol(A, Decl(decoratorWithUnderscoreMethod.ts, 8, 1))
+
+    @dec()
+>dec : Symbol(dec, Decl(decoratorWithUnderscoreMethod.ts, 1, 49))
+
+    private __foo(bar: string): void {
+>__foo : Symbol(A.__foo, Decl(decoratorWithUnderscoreMethod.ts, 10, 9))
+>bar : Symbol(bar, Decl(decoratorWithUnderscoreMethod.ts, 12, 18))
+
+        // do something with bar
+    }
+}

tests/baselines/reference/decoratorWithUnderscoreMethod.types

@@ -0,0 +1,46 @@
+=== tests/cases/compiler/decoratorWithUnderscoreMethod.ts ===
+
+declare var console : { log(arg: string): void };
+>console : { log(arg: string): void; }
+>log : (arg: string) => void
+>arg : string
+
+function dec(): Function {
+>dec : () => Function
+>Function : Function
+
+    return function (target: any, propKey: string, descr: PropertyDescriptor): void {
+>function (target: any, propKey: string, descr: PropertyDescriptor): void {        console.log(target[propKey]);        //logs undefined        //propKey has three underscores as prefix, but the method has only two underscores    } : (target: any, propKey: string, descr: PropertyDescriptor) => void
+>target : any
+>propKey : string
+>descr : PropertyDescriptor
+>PropertyDescriptor : PropertyDescriptor
+
+        console.log(target[propKey]);
+>console.log(target[propKey]) : void
+>console.log : (arg: string) => void
+>console : { log(arg: string): void; }
+>log : (arg: string) => void
+>target[propKey] : any
+>target : any
+>propKey : string
+
+        //logs undefined
+        //propKey has three underscores as prefix, but the method has only two underscores
+    };
+}
+
+class A {
+>A : A
+
+    @dec()
+>dec() : Function
+>dec : () => Function
+
+    private __foo(bar: string): void {
+>__foo : (bar: string) => void
+>bar : string
+
+        // do something with bar
+    }
+}

tests/baselines/reference/exhaustiveSwitchWithWideningLiteralTypes.js

@@ -0,0 +1,39 @@
+//// [exhaustiveSwitchWithWideningLiteralTypes.ts]
+
+// Repro from #12529
+
+class A {
+    readonly kind = "A"; // (property) A.kind: "A"
+}
+
+class B {
+    readonly kind = "B"; // (property) B.kind: "B"
+}
+
+function f(value: A | B): number {
+    switch(value.kind) {
+        case "A": return 0;
+        case "B": return 1;
+    }
+}
+
+//// [exhaustiveSwitchWithWideningLiteralTypes.js]
+// Repro from #12529
+var A = (function () {
+    function A() {
+        this.kind = "A"; // (property) A.kind: "A"
+    }
+    return A;
+}());
+var B = (function () {
+    function B() {
+        this.kind = "B"; // (property) B.kind: "B"
+    }
+    return B;
+}());
+function f(value) {
+    switch (value.kind) {
+        case "A": return 0;
+        case "B": return 1;
+    }
+}

tests/baselines/reference/exhaustiveSwitchWithWideningLiteralTypes.symbols

@@ -0,0 +1,33 @@
+=== tests/cases/compiler/exhaustiveSwitchWithWideningLiteralTypes.ts ===
+
+// Repro from #12529
+
+class A {
+>A : Symbol(A, Decl(exhaustiveSwitchWithWideningLiteralTypes.ts, 0, 0))
+
+    readonly kind = "A"; // (property) A.kind: "A"
+>kind : Symbol(A.kind, Decl(exhaustiveSwitchWithWideningLiteralTypes.ts, 3, 9))
+}
+
+class B {
+>B : Symbol(B, Decl(exhaustiveSwitchWithWideningLiteralTypes.ts, 5, 1))
+
+    readonly kind = "B"; // (property) B.kind: "B"
+>kind : Symbol(B.kind, Decl(exhaustiveSwitchWithWideningLiteralTypes.ts, 7, 9))
+}
+
+function f(value: A | B): number {
+>f : Symbol(f, Decl(exhaustiveSwitchWithWideningLiteralTypes.ts, 9, 1))
+>value : Symbol(value, Decl(exhaustiveSwitchWithWideningLiteralTypes.ts, 11, 11))
+>A : Symbol(A, Decl(exhaustiveSwitchWithWideningLiteralTypes.ts, 0, 0))
+>B : Symbol(B, Decl(exhaustiveSwitchWithWideningLiteralTypes.ts, 5, 1))
+
+    switch(value.kind) {
+>value.kind : Symbol(kind, Decl(exhaustiveSwitchWithWideningLiteralTypes.ts, 3, 9), Decl(exhaustiveSwitchWithWideningLiteralTypes.ts, 7, 9))
+>value : Symbol(value, Decl(exhaustiveSwitchWithWideningLiteralTypes.ts, 11, 11))
+>kind : Symbol(kind, Decl(exhaustiveSwitchWithWideningLiteralTypes.ts, 3, 9), Decl(exhaustiveSwitchWithWideningLiteralTypes.ts, 7, 9))
+
+        case "A": return 0;
+        case "B": return 1;
+    }
+}

tests/baselines/reference/exhaustiveSwitchWithWideningLiteralTypes.types

@@ -0,0 +1,40 @@
+=== tests/cases/compiler/exhaustiveSwitchWithWideningLiteralTypes.ts ===
+
+// Repro from #12529
+
+class A {
+>A : A
+
+    readonly kind = "A"; // (property) A.kind: "A"
+>kind : "A"
+>"A" : "A"
+}
+
+class B {
+>B : B
+
+    readonly kind = "B"; // (property) B.kind: "B"
+>kind : "B"
+>"B" : "B"
+}
+
+function f(value: A | B): number {
+>f : (value: A | B) => number
+>value : A | B
+>A : A
+>B : B
+
+    switch(value.kind) {
+>value.kind : "A" | "B"
+>value : A | B
+>kind : "A" | "B"
+
+        case "A": return 0;
+>"A" : "A"
+>0 : 0
+
+        case "B": return 1;
+>"B" : "B"
+>1 : 1
+    }
+}

tests/baselines/reference/importHelpersNoHelpers.errors.txt

@@ -1,32 +1,38 @@
-error TS2305: Module 'tslib' has no exported member '__assign'.
-error TS2305: Module 'tslib' has no exported member '__decorate'.
-error TS2305: Module 'tslib' has no exported member '__extends'.
-error TS2305: Module 'tslib' has no exported member '__metadata'.
-error TS2305: Module 'tslib' has no exported member '__param'.
-error TS2305: Module 'tslib' has no exported member '__rest'.
+tests/cases/compiler/external.ts(2,16): error TS2343: This syntax requires an imported helper named '__extends', but module 'tslib' has no exported member '__extends'.
+tests/cases/compiler/external.ts(6,1): error TS2343: This syntax requires an imported helper named '__decorate', but module 'tslib' has no exported member '__decorate'.
+tests/cases/compiler/external.ts(6,1): error TS2343: This syntax requires an imported helper named '__metadata', but module 'tslib' has no exported member '__metadata'.
+tests/cases/compiler/external.ts(8,12): error TS2343: This syntax requires an imported helper named '__param', but module 'tslib' has no exported member '__param'.
+tests/cases/compiler/external.ts(13,13): error TS2343: This syntax requires an imported helper named '__assign', but module 'tslib' has no exported member '__assign'.
+tests/cases/compiler/external.ts(14,12): error TS2343: This syntax requires an imported helper named '__rest', but module 'tslib' has no exported member '__rest'.
 
 
-!!! error TS2305: Module 'tslib' has no exported member '__assign'.
-!!! error TS2305: Module 'tslib' has no exported member '__decorate'.
-!!! error TS2305: Module 'tslib' has no exported member '__extends'.
-!!! error TS2305: Module 'tslib' has no exported member '__metadata'.
-!!! error TS2305: Module 'tslib' has no exported member '__param'.
-!!! error TS2305: Module 'tslib' has no exported member '__rest'.
-==== tests/cases/compiler/external.ts (0 errors) ====
+==== tests/cases/compiler/external.ts (6 errors) ====
     export class A { }
     export class B extends A { }
+                   ~~~~~~~~~
+!!! error TS2343: This syntax requires an imported helper named '__extends', but module 'tslib' has no exported member '__extends'.
     
     declare var dec: any;
     
     @dec
+    ~~~~
+!!! error TS2343: This syntax requires an imported helper named '__decorate', but module 'tslib' has no exported member '__decorate'.
+    ~~~~
+!!! error TS2343: This syntax requires an imported helper named '__metadata', but module 'tslib' has no exported member '__metadata'.
     class C {
         method(@dec x: number) {
+               ~~~~
+!!! error TS2343: This syntax requires an imported helper named '__param', but module 'tslib' has no exported member '__param'.
         }
     }
     
     const o = { a: 1 };
     const y = { ...o };
+                ~~~~
+!!! error TS2343: This syntax requires an imported helper named '__assign', but module 'tslib' has no exported member '__assign'.
     const { ...x } = y;
+               ~
+!!! error TS2343: This syntax requires an imported helper named '__rest', but module 'tslib' has no exported member '__rest'.
     
 ==== tests/cases/compiler/script.ts (0 errors) ====
     class A { }

tests/baselines/reference/importHelpersNoModule.errors.txt

@@ -1,10 +1,11 @@
-error TS2307: Cannot find module 'tslib'.
+tests/cases/compiler/external.ts(2,16): error TS2354: This syntax requires an imported helper but module 'tslib' cannot be found.
 
 
-!!! error TS2307: Cannot find module 'tslib'.
-==== tests/cases/compiler/external.ts (0 errors) ====
+==== tests/cases/compiler/external.ts (1 errors) ====
     export class A { }
     export class B extends A { }
+                   ~~~~~~~~~
+!!! error TS2354: This syntax requires an imported helper but module 'tslib' cannot be found.
     
     declare var dec: any;
     

tests/baselines/reference/intersectionTypeNormalization.js

@@ -58,6 +58,51 @@ function getValueAsString(value: IntersectionFail): string {
         return '' + value.num;
     }
     return value.str;
+}
+
+// Repro from #12535
+
+namespace enums {
+    export const enum A {
+        a1,
+        a2,
+        a3,
+       // ... elements omitted for the sake of clarity
+        a75,
+        a76,
+        a77,
+    }
+    export const enum B {
+        b1,
+        b2,
+       // ... elements omitted for the sake of clarity
+        b86,
+        b87,
+    }
+    export const enum C {
+        c1,
+        c2,
+       // ... elements omitted for the sake of clarity
+        c210,
+        c211,
+    }
+    export type Genre = A | B | C;
+}
+
+type Foo = {
+    genreId: enums.Genre;
+};
+
+type Bar = {
+    genreId: enums.Genre;
+};
+
+type FooBar = Foo & Bar;
+
+function foo(so: any) {
+    const val = so as FooBar;
+    const isGenre = val.genreId;
+    return isGenre;
 }
 
 //// [intersectionTypeNormalization.js]
@@ -77,3 +122,8 @@ function getValueAsString(value) {
     }
     return value.str;
 }
+function foo(so) {
+    var val = so;
+    var isGenre = val.genreId;
+    return isGenre;
+}

tests/baselines/reference/intersectionTypeNormalization.symbols

@@ -240,3 +240,113 @@ function getValueAsString(value: IntersectionFail): string {
 >value : Symbol(value, Decl(intersectionTypeNormalization.ts, 54, 26))
 >str : Symbol(str, Decl(intersectionTypeNormalization.ts, 47, 35))
 }
+
+// Repro from #12535
+
+namespace enums {
+>enums : Symbol(enums, Decl(intersectionTypeNormalization.ts, 59, 1))
+
+    export const enum A {
+>A : Symbol(A, Decl(intersectionTypeNormalization.ts, 63, 17))
+
+        a1,
+>a1 : Symbol(A.a1, Decl(intersectionTypeNormalization.ts, 64, 25))
+
+        a2,
+>a2 : Symbol(A.a2, Decl(intersectionTypeNormalization.ts, 65, 11))
+
+        a3,
+>a3 : Symbol(A.a3, Decl(intersectionTypeNormalization.ts, 66, 11))
+
+       // ... elements omitted for the sake of clarity
+        a75,
+>a75 : Symbol(A.a75, Decl(intersectionTypeNormalization.ts, 67, 11))
+
+        a76,
+>a76 : Symbol(A.a76, Decl(intersectionTypeNormalization.ts, 69, 12))
+
+        a77,
+>a77 : Symbol(A.a77, Decl(intersectionTypeNormalization.ts, 70, 12))
+    }
+    export const enum B {
+>B : Symbol(B, Decl(intersectionTypeNormalization.ts, 72, 5))
+
+        b1,
+>b1 : Symbol(B.b1, Decl(intersectionTypeNormalization.ts, 73, 25))
+
+        b2,
+>b2 : Symbol(B.b2, Decl(intersectionTypeNormalization.ts, 74, 11))
+
+       // ... elements omitted for the sake of clarity
+        b86,
+>b86 : Symbol(B.b86, Decl(intersectionTypeNormalization.ts, 75, 11))
+
+        b87,
+>b87 : Symbol(B.b87, Decl(intersectionTypeNormalization.ts, 77, 12))
+    }
+    export const enum C {
+>C : Symbol(C, Decl(intersectionTypeNormalization.ts, 79, 5))
+
+        c1,
+>c1 : Symbol(C.c1, Decl(intersectionTypeNormalization.ts, 80, 25))
+
+        c2,
+>c2 : Symbol(C.c2, Decl(intersectionTypeNormalization.ts, 81, 11))
+
+       // ... elements omitted for the sake of clarity
+        c210,
+>c210 : Symbol(C.c210, Decl(intersectionTypeNormalization.ts, 82, 11))
+
+        c211,
+>c211 : Symbol(C.c211, Decl(intersectionTypeNormalization.ts, 84, 13))
+    }
+    export type Genre = A | B | C;
+>Genre : Symbol(Genre, Decl(intersectionTypeNormalization.ts, 86, 5))
+>A : Symbol(A, Decl(intersectionTypeNormalization.ts, 63, 17))
+>B : Symbol(B, Decl(intersectionTypeNormalization.ts, 72, 5))
+>C : Symbol(C, Decl(intersectionTypeNormalization.ts, 79, 5))
+}
+
+type Foo = {
+>Foo : Symbol(Foo, Decl(intersectionTypeNormalization.ts, 88, 1))
+
+    genreId: enums.Genre;
+>genreId : Symbol(genreId, Decl(intersectionTypeNormalization.ts, 90, 12))
+>enums : Symbol(enums, Decl(intersectionTypeNormalization.ts, 59, 1))
+>Genre : Symbol(enums.Genre, Decl(intersectionTypeNormalization.ts, 86, 5))
+
+};
+
+type Bar = {
+>Bar : Symbol(Bar, Decl(intersectionTypeNormalization.ts, 92, 2))
+
+    genreId: enums.Genre;
+>genreId : Symbol(genreId, Decl(intersectionTypeNormalization.ts, 94, 12))
+>enums : Symbol(enums, Decl(intersectionTypeNormalization.ts, 59, 1))
+>Genre : Symbol(enums.Genre, Decl(intersectionTypeNormalization.ts, 86, 5))
+
+};
+
+type FooBar = Foo & Bar;
+>FooBar : Symbol(FooBar, Decl(intersectionTypeNormalization.ts, 96, 2))
+>Foo : Symbol(Foo, Decl(intersectionTypeNormalization.ts, 88, 1))
+>Bar : Symbol(Bar, Decl(intersectionTypeNormalization.ts, 92, 2))
+
+function foo(so: any) {
+>foo : Symbol(foo, Decl(intersectionTypeNormalization.ts, 98, 24))
+>so : Symbol(so, Decl(intersectionTypeNormalization.ts, 100, 13))
+
+    const val = so as FooBar;
+>val : Symbol(val, Decl(intersectionTypeNormalization.ts, 101, 9))
+>so : Symbol(so, Decl(intersectionTypeNormalization.ts, 100, 13))
+>FooBar : Symbol(FooBar, Decl(intersectionTypeNormalization.ts, 96, 2))
+
+    const isGenre = val.genreId;
+>isGenre : Symbol(isGenre, Decl(intersectionTypeNormalization.ts, 102, 9))
+>val.genreId : Symbol(genreId, Decl(intersectionTypeNormalization.ts, 90, 12), Decl(intersectionTypeNormalization.ts, 94, 12))
+>val : Symbol(val, Decl(intersectionTypeNormalization.ts, 101, 9))
+>genreId : Symbol(genreId, Decl(intersectionTypeNormalization.ts, 90, 12), Decl(intersectionTypeNormalization.ts, 94, 12))
+
+    return isGenre;
+>isGenre : Symbol(isGenre, Decl(intersectionTypeNormalization.ts, 102, 9))
+}

tests/baselines/reference/intersectionTypeNormalization.types

@@ -244,3 +244,114 @@ function getValueAsString(value: IntersectionFail): string {
 >value : { kind: "string"; str: string; } & ToString
 >str : string
 }
+
+// Repro from #12535
+
+namespace enums {
+>enums : typeof enums
+
+    export const enum A {
+>A : A
+
+        a1,
+>a1 : A.a1
+
+        a2,
+>a2 : A.a2
+
+        a3,
+>a3 : A.a3
+
+       // ... elements omitted for the sake of clarity
+        a75,
+>a75 : A.a75
+
+        a76,
+>a76 : A.a76
+
+        a77,
+>a77 : A.a77
+    }
+    export const enum B {
+>B : B
+
+        b1,
+>b1 : B.b1
+
+        b2,
+>b2 : B.b2
+
+       // ... elements omitted for the sake of clarity
+        b86,
+>b86 : B.b86
+
+        b87,
+>b87 : B.b87
+    }
+    export const enum C {
+>C : C
+
+        c1,
+>c1 : C.c1
+
+        c2,
+>c2 : C.c2
+
+       // ... elements omitted for the sake of clarity
+        c210,
+>c210 : C.c210
+
+        c211,
+>c211 : C.c211
+    }
+    export type Genre = A | B | C;
+>Genre : Genre
+>A : A
+>B : B
+>C : C
+}
+
+type Foo = {
+>Foo : Foo
+
+    genreId: enums.Genre;
+>genreId : enums.Genre
+>enums : any
+>Genre : enums.Genre
+
+};
+
+type Bar = {
+>Bar : Bar
+
+    genreId: enums.Genre;
+>genreId : enums.Genre
+>enums : any
+>Genre : enums.Genre
+
+};
+
+type FooBar = Foo & Bar;
+>FooBar : FooBar
+>Foo : Foo
+>Bar : Bar
+
+function foo(so: any) {
+>foo : (so: any) => enums.Genre
+>so : any
+
+    const val = so as FooBar;
+>val : FooBar
+>so as FooBar : FooBar
+>so : any
+>FooBar : FooBar
+
+    const isGenre = val.genreId;
+>isGenre : enums.Genre
+>val.genreId : enums.Genre
+>val : FooBar
+>genreId : enums.Genre
+
+    return isGenre;
+>isGenre : enums.Genre
+}

tests/baselines/reference/intersectionTypeWithLeadingOperator.js

@@ -0,0 +1,10 @@
+//// [intersectionTypeWithLeadingOperator.ts]
+type A = & string;
+type B =
+  & { foo: string }
+  & { bar: number };
+
+type C = [& { foo: 1 } & { bar: 2 }, & { foo: 3 } & { bar: 4 }];
+
+
+//// [intersectionTypeWithLeadingOperator.js]

tests/baselines/reference/intersectionTypeWithLeadingOperator.symbols

@@ -0,0 +1,20 @@
+=== tests/cases/compiler/intersectionTypeWithLeadingOperator.ts ===
+type A = & string;
+>A : Symbol(A, Decl(intersectionTypeWithLeadingOperator.ts, 0, 0))
+
+type B =
+>B : Symbol(B, Decl(intersectionTypeWithLeadingOperator.ts, 0, 18))
+
+  & { foo: string }
+>foo : Symbol(foo, Decl(intersectionTypeWithLeadingOperator.ts, 2, 5))
+
+  & { bar: number };
+>bar : Symbol(bar, Decl(intersectionTypeWithLeadingOperator.ts, 3, 5))
+
+type C = [& { foo: 1 } & { bar: 2 }, & { foo: 3 } & { bar: 4 }];
+>C : Symbol(C, Decl(intersectionTypeWithLeadingOperator.ts, 3, 20))
+>foo : Symbol(foo, Decl(intersectionTypeWithLeadingOperator.ts, 5, 13))
+>bar : Symbol(bar, Decl(intersectionTypeWithLeadingOperator.ts, 5, 26))
+>foo : Symbol(foo, Decl(intersectionTypeWithLeadingOperator.ts, 5, 40))
+>bar : Symbol(bar, Decl(intersectionTypeWithLeadingOperator.ts, 5, 53))
+

tests/baselines/reference/intersectionTypeWithLeadingOperator.types

@@ -0,0 +1,20 @@
+=== tests/cases/compiler/intersectionTypeWithLeadingOperator.ts ===
+type A = & string;
+>A : string
+
+type B =
+>B : B
+
+  & { foo: string }
+>foo : string
+
+  & { bar: number };
+>bar : number
+
+type C = [& { foo: 1 } & { bar: 2 }, & { foo: 3 } & { bar: 4 }];
+>C : [{ foo: 1; } & { bar: 2; }, { foo: 3; } & { bar: 4; }]
+>foo : 1
+>bar : 2
+>foo : 3
+>bar : 4
+

tests/baselines/reference/isomorphicMappedTypeInference.js

@@ -0,0 +1,330 @@
+//// [isomorphicMappedTypeInference.ts]
+
+type Box<T> = {
+    value: T;
+}
+
+type Boxified<T> = {
+    [P in keyof T]: Box<T[P]>;
+}
+
+function box<T>(x: T): Box<T> {
+    return { value: x };
+}
+
+function unbox<T>(x: Box<T>): T {
+    return x.value;
+}
+
+function boxify<T>(obj: T): Boxified<T> {
+    let result = {} as Boxified<T>;
+    for (let k in obj) {
+        result[k] = box(obj[k]);
+    }
+    return result;
+}
+
+function unboxify<T>(obj: Boxified<T>): T {
+    let result = {} as T;
+    for (let k in obj) {
+        result[k] = unbox(obj[k]);
+    }
+    return result;
+}
+
+function assignBoxified<T>(obj: Boxified<T>, values: T) {
+    for (let k in values) {
+        obj[k].value = values[k];
+    }
+}
+
+function f1() {
+    let v = {
+        a: 42,
+        b: "hello",
+        c: true
+    };
+    let b = boxify(v);
+    let x: number = b.a.value;
+}
+
+function f2() {
+    let b = {
+        a: box(42),
+        b: box("hello"),
+        c: box(true)
+    };
+    let v = unboxify(b);
+    let x: number = v.a;
+}
+
+function f3() {
+    let b = {
+        a: box(42),
+        b: box("hello"),
+        c: box(true)
+    };
+    assignBoxified(b, { c: false });
+}
+
+function f4() {
+    let b = {
+        a: box(42),
+        b: box("hello"),
+        c: box(true)
+    };
+    b = boxify(unboxify(b));
+    b = unboxify(boxify(b));
+}
+
+function makeRecord<T, K extends string>(obj: { [P in K]: T }) {
+    return obj;
+}
+
+function f5(s: string) {
+    let b = makeRecord({
+        a: box(42),
+        b: box("hello"),
+        c: box(true)
+    });
+    let v = unboxify(b);
+    let x: string | number | boolean = v.a;
+}
+
+function makeDictionary<T>(obj: { [x: string]: T }) {
+    return obj;
+}
+
+function f6(s: string) {
+    let b = makeDictionary({
+        a: box(42),
+        b: box("hello"),
+        c: box(true)
+    });
+    let v = unboxify(b);
+    let x: string | number | boolean = v[s];
+}
+
+declare function validate<T>(obj: { [P in keyof T]?: T[P] }): T;
+declare function clone<T>(obj: { readonly [P in keyof T]: T[P] }): T;
+declare function validateAndClone<T>(obj: { readonly [P in keyof T]?: T[P] }): T;
+
+type Foo = {
+    a?: number;
+    readonly b: string;
+}
+
+function f10(foo: Foo) {
+    let x = validate(foo);  // { a: number, readonly b: string }
+    let y = clone(foo);  // { a?: number, b: string }
+    let z = validateAndClone(foo);  // { a: number, b: string }
+}
+
+// Repro from #12606
+
+type Func<T> = (...args: any[]) => T;
+type Spec<T> = {
+    [P in keyof T]: Func<T[P]> | Spec<T[P]> ;
+};
+
+/**
+ * Given a spec object recursively mapping properties to functions, creates a function
+ * producing an object of the same structure, by mapping each property to the result
+ * of calling its associated function with the supplied arguments.
+ */
+declare function applySpec<T>(obj: Spec<T>): (...args: any[]) => T;
+
+// Infers g1: (...args: any[]) => { sum: number, nested: { mul: string } }
+var g1 = applySpec({
+    sum: (a: any) => 3,
+    nested: {
+        mul: (b: any) => "n"
+    }
+});
+
+// Infers g2: (...args: any[]) => { foo: { bar: { baz: boolean } } }
+var g2 = applySpec({ foo: { bar: { baz: (x: any) => true } } });
+
+// Repro from #12633
+
+const foo = <T>(object: T, partial: Partial<T>) => object;
+let o = {a: 5, b: 7};
+foo(o, {b: 9});
+o = foo(o, {b: 9});
+
+//// [isomorphicMappedTypeInference.js]
+function box(x) {
+    return { value: x };
+}
+function unbox(x) {
+    return x.value;
+}
+function boxify(obj) {
+    var result = {};
+    for (var k in obj) {
+        result[k] = box(obj[k]);
+    }
+    return result;
+}
+function unboxify(obj) {
+    var result = {};
+    for (var k in obj) {
+        result[k] = unbox(obj[k]);
+    }
+    return result;
+}
+function assignBoxified(obj, values) {
+    for (var k in values) {
+        obj[k].value = values[k];
+    }
+}
+function f1() {
+    var v = {
+        a: 42,
+        b: "hello",
+        c: true
+    };
+    var b = boxify(v);
+    var x = b.a.value;
+}
+function f2() {
+    var b = {
+        a: box(42),
+        b: box("hello"),
+        c: box(true)
+    };
+    var v = unboxify(b);
+    var x = v.a;
+}
+function f3() {
+    var b = {
+        a: box(42),
+        b: box("hello"),
+        c: box(true)
+    };
+    assignBoxified(b, { c: false });
+}
+function f4() {
+    var b = {
+        a: box(42),
+        b: box("hello"),
+        c: box(true)
+    };
+    b = boxify(unboxify(b));
+    b = unboxify(boxify(b));
+}
+function makeRecord(obj) {
+    return obj;
+}
+function f5(s) {
+    var b = makeRecord({
+        a: box(42),
+        b: box("hello"),
+        c: box(true)
+    });
+    var v = unboxify(b);
+    var x = v.a;
+}
+function makeDictionary(obj) {
+    return obj;
+}
+function f6(s) {
+    var b = makeDictionary({
+        a: box(42),
+        b: box("hello"),
+        c: box(true)
+    });
+    var v = unboxify(b);
+    var x = v[s];
+}
+function f10(foo) {
+    var x = validate(foo); // { a: number, readonly b: string }
+    var y = clone(foo); // { a?: number, b: string }
+    var z = validateAndClone(foo); // { a: number, b: string }
+}
+// Infers g1: (...args: any[]) => { sum: number, nested: { mul: string } }
+var g1 = applySpec({
+    sum: function (a) { return 3; },
+    nested: {
+        mul: function (b) { return "n"; }
+    }
+});
+// Infers g2: (...args: any[]) => { foo: { bar: { baz: boolean } } }
+var g2 = applySpec({ foo: { bar: { baz: function (x) { return true; } } } });
+// Repro from #12633
+var foo = function (object, partial) { return object; };
+var o = { a: 5, b: 7 };
+foo(o, { b: 9 });
+o = foo(o, { b: 9 });
+
+
+//// [isomorphicMappedTypeInference.d.ts]
+declare type Box<T> = {
+    value: T;
+};
+declare type Boxified<T> = {
+    [P in keyof T]: Box<T[P]>;
+};
+declare function box<T>(x: T): Box<T>;
+declare function unbox<T>(x: Box<T>): T;
+declare function boxify<T>(obj: T): Boxified<T>;
+declare function unboxify<T>(obj: Boxified<T>): T;
+declare function assignBoxified<T>(obj: Boxified<T>, values: T): void;
+declare function f1(): void;
+declare function f2(): void;
+declare function f3(): void;
+declare function f4(): void;
+declare function makeRecord<T, K extends string>(obj: {
+    [P in K]: T;
+}): {
+    [P in K]: T;
+};
+declare function f5(s: string): void;
+declare function makeDictionary<T>(obj: {
+    [x: string]: T;
+}): {
+    [x: string]: T;
+};
+declare function f6(s: string): void;
+declare function validate<T>(obj: {
+    [P in keyof T]?: T[P];
+}): T;
+declare function clone<T>(obj: {
+    readonly [P in keyof T]: T[P];
+}): T;
+declare function validateAndClone<T>(obj: {
+    readonly [P in keyof T]?: T[P];
+}): T;
+declare type Foo = {
+    a?: number;
+    readonly b: string;
+};
+declare function f10(foo: Foo): void;
+declare type Func<T> = (...args: any[]) => T;
+declare type Spec<T> = {
+    [P in keyof T]: Func<T[P]> | Spec<T[P]>;
+};
+/**
+ * Given a spec object recursively mapping properties to functions, creates a function
+ * producing an object of the same structure, by mapping each property to the result
+ * of calling its associated function with the supplied arguments.
+ */
+declare function applySpec<T>(obj: Spec<T>): (...args: any[]) => T;
+declare var g1: (...args: any[]) => {
+    sum: number;
+    nested: {
+        mul: string;
+    };
+};
+declare var g2: (...args: any[]) => {
+    foo: {
+        bar: {
+            baz: boolean;
+        };
+    };
+};
+declare const foo: <T>(object: T, partial: Partial<T>) => T;
+declare let o: {
+    a: number;
+    b: number;
+};

tests/baselines/reference/isomorphicMappedTypeInference.symbols

@@ -0,0 +1,489 @@
+=== tests/cases/conformance/types/mapped/isomorphicMappedTypeInference.ts ===
+
+type Box<T> = {
+>Box : Symbol(Box, Decl(isomorphicMappedTypeInference.ts, 0, 0))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 1, 9))
+
+    value: T;
+>value : Symbol(value, Decl(isomorphicMappedTypeInference.ts, 1, 15))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 1, 9))
+}
+
+type Boxified<T> = {
+>Boxified : Symbol(Boxified, Decl(isomorphicMappedTypeInference.ts, 3, 1))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 5, 14))
+
+    [P in keyof T]: Box<T[P]>;
+>P : Symbol(P, Decl(isomorphicMappedTypeInference.ts, 6, 5))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 5, 14))
+>Box : Symbol(Box, Decl(isomorphicMappedTypeInference.ts, 0, 0))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 5, 14))
+>P : Symbol(P, Decl(isomorphicMappedTypeInference.ts, 6, 5))
+}
+
+function box<T>(x: T): Box<T> {
+>box : Symbol(box, Decl(isomorphicMappedTypeInference.ts, 7, 1))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 9, 13))
+>x : Symbol(x, Decl(isomorphicMappedTypeInference.ts, 9, 16))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 9, 13))
+>Box : Symbol(Box, Decl(isomorphicMappedTypeInference.ts, 0, 0))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 9, 13))
+
+    return { value: x };
+>value : Symbol(value, Decl(isomorphicMappedTypeInference.ts, 10, 12))
+>x : Symbol(x, Decl(isomorphicMappedTypeInference.ts, 9, 16))
+}
+
+function unbox<T>(x: Box<T>): T {
+>unbox : Symbol(unbox, Decl(isomorphicMappedTypeInference.ts, 11, 1))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 13, 15))
+>x : Symbol(x, Decl(isomorphicMappedTypeInference.ts, 13, 18))
+>Box : Symbol(Box, Decl(isomorphicMappedTypeInference.ts, 0, 0))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 13, 15))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 13, 15))
+
+    return x.value;
+>x.value : Symbol(value, Decl(isomorphicMappedTypeInference.ts, 1, 15))
+>x : Symbol(x, Decl(isomorphicMappedTypeInference.ts, 13, 18))
+>value : Symbol(value, Decl(isomorphicMappedTypeInference.ts, 1, 15))
+}
+
+function boxify<T>(obj: T): Boxified<T> {
+>boxify : Symbol(boxify, Decl(isomorphicMappedTypeInference.ts, 15, 1))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 17, 16))
+>obj : Symbol(obj, Decl(isomorphicMappedTypeInference.ts, 17, 19))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 17, 16))
+>Boxified : Symbol(Boxified, Decl(isomorphicMappedTypeInference.ts, 3, 1))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 17, 16))
+
+    let result = {} as Boxified<T>;
+>result : Symbol(result, Decl(isomorphicMappedTypeInference.ts, 18, 7))
+>Boxified : Symbol(Boxified, Decl(isomorphicMappedTypeInference.ts, 3, 1))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 17, 16))
+
+    for (let k in obj) {
+>k : Symbol(k, Decl(isomorphicMappedTypeInference.ts, 19, 12))
+>obj : Symbol(obj, Decl(isomorphicMappedTypeInference.ts, 17, 19))
+
+        result[k] = box(obj[k]);
+>result : Symbol(result, Decl(isomorphicMappedTypeInference.ts, 18, 7))
+>k : Symbol(k, Decl(isomorphicMappedTypeInference.ts, 19, 12))
+>box : Symbol(box, Decl(isomorphicMappedTypeInference.ts, 7, 1))
+>obj : Symbol(obj, Decl(isomorphicMappedTypeInference.ts, 17, 19))
+>k : Symbol(k, Decl(isomorphicMappedTypeInference.ts, 19, 12))
+    }
+    return result;
+>result : Symbol(result, Decl(isomorphicMappedTypeInference.ts, 18, 7))
+}
+
+function unboxify<T>(obj: Boxified<T>): T {
+>unboxify : Symbol(unboxify, Decl(isomorphicMappedTypeInference.ts, 23, 1))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 25, 18))
+>obj : Symbol(obj, Decl(isomorphicMappedTypeInference.ts, 25, 21))
+>Boxified : Symbol(Boxified, Decl(isomorphicMappedTypeInference.ts, 3, 1))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 25, 18))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 25, 18))
+
+    let result = {} as T;
+>result : Symbol(result, Decl(isomorphicMappedTypeInference.ts, 26, 7))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 25, 18))
+
+    for (let k in obj) {
+>k : Symbol(k, Decl(isomorphicMappedTypeInference.ts, 27, 12))
+>obj : Symbol(obj, Decl(isomorphicMappedTypeInference.ts, 25, 21))
+
+        result[k] = unbox(obj[k]);
+>result : Symbol(result, Decl(isomorphicMappedTypeInference.ts, 26, 7))
+>k : Symbol(k, Decl(isomorphicMappedTypeInference.ts, 27, 12))
+>unbox : Symbol(unbox, Decl(isomorphicMappedTypeInference.ts, 11, 1))
+>obj : Symbol(obj, Decl(isomorphicMappedTypeInference.ts, 25, 21))
+>k : Symbol(k, Decl(isomorphicMappedTypeInference.ts, 27, 12))
+    }
+    return result;
+>result : Symbol(result, Decl(isomorphicMappedTypeInference.ts, 26, 7))
+}
+
+function assignBoxified<T>(obj: Boxified<T>, values: T) {
+>assignBoxified : Symbol(assignBoxified, Decl(isomorphicMappedTypeInference.ts, 31, 1))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 33, 24))
+>obj : Symbol(obj, Decl(isomorphicMappedTypeInference.ts, 33, 27))
+>Boxified : Symbol(Boxified, Decl(isomorphicMappedTypeInference.ts, 3, 1))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 33, 24))
+>values : Symbol(values, Decl(isomorphicMappedTypeInference.ts, 33, 44))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 33, 24))
+
+    for (let k in values) {
+>k : Symbol(k, Decl(isomorphicMappedTypeInference.ts, 34, 12))
+>values : Symbol(values, Decl(isomorphicMappedTypeInference.ts, 33, 44))
+
+        obj[k].value = values[k];
+>obj[k].value : Symbol(value, Decl(isomorphicMappedTypeInference.ts, 1, 15))
+>obj : Symbol(obj, Decl(isomorphicMappedTypeInference.ts, 33, 27))
+>k : Symbol(k, Decl(isomorphicMappedTypeInference.ts, 34, 12))
+>value : Symbol(value, Decl(isomorphicMappedTypeInference.ts, 1, 15))
+>values : Symbol(values, Decl(isomorphicMappedTypeInference.ts, 33, 44))
+>k : Symbol(k, Decl(isomorphicMappedTypeInference.ts, 34, 12))
+    }
+}
+
+function f1() {
+>f1 : Symbol(f1, Decl(isomorphicMappedTypeInference.ts, 37, 1))
+
+    let v = {
+>v : Symbol(v, Decl(isomorphicMappedTypeInference.ts, 40, 7))
+
+        a: 42,
+>a : Symbol(a, Decl(isomorphicMappedTypeInference.ts, 40, 13))
+
+        b: "hello",
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 41, 14))
+
+        c: true
+>c : Symbol(c, Decl(isomorphicMappedTypeInference.ts, 42, 19))
+
+    };
+    let b = boxify(v);
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 45, 7))
+>boxify : Symbol(boxify, Decl(isomorphicMappedTypeInference.ts, 15, 1))
+>v : Symbol(v, Decl(isomorphicMappedTypeInference.ts, 40, 7))
+
+    let x: number = b.a.value;
+>x : Symbol(x, Decl(isomorphicMappedTypeInference.ts, 46, 7))
+>b.a.value : Symbol(value, Decl(isomorphicMappedTypeInference.ts, 1, 15))
+>b.a : Symbol(a)
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 45, 7))
+>a : Symbol(a)
+>value : Symbol(value, Decl(isomorphicMappedTypeInference.ts, 1, 15))
+}
+
+function f2() {
+>f2 : Symbol(f2, Decl(isomorphicMappedTypeInference.ts, 47, 1))
+
+    let b = {
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 50, 7))
+
+        a: box(42),
+>a : Symbol(a, Decl(isomorphicMappedTypeInference.ts, 50, 13))
+>box : Symbol(box, Decl(isomorphicMappedTypeInference.ts, 7, 1))
+
+        b: box("hello"),
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 51, 19))
+>box : Symbol(box, Decl(isomorphicMappedTypeInference.ts, 7, 1))
+
+        c: box(true)
+>c : Symbol(c, Decl(isomorphicMappedTypeInference.ts, 52, 24))
+>box : Symbol(box, Decl(isomorphicMappedTypeInference.ts, 7, 1))
+
+    };
+    let v = unboxify(b);
+>v : Symbol(v, Decl(isomorphicMappedTypeInference.ts, 55, 7))
+>unboxify : Symbol(unboxify, Decl(isomorphicMappedTypeInference.ts, 23, 1))
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 50, 7))
+
+    let x: number = v.a;
+>x : Symbol(x, Decl(isomorphicMappedTypeInference.ts, 56, 7))
+>v.a : Symbol(a, Decl(isomorphicMappedTypeInference.ts, 50, 13))
+>v : Symbol(v, Decl(isomorphicMappedTypeInference.ts, 55, 7))
+>a : Symbol(a, Decl(isomorphicMappedTypeInference.ts, 50, 13))
+}
+
+function f3() {
+>f3 : Symbol(f3, Decl(isomorphicMappedTypeInference.ts, 57, 1))
+
+    let b = {
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 60, 7))
+
+        a: box(42),
+>a : Symbol(a, Decl(isomorphicMappedTypeInference.ts, 60, 13))
+>box : Symbol(box, Decl(isomorphicMappedTypeInference.ts, 7, 1))
+
+        b: box("hello"),
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 61, 19))
+>box : Symbol(box, Decl(isomorphicMappedTypeInference.ts, 7, 1))
+
+        c: box(true)
+>c : Symbol(c, Decl(isomorphicMappedTypeInference.ts, 62, 24))
+>box : Symbol(box, Decl(isomorphicMappedTypeInference.ts, 7, 1))
+
+    };
+    assignBoxified(b, { c: false });
+>assignBoxified : Symbol(assignBoxified, Decl(isomorphicMappedTypeInference.ts, 31, 1))
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 60, 7))
+>c : Symbol(c, Decl(isomorphicMappedTypeInference.ts, 65, 23))
+}
+
+function f4() {
+>f4 : Symbol(f4, Decl(isomorphicMappedTypeInference.ts, 66, 1))
+
+    let b = {
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 69, 7))
+
+        a: box(42),
+>a : Symbol(a, Decl(isomorphicMappedTypeInference.ts, 69, 13))
+>box : Symbol(box, Decl(isomorphicMappedTypeInference.ts, 7, 1))
+
+        b: box("hello"),
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 70, 19))
+>box : Symbol(box, Decl(isomorphicMappedTypeInference.ts, 7, 1))
+
+        c: box(true)
+>c : Symbol(c, Decl(isomorphicMappedTypeInference.ts, 71, 24))
+>box : Symbol(box, Decl(isomorphicMappedTypeInference.ts, 7, 1))
+
+    };
+    b = boxify(unboxify(b));
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 69, 7))
+>boxify : Symbol(boxify, Decl(isomorphicMappedTypeInference.ts, 15, 1))
+>unboxify : Symbol(unboxify, Decl(isomorphicMappedTypeInference.ts, 23, 1))
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 69, 7))
+
+    b = unboxify(boxify(b));
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 69, 7))
+>unboxify : Symbol(unboxify, Decl(isomorphicMappedTypeInference.ts, 23, 1))
+>boxify : Symbol(boxify, Decl(isomorphicMappedTypeInference.ts, 15, 1))
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 69, 7))
+}
+
+function makeRecord<T, K extends string>(obj: { [P in K]: T }) {
+>makeRecord : Symbol(makeRecord, Decl(isomorphicMappedTypeInference.ts, 76, 1))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 78, 20))
+>K : Symbol(K, Decl(isomorphicMappedTypeInference.ts, 78, 22))
+>obj : Symbol(obj, Decl(isomorphicMappedTypeInference.ts, 78, 41))
+>P : Symbol(P, Decl(isomorphicMappedTypeInference.ts, 78, 49))
+>K : Symbol(K, Decl(isomorphicMappedTypeInference.ts, 78, 22))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 78, 20))
+
+    return obj;
+>obj : Symbol(obj, Decl(isomorphicMappedTypeInference.ts, 78, 41))
+}
+
+function f5(s: string) {
+>f5 : Symbol(f5, Decl(isomorphicMappedTypeInference.ts, 80, 1))
+>s : Symbol(s, Decl(isomorphicMappedTypeInference.ts, 82, 12))
+
+    let b = makeRecord({
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 83, 7))
+>makeRecord : Symbol(makeRecord, Decl(isomorphicMappedTypeInference.ts, 76, 1))
+
+        a: box(42),
+>a : Symbol(a, Decl(isomorphicMappedTypeInference.ts, 83, 24))
+>box : Symbol(box, Decl(isomorphicMappedTypeInference.ts, 7, 1))
+
+        b: box("hello"),
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 84, 19))
+>box : Symbol(box, Decl(isomorphicMappedTypeInference.ts, 7, 1))
+
+        c: box(true)
+>c : Symbol(c, Decl(isomorphicMappedTypeInference.ts, 85, 24))
+>box : Symbol(box, Decl(isomorphicMappedTypeInference.ts, 7, 1))
+
+    });
+    let v = unboxify(b);
+>v : Symbol(v, Decl(isomorphicMappedTypeInference.ts, 88, 7))
+>unboxify : Symbol(unboxify, Decl(isomorphicMappedTypeInference.ts, 23, 1))
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 83, 7))
+
+    let x: string | number | boolean = v.a;
+>x : Symbol(x, Decl(isomorphicMappedTypeInference.ts, 89, 7))
+>v.a : Symbol(a)
+>v : Symbol(v, Decl(isomorphicMappedTypeInference.ts, 88, 7))
+>a : Symbol(a)
+}
+
+function makeDictionary<T>(obj: { [x: string]: T }) {
+>makeDictionary : Symbol(makeDictionary, Decl(isomorphicMappedTypeInference.ts, 90, 1))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 92, 24))
+>obj : Symbol(obj, Decl(isomorphicMappedTypeInference.ts, 92, 27))
+>x : Symbol(x, Decl(isomorphicMappedTypeInference.ts, 92, 35))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 92, 24))
+
+    return obj;
+>obj : Symbol(obj, Decl(isomorphicMappedTypeInference.ts, 92, 27))
+}
+
+function f6(s: string) {
+>f6 : Symbol(f6, Decl(isomorphicMappedTypeInference.ts, 94, 1))
+>s : Symbol(s, Decl(isomorphicMappedTypeInference.ts, 96, 12))
+
+    let b = makeDictionary({
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 97, 7))
+>makeDictionary : Symbol(makeDictionary, Decl(isomorphicMappedTypeInference.ts, 90, 1))
+
+        a: box(42),
+>a : Symbol(a, Decl(isomorphicMappedTypeInference.ts, 97, 28))
+>box : Symbol(box, Decl(isomorphicMappedTypeInference.ts, 7, 1))
+
+        b: box("hello"),
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 98, 19))
+>box : Symbol(box, Decl(isomorphicMappedTypeInference.ts, 7, 1))
+
+        c: box(true)
+>c : Symbol(c, Decl(isomorphicMappedTypeInference.ts, 99, 24))
+>box : Symbol(box, Decl(isomorphicMappedTypeInference.ts, 7, 1))
+
+    });
+    let v = unboxify(b);
+>v : Symbol(v, Decl(isomorphicMappedTypeInference.ts, 102, 7))
+>unboxify : Symbol(unboxify, Decl(isomorphicMappedTypeInference.ts, 23, 1))
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 97, 7))
+
+    let x: string | number | boolean = v[s];
+>x : Symbol(x, Decl(isomorphicMappedTypeInference.ts, 103, 7))
+>v : Symbol(v, Decl(isomorphicMappedTypeInference.ts, 102, 7))
+>s : Symbol(s, Decl(isomorphicMappedTypeInference.ts, 96, 12))
+}
+
+declare function validate<T>(obj: { [P in keyof T]?: T[P] }): T;
+>validate : Symbol(validate, Decl(isomorphicMappedTypeInference.ts, 104, 1))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 106, 26))
+>obj : Symbol(obj, Decl(isomorphicMappedTypeInference.ts, 106, 29))
+>P : Symbol(P, Decl(isomorphicMappedTypeInference.ts, 106, 37))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 106, 26))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 106, 26))
+>P : Symbol(P, Decl(isomorphicMappedTypeInference.ts, 106, 37))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 106, 26))
+
+declare function clone<T>(obj: { readonly [P in keyof T]: T[P] }): T;
+>clone : Symbol(clone, Decl(isomorphicMappedTypeInference.ts, 106, 64))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 107, 23))
+>obj : Symbol(obj, Decl(isomorphicMappedTypeInference.ts, 107, 26))
+>P : Symbol(P, Decl(isomorphicMappedTypeInference.ts, 107, 43))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 107, 23))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 107, 23))
+>P : Symbol(P, Decl(isomorphicMappedTypeInference.ts, 107, 43))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 107, 23))
+
+declare function validateAndClone<T>(obj: { readonly [P in keyof T]?: T[P] }): T;
+>validateAndClone : Symbol(validateAndClone, Decl(isomorphicMappedTypeInference.ts, 107, 69))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 108, 34))
+>obj : Symbol(obj, Decl(isomorphicMappedTypeInference.ts, 108, 37))
+>P : Symbol(P, Decl(isomorphicMappedTypeInference.ts, 108, 54))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 108, 34))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 108, 34))
+>P : Symbol(P, Decl(isomorphicMappedTypeInference.ts, 108, 54))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 108, 34))
+
+type Foo = {
+>Foo : Symbol(Foo, Decl(isomorphicMappedTypeInference.ts, 108, 81))
+
+    a?: number;
+>a : Symbol(a, Decl(isomorphicMappedTypeInference.ts, 110, 12))
+
+    readonly b: string;
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 111, 15))
+}
+
+function f10(foo: Foo) {
+>f10 : Symbol(f10, Decl(isomorphicMappedTypeInference.ts, 113, 1))
+>foo : Symbol(foo, Decl(isomorphicMappedTypeInference.ts, 115, 13))
+>Foo : Symbol(Foo, Decl(isomorphicMappedTypeInference.ts, 108, 81))
+
+    let x = validate(foo);  // { a: number, readonly b: string }
+>x : Symbol(x, Decl(isomorphicMappedTypeInference.ts, 116, 7))
+>validate : Symbol(validate, Decl(isomorphicMappedTypeInference.ts, 104, 1))
+>foo : Symbol(foo, Decl(isomorphicMappedTypeInference.ts, 115, 13))
+
+    let y = clone(foo);  // { a?: number, b: string }
+>y : Symbol(y, Decl(isomorphicMappedTypeInference.ts, 117, 7))
+>clone : Symbol(clone, Decl(isomorphicMappedTypeInference.ts, 106, 64))
+>foo : Symbol(foo, Decl(isomorphicMappedTypeInference.ts, 115, 13))
+
+    let z = validateAndClone(foo);  // { a: number, b: string }
+>z : Symbol(z, Decl(isomorphicMappedTypeInference.ts, 118, 7))
+>validateAndClone : Symbol(validateAndClone, Decl(isomorphicMappedTypeInference.ts, 107, 69))
+>foo : Symbol(foo, Decl(isomorphicMappedTypeInference.ts, 115, 13))
+}
+
+// Repro from #12606
+
+type Func<T> = (...args: any[]) => T;
+>Func : Symbol(Func, Decl(isomorphicMappedTypeInference.ts, 119, 1))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 123, 10))
+>args : Symbol(args, Decl(isomorphicMappedTypeInference.ts, 123, 16))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 123, 10))
+
+type Spec<T> = {
+>Spec : Symbol(Spec, Decl(isomorphicMappedTypeInference.ts, 123, 37))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 124, 10))
+
+    [P in keyof T]: Func<T[P]> | Spec<T[P]> ;
+>P : Symbol(P, Decl(isomorphicMappedTypeInference.ts, 125, 5))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 124, 10))
+>Func : Symbol(Func, Decl(isomorphicMappedTypeInference.ts, 119, 1))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 124, 10))
+>P : Symbol(P, Decl(isomorphicMappedTypeInference.ts, 125, 5))
+>Spec : Symbol(Spec, Decl(isomorphicMappedTypeInference.ts, 123, 37))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 124, 10))
+>P : Symbol(P, Decl(isomorphicMappedTypeInference.ts, 125, 5))
+
+};
+
+/**
+ * Given a spec object recursively mapping properties to functions, creates a function
+ * producing an object of the same structure, by mapping each property to the result
+ * of calling its associated function with the supplied arguments.
+ */
+declare function applySpec<T>(obj: Spec<T>): (...args: any[]) => T;
+>applySpec : Symbol(applySpec, Decl(isomorphicMappedTypeInference.ts, 126, 2))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 133, 27))
+>obj : Symbol(obj, Decl(isomorphicMappedTypeInference.ts, 133, 30))
+>Spec : Symbol(Spec, Decl(isomorphicMappedTypeInference.ts, 123, 37))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 133, 27))
+>args : Symbol(args, Decl(isomorphicMappedTypeInference.ts, 133, 46))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 133, 27))
+
+// Infers g1: (...args: any[]) => { sum: number, nested: { mul: string } }
+var g1 = applySpec({
+>g1 : Symbol(g1, Decl(isomorphicMappedTypeInference.ts, 136, 3))
+>applySpec : Symbol(applySpec, Decl(isomorphicMappedTypeInference.ts, 126, 2))
+
+    sum: (a: any) => 3,
+>sum : Symbol(sum, Decl(isomorphicMappedTypeInference.ts, 136, 20))
+>a : Symbol(a, Decl(isomorphicMappedTypeInference.ts, 137, 10))
+
+    nested: {
+>nested : Symbol(nested, Decl(isomorphicMappedTypeInference.ts, 137, 23))
+
+        mul: (b: any) => "n"
+>mul : Symbol(mul, Decl(isomorphicMappedTypeInference.ts, 138, 13))
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 139, 14))
+    }
+});
+
+// Infers g2: (...args: any[]) => { foo: { bar: { baz: boolean } } }
+var g2 = applySpec({ foo: { bar: { baz: (x: any) => true } } });
+>g2 : Symbol(g2, Decl(isomorphicMappedTypeInference.ts, 144, 3))
+>applySpec : Symbol(applySpec, Decl(isomorphicMappedTypeInference.ts, 126, 2))
+>foo : Symbol(foo, Decl(isomorphicMappedTypeInference.ts, 144, 20))
+>bar : Symbol(bar, Decl(isomorphicMappedTypeInference.ts, 144, 27))
+>baz : Symbol(baz, Decl(isomorphicMappedTypeInference.ts, 144, 34))
+>x : Symbol(x, Decl(isomorphicMappedTypeInference.ts, 144, 41))
+
+// Repro from #12633
+
+const foo = <T>(object: T, partial: Partial<T>) => object;
+>foo : Symbol(foo, Decl(isomorphicMappedTypeInference.ts, 148, 5))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 148, 13))
+>object : Symbol(object, Decl(isomorphicMappedTypeInference.ts, 148, 16))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 148, 13))
+>partial : Symbol(partial, Decl(isomorphicMappedTypeInference.ts, 148, 26))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(isomorphicMappedTypeInference.ts, 148, 13))
+>object : Symbol(object, Decl(isomorphicMappedTypeInference.ts, 148, 16))
+
+let o = {a: 5, b: 7};
+>o : Symbol(o, Decl(isomorphicMappedTypeInference.ts, 149, 3))
+>a : Symbol(a, Decl(isomorphicMappedTypeInference.ts, 149, 9))
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 149, 14))
+
+foo(o, {b: 9});
+>foo : Symbol(foo, Decl(isomorphicMappedTypeInference.ts, 148, 5))
+>o : Symbol(o, Decl(isomorphicMappedTypeInference.ts, 149, 3))
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 150, 8))
+
+o = foo(o, {b: 9});
+>o : Symbol(o, Decl(isomorphicMappedTypeInference.ts, 149, 3))
+>foo : Symbol(foo, Decl(isomorphicMappedTypeInference.ts, 148, 5))
+>o : Symbol(o, Decl(isomorphicMappedTypeInference.ts, 149, 3))
+>b : Symbol(b, Decl(isomorphicMappedTypeInference.ts, 151, 12))
+

tests/baselines/reference/isomorphicMappedTypeInference.types

@@ -0,0 +1,587 @@
+=== tests/cases/conformance/types/mapped/isomorphicMappedTypeInference.ts ===
+
+type Box<T> = {
+>Box : Box<T>
+>T : T
+
+    value: T;
+>value : T
+>T : T
+}
+
+type Boxified<T> = {
+>Boxified : Boxified<T>
+>T : T
+
+    [P in keyof T]: Box<T[P]>;
+>P : P
+>T : T
+>Box : Box<T>
+>T : T
+>P : P
+}
+
+function box<T>(x: T): Box<T> {
+>box : <T>(x: T) => Box<T>
+>T : T
+>x : T
+>T : T
+>Box : Box<T>
+>T : T
+
+    return { value: x };
+>{ value: x } : { value: T; }
+>value : T
+>x : T
+}
+
+function unbox<T>(x: Box<T>): T {
+>unbox : <T>(x: Box<T>) => T
+>T : T
+>x : Box<T>
+>Box : Box<T>
+>T : T
+>T : T
+
+    return x.value;
+>x.value : T
+>x : Box<T>
+>value : T
+}
+
+function boxify<T>(obj: T): Boxified<T> {
+>boxify : <T>(obj: T) => Boxified<T>
+>T : T
+>obj : T
+>T : T
+>Boxified : Boxified<T>
+>T : T
+
+    let result = {} as Boxified<T>;
+>result : Boxified<T>
+>{} as Boxified<T> : Boxified<T>
+>{} : {}
+>Boxified : Boxified<T>
+>T : T
+
+    for (let k in obj) {
+>k : keyof T
+>obj : T
+
+        result[k] = box(obj[k]);
+>result[k] = box(obj[k]) : Box<T[keyof T]>
+>result[k] : Box<T[keyof T]>
+>result : Boxified<T>
+>k : keyof T
+>box(obj[k]) : Box<T[keyof T]>
+>box : <T>(x: T) => Box<T>
+>obj[k] : T[keyof T]
+>obj : T
+>k : keyof T
+    }
+    return result;
+>result : Boxified<T>
+}
+
+function unboxify<T>(obj: Boxified<T>): T {
+>unboxify : <T>(obj: Boxified<T>) => T
+>T : T
+>obj : Boxified<T>
+>Boxified : Boxified<T>
+>T : T
+>T : T
+
+    let result = {} as T;
+>result : T
+>{} as T : T
+>{} : {}
+>T : T
+
+    for (let k in obj) {
+>k : keyof T
+>obj : Boxified<T>
+
+        result[k] = unbox(obj[k]);
+>result[k] = unbox(obj[k]) : T[keyof T]
+>result[k] : T[keyof T]
+>result : T
+>k : keyof T
+>unbox(obj[k]) : T[keyof T]
+>unbox : <T>(x: Box<T>) => T
+>obj[k] : Box<T[keyof T]>
+>obj : Boxified<T>
+>k : keyof T
+    }
+    return result;
+>result : T
+}
+
+function assignBoxified<T>(obj: Boxified<T>, values: T) {
+>assignBoxified : <T>(obj: Boxified<T>, values: T) => void
+>T : T
+>obj : Boxified<T>
+>Boxified : Boxified<T>
+>T : T
+>values : T
+>T : T
+
+    for (let k in values) {
+>k : keyof T
+>values : T
+
+        obj[k].value = values[k];
+>obj[k].value = values[k] : T[keyof T]
+>obj[k].value : T[keyof T]
+>obj[k] : Box<T[keyof T]>
+>obj : Boxified<T>
+>k : keyof T
+>value : T[keyof T]
+>values[k] : T[keyof T]
+>values : T
+>k : keyof T
+    }
+}
+
+function f1() {
+>f1 : () => void
+
+    let v = {
+>v : { a: number; b: string; c: boolean; }
+>{        a: 42,        b: "hello",        c: true    } : { a: number; b: string; c: boolean; }
+
+        a: 42,
+>a : number
+>42 : 42
+
+        b: "hello",
+>b : string
+>"hello" : "hello"
+
+        c: true
+>c : boolean
+>true : true
+
+    };
+    let b = boxify(v);
+>b : Boxified<{ a: number; b: string; c: boolean; }>
+>boxify(v) : Boxified<{ a: number; b: string; c: boolean; }>
+>boxify : <T>(obj: T) => Boxified<T>
+>v : { a: number; b: string; c: boolean; }
+
+    let x: number = b.a.value;
+>x : number
+>b.a.value : number
+>b.a : Box<number>
+>b : Boxified<{ a: number; b: string; c: boolean; }>
+>a : Box<number>
+>value : number
+}
+
+function f2() {
+>f2 : () => void
+
+    let b = {
+>b : { a: Box<number>; b: Box<string>; c: Box<boolean>; }
+>{        a: box(42),        b: box("hello"),        c: box(true)    } : { a: Box<number>; b: Box<string>; c: Box<boolean>; }
+
+        a: box(42),
+>a : Box<number>
+>box(42) : Box<number>
+>box : <T>(x: T) => Box<T>
+>42 : 42
+
+        b: box("hello"),
+>b : Box<string>
+>box("hello") : Box<string>
+>box : <T>(x: T) => Box<T>
+>"hello" : "hello"
+
+        c: box(true)
+>c : Box<boolean>
+>box(true) : Box<boolean>
+>box : <T>(x: T) => Box<T>
+>true : true
+
+    };
+    let v = unboxify(b);
+>v : { a: number; b: string; c: boolean; }
+>unboxify(b) : { a: number; b: string; c: boolean; }
+>unboxify : <T>(obj: Boxified<T>) => T
+>b : { a: Box<number>; b: Box<string>; c: Box<boolean>; }
+
+    let x: number = v.a;
+>x : number
+>v.a : number
+>v : { a: number; b: string; c: boolean; }
+>a : number
+}
+
+function f3() {
+>f3 : () => void
+
+    let b = {
+>b : { a: Box<number>; b: Box<string>; c: Box<boolean>; }
+>{        a: box(42),        b: box("hello"),        c: box(true)    } : { a: Box<number>; b: Box<string>; c: Box<boolean>; }
+
+        a: box(42),
+>a : Box<number>
+>box(42) : Box<number>
+>box : <T>(x: T) => Box<T>
+>42 : 42
+
+        b: box("hello"),
+>b : Box<string>
+>box("hello") : Box<string>
+>box : <T>(x: T) => Box<T>
+>"hello" : "hello"
+
+        c: box(true)
+>c : Box<boolean>
+>box(true) : Box<boolean>
+>box : <T>(x: T) => Box<T>
+>true : true
+
+    };
+    assignBoxified(b, { c: false });
+>assignBoxified(b, { c: false }) : void
+>assignBoxified : <T>(obj: Boxified<T>, values: T) => void
+>b : { a: Box<number>; b: Box<string>; c: Box<boolean>; }
+>{ c: false } : { c: false; }
+>c : boolean
+>false : false
+}
+
+function f4() {
+>f4 : () => void
+
+    let b = {
+>b : { a: Box<number>; b: Box<string>; c: Box<boolean>; }
+>{        a: box(42),        b: box("hello"),        c: box(true)    } : { a: Box<number>; b: Box<string>; c: Box<boolean>; }
+
+        a: box(42),
+>a : Box<number>
+>box(42) : Box<number>
+>box : <T>(x: T) => Box<T>
+>42 : 42
+
+        b: box("hello"),
+>b : Box<string>
+>box("hello") : Box<string>
+>box : <T>(x: T) => Box<T>
+>"hello" : "hello"
+
+        c: box(true)
+>c : Box<boolean>
+>box(true) : Box<boolean>
+>box : <T>(x: T) => Box<T>
+>true : true
+
+    };
+    b = boxify(unboxify(b));
+>b = boxify(unboxify(b)) : Boxified<{ a: number; b: string; c: boolean; }>
+>b : { a: Box<number>; b: Box<string>; c: Box<boolean>; }
+>boxify(unboxify(b)) : Boxified<{ a: number; b: string; c: boolean; }>
+>boxify : <T>(obj: T) => Boxified<T>
+>unboxify(b) : { a: number; b: string; c: boolean; }
+>unboxify : <T>(obj: Boxified<T>) => T
+>b : { a: Box<number>; b: Box<string>; c: Box<boolean>; }
+
+    b = unboxify(boxify(b));
+>b = unboxify(boxify(b)) : { a: Box<number>; b: Box<string>; c: Box<boolean>; }
+>b : { a: Box<number>; b: Box<string>; c: Box<boolean>; }
+>unboxify(boxify(b)) : { a: Box<number>; b: Box<string>; c: Box<boolean>; }
+>unboxify : <T>(obj: Boxified<T>) => T
+>boxify(b) : Boxified<{ a: Box<number>; b: Box<string>; c: Box<boolean>; }>
+>boxify : <T>(obj: T) => Boxified<T>
+>b : { a: Box<number>; b: Box<string>; c: Box<boolean>; }
+}
+
+function makeRecord<T, K extends string>(obj: { [P in K]: T }) {
+>makeRecord : <T, K extends string>(obj: { [P in K]: T; }) => { [P in K]: T; }
+>T : T
+>K : K
+>obj : { [P in K]: T; }
+>P : P
+>K : K
+>T : T
+
+    return obj;
+>obj : { [P in K]: T; }
+}
+
+function f5(s: string) {
+>f5 : (s: string) => void
+>s : string
+
+    let b = makeRecord({
+>b : { a: Box<number> | Box<string> | Box<boolean>; b: Box<number> | Box<string> | Box<boolean>; c: Box<number> | Box<string> | Box<boolean>; }
+>makeRecord({        a: box(42),        b: box("hello"),        c: box(true)    }) : { a: Box<number> | Box<string> | Box<boolean>; b: Box<number> | Box<string> | Box<boolean>; c: Box<number> | Box<string> | Box<boolean>; }
+>makeRecord : <T, K extends string>(obj: { [P in K]: T; }) => { [P in K]: T; }
+>{        a: box(42),        b: box("hello"),        c: box(true)    } : { a: Box<number>; b: Box<string>; c: Box<boolean>; }
+
+        a: box(42),
+>a : Box<number>
+>box(42) : Box<number>
+>box : <T>(x: T) => Box<T>
+>42 : 42
+
+        b: box("hello"),
+>b : Box<string>
+>box("hello") : Box<string>
+>box : <T>(x: T) => Box<T>
+>"hello" : "hello"
+
+        c: box(true)
+>c : Box<boolean>
+>box(true) : Box<boolean>
+>box : <T>(x: T) => Box<T>
+>true : true
+
+    });
+    let v = unboxify(b);
+>v : { a: string | number | boolean; b: string | number | boolean; c: string | number | boolean; }
+>unboxify(b) : { a: string | number | boolean; b: string | number | boolean; c: string | number | boolean; }
+>unboxify : <T>(obj: Boxified<T>) => T
+>b : { a: Box<number> | Box<string> | Box<boolean>; b: Box<number> | Box<string> | Box<boolean>; c: Box<number> | Box<string> | Box<boolean>; }
+
+    let x: string | number | boolean = v.a;
+>x : string | number | boolean
+>v.a : string | number | boolean
+>v : { a: string | number | boolean; b: string | number | boolean; c: string | number | boolean; }
+>a : string | number | boolean
+}
+
+function makeDictionary<T>(obj: { [x: string]: T }) {
+>makeDictionary : <T>(obj: { [x: string]: T; }) => { [x: string]: T; }
+>T : T
+>obj : { [x: string]: T; }
+>x : string
+>T : T
+
+    return obj;
+>obj : { [x: string]: T; }
+}
+
+function f6(s: string) {
+>f6 : (s: string) => void
+>s : string
+
+    let b = makeDictionary({
+>b : { [x: string]: Box<number> | Box<string> | Box<boolean>; }
+>makeDictionary({        a: box(42),        b: box("hello"),        c: box(true)    }) : { [x: string]: Box<number> | Box<string> | Box<boolean>; }
+>makeDictionary : <T>(obj: { [x: string]: T; }) => { [x: string]: T; }
+>{        a: box(42),        b: box("hello"),        c: box(true)    } : { a: Box<number>; b: Box<string>; c: Box<boolean>; }
+
+        a: box(42),
+>a : Box<number>
+>box(42) : Box<number>
+>box : <T>(x: T) => Box<T>
+>42 : 42
+
+        b: box("hello"),
+>b : Box<string>
+>box("hello") : Box<string>
+>box : <T>(x: T) => Box<T>
+>"hello" : "hello"
+
+        c: box(true)
+>c : Box<boolean>
+>box(true) : Box<boolean>
+>box : <T>(x: T) => Box<T>
+>true : true
+
+    });
+    let v = unboxify(b);
+>v : { [x: string]: string | number | boolean; }
+>unboxify(b) : { [x: string]: string | number | boolean; }
+>unboxify : <T>(obj: Boxified<T>) => T
+>b : { [x: string]: Box<number> | Box<string> | Box<boolean>; }
+
+    let x: string | number | boolean = v[s];
+>x : string | number | boolean
+>v[s] : string | number | boolean
+>v : { [x: string]: string | number | boolean; }
+>s : string
+}
+
+declare function validate<T>(obj: { [P in keyof T]?: T[P] }): T;
+>validate : <T>(obj: { [P in keyof T]?: T[P] | undefined; }) => T
+>T : T
+>obj : { [P in keyof T]?: T[P] | undefined; }
+>P : P
+>T : T
+>T : T
+>P : P
+>T : T
+
+declare function clone<T>(obj: { readonly [P in keyof T]: T[P] }): T;
+>clone : <T>(obj: { readonly [P in keyof T]: T[P]; }) => T
+>T : T
+>obj : { readonly [P in keyof T]: T[P]; }
+>P : P
+>T : T
+>T : T
+>P : P
+>T : T
+
+declare function validateAndClone<T>(obj: { readonly [P in keyof T]?: T[P] }): T;
+>validateAndClone : <T>(obj: { readonly [P in keyof T]?: T[P] | undefined; }) => T
+>T : T
+>obj : { readonly [P in keyof T]?: T[P] | undefined; }
+>P : P
+>T : T
+>T : T
+>P : P
+>T : T
+
+type Foo = {
+>Foo : Foo
+
+    a?: number;
+>a : number | undefined
+
+    readonly b: string;
+>b : string
+}
+
+function f10(foo: Foo) {
+>f10 : (foo: Foo) => void
+>foo : Foo
+>Foo : Foo
+
+    let x = validate(foo);  // { a: number, readonly b: string }
+>x : { a: number; readonly b: string; }
+>validate(foo) : { a: number; readonly b: string; }
+>validate : <T>(obj: { [P in keyof T]?: T[P] | undefined; }) => T
+>foo : Foo
+
+    let y = clone(foo);  // { a?: number, b: string }
+>y : { a?: number | undefined; b: string; }
+>clone(foo) : { a?: number | undefined; b: string; }
+>clone : <T>(obj: { readonly [P in keyof T]: T[P]; }) => T
+>foo : Foo
+
+    let z = validateAndClone(foo);  // { a: number, b: string }
+>z : { a: number; b: string; }
+>validateAndClone(foo) : { a: number; b: string; }
+>validateAndClone : <T>(obj: { readonly [P in keyof T]?: T[P] | undefined; }) => T
+>foo : Foo
+}
+
+// Repro from #12606
+
+type Func<T> = (...args: any[]) => T;
+>Func : Func<T>
+>T : T
+>args : any[]
+>T : T
+
+type Spec<T> = {
+>Spec : Spec<T>
+>T : T
+
+    [P in keyof T]: Func<T[P]> | Spec<T[P]> ;
+>P : P
+>T : T
+>Func : Func<T>
+>T : T
+>P : P
+>Spec : Spec<T>
+>T : T
+>P : P
+
+};
+
+/**
+ * Given a spec object recursively mapping properties to functions, creates a function
+ * producing an object of the same structure, by mapping each property to the result
+ * of calling its associated function with the supplied arguments.
+ */
+declare function applySpec<T>(obj: Spec<T>): (...args: any[]) => T;
+>applySpec : <T>(obj: Spec<T>) => (...args: any[]) => T
+>T : T
+>obj : Spec<T>
+>Spec : Spec<T>
+>T : T
+>args : any[]
+>T : T
+
+// Infers g1: (...args: any[]) => { sum: number, nested: { mul: string } }
+var g1 = applySpec({
+>g1 : (...args: any[]) => { sum: number; nested: { mul: string; }; }
+>applySpec({    sum: (a: any) => 3,    nested: {        mul: (b: any) => "n"    }}) : (...args: any[]) => { sum: number; nested: { mul: string; }; }
+>applySpec : <T>(obj: Spec<T>) => (...args: any[]) => T
+>{    sum: (a: any) => 3,    nested: {        mul: (b: any) => "n"    }} : { sum: (a: any) => number; nested: { mul: (b: any) => string; }; }
+
+    sum: (a: any) => 3,
+>sum : (a: any) => number
+>(a: any) => 3 : (a: any) => number
+>a : any
+>3 : 3
+
+    nested: {
+>nested : { mul: (b: any) => string; }
+>{        mul: (b: any) => "n"    } : { mul: (b: any) => string; }
+
+        mul: (b: any) => "n"
+>mul : (b: any) => string
+>(b: any) => "n" : (b: any) => string
+>b : any
+>"n" : "n"
+    }
+});
+
+// Infers g2: (...args: any[]) => { foo: { bar: { baz: boolean } } }
+var g2 = applySpec({ foo: { bar: { baz: (x: any) => true } } });
+>g2 : (...args: any[]) => { foo: { bar: { baz: boolean; }; }; }
+>applySpec({ foo: { bar: { baz: (x: any) => true } } }) : (...args: any[]) => { foo: { bar: { baz: boolean; }; }; }
+>applySpec : <T>(obj: Spec<T>) => (...args: any[]) => T
+>{ foo: { bar: { baz: (x: any) => true } } } : { foo: { bar: { baz: (x: any) => boolean; }; }; }
+>foo : { bar: { baz: (x: any) => boolean; }; }
+>{ bar: { baz: (x: any) => true } } : { bar: { baz: (x: any) => boolean; }; }
+>bar : { baz: (x: any) => boolean; }
+>{ baz: (x: any) => true } : { baz: (x: any) => boolean; }
+>baz : (x: any) => boolean
+>(x: any) => true : (x: any) => boolean
+>x : any
+>true : true
+
+// Repro from #12633
+
+const foo = <T>(object: T, partial: Partial<T>) => object;
+>foo : <T>(object: T, partial: Partial<T>) => T
+><T>(object: T, partial: Partial<T>) => object : <T>(object: T, partial: Partial<T>) => T
+>T : T
+>object : T
+>T : T
+>partial : Partial<T>
+>Partial : Partial<T>
+>T : T
+>object : T
+
+let o = {a: 5, b: 7};
+>o : { a: number; b: number; }
+>{a: 5, b: 7} : { a: number; b: number; }
+>a : number
+>5 : 5
+>b : number
+>7 : 7
+
+foo(o, {b: 9});
+>foo(o, {b: 9}) : { a: number; b: number; }
+>foo : <T>(object: T, partial: Partial<T>) => T
+>o : { a: number; b: number; }
+>{b: 9} : { b: number; }
+>b : number
+>9 : 9
+
+o = foo(o, {b: 9});
+>o = foo(o, {b: 9}) : { a: number; b: number; }
+>o : { a: number; b: number; }
+>foo(o, {b: 9}) : { a: number; b: number; }
+>foo : <T>(object: T, partial: Partial<T>) => T
+>o : { a: number; b: number; }
+>{b: 9} : { b: number; }
+>b : number
+>9 : 9
+

tests/baselines/reference/keyofAndIndexedAccess.js

@@ -21,11 +21,12 @@ class Options {
 }
 
 type Dictionary<T> = { [x: string]: T };
+type NumericallyIndexed<T> = { [x: number]: T };
 
 const enum E { A, B, C }
 
-type K00 = keyof any;  // string | number
-type K01 = keyof string;  // number | "toString" | "charAt" | ...
+type K00 = keyof any;  // string
+type K01 = keyof string;  // "toString" | "charAt" | ...
 type K02 = keyof number;  // "toString" | "toFixed" | "toExponential" | ...
 type K03 = keyof boolean;  // "valueOf"
 type K04 = keyof void;  // never
@@ -34,19 +35,20 @@ type K06 = keyof null;  // never
 type K07 = keyof never;  // never
 
 type K10 = keyof Shape;  // "name" | "width" | "height" | "visible"
-type K11 = keyof Shape[];  // number | "length" | "toString" | ...
-type K12 = keyof Dictionary<Shape>;  // string | number
+type K11 = keyof Shape[];  // "length" | "toString" | ...
+type K12 = keyof Dictionary<Shape>;  // string
 type K13 = keyof {};  // never
 type K14 = keyof Object;  // "constructor" | "toString" | ...
 type K15 = keyof E;  // "toString" | "toFixed" | "toExponential" | ...
-type K16 = keyof [string, number];  // number | "0" | "1" | "length" | "toString" | ...
+type K16 = keyof [string, number];  // "0" | "1" | "length" | "toString" | ...
 type K17 = keyof (Shape | Item);  // "name"
 type K18 = keyof (Shape & Item);  // "name" | "width" | "height" | "visible" | "price"
+type K19 = keyof NumericallyIndexed<Shape> // never
 
 type KeyOf<T> = keyof T;
 
 type K20 = KeyOf<Shape>;  // "name" | "width" | "height" | "visible"
-type K21 = KeyOf<Dictionary<Shape>>;  // string | number
+type K21 = KeyOf<Dictionary<Shape>>;  // string
 
 type NAME = "name";
 type WIDTH_OR_HEIGHT = "width" | "height";
@@ -217,6 +219,36 @@ function f60<T>(source: T, target: T) {
     }
 }
 
+function f70(func: <T, U>(k1: keyof (T | U), k2: keyof (T & U)) => void) {
+    func<{ a: any, b: any }, { a: any, c: any }>('a', 'a');
+    func<{ a: any, b: any }, { a: any, c: any }>('a', 'b');
+    func<{ a: any, b: any }, { a: any, c: any }>('a', 'c');
+}
+
+function f71(func: <T, U>(x: T, y: U) => Partial<T & U>) {
+    let x = func({ a: 1, b: "hello" }, { c: true });
+    x.a;  // number | undefined
+    x.b;  // string | undefined
+    x.c;  // boolean | undefined
+}
+
+function f72(func: <T, U, K extends keyof T | keyof U>(x: T, y: U, k: K) => (T & U)[K]) {
+    let a = func({ a: 1, b: "hello" }, { c: true }, 'a');  // number
+    let b = func({ a: 1, b: "hello" }, { c: true }, 'b');  // string
+    let c = func({ a: 1, b: "hello" }, { c: true }, 'c');  // boolean
+}
+
+function f73(func: <T, U, K extends keyof (T & U)>(x: T, y: U, k: K) => (T & U)[K]) {
+    let a = func({ a: 1, b: "hello" }, { c: true }, 'a');  // number
+    let b = func({ a: 1, b: "hello" }, { c: true }, 'b');  // string
+    let c = func({ a: 1, b: "hello" }, { c: true }, 'c');  // boolean
+}
+
+function f74(func: <T, U, K extends keyof (T | U)>(x: T, y: U, k: K) => (T | U)[K]) {
+    let a = func({ a: 1, b: "hello" }, { a: 2, b: true }, 'a');  // number
+    let b = func({ a: 1, b: "hello" }, { a: 2, b: true }, 'b');  // string | boolean
+}
+
 // Repros from #12011
 
 class Base {
@@ -247,6 +279,91 @@ class OtherPerson {
     getParts() {
         return getProperty(this, "parts")
     }
+}
+
+// Modified repro from #12544
+
+function path<T, K1 extends keyof T>(obj: T, key1: K1): T[K1];
+function path<T, K1 extends keyof T, K2 extends keyof T[K1]>(obj: T, key1: K1, key2: K2): T[K1][K2];
+function path<T, K1 extends keyof T, K2 extends keyof T[K1], K3 extends keyof T[K1][K2]>(obj: T, key1: K1, key2: K2, key3: K3): T[K1][K2][K3];
+function path(obj: any, ...keys: (string | number)[]): any;
+function path(obj: any, ...keys: (string | number)[]): any {
+    let result = obj;
+    for (let k of keys) {
+        result = result[k];
+    }
+    return result;
+}
+
+type Thing = {
+    a: { x: number, y: string },
+    b: boolean
+};
+
+
+function f1(thing: Thing) {
+    let x1 = path(thing, 'a');  // { x: number, y: string }
+    let x2 = path(thing, 'a', 'y');  // string
+    let x3 = path(thing, 'b');  // boolean
+    let x4 = path(thing, ...['a', 'x']);  // any
+}
+
+// Repro from comment in #12114
+
+const assignTo2 = <T, K1 extends keyof T, K2 extends keyof T[K1]>(object: T, key1: K1, key2: K2) =>
+    (value: T[K1][K2]) => object[key1][key2] = value;
+
+// Modified repro from #12573
+
+declare function one<T>(handler: (t: T) => void): T
+var empty = one(() => {}) // inferred as {}, expected
+
+type Handlers<T> = { [K in keyof T]: (t: T[K]) => void }
+declare function on<T>(handlerHash: Handlers<T>): T
+var hashOfEmpty1 = on({ test: () => {} });  // {}
+var hashOfEmpty2 = on({ test: (x: boolean) => {} });  // { test: boolean }
+
+// Repro from #12624
+
+interface Options1<Data, Computed> {
+    data?: Data
+    computed?: Computed;
+}
+
+declare class Component1<Data, Computed> {
+    constructor(options: Options1<Data, Computed>);
+    get<K extends keyof (Data & Computed)>(key: K): (Data & Computed)[K];
+}
+
+let c1 = new Component1({
+    data: {
+        hello: ""
+    }
+});
+
+c1.get("hello");
+
+// Repro from #12625
+
+interface Options2<Data, Computed> {
+    data?: Data
+    computed?: Computed;
+}
+
+declare class Component2<Data, Computed> {
+    constructor(options: Options2<Data, Computed>);
+    get<K extends keyof Data | keyof Computed>(key: K): (Data & Computed)[K];
+}
+
+// Repro from #12641
+
+interface R {
+    p: number;
+}
+
+function f<K extends keyof R>(p: K) {
+    let a: any;
+    a[p].add;  // any
 }
 
 //// [keyofAndIndexedAccess.js]
@@ -394,6 +511,31 @@ function f60(source, target) {
         target[k] = source[k];
     }
 }
+function f70(func) {
+    func('a', 'a');
+    func('a', 'b');
+    func('a', 'c');
+}
+function f71(func) {
+    var x = func({ a: 1, b: "hello" }, { c: true });
+    x.a; // number | undefined
+    x.b; // string | undefined
+    x.c; // boolean | undefined
+}
+function f72(func) {
+    var a = func({ a: 1, b: "hello" }, { c: true }, 'a'); // number
+    var b = func({ a: 1, b: "hello" }, { c: true }, 'b'); // string
+    var c = func({ a: 1, b: "hello" }, { c: true }, 'c'); // boolean
+}
+function f73(func) {
+    var a = func({ a: 1, b: "hello" }, { c: true }, 'a'); // number
+    var b = func({ a: 1, b: "hello" }, { c: true }, 'b'); // string
+    var c = func({ a: 1, b: "hello" }, { c: true }, 'c'); // boolean
+}
+function f74(func) {
+    var a = func({ a: 1, b: "hello" }, { a: 2, b: true }, 'a'); // number
+    var b = func({ a: 1, b: "hello" }, { a: 2, b: true }, 'b'); // string | boolean
+}
 // Repros from #12011
 var Base = (function () {
     function Base() {
@@ -427,6 +569,41 @@ var OtherPerson = (function () {
     };
     return OtherPerson;
 }());
+function path(obj) {
+    var keys = [];
+    for (var _i = 1; _i < arguments.length; _i++) {
+        keys[_i - 1] = arguments[_i];
+    }
+    var result = obj;
+    for (var _a = 0, keys_1 = keys; _a < keys_1.length; _a++) {
+        var k = keys_1[_a];
+        result = result[k];
+    }
+    return result;
+}
+function f1(thing) {
+    var x1 = path(thing, 'a'); // { x: number, y: string }
+    var x2 = path(thing, 'a', 'y'); // string
+    var x3 = path(thing, 'b'); // boolean
+    var x4 = path.apply(void 0, [thing].concat(['a', 'x'])); // any
+}
+// Repro from comment in #12114
+var assignTo2 = function (object, key1, key2) {
+    return function (value) { return object[key1][key2] = value; };
+};
+var empty = one(function () { }); // inferred as {}, expected
+var hashOfEmpty1 = on({ test: function () { } }); // {}
+var hashOfEmpty2 = on({ test: function (x) { } }); // { test: boolean }
+var c1 = new Component1({
+    data: {
+        hello: ""
+    }
+});
+c1.get("hello");
+function f(p) {
+    var a;
+    a[p].add; // any
+}
 
 
 //// [keyofAndIndexedAccess.d.ts]
@@ -449,6 +626,9 @@ declare class Options {
 declare type Dictionary<T> = {
     [x: string]: T;
 };
+declare type NumericallyIndexed<T> = {
+    [x: number]: T;
+};
 declare const enum E {
     A = 0,
     B = 1,
@@ -471,6 +651,7 @@ declare type K15 = keyof E;
 declare type K16 = keyof [string, number];
 declare type K17 = keyof (Shape | Item);
 declare type K18 = keyof (Shape & Item);
+declare type K19 = keyof NumericallyIndexed<Shape>;
 declare type KeyOf<T> = keyof T;
 declare type K20 = KeyOf<Shape>;
 declare type K21 = KeyOf<Dictionary<Shape>>;
@@ -530,6 +711,11 @@ declare function f53<T, K extends keyof T>(obj: {
 declare function f54<T>(obj: T, key: keyof T): void;
 declare function f55<T, K extends keyof T>(obj: T, key: K): void;
 declare function f60<T>(source: T, target: T): void;
+declare function f70(func: <T, U>(k1: keyof (T | U), k2: keyof (T & U)) => void): void;
+declare function f71(func: <T, U>(x: T, y: U) => Partial<T & U>): void;
+declare function f72(func: <T, U, K extends keyof T | keyof U>(x: T, y: U, k: K) => (T & U)[K]): void;
+declare function f73(func: <T, U, K extends keyof (T & U)>(x: T, y: U, k: K) => (T & U)[K]): void;
+declare function f74(func: <T, U, K extends keyof (T | U)>(x: T, y: U, k: K) => (T | U)[K]): void;
 declare class Base {
     get<K extends keyof this>(prop: K): this[K];
     set<K extends keyof this>(prop: K, value: this[K]): void;
@@ -544,3 +730,49 @@ declare class OtherPerson {
     constructor(parts: number);
     getParts(): number;
 }
+declare function path<T, K1 extends keyof T>(obj: T, key1: K1): T[K1];
+declare function path<T, K1 extends keyof T, K2 extends keyof T[K1]>(obj: T, key1: K1, key2: K2): T[K1][K2];
+declare function path<T, K1 extends keyof T, K2 extends keyof T[K1], K3 extends keyof T[K1][K2]>(obj: T, key1: K1, key2: K2, key3: K3): T[K1][K2][K3];
+declare function path(obj: any, ...keys: (string | number)[]): any;
+declare type Thing = {
+    a: {
+        x: number;
+        y: string;
+    };
+    b: boolean;
+};
+declare function f1(thing: Thing): void;
+declare const assignTo2: <T, K1 extends keyof T, K2 extends keyof T[K1]>(object: T, key1: K1, key2: K2) => (value: T[K1][K2]) => T[K1][K2];
+declare function one<T>(handler: (t: T) => void): T;
+declare var empty: {};
+declare type Handlers<T> = {
+    [K in keyof T]: (t: T[K]) => void;
+};
+declare function on<T>(handlerHash: Handlers<T>): T;
+declare var hashOfEmpty1: {};
+declare var hashOfEmpty2: {
+    test: boolean;
+};
+interface Options1<Data, Computed> {
+    data?: Data;
+    computed?: Computed;
+}
+declare class Component1<Data, Computed> {
+    constructor(options: Options1<Data, Computed>);
+    get<K extends keyof (Data & Computed)>(key: K): (Data & Computed)[K];
+}
+declare let c1: Component1<{
+    hello: string;
+}, {}>;
+interface Options2<Data, Computed> {
+    data?: Data;
+    computed?: Computed;
+}
+declare class Component2<Data, Computed> {
+    constructor(options: Options2<Data, Computed>);
+    get<K extends keyof Data | keyof Computed>(key: K): (Data & Computed)[K];
+}
+interface R {
+    p: number;
+}
+declare function f<K extends keyof R>(p: K): void;

tests/baselines/reference/keyofAndIndexedAccess.types

@@ -47,16 +47,22 @@ type Dictionary<T> = { [x: string]: T };
 >x : string
 >T : T
 
+type NumericallyIndexed<T> = { [x: number]: T };
+>NumericallyIndexed : NumericallyIndexed<T>
+>T : T
+>x : number
+>T : T
+
 const enum E { A, B, C }
 >E : E
 >A : E.A
 >B : E.B
 >C : E.C
 
-type K00 = keyof any;  // string | number
+type K00 = keyof any;  // string
 >K00 : string
 
-type K01 = keyof string;  // number | "toString" | "charAt" | ...
+type K01 = keyof string;  // "toString" | "charAt" | ...
 >K01 : "length" | "toString" | "concat" | "slice" | "indexOf" | "lastIndexOf" | "charAt" | "charCodeAt" | "localeCompare" | "match" | "replace" | "search" | "split" | "substring" | "toLowerCase" | "toLocaleLowerCase" | "toUpperCase" | "toLocaleUpperCase" | "trim" | "substr" | "valueOf"
 
 type K02 = keyof number;  // "toString" | "toFixed" | "toExponential" | ...
@@ -82,11 +88,11 @@ type K10 = keyof Shape;  // "name" | "width" | "height" | "visible"
 >K10 : "name" | "width" | "height" | "visible"
 >Shape : Shape
 
-type K11 = keyof Shape[];  // number | "length" | "toString" | ...
+type K11 = keyof Shape[];  // "length" | "toString" | ...
 >K11 : "length" | "toString" | "toLocaleString" | "push" | "pop" | "concat" | "join" | "reverse" | "shift" | "slice" | "sort" | "splice" | "unshift" | "indexOf" | "lastIndexOf" | "every" | "some" | "forEach" | "map" | "filter" | "reduce" | "reduceRight"
 >Shape : Shape
 
-type K12 = keyof Dictionary<Shape>;  // string | number
+type K12 = keyof Dictionary<Shape>;  // string
 >K12 : string
 >Dictionary : Dictionary<T>
 >Shape : Shape
@@ -102,7 +108,7 @@ type K15 = keyof E;  // "toString" | "toFixed" | "toExponential" | ...
 >K15 : "toString" | "toLocaleString" | "valueOf" | "toFixed" | "toExponential" | "toPrecision"
 >E : E
 
-type K16 = keyof [string, number];  // number | "0" | "1" | "length" | "toString" | ...
+type K16 = keyof [string, number];  // "0" | "1" | "length" | "toString" | ...
 >K16 : "0" | "1" | "length" | "toString" | "toLocaleString" | "push" | "pop" | "concat" | "join" | "reverse" | "shift" | "slice" | "sort" | "splice" | "unshift" | "indexOf" | "lastIndexOf" | "every" | "some" | "forEach" | "map" | "filter" | "reduce" | "reduceRight"
 
 type K17 = keyof (Shape | Item);  // "name"
@@ -115,6 +121,11 @@ type K18 = keyof (Shape & Item);  // "name" | "width" | "height" | "visible" | "
 >Shape : Shape
 >Item : Item
 
+type K19 = keyof NumericallyIndexed<Shape> // never
+>K19 : never
+>NumericallyIndexed : NumericallyIndexed<T>
+>Shape : Shape
+
 type KeyOf<T> = keyof T;
 >KeyOf : keyof T
 >T : T
@@ -125,7 +136,7 @@ type K20 = KeyOf<Shape>;  // "name" | "width" | "height" | "visible"
 >KeyOf : keyof T
 >Shape : Shape
 
-type K21 = KeyOf<Dictionary<Shape>>;  // string | number
+type K21 = KeyOf<Dictionary<Shape>>;  // string
 >K21 : string
 >KeyOf : keyof T
 >Dictionary : Dictionary<T>
@@ -769,8 +780,8 @@ function f52<T>(obj: { [x: string]: boolean }, k: keyof T, s: string, n: number)
 >n : number
 
     const x3 = obj[k];
->x3 : boolean
->obj[k] : boolean
+>x3 : { [x: string]: boolean; }[keyof T]
+>obj[k] : { [x: string]: boolean; }[keyof T]
 >obj : { [x: string]: boolean; }
 >k : keyof T
 }
@@ -815,7 +826,7 @@ function f54<T>(obj: T, key: keyof T) {
 >T : T
 
     for (let s in obj[key]) {
->s : string
+>s : keyof T[keyof T]
 >obj[key] : T[keyof T]
 >obj : T
 >key : keyof T
@@ -840,7 +851,7 @@ function f55<T, K extends keyof T>(obj: T, key: K) {
 >K : K
 
     for (let s in obj[key]) {
->s : string
+>s : keyof T[K]
 >obj[key] : T[K]
 >obj : T
 >key : K
@@ -877,6 +888,264 @@ function f60<T>(source: T, target: T) {
     }
 }
 
+function f70(func: <T, U>(k1: keyof (T | U), k2: keyof (T & U)) => void) {
+>f70 : (func: <T, U>(k1: keyof (T | U), k2: keyof (T & U)) => void) => void
+>func : <T, U>(k1: keyof (T | U), k2: keyof (T & U)) => void
+>T : T
+>U : U
+>k1 : keyof (T | U)
+>T : T
+>U : U
+>k2 : keyof (T & U)
+>T : T
+>U : U
+
+    func<{ a: any, b: any }, { a: any, c: any }>('a', 'a');
+>func<{ a: any, b: any }, { a: any, c: any }>('a', 'a') : void
+>func : <T, U>(k1: keyof (T | U), k2: keyof (T & U)) => void
+>a : any
+>b : any
+>a : any
+>c : any
+>'a' : "a"
+>'a' : "a"
+
+    func<{ a: any, b: any }, { a: any, c: any }>('a', 'b');
+>func<{ a: any, b: any }, { a: any, c: any }>('a', 'b') : void
+>func : <T, U>(k1: keyof (T | U), k2: keyof (T & U)) => void
+>a : any
+>b : any
+>a : any
+>c : any
+>'a' : "a"
+>'b' : "b"
+
+    func<{ a: any, b: any }, { a: any, c: any }>('a', 'c');
+>func<{ a: any, b: any }, { a: any, c: any }>('a', 'c') : void
+>func : <T, U>(k1: keyof (T | U), k2: keyof (T & U)) => void
+>a : any
+>b : any
+>a : any
+>c : any
+>'a' : "a"
+>'c' : "c"
+}
+
+function f71(func: <T, U>(x: T, y: U) => Partial<T & U>) {
+>f71 : (func: <T, U>(x: T, y: U) => Partial<T & U>) => void
+>func : <T, U>(x: T, y: U) => Partial<T & U>
+>T : T
+>U : U
+>x : T
+>T : T
+>y : U
+>U : U
+>Partial : Partial<T>
+>T : T
+>U : U
+
+    let x = func({ a: 1, b: "hello" }, { c: true });
+>x : Partial<{ a: number; b: string; } & { c: boolean; }>
+>func({ a: 1, b: "hello" }, { c: true }) : Partial<{ a: number; b: string; } & { c: boolean; }>
+>func : <T, U>(x: T, y: U) => Partial<T & U>
+>{ a: 1, b: "hello" } : { a: number; b: string; }
+>a : number
+>1 : 1
+>b : string
+>"hello" : "hello"
+>{ c: true } : { c: true; }
+>c : boolean
+>true : true
+
+    x.a;  // number | undefined
+>x.a : number | undefined
+>x : Partial<{ a: number; b: string; } & { c: boolean; }>
+>a : number | undefined
+
+    x.b;  // string | undefined
+>x.b : string | undefined
+>x : Partial<{ a: number; b: string; } & { c: boolean; }>
+>b : string | undefined
+
+    x.c;  // boolean | undefined
+>x.c : boolean | undefined
+>x : Partial<{ a: number; b: string; } & { c: boolean; }>
+>c : boolean | undefined
+}
+
+function f72(func: <T, U, K extends keyof T | keyof U>(x: T, y: U, k: K) => (T & U)[K]) {
+>f72 : (func: <T, U, K extends keyof T | keyof U>(x: T, y: U, k: K) => (T & U)[K]) => void
+>func : <T, U, K extends keyof T | keyof U>(x: T, y: U, k: K) => (T & U)[K]
+>T : T
+>U : U
+>K : K
+>T : T
+>U : U
+>x : T
+>T : T
+>y : U
+>U : U
+>k : K
+>K : K
+>T : T
+>U : U
+>K : K
+
+    let a = func({ a: 1, b: "hello" }, { c: true }, 'a');  // number
+>a : number
+>func({ a: 1, b: "hello" }, { c: true }, 'a') : number
+>func : <T, U, K extends keyof T | keyof U>(x: T, y: U, k: K) => (T & U)[K]
+>{ a: 1, b: "hello" } : { a: number; b: string; }
+>a : number
+>1 : 1
+>b : string
+>"hello" : "hello"
+>{ c: true } : { c: true; }
+>c : boolean
+>true : true
+>'a' : "a"
+
+    let b = func({ a: 1, b: "hello" }, { c: true }, 'b');  // string
+>b : string
+>func({ a: 1, b: "hello" }, { c: true }, 'b') : string
+>func : <T, U, K extends keyof T | keyof U>(x: T, y: U, k: K) => (T & U)[K]
+>{ a: 1, b: "hello" } : { a: number; b: string; }
+>a : number
+>1 : 1
+>b : string
+>"hello" : "hello"
+>{ c: true } : { c: true; }
+>c : boolean
+>true : true
+>'b' : "b"
+
+    let c = func({ a: 1, b: "hello" }, { c: true }, 'c');  // boolean
+>c : boolean
+>func({ a: 1, b: "hello" }, { c: true }, 'c') : boolean
+>func : <T, U, K extends keyof T | keyof U>(x: T, y: U, k: K) => (T & U)[K]
+>{ a: 1, b: "hello" } : { a: number; b: string; }
+>a : number
+>1 : 1
+>b : string
+>"hello" : "hello"
+>{ c: true } : { c: true; }
+>c : boolean
+>true : true
+>'c' : "c"
+}
+
+function f73(func: <T, U, K extends keyof (T & U)>(x: T, y: U, k: K) => (T & U)[K]) {
+>f73 : (func: <T, U, K extends keyof (T & U)>(x: T, y: U, k: K) => (T & U)[K]) => void
+>func : <T, U, K extends keyof (T & U)>(x: T, y: U, k: K) => (T & U)[K]
+>T : T
+>U : U
+>K : K
+>T : T
+>U : U
+>x : T
+>T : T
+>y : U
+>U : U
+>k : K
+>K : K
+>T : T
+>U : U
+>K : K
+
+    let a = func({ a: 1, b: "hello" }, { c: true }, 'a');  // number
+>a : number
+>func({ a: 1, b: "hello" }, { c: true }, 'a') : number
+>func : <T, U, K extends keyof (T & U)>(x: T, y: U, k: K) => (T & U)[K]
+>{ a: 1, b: "hello" } : { a: number; b: string; }
+>a : number
+>1 : 1
+>b : string
+>"hello" : "hello"
+>{ c: true } : { c: true; }
+>c : boolean
+>true : true
+>'a' : "a"
+
+    let b = func({ a: 1, b: "hello" }, { c: true }, 'b');  // string
+>b : string
+>func({ a: 1, b: "hello" }, { c: true }, 'b') : string
+>func : <T, U, K extends keyof (T & U)>(x: T, y: U, k: K) => (T & U)[K]
+>{ a: 1, b: "hello" } : { a: number; b: string; }
+>a : number
+>1 : 1
+>b : string
+>"hello" : "hello"
+>{ c: true } : { c: true; }
+>c : boolean
+>true : true
+>'b' : "b"
+
+    let c = func({ a: 1, b: "hello" }, { c: true }, 'c');  // boolean
+>c : boolean
+>func({ a: 1, b: "hello" }, { c: true }, 'c') : boolean
+>func : <T, U, K extends keyof (T & U)>(x: T, y: U, k: K) => (T & U)[K]
+>{ a: 1, b: "hello" } : { a: number; b: string; }
+>a : number
+>1 : 1
+>b : string
+>"hello" : "hello"
+>{ c: true } : { c: true; }
+>c : boolean
+>true : true
+>'c' : "c"
+}
+
+function f74(func: <T, U, K extends keyof (T | U)>(x: T, y: U, k: K) => (T | U)[K]) {
+>f74 : (func: <T, U, K extends keyof (T | U)>(x: T, y: U, k: K) => (T | U)[K]) => void
+>func : <T, U, K extends keyof (T | U)>(x: T, y: U, k: K) => (T | U)[K]
+>T : T
+>U : U
+>K : K
+>T : T
+>U : U
+>x : T
+>T : T
+>y : U
+>U : U
+>k : K
+>K : K
+>T : T
+>U : U
+>K : K
+
+    let a = func({ a: 1, b: "hello" }, { a: 2, b: true }, 'a');  // number
+>a : number
+>func({ a: 1, b: "hello" }, { a: 2, b: true }, 'a') : number
+>func : <T, U, K extends keyof (T | U)>(x: T, y: U, k: K) => (T | U)[K]
+>{ a: 1, b: "hello" } : { a: number; b: string; }
+>a : number
+>1 : 1
+>b : string
+>"hello" : "hello"
+>{ a: 2, b: true } : { a: number; b: true; }
+>a : number
+>2 : 2
+>b : boolean
+>true : true
+>'a' : "a"
+
+    let b = func({ a: 1, b: "hello" }, { a: 2, b: true }, 'b');  // string | boolean
+>b : string | boolean
+>func({ a: 1, b: "hello" }, { a: 2, b: true }, 'b') : string | boolean
+>func : <T, U, K extends keyof (T | U)>(x: T, y: U, k: K) => (T | U)[K]
+>{ a: 1, b: "hello" } : { a: number; b: string; }
+>a : number
+>1 : 1
+>b : string
+>"hello" : "hello"
+>{ a: 2, b: true } : { a: number; b: true; }
+>a : number
+>2 : 2
+>b : boolean
+>true : true
+>'b' : "b"
+}
+
 // Repros from #12011
 
 class Base {
@@ -970,3 +1239,351 @@ class OtherPerson {
 >"parts" : "parts"
     }
 }
+
+// Modified repro from #12544
+
+function path<T, K1 extends keyof T>(obj: T, key1: K1): T[K1];
+>path : { <T, K1 extends keyof T>(obj: T, key1: K1): T[K1]; <T, K1 extends keyof T, K2 extends keyof T[K1]>(obj: T, key1: K1, key2: K2): T[K1][K2]; <T, K1 extends keyof T, K2 extends keyof T[K1], K3 extends keyof T[K1][K2]>(obj: T, key1: K1, key2: K2, key3: K3): T[K1][K2][K3]; (obj: any, ...keys: (string | number)[]): any; }
+>T : T
+>K1 : K1
+>T : T
+>obj : T
+>T : T
+>key1 : K1
+>K1 : K1
+>T : T
+>K1 : K1
+
+function path<T, K1 extends keyof T, K2 extends keyof T[K1]>(obj: T, key1: K1, key2: K2): T[K1][K2];
+>path : { <T, K1 extends keyof T>(obj: T, key1: K1): T[K1]; <T, K1 extends keyof T, K2 extends keyof T[K1]>(obj: T, key1: K1, key2: K2): T[K1][K2]; <T, K1 extends keyof T, K2 extends keyof T[K1], K3 extends keyof T[K1][K2]>(obj: T, key1: K1, key2: K2, key3: K3): T[K1][K2][K3]; (obj: any, ...keys: (string | number)[]): any; }
+>T : T
+>K1 : K1
+>T : T
+>K2 : K2
+>T : T
+>K1 : K1
+>obj : T
+>T : T
+>key1 : K1
+>K1 : K1
+>key2 : K2
+>K2 : K2
+>T : T
+>K1 : K1
+>K2 : K2
+
+function path<T, K1 extends keyof T, K2 extends keyof T[K1], K3 extends keyof T[K1][K2]>(obj: T, key1: K1, key2: K2, key3: K3): T[K1][K2][K3];
+>path : { <T, K1 extends keyof T>(obj: T, key1: K1): T[K1]; <T, K1 extends keyof T, K2 extends keyof T[K1]>(obj: T, key1: K1, key2: K2): T[K1][K2]; <T, K1 extends keyof T, K2 extends keyof T[K1], K3 extends keyof T[K1][K2]>(obj: T, key1: K1, key2: K2, key3: K3): T[K1][K2][K3]; (obj: any, ...keys: (string | number)[]): any; }
+>T : T
+>K1 : K1
+>T : T
+>K2 : K2
+>T : T
+>K1 : K1
+>K3 : K3
+>T : T
+>K1 : K1
+>K2 : K2
+>obj : T
+>T : T
+>key1 : K1
+>K1 : K1
+>key2 : K2
+>K2 : K2
+>key3 : K3
+>K3 : K3
+>T : T
+>K1 : K1
+>K2 : K2
+>K3 : K3
+
+function path(obj: any, ...keys: (string | number)[]): any;
+>path : { <T, K1 extends keyof T>(obj: T, key1: K1): T[K1]; <T, K1 extends keyof T, K2 extends keyof T[K1]>(obj: T, key1: K1, key2: K2): T[K1][K2]; <T, K1 extends keyof T, K2 extends keyof T[K1], K3 extends keyof T[K1][K2]>(obj: T, key1: K1, key2: K2, key3: K3): T[K1][K2][K3]; (obj: any, ...keys: (string | number)[]): any; }
+>obj : any
+>keys : (string | number)[]
+
+function path(obj: any, ...keys: (string | number)[]): any {
+>path : { <T, K1 extends keyof T>(obj: T, key1: K1): T[K1]; <T, K1 extends keyof T, K2 extends keyof T[K1]>(obj: T, key1: K1, key2: K2): T[K1][K2]; <T, K1 extends keyof T, K2 extends keyof T[K1], K3 extends keyof T[K1][K2]>(obj: T, key1: K1, key2: K2, key3: K3): T[K1][K2][K3]; (obj: any, ...keys: (string | number)[]): any; }
+>obj : any
+>keys : (string | number)[]
+
+    let result = obj;
+>result : any
+>obj : any
+
+    for (let k of keys) {
+>k : string | number
+>keys : (string | number)[]
+
+        result = result[k];
+>result = result[k] : any
+>result : any
+>result[k] : any
+>result : any
+>k : string | number
+    }
+    return result;
+>result : any
+}
+
+type Thing = {
+>Thing : Thing
+
+    a: { x: number, y: string },
+>a : { x: number; y: string; }
+>x : number
+>y : string
+
+    b: boolean
+>b : boolean
+
+};
+
+
+function f1(thing: Thing) {
+>f1 : (thing: Thing) => void
+>thing : Thing
+>Thing : Thing
+
+    let x1 = path(thing, 'a');  // { x: number, y: string }
+>x1 : { x: number; y: string; }
+>path(thing, 'a') : { x: number; y: string; }
+>path : { <T, K1 extends keyof T>(obj: T, key1: K1): T[K1]; <T, K1 extends keyof T, K2 extends keyof T[K1]>(obj: T, key1: K1, key2: K2): T[K1][K2]; <T, K1 extends keyof T, K2 extends keyof T[K1], K3 extends keyof T[K1][K2]>(obj: T, key1: K1, key2: K2, key3: K3): T[K1][K2][K3]; (obj: any, ...keys: (string | number)[]): any; }
+>thing : Thing
+>'a' : "a"
+
+    let x2 = path(thing, 'a', 'y');  // string
+>x2 : string
+>path(thing, 'a', 'y') : string
+>path : { <T, K1 extends keyof T>(obj: T, key1: K1): T[K1]; <T, K1 extends keyof T, K2 extends keyof T[K1]>(obj: T, key1: K1, key2: K2): T[K1][K2]; <T, K1 extends keyof T, K2 extends keyof T[K1], K3 extends keyof T[K1][K2]>(obj: T, key1: K1, key2: K2, key3: K3): T[K1][K2][K3]; (obj: any, ...keys: (string | number)[]): any; }
+>thing : Thing
+>'a' : "a"
+>'y' : "y"
+
+    let x3 = path(thing, 'b');  // boolean
+>x3 : boolean
+>path(thing, 'b') : boolean
+>path : { <T, K1 extends keyof T>(obj: T, key1: K1): T[K1]; <T, K1 extends keyof T, K2 extends keyof T[K1]>(obj: T, key1: K1, key2: K2): T[K1][K2]; <T, K1 extends keyof T, K2 extends keyof T[K1], K3 extends keyof T[K1][K2]>(obj: T, key1: K1, key2: K2, key3: K3): T[K1][K2][K3]; (obj: any, ...keys: (string | number)[]): any; }
+>thing : Thing
+>'b' : "b"
+
+    let x4 = path(thing, ...['a', 'x']);  // any
+>x4 : any
+>path(thing, ...['a', 'x']) : any
+>path : { <T, K1 extends keyof T>(obj: T, key1: K1): T[K1]; <T, K1 extends keyof T, K2 extends keyof T[K1]>(obj: T, key1: K1, key2: K2): T[K1][K2]; <T, K1 extends keyof T, K2 extends keyof T[K1], K3 extends keyof T[K1][K2]>(obj: T, key1: K1, key2: K2, key3: K3): T[K1][K2][K3]; (obj: any, ...keys: (string | number)[]): any; }
+>thing : Thing
+>...['a', 'x'] : string
+>['a', 'x'] : string[]
+>'a' : "a"
+>'x' : "x"
+}
+
+// Repro from comment in #12114
+
+const assignTo2 = <T, K1 extends keyof T, K2 extends keyof T[K1]>(object: T, key1: K1, key2: K2) =>
+>assignTo2 : <T, K1 extends keyof T, K2 extends keyof T[K1]>(object: T, key1: K1, key2: K2) => (value: T[K1][K2]) => T[K1][K2]
+><T, K1 extends keyof T, K2 extends keyof T[K1]>(object: T, key1: K1, key2: K2) =>    (value: T[K1][K2]) => object[key1][key2] = value : <T, K1 extends keyof T, K2 extends keyof T[K1]>(object: T, key1: K1, key2: K2) => (value: T[K1][K2]) => T[K1][K2]
+>T : T
+>K1 : K1
+>T : T
+>K2 : K2
+>T : T
+>K1 : K1
+>object : T
+>T : T
+>key1 : K1
+>K1 : K1
+>key2 : K2
+>K2 : K2
+
+    (value: T[K1][K2]) => object[key1][key2] = value;
+>(value: T[K1][K2]) => object[key1][key2] = value : (value: T[K1][K2]) => T[K1][K2]
+>value : T[K1][K2]
+>T : T
+>K1 : K1
+>K2 : K2
+>object[key1][key2] = value : T[K1][K2]
+>object[key1][key2] : T[K1][K2]
+>object[key1] : T[K1]
+>object : T
+>key1 : K1
+>key2 : K2
+>value : T[K1][K2]
+
+// Modified repro from #12573
+
+declare function one<T>(handler: (t: T) => void): T
+>one : <T>(handler: (t: T) => void) => T
+>T : T
+>handler : (t: T) => void
+>t : T
+>T : T
+>T : T
+
+var empty = one(() => {}) // inferred as {}, expected
+>empty : {}
+>one(() => {}) : {}
+>one : <T>(handler: (t: T) => void) => T
+>() => {} : () => void
+
+type Handlers<T> = { [K in keyof T]: (t: T[K]) => void }
+>Handlers : Handlers<T>
+>T : T
+>K : K
+>T : T
+>t : T[K]
+>T : T
+>K : K
+
+declare function on<T>(handlerHash: Handlers<T>): T
+>on : <T>(handlerHash: Handlers<T>) => T
+>T : T
+>handlerHash : Handlers<T>
+>Handlers : Handlers<T>
+>T : T
+>T : T
+
+var hashOfEmpty1 = on({ test: () => {} });  // {}
+>hashOfEmpty1 : {}
+>on({ test: () => {} }) : {}
+>on : <T>(handlerHash: Handlers<T>) => T
+>{ test: () => {} } : { test: () => void; }
+>test : () => void
+>() => {} : () => void
+
+var hashOfEmpty2 = on({ test: (x: boolean) => {} });  // { test: boolean }
+>hashOfEmpty2 : { test: boolean; }
+>on({ test: (x: boolean) => {} }) : { test: boolean; }
+>on : <T>(handlerHash: Handlers<T>) => T
+>{ test: (x: boolean) => {} } : { test: (x: boolean) => void; }
+>test : (x: boolean) => void
+>(x: boolean) => {} : (x: boolean) => void
+>x : boolean
+
+// Repro from #12624
+
+interface Options1<Data, Computed> {
+>Options1 : Options1<Data, Computed>
+>Data : Data
+>Computed : Computed
+
+    data?: Data
+>data : Data | undefined
+>Data : Data
+
+    computed?: Computed;
+>computed : Computed | undefined
+>Computed : Computed
+}
+
+declare class Component1<Data, Computed> {
+>Component1 : Component1<Data, Computed>
+>Data : Data
+>Computed : Computed
+
+    constructor(options: Options1<Data, Computed>);
+>options : Options1<Data, Computed>
+>Options1 : Options1<Data, Computed>
+>Data : Data
+>Computed : Computed
+
+    get<K extends keyof (Data & Computed)>(key: K): (Data & Computed)[K];
+>get : <K extends keyof (Data & Computed)>(key: K) => (Data & Computed)[K]
+>K : K
+>Data : Data
+>Computed : Computed
+>key : K
+>K : K
+>Data : Data
+>Computed : Computed
+>K : K
+}
+
+let c1 = new Component1({
+>c1 : Component1<{ hello: string; }, {}>
+>new Component1({    data: {        hello: ""    }}) : Component1<{ hello: string; }, {}>
+>Component1 : typeof Component1
+>{    data: {        hello: ""    }} : { data: { hello: string; }; }
+
+    data: {
+>data : { hello: string; }
+>{        hello: ""    } : { hello: string; }
+
+        hello: ""
+>hello : string
+>"" : ""
+    }
+});
+
+c1.get("hello");
+>c1.get("hello") : string
+>c1.get : <K extends "hello">(key: K) => ({ hello: string; } & {})[K]
+>c1 : Component1<{ hello: string; }, {}>
+>get : <K extends "hello">(key: K) => ({ hello: string; } & {})[K]
+>"hello" : "hello"
+
+// Repro from #12625
+
+interface Options2<Data, Computed> {
+>Options2 : Options2<Data, Computed>
+>Data : Data
+>Computed : Computed
+
+    data?: Data
+>data : Data | undefined
+>Data : Data
+
+    computed?: Computed;
+>computed : Computed | undefined
+>Computed : Computed
+}
+
+declare class Component2<Data, Computed> {
+>Component2 : Component2<Data, Computed>
+>Data : Data
+>Computed : Computed
+
+    constructor(options: Options2<Data, Computed>);
+>options : Options2<Data, Computed>
+>Options2 : Options2<Data, Computed>
+>Data : Data
+>Computed : Computed
+
+    get<K extends keyof Data | keyof Computed>(key: K): (Data & Computed)[K];
+>get : <K extends keyof Data | keyof Computed>(key: K) => (Data & Computed)[K]
+>K : K
+>Data : Data
+>Computed : Computed
+>key : K
+>K : K
+>Data : Data
+>Computed : Computed
+>K : K
+}
+
+// Repro from #12641
+
+interface R {
+>R : R
+
+    p: number;
+>p : number
+}
+
+function f<K extends keyof R>(p: K) {
+>f : <K extends "p">(p: K) => void
+>K : K
+>R : R
+>p : K
+>K : K
+
+    let a: any;
+>a : any
+
+    a[p].add;  // any
+>a[p].add : any
+>a[p] : any
+>a : any
+>p : K
+>add : any
+}

tests/baselines/reference/keyofAndIndexedAccessErrors.errors.txt

@@ -21,9 +21,14 @@ tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(64,33): error
 tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(66,24): error TS2345: Argument of type '"size"' is not assignable to parameter of type '"name" | "width" | "height" | "visible"'.
 tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(67,24): error TS2345: Argument of type '"name" | "size"' is not assignable to parameter of type '"name" | "width" | "height" | "visible"'.
   Type '"size"' is not assignable to type '"name" | "width" | "height" | "visible"'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(72,5): error TS2536: Type 'keyof (T & U)' cannot be used to index type 'T | U'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(76,5): error TS2322: Type 'T | U' is not assignable to type 'T & U'.
+  Type 'T' is not assignable to type 'T & U'.
+    Type 'T' is not assignable to type 'U'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(77,5): error TS2322: Type 'keyof (T & U)' is not assignable to type 'keyof (T | U)'.
 
 
-==== tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts (21 errors) ====
+==== tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts (24 errors) ====
     class Shape {
         name: string;
         width: number;
@@ -135,4 +140,23 @@ tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(67,24): error
                            ~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type '"name" | "size"' is not assignable to parameter of type '"name" | "width" | "height" | "visible"'.
 !!! error TS2345:   Type '"size"' is not assignable to type '"name" | "width" | "height" | "visible"'.
+    }
+    
+    function f20<T, U>(k1: keyof (T | U), k2: keyof (T & U), o1: T | U, o2: T & U) {
+        o1[k1];
+        o1[k2];   // Error
+        ~~~~~~
+!!! error TS2536: Type 'keyof (T & U)' cannot be used to index type 'T | U'.
+        o2[k1];
+        o2[k2];
+        o1 = o2;
+        o2 = o1;  // Error
+        ~~
+!!! error TS2322: Type 'T | U' is not assignable to type 'T & U'.
+!!! error TS2322:   Type 'T' is not assignable to type 'T & U'.
+!!! error TS2322:     Type 'T' is not assignable to type 'U'.
+        k1 = k2;  // Error
+        ~~
+!!! error TS2322: Type 'keyof (T & U)' is not assignable to type 'keyof (T | U)'.
+        k2 = k1;
     }

tests/baselines/reference/keyofAndIndexedAccessErrors.js

@@ -66,6 +66,17 @@ function f10(shape: Shape) {
     setProperty(shape, "name", "rectangle");
     setProperty(shape, "size", 10);  // Error
     setProperty(shape, cond ? "name" : "size", 10);  // Error
+}
+
+function f20<T, U>(k1: keyof (T | U), k2: keyof (T & U), o1: T | U, o2: T & U) {
+    o1[k1];
+    o1[k2];   // Error
+    o2[k1];
+    o2[k2];
+    o1 = o2;
+    o2 = o1;  // Error
+    k1 = k2;  // Error
+    k2 = k1;
 }
 
 //// [keyofAndIndexedAccessErrors.js]
@@ -88,3 +99,13 @@ function f10(shape) {
     setProperty(shape, "size", 10); // Error
     setProperty(shape, cond ? "name" : "size", 10); // Error
 }
+function f20(k1, k2, o1, o2) {
+    o1[k1];
+    o1[k2]; // Error
+    o2[k1];
+    o2[k2];
+    o1 = o2;
+    o2 = o1; // Error
+    k1 = k2; // Error
+    k2 = k1;
+}

tests/baselines/reference/mappedTypeErrors.errors.txt

@@ -16,13 +16,19 @@ tests/cases/conformance/types/mapped/mappedTypeErrors.ts(38,24): error TS2344: T
       Type 'T' is not assignable to type '"visible"'.
         Type 'string | number' is not assignable to type '"visible"'.
           Type 'string' is not assignable to type '"visible"'.
-tests/cases/conformance/types/mapped/mappedTypeErrors.ts(60,9): error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ [P in keyof T]?: T[P]; }'.
+tests/cases/conformance/types/mapped/mappedTypeErrors.ts(60,9): error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ [P in keyof T]?: T[P] | undefined; }'.
 tests/cases/conformance/types/mapped/mappedTypeErrors.ts(61,9): error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ readonly [P in keyof T]: T[P]; }'.
-tests/cases/conformance/types/mapped/mappedTypeErrors.ts(62,9): error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ readonly [P in keyof T]?: T[P]; }'.
+tests/cases/conformance/types/mapped/mappedTypeErrors.ts(62,9): error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ readonly [P in keyof T]?: T[P] | undefined; }'.
 tests/cases/conformance/types/mapped/mappedTypeErrors.ts(67,9): error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ [P in keyof T]: T[P][]; }'.
+tests/cases/conformance/types/mapped/mappedTypeErrors.ts(76,45): error TS2345: Argument of type '{ x: number; }' is not assignable to parameter of type 'Readonly<{ x: number; y: number; }>'.
+  Property 'y' is missing in type '{ x: number; }'.
+tests/cases/conformance/types/mapped/mappedTypeErrors.ts(78,59): error TS2345: Argument of type '{ x: number; y: number; z: number; }' is not assignable to parameter of type 'Readonly<{ x: number; y: number; }>'.
+  Object literal may only specify known properties, and 'z' does not exist in type 'Readonly<{ x: number; y: number; }>'.
+tests/cases/conformance/types/mapped/mappedTypeErrors.ts(84,58): error TS2345: Argument of type '{ x: number; y: number; z: number; }' is not assignable to parameter of type 'Partial<{ x: number; y: number; }>'.
+  Object literal may only specify known properties, and 'z' does not exist in type 'Partial<{ x: number; y: number; }>'.
 
 
-==== tests/cases/conformance/types/mapped/mappedTypeErrors.ts (14 errors) ====
+==== tests/cases/conformance/types/mapped/mappedTypeErrors.ts (17 errors) ====
     
     interface Shape {
         name: string;
@@ -112,13 +118,13 @@ tests/cases/conformance/types/mapped/mappedTypeErrors.ts(67,9): error TS2403: Su
         var x: { [P in keyof T]: T[P] };
         var x: { [P in keyof T]?: T[P] };  // Error
             ~
-!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ [P in keyof T]?: T[P]; }'.
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ [P in keyof T]?: T[P] | undefined; }'.
         var x: { readonly [P in keyof T]: T[P] };  // Error
             ~
 !!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ readonly [P in keyof T]: T[P]; }'.
         var x: { readonly [P in keyof T]?: T[P] };  // Error
             ~
-!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ readonly [P in keyof T]?: T[P]; }'.
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ readonly [P in keyof T]?: T[P] | undefined; }'.
     }
     
     function f12<T>() {
@@ -126,4 +132,30 @@ tests/cases/conformance/types/mapped/mappedTypeErrors.ts(67,9): error TS2403: Su
         var x: { [P in keyof T]: T[P][] };  // Error
             ~
 !!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ [P in keyof T]: T[P][]; }'.
+    }
+    
+    // Check that inferences to mapped types are secondary
+    
+    declare function objAndReadonly<T>(primary: T, secondary: Readonly<T>): T;
+    declare function objAndPartial<T>(primary: T, secondary: Partial<T>): T;
+    
+    function f20() {
+        let x1 = objAndReadonly({ x: 0, y: 0 }, { x: 1 });  // Error
+                                                ~~~~~~~~
+!!! error TS2345: Argument of type '{ x: number; }' is not assignable to parameter of type 'Readonly<{ x: number; y: number; }>'.
+!!! error TS2345:   Property 'y' is missing in type '{ x: number; }'.
+        let x2 = objAndReadonly({ x: 0, y: 0 }, { x: 1, y: 1 });
+        let x3 = objAndReadonly({ x: 0, y: 0 }, { x: 1, y: 1, z: 1 });  // Error
+                                                              ~~~~
+!!! error TS2345: Argument of type '{ x: number; y: number; z: number; }' is not assignable to parameter of type 'Readonly<{ x: number; y: number; }>'.
+!!! error TS2345:   Object literal may only specify known properties, and 'z' does not exist in type 'Readonly<{ x: number; y: number; }>'.
+    }
+    
+    function f21() {
+        let x1 = objAndPartial({ x: 0, y: 0 }, { x: 1 });
+        let x2 = objAndPartial({ x: 0, y: 0 }, { x: 1, y: 1 });
+        let x3 = objAndPartial({ x: 0, y: 0 }, { x: 1, y: 1, z: 1 });  // Error
+                                                             ~~~~
+!!! error TS2345: Argument of type '{ x: number; y: number; z: number; }' is not assignable to parameter of type 'Partial<{ x: number; y: number; }>'.
+!!! error TS2345:   Object literal may only specify known properties, and 'z' does not exist in type 'Partial<{ x: number; y: number; }>'.
     }

tests/baselines/reference/mappedTypeErrors.js

@@ -66,6 +66,23 @@ function f11<T>() {
 function f12<T>() {
     var x: { [P in keyof T]: T[P] };
     var x: { [P in keyof T]: T[P][] };  // Error
+}
+
+// Check that inferences to mapped types are secondary
+
+declare function objAndReadonly<T>(primary: T, secondary: Readonly<T>): T;
+declare function objAndPartial<T>(primary: T, secondary: Partial<T>): T;
+
+function f20() {
+    let x1 = objAndReadonly({ x: 0, y: 0 }, { x: 1 });  // Error
+    let x2 = objAndReadonly({ x: 0, y: 0 }, { x: 1, y: 1 });
+    let x3 = objAndReadonly({ x: 0, y: 0 }, { x: 1, y: 1, z: 1 });  // Error
+}
+
+function f21() {
+    let x1 = objAndPartial({ x: 0, y: 0 }, { x: 1 });
+    let x2 = objAndPartial({ x: 0, y: 0 }, { x: 1, y: 1 });
+    let x3 = objAndPartial({ x: 0, y: 0 }, { x: 1, y: 1, z: 1 });  // Error
 }
 
 //// [mappedTypeErrors.js]
@@ -97,6 +114,16 @@ function f12() {
     var x;
     var x; // Error
 }
+function f20() {
+    var x1 = objAndReadonly({ x: 0, y: 0 }, { x: 1 }); // Error
+    var x2 = objAndReadonly({ x: 0, y: 0 }, { x: 1, y: 1 });
+    var x3 = objAndReadonly({ x: 0, y: 0 }, { x: 1, y: 1, z: 1 }); // Error
+}
+function f21() {
+    var x1 = objAndPartial({ x: 0, y: 0 }, { x: 1 });
+    var x2 = objAndPartial({ x: 0, y: 0 }, { x: 1, y: 1 });
+    var x3 = objAndPartial({ x: 0, y: 0 }, { x: 1, y: 1, z: 1 }); // Error
+}
 
 
 //// [mappedTypeErrors.d.ts]
@@ -137,3 +164,7 @@ declare function f4<T extends keyof Named>(x: T): void;
 declare function f10<T>(): void;
 declare function f11<T>(): void;
 declare function f12<T>(): void;
+declare function objAndReadonly<T>(primary: T, secondary: Readonly<T>): T;
+declare function objAndPartial<T>(primary: T, secondary: Partial<T>): T;
+declare function f20(): void;
+declare function f21(): void;

tests/baselines/reference/mappedTypeModifiers.js

@@ -0,0 +1,145 @@
+//// [mappedTypeModifiers.ts]
+
+type T = { a: number, b: string };
+type TU = { a: number | undefined, b: string | undefined };
+type TP = { a?: number, b?: string };
+type TR = { readonly a: number, readonly b: string };
+type TPR = { readonly a?: number, readonly b?: string };
+
+// Validate they all have the same keys
+var v00: "a" | "b";
+var v00: keyof T;
+var v00: keyof TU;
+var v00: keyof TP;
+var v00: keyof TR;
+var v00: keyof TPR;
+
+// Validate that non-isomorphic mapped types strip modifiers
+var v01: T;
+var v01: Pick<TR, keyof T>;
+var v01: Pick<Readonly<T>, keyof T>;
+
+// Validate that non-isomorphic mapped types strip modifiers
+var v02: TU;
+var v02: Pick<TP, keyof T>;
+var v02: Pick<TPR, keyof T>;
+var v02: Pick<Partial<T>, keyof T>;
+var v02: Pick<Partial<Readonly<T>>, keyof T>;
+
+// Validate that isomorphic mapped types preserve optional modifier
+var v03: TP;
+var v03: Partial<T>;
+
+// Validate that isomorphic mapped types preserve readonly modifier
+var v04: TR;
+var v04: Readonly<T>;
+
+// Validate that isomorphic mapped types preserve both partial and readonly modifiers
+var v05: TPR;
+var v05: Partial<TR>;
+var v05: Readonly<TP>;
+var v05: Partial<Readonly<T>>;
+var v05: Readonly<Partial<T>>;
+
+type Boxified<T> = { [P in keyof T]: { x: T[P] } };
+
+type B = { a: { x: number }, b: { x: string } };
+type BU = { a: { x: number } | undefined, b: { x: string } | undefined };
+type BP = { a?: { x: number }, b?: { x: string } };
+type BR = { readonly a: { x: number }, readonly b: { x: string } };
+type BPR = { readonly a?: { x: number }, readonly b?: { x: string } };
+
+// Validate they all have the same keys
+var b00: "a" | "b";
+var b00: keyof B;
+var b00: keyof BU;
+var b00: keyof BP;
+var b00: keyof BR;
+var b00: keyof BPR;
+
+// Validate that non-isomorphic mapped types strip modifiers
+var b01: B;
+var b01: Pick<BR, keyof B>;
+var b01: Pick<Readonly<BR>, keyof B>;
+
+// Validate that non-isomorphic mapped types strip modifiers
+var b02: BU;
+var b02: Pick<BP, keyof B>;
+var b02: Pick<BPR, keyof B>;
+var b02: Pick<Partial<B>, keyof B>;
+var b02: Pick<Partial<Readonly<B>>, keyof B>;
+
+// Validate that isomorphic mapped types preserve optional modifier
+var b03: BP;
+var b03: Partial<B>;
+
+// Validate that isomorphic mapped types preserve readonly modifier
+var b04: BR;
+var b04: Readonly<B>;
+
+// Validate that isomorphic mapped types preserve both partial and readonly modifiers
+var b05: BPR;
+var b05: Partial<BR>;
+var b05: Readonly<BP>;
+var b05: Partial<Readonly<B>>;
+var b05: Readonly<Partial<B>>;
+
+//// [mappedTypeModifiers.js]
+// Validate they all have the same keys
+var v00;
+var v00;
+var v00;
+var v00;
+var v00;
+var v00;
+// Validate that non-isomorphic mapped types strip modifiers
+var v01;
+var v01;
+var v01;
+// Validate that non-isomorphic mapped types strip modifiers
+var v02;
+var v02;
+var v02;
+var v02;
+var v02;
+// Validate that isomorphic mapped types preserve optional modifier
+var v03;
+var v03;
+// Validate that isomorphic mapped types preserve readonly modifier
+var v04;
+var v04;
+// Validate that isomorphic mapped types preserve both partial and readonly modifiers
+var v05;
+var v05;
+var v05;
+var v05;
+var v05;
+// Validate they all have the same keys
+var b00;
+var b00;
+var b00;
+var b00;
+var b00;
+var b00;
+// Validate that non-isomorphic mapped types strip modifiers
+var b01;
+var b01;
+var b01;
+// Validate that non-isomorphic mapped types strip modifiers
+var b02;
+var b02;
+var b02;
+var b02;
+var b02;
+// Validate that isomorphic mapped types preserve optional modifier
+var b03;
+var b03;
+// Validate that isomorphic mapped types preserve readonly modifier
+var b04;
+var b04;
+// Validate that isomorphic mapped types preserve both partial and readonly modifiers
+var b05;
+var b05;
+var b05;
+var b05;
+var b05;

tests/baselines/reference/mappedTypeModifiers.symbols

@@ -0,0 +1,313 @@
+=== tests/cases/conformance/types/mapped/mappedTypeModifiers.ts ===
+
+type T = { a: number, b: string };
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 0, 0))
+>a : Symbol(a, Decl(mappedTypeModifiers.ts, 1, 10))
+>b : Symbol(b, Decl(mappedTypeModifiers.ts, 1, 21))
+
+type TU = { a: number | undefined, b: string | undefined };
+>TU : Symbol(TU, Decl(mappedTypeModifiers.ts, 1, 34))
+>a : Symbol(a, Decl(mappedTypeModifiers.ts, 2, 11))
+>b : Symbol(b, Decl(mappedTypeModifiers.ts, 2, 34))
+
+type TP = { a?: number, b?: string };
+>TP : Symbol(TP, Decl(mappedTypeModifiers.ts, 2, 59))
+>a : Symbol(a, Decl(mappedTypeModifiers.ts, 3, 11))
+>b : Symbol(b, Decl(mappedTypeModifiers.ts, 3, 23))
+
+type TR = { readonly a: number, readonly b: string };
+>TR : Symbol(TR, Decl(mappedTypeModifiers.ts, 3, 37))
+>a : Symbol(a, Decl(mappedTypeModifiers.ts, 4, 11))
+>b : Symbol(b, Decl(mappedTypeModifiers.ts, 4, 31))
+
+type TPR = { readonly a?: number, readonly b?: string };
+>TPR : Symbol(TPR, Decl(mappedTypeModifiers.ts, 4, 53))
+>a : Symbol(a, Decl(mappedTypeModifiers.ts, 5, 12))
+>b : Symbol(b, Decl(mappedTypeModifiers.ts, 5, 33))
+
+// Validate they all have the same keys
+var v00: "a" | "b";
+>v00 : Symbol(v00, Decl(mappedTypeModifiers.ts, 8, 3), Decl(mappedTypeModifiers.ts, 9, 3), Decl(mappedTypeModifiers.ts, 10, 3), Decl(mappedTypeModifiers.ts, 11, 3), Decl(mappedTypeModifiers.ts, 12, 3), Decl(mappedTypeModifiers.ts, 13, 3))
+
+var v00: keyof T;
+>v00 : Symbol(v00, Decl(mappedTypeModifiers.ts, 8, 3), Decl(mappedTypeModifiers.ts, 9, 3), Decl(mappedTypeModifiers.ts, 10, 3), Decl(mappedTypeModifiers.ts, 11, 3), Decl(mappedTypeModifiers.ts, 12, 3), Decl(mappedTypeModifiers.ts, 13, 3))
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 0, 0))
+
+var v00: keyof TU;
+>v00 : Symbol(v00, Decl(mappedTypeModifiers.ts, 8, 3), Decl(mappedTypeModifiers.ts, 9, 3), Decl(mappedTypeModifiers.ts, 10, 3), Decl(mappedTypeModifiers.ts, 11, 3), Decl(mappedTypeModifiers.ts, 12, 3), Decl(mappedTypeModifiers.ts, 13, 3))
+>TU : Symbol(TU, Decl(mappedTypeModifiers.ts, 1, 34))
+
+var v00: keyof TP;
+>v00 : Symbol(v00, Decl(mappedTypeModifiers.ts, 8, 3), Decl(mappedTypeModifiers.ts, 9, 3), Decl(mappedTypeModifiers.ts, 10, 3), Decl(mappedTypeModifiers.ts, 11, 3), Decl(mappedTypeModifiers.ts, 12, 3), Decl(mappedTypeModifiers.ts, 13, 3))
+>TP : Symbol(TP, Decl(mappedTypeModifiers.ts, 2, 59))
+
+var v00: keyof TR;
+>v00 : Symbol(v00, Decl(mappedTypeModifiers.ts, 8, 3), Decl(mappedTypeModifiers.ts, 9, 3), Decl(mappedTypeModifiers.ts, 10, 3), Decl(mappedTypeModifiers.ts, 11, 3), Decl(mappedTypeModifiers.ts, 12, 3), Decl(mappedTypeModifiers.ts, 13, 3))
+>TR : Symbol(TR, Decl(mappedTypeModifiers.ts, 3, 37))
+
+var v00: keyof TPR;
+>v00 : Symbol(v00, Decl(mappedTypeModifiers.ts, 8, 3), Decl(mappedTypeModifiers.ts, 9, 3), Decl(mappedTypeModifiers.ts, 10, 3), Decl(mappedTypeModifiers.ts, 11, 3), Decl(mappedTypeModifiers.ts, 12, 3), Decl(mappedTypeModifiers.ts, 13, 3))
+>TPR : Symbol(TPR, Decl(mappedTypeModifiers.ts, 4, 53))
+
+// Validate that non-isomorphic mapped types strip modifiers
+var v01: T;
+>v01 : Symbol(v01, Decl(mappedTypeModifiers.ts, 16, 3), Decl(mappedTypeModifiers.ts, 17, 3), Decl(mappedTypeModifiers.ts, 18, 3))
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 0, 0))
+
+var v01: Pick<TR, keyof T>;
+>v01 : Symbol(v01, Decl(mappedTypeModifiers.ts, 16, 3), Decl(mappedTypeModifiers.ts, 17, 3), Decl(mappedTypeModifiers.ts, 18, 3))
+>Pick : Symbol(Pick, Decl(lib.d.ts, --, --))
+>TR : Symbol(TR, Decl(mappedTypeModifiers.ts, 3, 37))
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 0, 0))
+
+var v01: Pick<Readonly<T>, keyof T>;
+>v01 : Symbol(v01, Decl(mappedTypeModifiers.ts, 16, 3), Decl(mappedTypeModifiers.ts, 17, 3), Decl(mappedTypeModifiers.ts, 18, 3))
+>Pick : Symbol(Pick, Decl(lib.d.ts, --, --))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 0, 0))
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 0, 0))
+
+// Validate that non-isomorphic mapped types strip modifiers
+var v02: TU;
+>v02 : Symbol(v02, Decl(mappedTypeModifiers.ts, 21, 3), Decl(mappedTypeModifiers.ts, 22, 3), Decl(mappedTypeModifiers.ts, 23, 3), Decl(mappedTypeModifiers.ts, 24, 3), Decl(mappedTypeModifiers.ts, 25, 3))
+>TU : Symbol(TU, Decl(mappedTypeModifiers.ts, 1, 34))
+
+var v02: Pick<TP, keyof T>;
+>v02 : Symbol(v02, Decl(mappedTypeModifiers.ts, 21, 3), Decl(mappedTypeModifiers.ts, 22, 3), Decl(mappedTypeModifiers.ts, 23, 3), Decl(mappedTypeModifiers.ts, 24, 3), Decl(mappedTypeModifiers.ts, 25, 3))
+>Pick : Symbol(Pick, Decl(lib.d.ts, --, --))
+>TP : Symbol(TP, Decl(mappedTypeModifiers.ts, 2, 59))
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 0, 0))
+
+var v02: Pick<TPR, keyof T>;
+>v02 : Symbol(v02, Decl(mappedTypeModifiers.ts, 21, 3), Decl(mappedTypeModifiers.ts, 22, 3), Decl(mappedTypeModifiers.ts, 23, 3), Decl(mappedTypeModifiers.ts, 24, 3), Decl(mappedTypeModifiers.ts, 25, 3))
+>Pick : Symbol(Pick, Decl(lib.d.ts, --, --))
+>TPR : Symbol(TPR, Decl(mappedTypeModifiers.ts, 4, 53))
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 0, 0))
+
+var v02: Pick<Partial<T>, keyof T>;
+>v02 : Symbol(v02, Decl(mappedTypeModifiers.ts, 21, 3), Decl(mappedTypeModifiers.ts, 22, 3), Decl(mappedTypeModifiers.ts, 23, 3), Decl(mappedTypeModifiers.ts, 24, 3), Decl(mappedTypeModifiers.ts, 25, 3))
+>Pick : Symbol(Pick, Decl(lib.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 0, 0))
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 0, 0))
+
+var v02: Pick<Partial<Readonly<T>>, keyof T>;
+>v02 : Symbol(v02, Decl(mappedTypeModifiers.ts, 21, 3), Decl(mappedTypeModifiers.ts, 22, 3), Decl(mappedTypeModifiers.ts, 23, 3), Decl(mappedTypeModifiers.ts, 24, 3), Decl(mappedTypeModifiers.ts, 25, 3))
+>Pick : Symbol(Pick, Decl(lib.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 0, 0))
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 0, 0))
+
+// Validate that isomorphic mapped types preserve optional modifier
+var v03: TP;
+>v03 : Symbol(v03, Decl(mappedTypeModifiers.ts, 28, 3), Decl(mappedTypeModifiers.ts, 29, 3))
+>TP : Symbol(TP, Decl(mappedTypeModifiers.ts, 2, 59))
+
+var v03: Partial<T>;
+>v03 : Symbol(v03, Decl(mappedTypeModifiers.ts, 28, 3), Decl(mappedTypeModifiers.ts, 29, 3))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 0, 0))
+
+// Validate that isomorphic mapped types preserve readonly modifier
+var v04: TR;
+>v04 : Symbol(v04, Decl(mappedTypeModifiers.ts, 32, 3), Decl(mappedTypeModifiers.ts, 33, 3))
+>TR : Symbol(TR, Decl(mappedTypeModifiers.ts, 3, 37))
+
+var v04: Readonly<T>;
+>v04 : Symbol(v04, Decl(mappedTypeModifiers.ts, 32, 3), Decl(mappedTypeModifiers.ts, 33, 3))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 0, 0))
+
+// Validate that isomorphic mapped types preserve both partial and readonly modifiers
+var v05: TPR;
+>v05 : Symbol(v05, Decl(mappedTypeModifiers.ts, 36, 3), Decl(mappedTypeModifiers.ts, 37, 3), Decl(mappedTypeModifiers.ts, 38, 3), Decl(mappedTypeModifiers.ts, 39, 3), Decl(mappedTypeModifiers.ts, 40, 3))
+>TPR : Symbol(TPR, Decl(mappedTypeModifiers.ts, 4, 53))
+
+var v05: Partial<TR>;
+>v05 : Symbol(v05, Decl(mappedTypeModifiers.ts, 36, 3), Decl(mappedTypeModifiers.ts, 37, 3), Decl(mappedTypeModifiers.ts, 38, 3), Decl(mappedTypeModifiers.ts, 39, 3), Decl(mappedTypeModifiers.ts, 40, 3))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>TR : Symbol(TR, Decl(mappedTypeModifiers.ts, 3, 37))
+
+var v05: Readonly<TP>;
+>v05 : Symbol(v05, Decl(mappedTypeModifiers.ts, 36, 3), Decl(mappedTypeModifiers.ts, 37, 3), Decl(mappedTypeModifiers.ts, 38, 3), Decl(mappedTypeModifiers.ts, 39, 3), Decl(mappedTypeModifiers.ts, 40, 3))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>TP : Symbol(TP, Decl(mappedTypeModifiers.ts, 2, 59))
+
+var v05: Partial<Readonly<T>>;
+>v05 : Symbol(v05, Decl(mappedTypeModifiers.ts, 36, 3), Decl(mappedTypeModifiers.ts, 37, 3), Decl(mappedTypeModifiers.ts, 38, 3), Decl(mappedTypeModifiers.ts, 39, 3), Decl(mappedTypeModifiers.ts, 40, 3))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 0, 0))
+
+var v05: Readonly<Partial<T>>;
+>v05 : Symbol(v05, Decl(mappedTypeModifiers.ts, 36, 3), Decl(mappedTypeModifiers.ts, 37, 3), Decl(mappedTypeModifiers.ts, 38, 3), Decl(mappedTypeModifiers.ts, 39, 3), Decl(mappedTypeModifiers.ts, 40, 3))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 0, 0))
+
+type Boxified<T> = { [P in keyof T]: { x: T[P] } };
+>Boxified : Symbol(Boxified, Decl(mappedTypeModifiers.ts, 40, 30))
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 42, 14))
+>P : Symbol(P, Decl(mappedTypeModifiers.ts, 42, 22))
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 42, 14))
+>x : Symbol(x, Decl(mappedTypeModifiers.ts, 42, 38))
+>T : Symbol(T, Decl(mappedTypeModifiers.ts, 42, 14))
+>P : Symbol(P, Decl(mappedTypeModifiers.ts, 42, 22))
+
+type B = { a: { x: number }, b: { x: string } };
+>B : Symbol(B, Decl(mappedTypeModifiers.ts, 42, 51))
+>a : Symbol(a, Decl(mappedTypeModifiers.ts, 44, 10))
+>x : Symbol(x, Decl(mappedTypeModifiers.ts, 44, 15))
+>b : Symbol(b, Decl(mappedTypeModifiers.ts, 44, 28))
+>x : Symbol(x, Decl(mappedTypeModifiers.ts, 44, 33))
+
+type BU = { a: { x: number } | undefined, b: { x: string } | undefined };
+>BU : Symbol(BU, Decl(mappedTypeModifiers.ts, 44, 48))
+>a : Symbol(a, Decl(mappedTypeModifiers.ts, 45, 11))
+>x : Symbol(x, Decl(mappedTypeModifiers.ts, 45, 16))
+>b : Symbol(b, Decl(mappedTypeModifiers.ts, 45, 41))
+>x : Symbol(x, Decl(mappedTypeModifiers.ts, 45, 46))
+
+type BP = { a?: { x: number }, b?: { x: string } };
+>BP : Symbol(BP, Decl(mappedTypeModifiers.ts, 45, 73))
+>a : Symbol(a, Decl(mappedTypeModifiers.ts, 46, 11))
+>x : Symbol(x, Decl(mappedTypeModifiers.ts, 46, 17))
+>b : Symbol(b, Decl(mappedTypeModifiers.ts, 46, 30))
+>x : Symbol(x, Decl(mappedTypeModifiers.ts, 46, 36))
+
+type BR = { readonly a: { x: number }, readonly b: { x: string } };
+>BR : Symbol(BR, Decl(mappedTypeModifiers.ts, 46, 51))
+>a : Symbol(a, Decl(mappedTypeModifiers.ts, 47, 11))
+>x : Symbol(x, Decl(mappedTypeModifiers.ts, 47, 25))
+>b : Symbol(b, Decl(mappedTypeModifiers.ts, 47, 38))
+>x : Symbol(x, Decl(mappedTypeModifiers.ts, 47, 52))
+
+type BPR = { readonly a?: { x: number }, readonly b?: { x: string } };
+>BPR : Symbol(BPR, Decl(mappedTypeModifiers.ts, 47, 67))
+>a : Symbol(a, Decl(mappedTypeModifiers.ts, 48, 12))
+>x : Symbol(x, Decl(mappedTypeModifiers.ts, 48, 27))
+>b : Symbol(b, Decl(mappedTypeModifiers.ts, 48, 40))
+>x : Symbol(x, Decl(mappedTypeModifiers.ts, 48, 55))
+
+// Validate they all have the same keys
+var b00: "a" | "b";
+>b00 : Symbol(b00, Decl(mappedTypeModifiers.ts, 51, 3), Decl(mappedTypeModifiers.ts, 52, 3), Decl(mappedTypeModifiers.ts, 53, 3), Decl(mappedTypeModifiers.ts, 54, 3), Decl(mappedTypeModifiers.ts, 55, 3), Decl(mappedTypeModifiers.ts, 56, 3))
+
+var b00: keyof B;
+>b00 : Symbol(b00, Decl(mappedTypeModifiers.ts, 51, 3), Decl(mappedTypeModifiers.ts, 52, 3), Decl(mappedTypeModifiers.ts, 53, 3), Decl(mappedTypeModifiers.ts, 54, 3), Decl(mappedTypeModifiers.ts, 55, 3), Decl(mappedTypeModifiers.ts, 56, 3))
+>B : Symbol(B, Decl(mappedTypeModifiers.ts, 42, 51))
+
+var b00: keyof BU;
+>b00 : Symbol(b00, Decl(mappedTypeModifiers.ts, 51, 3), Decl(mappedTypeModifiers.ts, 52, 3), Decl(mappedTypeModifiers.ts, 53, 3), Decl(mappedTypeModifiers.ts, 54, 3), Decl(mappedTypeModifiers.ts, 55, 3), Decl(mappedTypeModifiers.ts, 56, 3))
+>BU : Symbol(BU, Decl(mappedTypeModifiers.ts, 44, 48))
+
+var b00: keyof BP;
+>b00 : Symbol(b00, Decl(mappedTypeModifiers.ts, 51, 3), Decl(mappedTypeModifiers.ts, 52, 3), Decl(mappedTypeModifiers.ts, 53, 3), Decl(mappedTypeModifiers.ts, 54, 3), Decl(mappedTypeModifiers.ts, 55, 3), Decl(mappedTypeModifiers.ts, 56, 3))
+>BP : Symbol(BP, Decl(mappedTypeModifiers.ts, 45, 73))
+
+var b00: keyof BR;
+>b00 : Symbol(b00, Decl(mappedTypeModifiers.ts, 51, 3), Decl(mappedTypeModifiers.ts, 52, 3), Decl(mappedTypeModifiers.ts, 53, 3), Decl(mappedTypeModifiers.ts, 54, 3), Decl(mappedTypeModifiers.ts, 55, 3), Decl(mappedTypeModifiers.ts, 56, 3))
+>BR : Symbol(BR, Decl(mappedTypeModifiers.ts, 46, 51))
+
+var b00: keyof BPR;
+>b00 : Symbol(b00, Decl(mappedTypeModifiers.ts, 51, 3), Decl(mappedTypeModifiers.ts, 52, 3), Decl(mappedTypeModifiers.ts, 53, 3), Decl(mappedTypeModifiers.ts, 54, 3), Decl(mappedTypeModifiers.ts, 55, 3), Decl(mappedTypeModifiers.ts, 56, 3))
+>BPR : Symbol(BPR, Decl(mappedTypeModifiers.ts, 47, 67))
+
+// Validate that non-isomorphic mapped types strip modifiers
+var b01: B;
+>b01 : Symbol(b01, Decl(mappedTypeModifiers.ts, 59, 3), Decl(mappedTypeModifiers.ts, 60, 3), Decl(mappedTypeModifiers.ts, 61, 3))
+>B : Symbol(B, Decl(mappedTypeModifiers.ts, 42, 51))
+
+var b01: Pick<BR, keyof B>;
+>b01 : Symbol(b01, Decl(mappedTypeModifiers.ts, 59, 3), Decl(mappedTypeModifiers.ts, 60, 3), Decl(mappedTypeModifiers.ts, 61, 3))
+>Pick : Symbol(Pick, Decl(lib.d.ts, --, --))
+>BR : Symbol(BR, Decl(mappedTypeModifiers.ts, 46, 51))
+>B : Symbol(B, Decl(mappedTypeModifiers.ts, 42, 51))
+
+var b01: Pick<Readonly<BR>, keyof B>;
+>b01 : Symbol(b01, Decl(mappedTypeModifiers.ts, 59, 3), Decl(mappedTypeModifiers.ts, 60, 3), Decl(mappedTypeModifiers.ts, 61, 3))
+>Pick : Symbol(Pick, Decl(lib.d.ts, --, --))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>BR : Symbol(BR, Decl(mappedTypeModifiers.ts, 46, 51))
+>B : Symbol(B, Decl(mappedTypeModifiers.ts, 42, 51))
+
+// Validate that non-isomorphic mapped types strip modifiers
+var b02: BU;
+>b02 : Symbol(b02, Decl(mappedTypeModifiers.ts, 64, 3), Decl(mappedTypeModifiers.ts, 65, 3), Decl(mappedTypeModifiers.ts, 66, 3), Decl(mappedTypeModifiers.ts, 67, 3), Decl(mappedTypeModifiers.ts, 68, 3))
+>BU : Symbol(BU, Decl(mappedTypeModifiers.ts, 44, 48))
+
+var b02: Pick<BP, keyof B>;
+>b02 : Symbol(b02, Decl(mappedTypeModifiers.ts, 64, 3), Decl(mappedTypeModifiers.ts, 65, 3), Decl(mappedTypeModifiers.ts, 66, 3), Decl(mappedTypeModifiers.ts, 67, 3), Decl(mappedTypeModifiers.ts, 68, 3))
+>Pick : Symbol(Pick, Decl(lib.d.ts, --, --))
+>BP : Symbol(BP, Decl(mappedTypeModifiers.ts, 45, 73))
+>B : Symbol(B, Decl(mappedTypeModifiers.ts, 42, 51))
+
+var b02: Pick<BPR, keyof B>;
+>b02 : Symbol(b02, Decl(mappedTypeModifiers.ts, 64, 3), Decl(mappedTypeModifiers.ts, 65, 3), Decl(mappedTypeModifiers.ts, 66, 3), Decl(mappedTypeModifiers.ts, 67, 3), Decl(mappedTypeModifiers.ts, 68, 3))
+>Pick : Symbol(Pick, Decl(lib.d.ts, --, --))
+>BPR : Symbol(BPR, Decl(mappedTypeModifiers.ts, 47, 67))
+>B : Symbol(B, Decl(mappedTypeModifiers.ts, 42, 51))
+
+var b02: Pick<Partial<B>, keyof B>;
+>b02 : Symbol(b02, Decl(mappedTypeModifiers.ts, 64, 3), Decl(mappedTypeModifiers.ts, 65, 3), Decl(mappedTypeModifiers.ts, 66, 3), Decl(mappedTypeModifiers.ts, 67, 3), Decl(mappedTypeModifiers.ts, 68, 3))
+>Pick : Symbol(Pick, Decl(lib.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>B : Symbol(B, Decl(mappedTypeModifiers.ts, 42, 51))
+>B : Symbol(B, Decl(mappedTypeModifiers.ts, 42, 51))
+
+var b02: Pick<Partial<Readonly<B>>, keyof B>;
+>b02 : Symbol(b02, Decl(mappedTypeModifiers.ts, 64, 3), Decl(mappedTypeModifiers.ts, 65, 3), Decl(mappedTypeModifiers.ts, 66, 3), Decl(mappedTypeModifiers.ts, 67, 3), Decl(mappedTypeModifiers.ts, 68, 3))
+>Pick : Symbol(Pick, Decl(lib.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>B : Symbol(B, Decl(mappedTypeModifiers.ts, 42, 51))
+>B : Symbol(B, Decl(mappedTypeModifiers.ts, 42, 51))
+
+// Validate that isomorphic mapped types preserve optional modifier
+var b03: BP;
+>b03 : Symbol(b03, Decl(mappedTypeModifiers.ts, 71, 3), Decl(mappedTypeModifiers.ts, 72, 3))
+>BP : Symbol(BP, Decl(mappedTypeModifiers.ts, 45, 73))
+
+var b03: Partial<B>;
+>b03 : Symbol(b03, Decl(mappedTypeModifiers.ts, 71, 3), Decl(mappedTypeModifiers.ts, 72, 3))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>B : Symbol(B, Decl(mappedTypeModifiers.ts, 42, 51))
+
+// Validate that isomorphic mapped types preserve readonly modifier
+var b04: BR;
+>b04 : Symbol(b04, Decl(mappedTypeModifiers.ts, 75, 3), Decl(mappedTypeModifiers.ts, 76, 3))
+>BR : Symbol(BR, Decl(mappedTypeModifiers.ts, 46, 51))
+
+var b04: Readonly<B>;
+>b04 : Symbol(b04, Decl(mappedTypeModifiers.ts, 75, 3), Decl(mappedTypeModifiers.ts, 76, 3))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>B : Symbol(B, Decl(mappedTypeModifiers.ts, 42, 51))
+
+// Validate that isomorphic mapped types preserve both partial and readonly modifiers
+var b05: BPR;
+>b05 : Symbol(b05, Decl(mappedTypeModifiers.ts, 79, 3), Decl(mappedTypeModifiers.ts, 80, 3), Decl(mappedTypeModifiers.ts, 81, 3), Decl(mappedTypeModifiers.ts, 82, 3), Decl(mappedTypeModifiers.ts, 83, 3))
+>BPR : Symbol(BPR, Decl(mappedTypeModifiers.ts, 47, 67))
+
+var b05: Partial<BR>;
+>b05 : Symbol(b05, Decl(mappedTypeModifiers.ts, 79, 3), Decl(mappedTypeModifiers.ts, 80, 3), Decl(mappedTypeModifiers.ts, 81, 3), Decl(mappedTypeModifiers.ts, 82, 3), Decl(mappedTypeModifiers.ts, 83, 3))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>BR : Symbol(BR, Decl(mappedTypeModifiers.ts, 46, 51))
+
+var b05: Readonly<BP>;
+>b05 : Symbol(b05, Decl(mappedTypeModifiers.ts, 79, 3), Decl(mappedTypeModifiers.ts, 80, 3), Decl(mappedTypeModifiers.ts, 81, 3), Decl(mappedTypeModifiers.ts, 82, 3), Decl(mappedTypeModifiers.ts, 83, 3))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>BP : Symbol(BP, Decl(mappedTypeModifiers.ts, 45, 73))
+
+var b05: Partial<Readonly<B>>;
+>b05 : Symbol(b05, Decl(mappedTypeModifiers.ts, 79, 3), Decl(mappedTypeModifiers.ts, 80, 3), Decl(mappedTypeModifiers.ts, 81, 3), Decl(mappedTypeModifiers.ts, 82, 3), Decl(mappedTypeModifiers.ts, 83, 3))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>B : Symbol(B, Decl(mappedTypeModifiers.ts, 42, 51))
+
+var b05: Readonly<Partial<B>>;
+>b05 : Symbol(b05, Decl(mappedTypeModifiers.ts, 79, 3), Decl(mappedTypeModifiers.ts, 80, 3), Decl(mappedTypeModifiers.ts, 81, 3), Decl(mappedTypeModifiers.ts, 82, 3), Decl(mappedTypeModifiers.ts, 83, 3))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>B : Symbol(B, Decl(mappedTypeModifiers.ts, 42, 51))
+

tests/baselines/reference/mappedTypeModifiers.types

@@ -0,0 +1,313 @@
+=== tests/cases/conformance/types/mapped/mappedTypeModifiers.ts ===
+
+type T = { a: number, b: string };
+>T : T
+>a : number
+>b : string
+
+type TU = { a: number | undefined, b: string | undefined };
+>TU : TU
+>a : number | undefined
+>b : string | undefined
+
+type TP = { a?: number, b?: string };
+>TP : TP
+>a : number | undefined
+>b : string | undefined
+
+type TR = { readonly a: number, readonly b: string };
+>TR : TR
+>a : number
+>b : string
+
+type TPR = { readonly a?: number, readonly b?: string };
+>TPR : TPR
+>a : number | undefined
+>b : string | undefined
+
+// Validate they all have the same keys
+var v00: "a" | "b";
+>v00 : "a" | "b"
+
+var v00: keyof T;
+>v00 : "a" | "b"
+>T : T
+
+var v00: keyof TU;
+>v00 : "a" | "b"
+>TU : TU
+
+var v00: keyof TP;
+>v00 : "a" | "b"
+>TP : TP
+
+var v00: keyof TR;
+>v00 : "a" | "b"
+>TR : TR
+
+var v00: keyof TPR;
+>v00 : "a" | "b"
+>TPR : TPR
+
+// Validate that non-isomorphic mapped types strip modifiers
+var v01: T;
+>v01 : T
+>T : T
+
+var v01: Pick<TR, keyof T>;
+>v01 : T
+>Pick : Pick<T, K>
+>TR : TR
+>T : T
+
+var v01: Pick<Readonly<T>, keyof T>;
+>v01 : T
+>Pick : Pick<T, K>
+>Readonly : Readonly<T>
+>T : T
+>T : T
+
+// Validate that non-isomorphic mapped types strip modifiers
+var v02: TU;
+>v02 : TU
+>TU : TU
+
+var v02: Pick<TP, keyof T>;
+>v02 : TU
+>Pick : Pick<T, K>
+>TP : TP
+>T : T
+
+var v02: Pick<TPR, keyof T>;
+>v02 : TU
+>Pick : Pick<T, K>
+>TPR : TPR
+>T : T
+
+var v02: Pick<Partial<T>, keyof T>;
+>v02 : TU
+>Pick : Pick<T, K>
+>Partial : Partial<T>
+>T : T
+>T : T
+
+var v02: Pick<Partial<Readonly<T>>, keyof T>;
+>v02 : TU
+>Pick : Pick<T, K>
+>Partial : Partial<T>
+>Readonly : Readonly<T>
+>T : T
+>T : T
+
+// Validate that isomorphic mapped types preserve optional modifier
+var v03: TP;
+>v03 : TP
+>TP : TP
+
+var v03: Partial<T>;
+>v03 : TP
+>Partial : Partial<T>
+>T : T
+
+// Validate that isomorphic mapped types preserve readonly modifier
+var v04: TR;
+>v04 : TR
+>TR : TR
+
+var v04: Readonly<T>;
+>v04 : TR
+>Readonly : Readonly<T>
+>T : T
+
+// Validate that isomorphic mapped types preserve both partial and readonly modifiers
+var v05: TPR;
+>v05 : TPR
+>TPR : TPR
+
+var v05: Partial<TR>;
+>v05 : TPR
+>Partial : Partial<T>
+>TR : TR
+
+var v05: Readonly<TP>;
+>v05 : TPR
+>Readonly : Readonly<T>
+>TP : TP
+
+var v05: Partial<Readonly<T>>;
+>v05 : TPR
+>Partial : Partial<T>
+>Readonly : Readonly<T>
+>T : T
+
+var v05: Readonly<Partial<T>>;
+>v05 : TPR
+>Readonly : Readonly<T>
+>Partial : Partial<T>
+>T : T
+
+type Boxified<T> = { [P in keyof T]: { x: T[P] } };
+>Boxified : Boxified<T>
+>T : T
+>P : P
+>T : T
+>x : T[P]
+>T : T
+>P : P
+
+type B = { a: { x: number }, b: { x: string } };
+>B : B
+>a : { x: number; }
+>x : number
+>b : { x: string; }
+>x : string
+
+type BU = { a: { x: number } | undefined, b: { x: string } | undefined };
+>BU : BU
+>a : { x: number; } | undefined
+>x : number
+>b : { x: string; } | undefined
+>x : string
+
+type BP = { a?: { x: number }, b?: { x: string } };
+>BP : BP
+>a : { x: number; } | undefined
+>x : number
+>b : { x: string; } | undefined
+>x : string
+
+type BR = { readonly a: { x: number }, readonly b: { x: string } };
+>BR : BR
+>a : { x: number; }
+>x : number
+>b : { x: string; }
+>x : string
+
+type BPR = { readonly a?: { x: number }, readonly b?: { x: string } };
+>BPR : BPR
+>a : { x: number; } | undefined
+>x : number
+>b : { x: string; } | undefined
+>x : string
+
+// Validate they all have the same keys
+var b00: "a" | "b";
+>b00 : "a" | "b"
+
+var b00: keyof B;
+>b00 : "a" | "b"
+>B : B
+
+var b00: keyof BU;
+>b00 : "a" | "b"
+>BU : BU
+
+var b00: keyof BP;
+>b00 : "a" | "b"
+>BP : BP
+
+var b00: keyof BR;
+>b00 : "a" | "b"
+>BR : BR
+
+var b00: keyof BPR;
+>b00 : "a" | "b"
+>BPR : BPR
+
+// Validate that non-isomorphic mapped types strip modifiers
+var b01: B;
+>b01 : B
+>B : B
+
+var b01: Pick<BR, keyof B>;
+>b01 : B
+>Pick : Pick<T, K>
+>BR : BR
+>B : B
+
+var b01: Pick<Readonly<BR>, keyof B>;
+>b01 : B
+>Pick : Pick<T, K>
+>Readonly : Readonly<T>
+>BR : BR
+>B : B
+
+// Validate that non-isomorphic mapped types strip modifiers
+var b02: BU;
+>b02 : BU
+>BU : BU
+
+var b02: Pick<BP, keyof B>;
+>b02 : BU
+>Pick : Pick<T, K>
+>BP : BP
+>B : B
+
+var b02: Pick<BPR, keyof B>;
+>b02 : BU
+>Pick : Pick<T, K>
+>BPR : BPR
+>B : B
+
+var b02: Pick<Partial<B>, keyof B>;
+>b02 : BU
+>Pick : Pick<T, K>
+>Partial : Partial<T>
+>B : B
+>B : B
+
+var b02: Pick<Partial<Readonly<B>>, keyof B>;
+>b02 : BU
+>Pick : Pick<T, K>
+>Partial : Partial<T>
+>Readonly : Readonly<T>
+>B : B
+>B : B
+
+// Validate that isomorphic mapped types preserve optional modifier
+var b03: BP;
+>b03 : BP
+>BP : BP
+
+var b03: Partial<B>;
+>b03 : BP
+>Partial : Partial<T>
+>B : B
+
+// Validate that isomorphic mapped types preserve readonly modifier
+var b04: BR;
+>b04 : BR
+>BR : BR
+
+var b04: Readonly<B>;
+>b04 : BR
+>Readonly : Readonly<T>
+>B : B
+
+// Validate that isomorphic mapped types preserve both partial and readonly modifiers
+var b05: BPR;
+>b05 : BPR
+>BPR : BPR
+
+var b05: Partial<BR>;
+>b05 : BPR
+>Partial : Partial<T>
+>BR : BR
+
+var b05: Readonly<BP>;
+>b05 : BPR
+>Readonly : Readonly<T>
+>BP : BP
+
+var b05: Partial<Readonly<B>>;
+>b05 : BPR
+>Partial : Partial<T>
+>Readonly : Readonly<T>
+>B : B
+
+var b05: Readonly<Partial<B>>;
+>b05 : BPR
+>Readonly : Readonly<T>
+>Partial : Partial<T>
+>B : B
+

tests/baselines/reference/objectRest.js

@@ -36,6 +36,8 @@ let computed = 'b';
 let computed2 = 'a';
 var { [computed]: stillNotGreat, [computed2]: soSo,  ...o } = o;
 ({ [computed]: stillNotGreat, [computed2]: soSo, ...o } = o);
+
+var noContextualType = ({ aNumber = 12, ...notEmptyObject }) => aNumber + notEmptyObject['anythingGoes'];
 
 
 //// [objectRest.js]
@@ -43,7 +45,7 @@ var __rest = (this && this.__rest) || function (s, e) {
     var t = {};
     for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p) && e.indexOf(p) < 0)
         t[p] = s[p];
-    if (typeof Object.getOwnPropertySymbols === "function")
+    if (s != null && typeof Object.getOwnPropertySymbols === "function")
         for (var i = 0, p = Object.getOwnPropertySymbols(s); i < p.length; i++) if (e.indexOf(p[i]) < 0)
             t[p[i]] = s[p[i]];
     return t;
@@ -76,4 +78,8 @@ let computed = 'b';
 let computed2 = 'a';
 var _g = computed, stillNotGreat = o[_g], _h = computed2, soSo = o[_h], o = __rest(o, [typeof _g === "symbol" ? _g : _g + "", typeof _h === "symbol" ? _h : _h + ""]);
 (_j = computed, stillNotGreat = o[_j], _k = computed2, soSo = o[_k], o = __rest(o, [typeof _j === "symbol" ? _j : _j + "", typeof _k === "symbol" ? _k : _k + ""]));
+var noContextualType = (_a) => {
+    var { aNumber = 12 } = _a, notEmptyObject = __rest(_a, ["aNumber"]);
+    return aNumber + notEmptyObject['anythingGoes'];
+};
 var _d, _f, _j, _k;

tests/baselines/reference/objectRest.symbols

@@ -169,3 +169,10 @@ var { [computed]: stillNotGreat, [computed2]: soSo,  ...o } = o;
 >o : Symbol(o, Decl(objectRest.ts, 0, 3), Decl(objectRest.ts, 35, 51))
 >o : Symbol(o, Decl(objectRest.ts, 0, 3), Decl(objectRest.ts, 35, 51))
 
+var noContextualType = ({ aNumber = 12, ...notEmptyObject }) => aNumber + notEmptyObject['anythingGoes'];
+>noContextualType : Symbol(noContextualType, Decl(objectRest.ts, 38, 3))
+>aNumber : Symbol(aNumber, Decl(objectRest.ts, 38, 25))
+>notEmptyObject : Symbol(notEmptyObject, Decl(objectRest.ts, 38, 39))
+>aNumber : Symbol(aNumber, Decl(objectRest.ts, 38, 25))
+>notEmptyObject : Symbol(notEmptyObject, Decl(objectRest.ts, 38, 39))
+

tests/baselines/reference/objectRest.types

@@ -195,3 +195,15 @@ var { [computed]: stillNotGreat, [computed2]: soSo,  ...o } = o;
 >o : { a: number; b: string; }
 >o : { a: number; b: string; }
 
+var noContextualType = ({ aNumber = 12, ...notEmptyObject }) => aNumber + notEmptyObject['anythingGoes'];
+>noContextualType : ({aNumber, ...notEmptyObject}: { [x: string]: any; aNumber?: number; }) => any
+>({ aNumber = 12, ...notEmptyObject }) => aNumber + notEmptyObject['anythingGoes'] : ({aNumber, ...notEmptyObject}: { [x: string]: any; aNumber?: number; }) => any
+>aNumber : number
+>12 : 12
+>notEmptyObject : { [x: string]: any; }
+>aNumber + notEmptyObject['anythingGoes'] : any
+>aNumber : number
+>notEmptyObject['anythingGoes'] : any
+>notEmptyObject : { [x: string]: any; }
+>'anythingGoes' : "anythingGoes"
+

tests/baselines/reference/objectRestAssignment.js

@@ -19,7 +19,7 @@ var __rest = (this && this.__rest) || function (s, e) {
     var t = {};
     for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p) && e.indexOf(p) < 0)
         t[p] = s[p];
-    if (typeof Object.getOwnPropertySymbols === "function")
+    if (s != null && typeof Object.getOwnPropertySymbols === "function")
         for (var i = 0, p = Object.getOwnPropertySymbols(s); i < p.length; i++) if (e.indexOf(p[i]) < 0)
             t[p[i]] = s[p[i]];
     return t;

tests/baselines/reference/objectRestForOf.js

@@ -27,7 +27,7 @@ var __rest = (this && this.__rest) || function (s, e) {
     var t = {};
     for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p) && e.indexOf(p) < 0)
         t[p] = s[p];
-    if (typeof Object.getOwnPropertySymbols === "function")
+    if (s != null && typeof Object.getOwnPropertySymbols === "function")
         for (var i = 0, p = Object.getOwnPropertySymbols(s); i < p.length; i++) if (e.indexOf(p[i]) < 0)
             t[p[i]] = s[p[i]];
     return t;

tests/baselines/reference/objectRestNegative.errors.txt

@@ -3,11 +3,14 @@ tests/cases/conformance/types/rest/objectRestNegative.ts(6,10): error TS2322: Ty
   Types of property 'a' are incompatible.
     Type 'number' is not assignable to type 'string'.
 tests/cases/conformance/types/rest/objectRestNegative.ts(9,31): error TS2462: A rest element must be last in a destructuring pattern
+tests/cases/conformance/types/rest/objectRestNegative.ts(11,30): error TS7008: Member 'x' implicitly has an 'any' type.
+tests/cases/conformance/types/rest/objectRestNegative.ts(11,33): error TS7008: Member 'y' implicitly has an 'any' type.
 tests/cases/conformance/types/rest/objectRestNegative.ts(12,17): error TS2700: Rest types may only be created from object types.
 tests/cases/conformance/types/rest/objectRestNegative.ts(17,9): error TS2701: The target of an object rest assignment must be a variable or a property access.
+tests/cases/conformance/types/rest/objectRestNegative.ts(19,90): error TS2339: Property 'anythingGoes' does not exist on type '{ [x: string]: any; }'.
 
 
-==== tests/cases/conformance/types/rest/objectRestNegative.ts (5 errors) ====
+==== tests/cases/conformance/types/rest/objectRestNegative.ts (8 errors) ====
     let o = { a: 1, b: 'no' };
     var { ...mustBeLast, a } = o;
              ~~~~~~~~~~
@@ -27,6 +30,10 @@ tests/cases/conformance/types/rest/objectRestNegative.ts(17,9): error TS2701: Th
 !!! error TS2462: A rest element must be last in a destructuring pattern
     }
     function generic<T extends { x, y }>(t: T) {
+                                 ~~
+!!! error TS7008: Member 'x' implicitly has an 'any' type.
+                                    ~
+!!! error TS7008: Member 'y' implicitly has an 'any' type.
         let { x, ...rest } = t;
                     ~~~~
 !!! error TS2700: Rest types may only be created from object types.
@@ -37,4 +44,8 @@ tests/cases/conformance/types/rest/objectRestNegative.ts(17,9): error TS2701: Th
     ({a, ...rest.b + rest.b} = o);
             ~~~~~~~~~~~~~~~
 !!! error TS2701: The target of an object rest assignment must be a variable or a property access.
+    
+    var noContextualType = ({ aNumber = 12, ...notEmptyObject }) => aNumber + notEmptyObject.anythingGoes;
+                                                                                             ~~~~~~~~~~~~
+!!! error TS2339: Property 'anythingGoes' does not exist on type '{ [x: string]: any; }'.
     

tests/baselines/reference/objectRestNegative.js

@@ -16,6 +16,8 @@ function generic<T extends { x, y }>(t: T) {
 
 let rest: { b: string }
 ({a, ...rest.b + rest.b} = o);
+
+var noContextualType = ({ aNumber = 12, ...notEmptyObject }) => aNumber + notEmptyObject.anythingGoes;
 
 
 //// [objectRestNegative.js]
@@ -23,7 +25,7 @@ var __rest = (this && this.__rest) || function (s, e) {
     var t = {};
     for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p) && e.indexOf(p) < 0)
         t[p] = s[p];
-    if (typeof Object.getOwnPropertySymbols === "function")
+    if (s != null && typeof Object.getOwnPropertySymbols === "function")
         for (var i = 0, p = Object.getOwnPropertySymbols(s); i < p.length; i++) if (e.indexOf(p[i]) < 0)
             t[p[i]] = s[p[i]];
     return t;
@@ -42,3 +44,7 @@ function generic(t) {
 }
 var rest;
 (a = o.a, o, rest.b + rest.b = __rest(o, ["a"]));
+var noContextualType = function (_a) {
+    var _b = _a.aNumber, aNumber = _b === void 0 ? 12 : _b, notEmptyObject = __rest(_a, ["aNumber"]);
+    return aNumber + notEmptyObject.anythingGoes;
+};

tests/baselines/reference/objectRestParameter.js

@@ -22,7 +22,7 @@ var __rest = (this && this.__rest) || function (s, e) {
     var t = {};
     for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p) && e.indexOf(p) < 0)
         t[p] = s[p];
-    if (typeof Object.getOwnPropertySymbols === "function")
+    if (s != null && typeof Object.getOwnPropertySymbols === "function")
         for (var i = 0, p = Object.getOwnPropertySymbols(s); i < p.length; i++) if (e.indexOf(p[i]) < 0)
             t[p[i]] = s[p[i]];
     return t;

tests/baselines/reference/objectSpreadNegative.errors.txt

@@ -7,20 +7,18 @@ tests/cases/conformance/types/spread/objectSpreadNegative.ts(25,1): error TS2322
   Property 's' is missing in type '{ b: boolean; }'.
 tests/cases/conformance/types/spread/objectSpreadNegative.ts(28,36): error TS2300: Duplicate identifier 'b'.
 tests/cases/conformance/types/spread/objectSpreadNegative.ts(28,53): error TS2300: Duplicate identifier 'b'.
-tests/cases/conformance/types/spread/objectSpreadNegative.ts(32,20): error TS2698: Spread types may only be created from object types.
-tests/cases/conformance/types/spread/objectSpreadNegative.ts(33,24): error TS2698: Spread types may only be created from object types.
-tests/cases/conformance/types/spread/objectSpreadNegative.ts(34,19): error TS2698: Spread types may only be created from object types.
-tests/cases/conformance/types/spread/objectSpreadNegative.ts(35,19): error TS2698: Spread types may only be created from object types.
-tests/cases/conformance/types/spread/objectSpreadNegative.ts(37,20): error TS2698: Spread types may only be created from object types.
-tests/cases/conformance/types/spread/objectSpreadNegative.ts(39,19): error TS2698: Spread types may only be created from object types.
-tests/cases/conformance/types/spread/objectSpreadNegative.ts(44,1): error TS2349: Cannot invoke an expression whose type lacks a call signature. Type '{}' has no compatible call signatures.
-tests/cases/conformance/types/spread/objectSpreadNegative.ts(48,12): error TS2339: Property 'b' does not exist on type '{}'.
-tests/cases/conformance/types/spread/objectSpreadNegative.ts(54,9): error TS2339: Property 'm' does not exist on type '{ p: number; }'.
-tests/cases/conformance/types/spread/objectSpreadNegative.ts(58,14): error TS2698: Spread types may only be created from object types.
-tests/cases/conformance/types/spread/objectSpreadNegative.ts(61,14): error TS2698: Spread types may only be created from object types.
+tests/cases/conformance/types/spread/objectSpreadNegative.ts(32,19): error TS2698: Spread types may only be created from object types.
+tests/cases/conformance/types/spread/objectSpreadNegative.ts(33,19): error TS2698: Spread types may only be created from object types.
+tests/cases/conformance/types/spread/objectSpreadNegative.ts(35,20): error TS2698: Spread types may only be created from object types.
+tests/cases/conformance/types/spread/objectSpreadNegative.ts(37,19): error TS2698: Spread types may only be created from object types.
+tests/cases/conformance/types/spread/objectSpreadNegative.ts(42,1): error TS2349: Cannot invoke an expression whose type lacks a call signature. Type '{}' has no compatible call signatures.
+tests/cases/conformance/types/spread/objectSpreadNegative.ts(46,12): error TS2339: Property 'b' does not exist on type '{}'.
+tests/cases/conformance/types/spread/objectSpreadNegative.ts(52,9): error TS2339: Property 'm' does not exist on type '{ p: number; }'.
+tests/cases/conformance/types/spread/objectSpreadNegative.ts(56,14): error TS2698: Spread types may only be created from object types.
+tests/cases/conformance/types/spread/objectSpreadNegative.ts(59,14): error TS2698: Spread types may only be created from object types.
 
 
-==== tests/cases/conformance/types/spread/objectSpreadNegative.ts (17 errors) ====
+==== tests/cases/conformance/types/spread/objectSpreadNegative.ts (15 errors) ====
     let o = { a: 1, b: 'no' }
     
     /// private propagates
@@ -66,13 +64,7 @@ tests/cases/conformance/types/spread/objectSpreadNegative.ts(61,14): error TS269
 !!! error TS2300: Duplicate identifier 'b'.
     let duplicatedSpread = { ...o, ...o }
     
-    // null, undefined and primitives are not allowed
-    let spreadNull = { ...null };
-                       ~~~~~~~
-!!! error TS2698: Spread types may only be created from object types.
-    let spreadUndefind = { ...undefined };
-                           ~~~~~~~~~~~~
-!!! error TS2698: Spread types may only be created from object types.
+    // primitives are not allowed
     let spreadNum = { ...12 };
                       ~~~~~
 !!! error TS2698: Spread types may only be created from object types.

tests/baselines/reference/objectSpreadNegative.js

@@ -29,9 +29,7 @@ spread = b; // error, missing 's'
 let duplicated = { b: 'bad', ...o, b: 'bad', ...o2, b: 'bad' }
 let duplicatedSpread = { ...o, ...o }
 
-// null, undefined and primitives are not allowed
-let spreadNull = { ...null };
-let spreadUndefind = { ...undefined };
+// primitives are not allowed
 let spreadNum = { ...12 };
 let spreadSum = { ...1 + 1 };
 spreadSum.toFixed(); // error, no methods from number
@@ -108,9 +106,7 @@ spread = b; // error, missing 's'
 // literal repeats are not allowed, but spread repeats are fine
 var duplicated = __assign({ b: 'bad' }, o, { b: 'bad' }, o2, { b: 'bad' });
 var duplicatedSpread = __assign({}, o, o);
-// null, undefined and primitives are not allowed
-var spreadNull = __assign({}, null);
-var spreadUndefind = __assign({}, undefined);
+// primitives are not allowed
 var spreadNum = __assign({}, 12);
 var spreadSum = __assign({}, 1 + 1);
 spreadSum.toFixed(); // error, no methods from number

tests/baselines/reference/restIntersection.js

@@ -0,0 +1,20 @@
+//// [restIntersection.ts]
+var intersection: { x: number, y: number } & { w: string, z: string };
+
+var rest1: { y: number, w: string, z: string };
+var {x, ...rest1 } = intersection;
+
+
+//// [restIntersection.js]
+var __rest = (this && this.__rest) || function (s, e) {
+    var t = {};
+    for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p) && e.indexOf(p) < 0)
+        t[p] = s[p];
+    if (s != null && typeof Object.getOwnPropertySymbols === "function")
+        for (var i = 0, p = Object.getOwnPropertySymbols(s); i < p.length; i++) if (e.indexOf(p[i]) < 0)
+            t[p[i]] = s[p[i]];
+    return t;
+};
+var intersection;
+var rest1;
+var x = intersection.x, rest1 = __rest(intersection, ["x"]);

tests/baselines/reference/restIntersection.symbols

@@ -0,0 +1,19 @@
+=== tests/cases/compiler/restIntersection.ts ===
+var intersection: { x: number, y: number } & { w: string, z: string };
+>intersection : Symbol(intersection, Decl(restIntersection.ts, 0, 3))
+>x : Symbol(x, Decl(restIntersection.ts, 0, 19))
+>y : Symbol(y, Decl(restIntersection.ts, 0, 30))
+>w : Symbol(w, Decl(restIntersection.ts, 0, 46))
+>z : Symbol(z, Decl(restIntersection.ts, 0, 57))
+
+var rest1: { y: number, w: string, z: string };
+>rest1 : Symbol(rest1, Decl(restIntersection.ts, 2, 3), Decl(restIntersection.ts, 3, 7))
+>y : Symbol(y, Decl(restIntersection.ts, 2, 12))
+>w : Symbol(w, Decl(restIntersection.ts, 2, 23))
+>z : Symbol(z, Decl(restIntersection.ts, 2, 34))
+
+var {x, ...rest1 } = intersection;
+>x : Symbol(x, Decl(restIntersection.ts, 3, 5))
+>rest1 : Symbol(rest1, Decl(restIntersection.ts, 2, 3), Decl(restIntersection.ts, 3, 7))
+>intersection : Symbol(intersection, Decl(restIntersection.ts, 0, 3))
+

tests/baselines/reference/restIntersection.types

@@ -0,0 +1,19 @@
+=== tests/cases/compiler/restIntersection.ts ===
+var intersection: { x: number, y: number } & { w: string, z: string };
+>intersection : { x: number; y: number; } & { w: string; z: string; }
+>x : number
+>y : number
+>w : string
+>z : string
+
+var rest1: { y: number, w: string, z: string };
+>rest1 : { y: number; w: string; z: string; }
+>y : number
+>w : string
+>z : string
+
+var {x, ...rest1 } = intersection;
+>x : number
+>rest1 : { y: number; w: string; z: string; }
+>intersection : { x: number; y: number; } & { w: string; z: string; }
+

tests/baselines/reference/restInvalidArgumentType.errors.txt

@@ -0,0 +1,104 @@
+tests/cases/compiler/restInvalidArgumentType.ts(31,13): error TS2700: Rest types may only be created from object types.
+tests/cases/compiler/restInvalidArgumentType.ts(33,13): error TS2700: Rest types may only be created from object types.
+tests/cases/compiler/restInvalidArgumentType.ts(35,13): error TS2700: Rest types may only be created from object types.
+tests/cases/compiler/restInvalidArgumentType.ts(36,13): error TS2700: Rest types may only be created from object types.
+tests/cases/compiler/restInvalidArgumentType.ts(38,13): error TS2700: Rest types may only be created from object types.
+tests/cases/compiler/restInvalidArgumentType.ts(41,13): error TS2700: Rest types may only be created from object types.
+tests/cases/compiler/restInvalidArgumentType.ts(42,13): error TS2700: Rest types may only be created from object types.
+tests/cases/compiler/restInvalidArgumentType.ts(44,13): error TS2700: Rest types may only be created from object types.
+tests/cases/compiler/restInvalidArgumentType.ts(45,13): error TS2700: Rest types may only be created from object types.
+tests/cases/compiler/restInvalidArgumentType.ts(47,13): error TS2700: Rest types may only be created from object types.
+tests/cases/compiler/restInvalidArgumentType.ts(48,13): error TS2700: Rest types may only be created from object types.
+tests/cases/compiler/restInvalidArgumentType.ts(55,13): error TS2700: Rest types may only be created from object types.
+tests/cases/compiler/restInvalidArgumentType.ts(56,13): error TS2700: Rest types may only be created from object types.
+tests/cases/compiler/restInvalidArgumentType.ts(58,13): error TS2700: Rest types may only be created from object types.
+
+
+==== tests/cases/compiler/restInvalidArgumentType.ts (14 errors) ====
+    enum E { v1, v2 };
+    
+    function f<T extends { b: string }>(p1: T, p2: T[]) {
+        var t: T;
+    
+        var i: T["b"];
+        var k: keyof T;
+    
+        var mapped_generic: {[P in keyof T]: T[P]};
+        var mapped: {[P in "b"]: T[P]};
+    
+        var union_generic: T | { a: number };
+        var union_primitive: { a: number } | number;
+    
+        var intersection_generic: T & { a: number };
+        var intersection_premitive: { a: number } | string;
+    
+        var num: number;
+        var str: number;
+    
+        var u: undefined;
+        var n: null;
+    
+        var a: any;
+    
+        var literal_string: "string";
+        var literal_number: 42;
+    
+        var e: E;
+    
+        var {...r1} = p1;   // Error, generic type paramterre
+                ~~
+!!! error TS2700: Rest types may only be created from object types.
+        var {...r2} = p2;   // OK
+        var {...r3} = t;   // Error, generic type paramter
+                ~~
+!!! error TS2700: Rest types may only be created from object types.
+    
+        var {...r4} = i;   // Error, index access
+                ~~
+!!! error TS2700: Rest types may only be created from object types.
+        var {...r5} = k;   // Error, index
+                ~~
+!!! error TS2700: Rest types may only be created from object types.
+    
+        var {...r6} = mapped_generic; // Error, generic mapped object type
+                ~~
+!!! error TS2700: Rest types may only be created from object types.
+        var {...r7} = mapped;  // OK, non-generic mapped type
+    
+        var {...r8} = union_generic;  // Error, union with generic type parameter
+                ~~
+!!! error TS2700: Rest types may only be created from object types.
+        var {...r9} = union_primitive;  // Error, union with generic type parameter
+                ~~
+!!! error TS2700: Rest types may only be created from object types.
+    
+        var {...r10} = intersection_generic;  // Error, intersection with generic type parameter
+                ~~~
+!!! error TS2700: Rest types may only be created from object types.
+        var {...r11} = intersection_premitive;  // Error, intersection with generic type parameter
+                ~~~
+!!! error TS2700: Rest types may only be created from object types.
+    
+        var {...r12} = num;  // Error
+                ~~~
+!!! error TS2700: Rest types may only be created from object types.
+        var {...r13} = str;  // Error
+                ~~~
+!!! error TS2700: Rest types may only be created from object types.
+    
+        var {...r14} = u;  // OK
+        var {...r15} = n;  // OK
+    
+        var {...r16} = a;  // OK
+    
+        var {...r17} = literal_string;  // Error
+                ~~~
+!!! error TS2700: Rest types may only be created from object types.
+        var {...r18} = literal_number;  // Error
+                ~~~
+!!! error TS2700: Rest types may only be created from object types.
+    
+        var {...r19} = e;  // Error, enum
+                ~~~
+!!! error TS2700: Rest types may only be created from object types.
+    }

tests/baselines/reference/restInvalidArgumentType.js

@@ -0,0 +1,115 @@
+//// [restInvalidArgumentType.ts]
+enum E { v1, v2 };
+
+function f<T extends { b: string }>(p1: T, p2: T[]) {
+    var t: T;
+
+    var i: T["b"];
+    var k: keyof T;
+
+    var mapped_generic: {[P in keyof T]: T[P]};
+    var mapped: {[P in "b"]: T[P]};
+
+    var union_generic: T | { a: number };
+    var union_primitive: { a: number } | number;
+
+    var intersection_generic: T & { a: number };
+    var intersection_premitive: { a: number } | string;
+
+    var num: number;
+    var str: number;
+
+    var u: undefined;
+    var n: null;
+
+    var a: any;
+
+    var literal_string: "string";
+    var literal_number: 42;
+
+    var e: E;
+
+    var {...r1} = p1;   // Error, generic type paramterre
+    var {...r2} = p2;   // OK
+    var {...r3} = t;   // Error, generic type paramter
+
+    var {...r4} = i;   // Error, index access
+    var {...r5} = k;   // Error, index
+
+    var {...r6} = mapped_generic; // Error, generic mapped object type
+    var {...r7} = mapped;  // OK, non-generic mapped type
+
+    var {...r8} = union_generic;  // Error, union with generic type parameter
+    var {...r9} = union_primitive;  // Error, union with generic type parameter
+
+    var {...r10} = intersection_generic;  // Error, intersection with generic type parameter
+    var {...r11} = intersection_premitive;  // Error, intersection with generic type parameter
+
+    var {...r12} = num;  // Error
+    var {...r13} = str;  // Error
+
+    var {...r14} = u;  // OK
+    var {...r15} = n;  // OK
+
+    var {...r16} = a;  // OK
+
+    var {...r17} = literal_string;  // Error
+    var {...r18} = literal_number;  // Error
+
+    var {...r19} = e;  // Error, enum
+}
+
+//// [restInvalidArgumentType.js]
+var __rest = (this && this.__rest) || function (s, e) {
+    var t = {};
+    for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p) && e.indexOf(p) < 0)
+        t[p] = s[p];
+    if (s != null && typeof Object.getOwnPropertySymbols === "function")
+        for (var i = 0, p = Object.getOwnPropertySymbols(s); i < p.length; i++) if (e.indexOf(p[i]) < 0)
+            t[p[i]] = s[p[i]];
+    return t;
+};
+var E;
+(function (E) {
+    E[E["v1"] = 0] = "v1";
+    E[E["v2"] = 1] = "v2";
+})(E || (E = {}));
+;
+function f(p1, p2) {
+    var t;
+    var i;
+    var k;
+    var mapped_generic;
+    var mapped;
+    var union_generic;
+    var union_primitive;
+    var intersection_generic;
+    var intersection_premitive;
+    var num;
+    var str;
+    var u;
+    var n;
+    var a;
+    var literal_string;
+    var literal_number;
+    var e;
+    var r1 = __rest(p1, []); // Error, generic type paramterre
+    var r2 = __rest(p2, []); // OK
+    var r3 = __rest(t, []); // Error, generic type paramter
+    var r4 = __rest(i, []); // Error, index access
+    var r5 = __rest(k, []); // Error, index
+    var r6 = __rest(mapped_generic, []); // Error, generic mapped object type
+    var r7 = __rest(mapped, []); // OK, non-generic mapped type
+    var r8 = __rest(union_generic, []); // Error, union with generic type parameter
+    var r9 = __rest(union_primitive, []); // Error, union with generic type parameter
+    var r10 = __rest(intersection_generic, []); // Error, intersection with generic type parameter
+    var r11 = __rest(intersection_premitive, []); // Error, intersection with generic type parameter
+    var r12 = __rest(num, []); // Error
+    var r13 = __rest(str, []); // Error
+    var r14 = __rest(u, []); // OK
+    var r15 = __rest(n, []); // OK
+    var r16 = __rest(a, []); // OK
+    var r17 = __rest(literal_string, []); // Error
+    var r18 = __rest(literal_number, []); // Error
+    var r19 = __rest(e, []); // Error, enum
+}

tests/baselines/reference/restUnion.js

@@ -0,0 +1,36 @@
+//// [restUnion.ts]
+var union: { a: number, c: boolean } | { a: string, b: string };
+
+var rest1: { c: boolean } | { b: string };
+var {a, ...rest1 } = union;
+
+
+var undefinedUnion: { n: number } | undefined;
+var rest2: {};
+var {n, ...rest2 } = undefinedUnion;
+
+
+var nullUnion: { n: number } | null;
+var rest3: {};
+var {n, ...rest3 } = nullUnion;
+
+
+//// [restUnion.js]
+var __rest = (this && this.__rest) || function (s, e) {
+    var t = {};
+    for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p) && e.indexOf(p) < 0)
+        t[p] = s[p];
+    if (s != null && typeof Object.getOwnPropertySymbols === "function")
+        for (var i = 0, p = Object.getOwnPropertySymbols(s); i < p.length; i++) if (e.indexOf(p[i]) < 0)
+            t[p[i]] = s[p[i]];
+    return t;
+};
+var union;
+var rest1;
+var a = union.a, rest1 = __rest(union, ["a"]);
+var undefinedUnion;
+var rest2;
+var n = undefinedUnion.n, rest2 = __rest(undefinedUnion, ["n"]);
+var nullUnion;
+var rest3;
+var n = nullUnion.n, rest3 = __rest(nullUnion, ["n"]);

tests/baselines/reference/restUnion.symbols

@@ -0,0 +1,44 @@
+=== tests/cases/compiler/restUnion.ts ===
+var union: { a: number, c: boolean } | { a: string, b: string };
+>union : Symbol(union, Decl(restUnion.ts, 0, 3))
+>a : Symbol(a, Decl(restUnion.ts, 0, 12))
+>c : Symbol(c, Decl(restUnion.ts, 0, 23))
+>a : Symbol(a, Decl(restUnion.ts, 0, 40))
+>b : Symbol(b, Decl(restUnion.ts, 0, 51))
+
+var rest1: { c: boolean } | { b: string };
+>rest1 : Symbol(rest1, Decl(restUnion.ts, 2, 3), Decl(restUnion.ts, 3, 7))
+>c : Symbol(c, Decl(restUnion.ts, 2, 12))
+>b : Symbol(b, Decl(restUnion.ts, 2, 29))
+
+var {a, ...rest1 } = union;
+>a : Symbol(a, Decl(restUnion.ts, 3, 5))
+>rest1 : Symbol(rest1, Decl(restUnion.ts, 2, 3), Decl(restUnion.ts, 3, 7))
+>union : Symbol(union, Decl(restUnion.ts, 0, 3))
+
+
+var undefinedUnion: { n: number } | undefined;
+>undefinedUnion : Symbol(undefinedUnion, Decl(restUnion.ts, 6, 3))
+>n : Symbol(n, Decl(restUnion.ts, 6, 21))
+
+var rest2: {};
+>rest2 : Symbol(rest2, Decl(restUnion.ts, 7, 3), Decl(restUnion.ts, 8, 7))
+
+var {n, ...rest2 } = undefinedUnion;
+>n : Symbol(n, Decl(restUnion.ts, 8, 5), Decl(restUnion.ts, 13, 5))
+>rest2 : Symbol(rest2, Decl(restUnion.ts, 7, 3), Decl(restUnion.ts, 8, 7))
+>undefinedUnion : Symbol(undefinedUnion, Decl(restUnion.ts, 6, 3))
+
+
+var nullUnion: { n: number } | null;
+>nullUnion : Symbol(nullUnion, Decl(restUnion.ts, 11, 3))
+>n : Symbol(n, Decl(restUnion.ts, 11, 16))
+
+var rest3: {};
+>rest3 : Symbol(rest3, Decl(restUnion.ts, 12, 3), Decl(restUnion.ts, 13, 7))
+
+var {n, ...rest3 } = nullUnion;
+>n : Symbol(n, Decl(restUnion.ts, 8, 5), Decl(restUnion.ts, 13, 5))
+>rest3 : Symbol(rest3, Decl(restUnion.ts, 12, 3), Decl(restUnion.ts, 13, 7))
+>nullUnion : Symbol(nullUnion, Decl(restUnion.ts, 11, 3))
+

tests/baselines/reference/restUnion.types

@@ -0,0 +1,45 @@
+=== tests/cases/compiler/restUnion.ts ===
+var union: { a: number, c: boolean } | { a: string, b: string };
+>union : { a: number; c: boolean; } | { a: string; b: string; }
+>a : number
+>c : boolean
+>a : string
+>b : string
+
+var rest1: { c: boolean } | { b: string };
+>rest1 : { c: boolean; } | { b: string; }
+>c : boolean
+>b : string
+
+var {a, ...rest1 } = union;
+>a : string | number
+>rest1 : { c: boolean; } | { b: string; }
+>union : { a: number; c: boolean; } | { a: string; b: string; }
+
+
+var undefinedUnion: { n: number } | undefined;
+>undefinedUnion : { n: number; }
+>n : number
+
+var rest2: {};
+>rest2 : {}
+
+var {n, ...rest2 } = undefinedUnion;
+>n : number
+>rest2 : {}
+>undefinedUnion : { n: number; }
+
+
+var nullUnion: { n: number } | null;
+>nullUnion : { n: number; }
+>n : number
+>null : null
+
+var rest3: {};
+>rest3 : {}
+
+var {n, ...rest3 } = nullUnion;
+>n : number
+>rest3 : {}
+>nullUnion : { n: number; }
+

tests/baselines/reference/restUnion2.js

@@ -0,0 +1,38 @@
+//// [restUnion2.ts]
+
+declare const undefinedUnion: { n: number } | undefined;
+var rest2: { n: number };
+var {...rest2 } = undefinedUnion;
+
+
+declare const nullUnion: { n: number } | null;
+var rest3: { n: number };
+var {...rest3 } = nullUnion;
+
+
+declare const nullAndUndefinedUnion: null | undefined;
+var rest4: { };
+var {...rest4 } = nullAndUndefinedUnion;
+
+declare const unionWithIntersection: ({ n: number } & { s: string }) & undefined | null;
+var rest5: { n: number, s: string };
+var {...rest5 } = unionWithIntersection;
+
+//// [restUnion2.js]
+var __rest = (this && this.__rest) || function (s, e) {
+    var t = {};
+    for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p) && e.indexOf(p) < 0)
+        t[p] = s[p];
+    if (s != null && typeof Object.getOwnPropertySymbols === "function")
+        for (var i = 0, p = Object.getOwnPropertySymbols(s); i < p.length; i++) if (e.indexOf(p[i]) < 0)
+            t[p[i]] = s[p[i]];
+    return t;
+};
+var rest2;
+var rest2 = __rest(undefinedUnion, []);
+var rest3;
+var rest3 = __rest(nullUnion, []);
+var rest4;
+var rest4 = __rest(nullAndUndefinedUnion, []);
+var rest5;
+var rest5 = __rest(unionWithIntersection, []);

tests/baselines/reference/restUnion2.symbols

@@ -0,0 +1,52 @@
+=== tests/cases/compiler/restUnion2.ts ===
+
+declare const undefinedUnion: { n: number } | undefined;
+>undefinedUnion : Symbol(undefinedUnion, Decl(restUnion2.ts, 1, 13))
+>n : Symbol(n, Decl(restUnion2.ts, 1, 31))
+
+var rest2: { n: number };
+>rest2 : Symbol(rest2, Decl(restUnion2.ts, 2, 3), Decl(restUnion2.ts, 3, 5))
+>n : Symbol(n, Decl(restUnion2.ts, 2, 12))
+
+var {...rest2 } = undefinedUnion;
+>rest2 : Symbol(rest2, Decl(restUnion2.ts, 2, 3), Decl(restUnion2.ts, 3, 5))
+>undefinedUnion : Symbol(undefinedUnion, Decl(restUnion2.ts, 1, 13))
+
+
+declare const nullUnion: { n: number } | null;
+>nullUnion : Symbol(nullUnion, Decl(restUnion2.ts, 6, 13))
+>n : Symbol(n, Decl(restUnion2.ts, 6, 26))
+
+var rest3: { n: number };
+>rest3 : Symbol(rest3, Decl(restUnion2.ts, 7, 3), Decl(restUnion2.ts, 8, 5))
+>n : Symbol(n, Decl(restUnion2.ts, 7, 12))
+
+var {...rest3 } = nullUnion;
+>rest3 : Symbol(rest3, Decl(restUnion2.ts, 7, 3), Decl(restUnion2.ts, 8, 5))
+>nullUnion : Symbol(nullUnion, Decl(restUnion2.ts, 6, 13))
+
+
+declare const nullAndUndefinedUnion: null | undefined;
+>nullAndUndefinedUnion : Symbol(nullAndUndefinedUnion, Decl(restUnion2.ts, 11, 13))
+
+var rest4: { };
+>rest4 : Symbol(rest4, Decl(restUnion2.ts, 12, 3), Decl(restUnion2.ts, 13, 5))
+
+var {...rest4 } = nullAndUndefinedUnion;
+>rest4 : Symbol(rest4, Decl(restUnion2.ts, 12, 3), Decl(restUnion2.ts, 13, 5))
+>nullAndUndefinedUnion : Symbol(nullAndUndefinedUnion, Decl(restUnion2.ts, 11, 13))
+
+declare const unionWithIntersection: ({ n: number } & { s: string }) & undefined | null;
+>unionWithIntersection : Symbol(unionWithIntersection, Decl(restUnion2.ts, 15, 13))
+>n : Symbol(n, Decl(restUnion2.ts, 15, 39))
+>s : Symbol(s, Decl(restUnion2.ts, 15, 55))
+
+var rest5: { n: number, s: string };
+>rest5 : Symbol(rest5, Decl(restUnion2.ts, 16, 3), Decl(restUnion2.ts, 17, 5))
+>n : Symbol(n, Decl(restUnion2.ts, 16, 12))
+>s : Symbol(s, Decl(restUnion2.ts, 16, 23))
+
+var {...rest5 } = unionWithIntersection;
+>rest5 : Symbol(rest5, Decl(restUnion2.ts, 16, 3), Decl(restUnion2.ts, 17, 5))
+>unionWithIntersection : Symbol(unionWithIntersection, Decl(restUnion2.ts, 15, 13))
+

tests/baselines/reference/restUnion2.types

@@ -0,0 +1,55 @@
+=== tests/cases/compiler/restUnion2.ts ===
+
+declare const undefinedUnion: { n: number } | undefined;
+>undefinedUnion : { n: number; } | undefined
+>n : number
+
+var rest2: { n: number };
+>rest2 : { n: number; }
+>n : number
+
+var {...rest2 } = undefinedUnion;
+>rest2 : { n: number; }
+>undefinedUnion : { n: number; } | undefined
+
+
+declare const nullUnion: { n: number } | null;
+>nullUnion : { n: number; } | null
+>n : number
+>null : null
+
+var rest3: { n: number };
+>rest3 : { n: number; }
+>n : number
+
+var {...rest3 } = nullUnion;
+>rest3 : { n: number; }
+>nullUnion : { n: number; } | null
+
+
+declare const nullAndUndefinedUnion: null | undefined;
+>nullAndUndefinedUnion : null | undefined
+>null : null
+
+var rest4: { };
+>rest4 : {}
+
+var {...rest4 } = nullAndUndefinedUnion;
+>rest4 : {}
+>nullAndUndefinedUnion : null | undefined
+
+declare const unionWithIntersection: ({ n: number } & { s: string }) & undefined | null;
+>unionWithIntersection : ({ n: number; } & { s: string; } & undefined) | null
+>n : number
+>s : string
+>null : null
+
+var rest5: { n: number, s: string };
+>rest5 : { n: number; s: string; }
+>n : number
+>s : string
+
+var {...rest5 } = unionWithIntersection;
+>rest5 : { n: number; s: string; }
+>unionWithIntersection : ({ n: number; } & { s: string; } & undefined) | null
+

tests/baselines/reference/spreadIntersection.js

@@ -0,0 +1,23 @@
+//// [spreadIntersection.ts]
+var intersection: { a: number } & { b: string };
+
+var o1: { a: number, b: string };
+var o1 = { ...intersection };
+
+var o2: { a: number, b: string, c: boolean };
+var o2 = { ...intersection, c: false };
+
+//// [spreadIntersection.js]
+var __assign = (this && this.__assign) || Object.assign || function(t) {
+    for (var s, i = 1, n = arguments.length; i < n; i++) {
+        s = arguments[i];
+        for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p))
+            t[p] = s[p];
+    }
+    return t;
+};
+var intersection;
+var o1;
+var o1 = __assign({}, intersection);
+var o2;
+var o2 = __assign({}, intersection, { c: false });

tests/baselines/reference/spreadIntersection.symbols

@@ -0,0 +1,26 @@
+=== tests/cases/compiler/spreadIntersection.ts ===
+var intersection: { a: number } & { b: string };
+>intersection : Symbol(intersection, Decl(spreadIntersection.ts, 0, 3))
+>a : Symbol(a, Decl(spreadIntersection.ts, 0, 19))
+>b : Symbol(b, Decl(spreadIntersection.ts, 0, 35))
+
+var o1: { a: number, b: string };
+>o1 : Symbol(o1, Decl(spreadIntersection.ts, 2, 3), Decl(spreadIntersection.ts, 3, 3))
+>a : Symbol(a, Decl(spreadIntersection.ts, 2, 9))
+>b : Symbol(b, Decl(spreadIntersection.ts, 2, 20))
+
+var o1 = { ...intersection };
+>o1 : Symbol(o1, Decl(spreadIntersection.ts, 2, 3), Decl(spreadIntersection.ts, 3, 3))
+>intersection : Symbol(intersection, Decl(spreadIntersection.ts, 0, 3))
+
+var o2: { a: number, b: string, c: boolean };
+>o2 : Symbol(o2, Decl(spreadIntersection.ts, 5, 3), Decl(spreadIntersection.ts, 6, 3))
+>a : Symbol(a, Decl(spreadIntersection.ts, 5, 9))
+>b : Symbol(b, Decl(spreadIntersection.ts, 5, 20))
+>c : Symbol(c, Decl(spreadIntersection.ts, 5, 31))
+
+var o2 = { ...intersection, c: false };
+>o2 : Symbol(o2, Decl(spreadIntersection.ts, 5, 3), Decl(spreadIntersection.ts, 6, 3))
+>intersection : Symbol(intersection, Decl(spreadIntersection.ts, 0, 3))
+>c : Symbol(c, Decl(spreadIntersection.ts, 6, 27))
+

tests/baselines/reference/spreadIntersection.types

@@ -0,0 +1,29 @@
+=== tests/cases/compiler/spreadIntersection.ts ===
+var intersection: { a: number } & { b: string };
+>intersection : { a: number; } & { b: string; }
+>a : number
+>b : string
+
+var o1: { a: number, b: string };
+>o1 : { a: number; b: string; }
+>a : number
+>b : string
+
+var o1 = { ...intersection };
+>o1 : { a: number; b: string; }
+>{ ...intersection } : { a: number; b: string; }
+>intersection : { a: number; } & { b: string; }
+
+var o2: { a: number, b: string, c: boolean };
+>o2 : { a: number; b: string; c: boolean; }
+>a : number
+>b : string
+>c : boolean
+
+var o2 = { ...intersection, c: false };
+>o2 : { a: number; b: string; c: boolean; }
+>{ ...intersection, c: false } : { c: boolean; a: number; b: string; }
+>intersection : { a: number; } & { b: string; }
+>c : boolean
+>false : false
+

tests/baselines/reference/spreadInvalidArgumentType.errors.txt

@@ -0,0 +1,104 @@
+tests/cases/compiler/spreadInvalidArgumentType.ts(31,16): error TS2698: Spread types may only be created from object types.
+tests/cases/compiler/spreadInvalidArgumentType.ts(33,16): error TS2698: Spread types may only be created from object types.
+tests/cases/compiler/spreadInvalidArgumentType.ts(35,16): error TS2698: Spread types may only be created from object types.
+tests/cases/compiler/spreadInvalidArgumentType.ts(36,16): error TS2698: Spread types may only be created from object types.
+tests/cases/compiler/spreadInvalidArgumentType.ts(38,16): error TS2698: Spread types may only be created from object types.
+tests/cases/compiler/spreadInvalidArgumentType.ts(41,16): error TS2698: Spread types may only be created from object types.
+tests/cases/compiler/spreadInvalidArgumentType.ts(42,16): error TS2698: Spread types may only be created from object types.
+tests/cases/compiler/spreadInvalidArgumentType.ts(44,17): error TS2698: Spread types may only be created from object types.
+tests/cases/compiler/spreadInvalidArgumentType.ts(45,17): error TS2698: Spread types may only be created from object types.
+tests/cases/compiler/spreadInvalidArgumentType.ts(47,17): error TS2698: Spread types may only be created from object types.
+tests/cases/compiler/spreadInvalidArgumentType.ts(48,17): error TS2698: Spread types may only be created from object types.
+tests/cases/compiler/spreadInvalidArgumentType.ts(55,17): error TS2698: Spread types may only be created from object types.
+tests/cases/compiler/spreadInvalidArgumentType.ts(56,17): error TS2698: Spread types may only be created from object types.
+tests/cases/compiler/spreadInvalidArgumentType.ts(58,17): error TS2698: Spread types may only be created from object types.
+
+
+==== tests/cases/compiler/spreadInvalidArgumentType.ts (14 errors) ====
+    enum E { v1, v2 };
+    
+    function f<T extends { b: string }>(p1: T, p2: T[]) {
+        var t: T;
+    
+        var i: T["b"];
+        var k: keyof T;
+    
+        var mapped_generic: {[P in keyof T]: T[P]};
+        var mapped: {[P in "b"]: T[P]};
+    
+        var union_generic: T | { a: number };
+        var union_primitive: { a: number } | number;
+    
+        var intersection_generic: T & { a: number };
+        var intersection_premitive: { a: number } | string;
+    
+        var num: number;
+        var str: number;
+    
+        var u: undefined;
+        var n: null;
+    
+        var a: any;
+    
+        var literal_string: "string";
+        var literal_number: 42;
+    
+        var e: E;
+    
+        var o1 = { ...p1 };   // Error, generic type paramterre
+                   ~~~~~
+!!! error TS2698: Spread types may only be created from object types.
+        var o2 = { ...p2 };   // OK
+        var o3 = { ...t };   // Error, generic type paramter
+                   ~~~~
+!!! error TS2698: Spread types may only be created from object types.
+    
+        var o4 = { ...i };   // Error, index access
+                   ~~~~
+!!! error TS2698: Spread types may only be created from object types.
+        var o5 = { ...k };   // Error, index
+                   ~~~~
+!!! error TS2698: Spread types may only be created from object types.
+    
+        var o6 = { ...mapped_generic }; // Error, generic mapped object type
+                   ~~~~~~~~~~~~~~~~~
+!!! error TS2698: Spread types may only be created from object types.
+        var o7 = { ...mapped };  // OK, non-generic mapped type
+    
+        var o8 = { ...union_generic };  // Error, union with generic type parameter
+                   ~~~~~~~~~~~~~~~~
+!!! error TS2698: Spread types may only be created from object types.
+        var o9 = { ...union_primitive };  // Error, union with generic type parameter
+                   ~~~~~~~~~~~~~~~~~~
+!!! error TS2698: Spread types may only be created from object types.
+    
+        var o10 = { ...intersection_generic };  // Error, intersection with generic type parameter
+                    ~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2698: Spread types may only be created from object types.
+        var o11 = { ...intersection_premitive };  // Error, intersection with generic type parameter
+                    ~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2698: Spread types may only be created from object types.
+    
+        var o12 = { ...num };  // Error
+                    ~~~~~~
+!!! error TS2698: Spread types may only be created from object types.
+        var o13 = { ...str };  // Error
+                    ~~~~~~
+!!! error TS2698: Spread types may only be created from object types.
+    
+        var o14 = { ...u };  // OK
+        var o15 = { ...n };  // OK
+    
+        var o16 = { ...a };  // OK
+    
+        var o17 = { ...literal_string };  // Error
+                    ~~~~~~~~~~~~~~~~~
+!!! error TS2698: Spread types may only be created from object types.
+        var o18 = { ...literal_number };  // Error
+                    ~~~~~~~~~~~~~~~~~
+!!! error TS2698: Spread types may only be created from object types.
+    
+        var o19 = { ...e };  // Error, enum
+                    ~~~~
+!!! error TS2698: Spread types may only be created from object types.
+    }

tests/baselines/reference/spreadInvalidArgumentType.js

@@ -0,0 +1,114 @@
+//// [spreadInvalidArgumentType.ts]
+enum E { v1, v2 };
+
+function f<T extends { b: string }>(p1: T, p2: T[]) {
+    var t: T;
+
+    var i: T["b"];
+    var k: keyof T;
+
+    var mapped_generic: {[P in keyof T]: T[P]};
+    var mapped: {[P in "b"]: T[P]};
+
+    var union_generic: T | { a: number };
+    var union_primitive: { a: number } | number;
+
+    var intersection_generic: T & { a: number };
+    var intersection_premitive: { a: number } | string;
+
+    var num: number;
+    var str: number;
+
+    var u: undefined;
+    var n: null;
+
+    var a: any;
+
+    var literal_string: "string";
+    var literal_number: 42;
+
+    var e: E;
+
+    var o1 = { ...p1 };   // Error, generic type paramterre
+    var o2 = { ...p2 };   // OK
+    var o3 = { ...t };   // Error, generic type paramter
+
+    var o4 = { ...i };   // Error, index access
+    var o5 = { ...k };   // Error, index
+
+    var o6 = { ...mapped_generic }; // Error, generic mapped object type
+    var o7 = { ...mapped };  // OK, non-generic mapped type
+
+    var o8 = { ...union_generic };  // Error, union with generic type parameter
+    var o9 = { ...union_primitive };  // Error, union with generic type parameter
+
+    var o10 = { ...intersection_generic };  // Error, intersection with generic type parameter
+    var o11 = { ...intersection_premitive };  // Error, intersection with generic type parameter
+
+    var o12 = { ...num };  // Error
+    var o13 = { ...str };  // Error
+
+    var o14 = { ...u };  // OK
+    var o15 = { ...n };  // OK
+
+    var o16 = { ...a };  // OK
+
+    var o17 = { ...literal_string };  // Error
+    var o18 = { ...literal_number };  // Error
+
+    var o19 = { ...e };  // Error, enum
+}
+
+//// [spreadInvalidArgumentType.js]
+var __assign = (this && this.__assign) || Object.assign || function(t) {
+    for (var s, i = 1, n = arguments.length; i < n; i++) {
+        s = arguments[i];
+        for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p))
+            t[p] = s[p];
+    }
+    return t;
+};
+var E;
+(function (E) {
+    E[E["v1"] = 0] = "v1";
+    E[E["v2"] = 1] = "v2";
+})(E || (E = {}));
+;
+function f(p1, p2) {
+    var t;
+    var i;
+    var k;
+    var mapped_generic;
+    var mapped;
+    var union_generic;
+    var union_primitive;
+    var intersection_generic;
+    var intersection_premitive;
+    var num;
+    var str;
+    var u;
+    var n;
+    var a;
+    var literal_string;
+    var literal_number;
+    var e;
+    var o1 = __assign({}, p1); // Error, generic type paramterre
+    var o2 = __assign({}, p2); // OK
+    var o3 = __assign({}, t); // Error, generic type paramter
+    var o4 = __assign({}, i); // Error, index access
+    var o5 = __assign({}, k); // Error, index
+    var o6 = __assign({}, mapped_generic); // Error, generic mapped object type
+    var o7 = __assign({}, mapped); // OK, non-generic mapped type
+    var o8 = __assign({}, union_generic); // Error, union with generic type parameter
+    var o9 = __assign({}, union_primitive); // Error, union with generic type parameter
+    var o10 = __assign({}, intersection_generic); // Error, intersection with generic type parameter
+    var o11 = __assign({}, intersection_premitive); // Error, intersection with generic type parameter
+    var o12 = __assign({}, num); // Error
+    var o13 = __assign({}, str); // Error
+    var o14 = __assign({}, u); // OK
+    var o15 = __assign({}, n); // OK
+    var o16 = __assign({}, a); // OK
+    var o17 = __assign({}, literal_string); // Error
+    var o18 = __assign({}, literal_number); // Error
+    var o19 = __assign({}, e); // Error, enum
+}

tests/baselines/reference/spreadUnion.js

@@ -0,0 +1,28 @@
+//// [spreadUnion.ts]
+var union: { a: number } | { b: string };
+
+var o3: { a: number } | { b: string };
+var o3 =  { ...union };
+
+var o4: { a: boolean } | { b: string , a: boolean};
+var o4 =  { ...union, a: false };
+
+var o5: { a: number } | { b: string } | { a: number, b: string };
+var o5 =  { ...union, ...union };
+
+//// [spreadUnion.js]
+var __assign = (this && this.__assign) || Object.assign || function(t) {
+    for (var s, i = 1, n = arguments.length; i < n; i++) {
+        s = arguments[i];
+        for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p))
+            t[p] = s[p];
+    }
+    return t;
+};
+var union;
+var o3;
+var o3 = __assign({}, union);
+var o4;
+var o4 = __assign({}, union, { a: false });
+var o5;
+var o5 = __assign({}, union, union);

tests/baselines/reference/spreadUnion.symbols

@@ -0,0 +1,38 @@
+=== tests/cases/compiler/spreadUnion.ts ===
+var union: { a: number } | { b: string };
+>union : Symbol(union, Decl(spreadUnion.ts, 0, 3))
+>a : Symbol(a, Decl(spreadUnion.ts, 0, 12))
+>b : Symbol(b, Decl(spreadUnion.ts, 0, 28))
+
+var o3: { a: number } | { b: string };
+>o3 : Symbol(o3, Decl(spreadUnion.ts, 2, 3), Decl(spreadUnion.ts, 3, 3))
+>a : Symbol(a, Decl(spreadUnion.ts, 2, 9))
+>b : Symbol(b, Decl(spreadUnion.ts, 2, 25))
+
+var o3 =  { ...union };
+>o3 : Symbol(o3, Decl(spreadUnion.ts, 2, 3), Decl(spreadUnion.ts, 3, 3))
+>union : Symbol(union, Decl(spreadUnion.ts, 0, 3))
+
+var o4: { a: boolean } | { b: string , a: boolean};
+>o4 : Symbol(o4, Decl(spreadUnion.ts, 5, 3), Decl(spreadUnion.ts, 6, 3))
+>a : Symbol(a, Decl(spreadUnion.ts, 5, 9))
+>b : Symbol(b, Decl(spreadUnion.ts, 5, 26))
+>a : Symbol(a, Decl(spreadUnion.ts, 5, 38))
+
+var o4 =  { ...union, a: false };
+>o4 : Symbol(o4, Decl(spreadUnion.ts, 5, 3), Decl(spreadUnion.ts, 6, 3))
+>union : Symbol(union, Decl(spreadUnion.ts, 0, 3))
+>a : Symbol(a, Decl(spreadUnion.ts, 6, 21))
+
+var o5: { a: number } | { b: string } | { a: number, b: string };
+>o5 : Symbol(o5, Decl(spreadUnion.ts, 8, 3), Decl(spreadUnion.ts, 9, 3))
+>a : Symbol(a, Decl(spreadUnion.ts, 8, 9))
+>b : Symbol(b, Decl(spreadUnion.ts, 8, 25))
+>a : Symbol(a, Decl(spreadUnion.ts, 8, 41))
+>b : Symbol(b, Decl(spreadUnion.ts, 8, 52))
+
+var o5 =  { ...union, ...union };
+>o5 : Symbol(o5, Decl(spreadUnion.ts, 8, 3), Decl(spreadUnion.ts, 9, 3))
+>union : Symbol(union, Decl(spreadUnion.ts, 0, 3))
+>union : Symbol(union, Decl(spreadUnion.ts, 0, 3))
+

tests/baselines/reference/spreadUnion.types

@@ -0,0 +1,42 @@
+=== tests/cases/compiler/spreadUnion.ts ===
+var union: { a: number } | { b: string };
+>union : { a: number; } | { b: string; }
+>a : number
+>b : string
+
+var o3: { a: number } | { b: string };
+>o3 : { a: number; } | { b: string; }
+>a : number
+>b : string
+
+var o3 =  { ...union };
+>o3 : { a: number; } | { b: string; }
+>{ ...union } : { a: number; } | { b: string; }
+>union : { a: number; } | { b: string; }
+
+var o4: { a: boolean } | { b: string , a: boolean};
+>o4 : { a: boolean; } | { b: string; a: boolean; }
+>a : boolean
+>b : string
+>a : boolean
+
+var o4 =  { ...union, a: false };
+>o4 : { a: boolean; } | { b: string; a: boolean; }
+>{ ...union, a: false } : { a: boolean; } | { a: boolean; b: string; }
+>union : { a: number; } | { b: string; }
+>a : boolean
+>false : false
+
+var o5: { a: number } | { b: string } | { a: number, b: string };
+>o5 : { a: number; } | { b: string; } | { a: number; b: string; }
+>a : number
+>b : string
+>a : number
+>b : string
+
+var o5 =  { ...union, ...union };
+>o5 : { a: number; } | { b: string; } | { a: number; b: string; }
+>{ ...union, ...union } : { a: number; } | { b: string; a: number; } | { a: number; b: string; } | { b: string; }
+>union : { a: number; } | { b: string; }
+>union : { a: number; } | { b: string; }
+

tests/baselines/reference/spreadUnion2.js

@@ -0,0 +1,49 @@
+//// [spreadUnion2.ts]
+
+declare const undefinedUnion: { a: number } | undefined;
+declare const nullUnion: { b: number } | null;
+declare const nullAndUndefinedUnion: null | undefined;
+
+var o1: { a: number };
+var o1 = { ...undefinedUnion };
+
+var o2: { b: number };
+var o2 = { ...nullUnion };
+
+var o3: { a: number, b: number };
+var o3 = { ...undefinedUnion, ...nullUnion };
+var o3 = { ...nullUnion, ...undefinedUnion };
+
+var o4: { a: number };
+var o4 = { ...undefinedUnion, ...undefinedUnion };
+
+var o5: { b: number };
+var o5 = { ...nullUnion, ...nullUnion };
+
+var o6: { };
+var o6 = { ...nullAndUndefinedUnion, ...nullAndUndefinedUnion };
+var o6 = { ...nullAndUndefinedUnion };
+
+//// [spreadUnion2.js]
+var __assign = (this && this.__assign) || Object.assign || function(t) {
+    for (var s, i = 1, n = arguments.length; i < n; i++) {
+        s = arguments[i];
+        for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p))
+            t[p] = s[p];
+    }
+    return t;
+};
+var o1;
+var o1 = __assign({}, undefinedUnion);
+var o2;
+var o2 = __assign({}, nullUnion);
+var o3;
+var o3 = __assign({}, undefinedUnion, nullUnion);
+var o3 = __assign({}, nullUnion, undefinedUnion);
+var o4;
+var o4 = __assign({}, undefinedUnion, undefinedUnion);
+var o5;
+var o5 = __assign({}, nullUnion, nullUnion);
+var o6;
+var o6 = __assign({}, nullAndUndefinedUnion, nullAndUndefinedUnion);
+var o6 = __assign({}, nullAndUndefinedUnion);

tests/baselines/reference/spreadUnion2.symbols

@@ -0,0 +1,74 @@
+=== tests/cases/compiler/spreadUnion2.ts ===
+
+declare const undefinedUnion: { a: number } | undefined;
+>undefinedUnion : Symbol(undefinedUnion, Decl(spreadUnion2.ts, 1, 13))
+>a : Symbol(a, Decl(spreadUnion2.ts, 1, 31))
+
+declare const nullUnion: { b: number } | null;
+>nullUnion : Symbol(nullUnion, Decl(spreadUnion2.ts, 2, 13))
+>b : Symbol(b, Decl(spreadUnion2.ts, 2, 26))
+
+declare const nullAndUndefinedUnion: null | undefined;
+>nullAndUndefinedUnion : Symbol(nullAndUndefinedUnion, Decl(spreadUnion2.ts, 3, 13))
+
+var o1: { a: number };
+>o1 : Symbol(o1, Decl(spreadUnion2.ts, 5, 3), Decl(spreadUnion2.ts, 6, 3))
+>a : Symbol(a, Decl(spreadUnion2.ts, 5, 9))
+
+var o1 = { ...undefinedUnion };
+>o1 : Symbol(o1, Decl(spreadUnion2.ts, 5, 3), Decl(spreadUnion2.ts, 6, 3))
+>undefinedUnion : Symbol(undefinedUnion, Decl(spreadUnion2.ts, 1, 13))
+
+var o2: { b: number };
+>o2 : Symbol(o2, Decl(spreadUnion2.ts, 8, 3), Decl(spreadUnion2.ts, 9, 3))
+>b : Symbol(b, Decl(spreadUnion2.ts, 8, 9))
+
+var o2 = { ...nullUnion };
+>o2 : Symbol(o2, Decl(spreadUnion2.ts, 8, 3), Decl(spreadUnion2.ts, 9, 3))
+>nullUnion : Symbol(nullUnion, Decl(spreadUnion2.ts, 2, 13))
+
+var o3: { a: number, b: number };
+>o3 : Symbol(o3, Decl(spreadUnion2.ts, 11, 3), Decl(spreadUnion2.ts, 12, 3), Decl(spreadUnion2.ts, 13, 3))
+>a : Symbol(a, Decl(spreadUnion2.ts, 11, 9))
+>b : Symbol(b, Decl(spreadUnion2.ts, 11, 20))
+
+var o3 = { ...undefinedUnion, ...nullUnion };
+>o3 : Symbol(o3, Decl(spreadUnion2.ts, 11, 3), Decl(spreadUnion2.ts, 12, 3), Decl(spreadUnion2.ts, 13, 3))
+>undefinedUnion : Symbol(undefinedUnion, Decl(spreadUnion2.ts, 1, 13))
+>nullUnion : Symbol(nullUnion, Decl(spreadUnion2.ts, 2, 13))
+
+var o3 = { ...nullUnion, ...undefinedUnion };
+>o3 : Symbol(o3, Decl(spreadUnion2.ts, 11, 3), Decl(spreadUnion2.ts, 12, 3), Decl(spreadUnion2.ts, 13, 3))
+>nullUnion : Symbol(nullUnion, Decl(spreadUnion2.ts, 2, 13))
+>undefinedUnion : Symbol(undefinedUnion, Decl(spreadUnion2.ts, 1, 13))
+
+var o4: { a: number };
+>o4 : Symbol(o4, Decl(spreadUnion2.ts, 15, 3), Decl(spreadUnion2.ts, 16, 3))
+>a : Symbol(a, Decl(spreadUnion2.ts, 15, 9))
+
+var o4 = { ...undefinedUnion, ...undefinedUnion };
+>o4 : Symbol(o4, Decl(spreadUnion2.ts, 15, 3), Decl(spreadUnion2.ts, 16, 3))
+>undefinedUnion : Symbol(undefinedUnion, Decl(spreadUnion2.ts, 1, 13))
+>undefinedUnion : Symbol(undefinedUnion, Decl(spreadUnion2.ts, 1, 13))
+
+var o5: { b: number };
+>o5 : Symbol(o5, Decl(spreadUnion2.ts, 18, 3), Decl(spreadUnion2.ts, 19, 3))
+>b : Symbol(b, Decl(spreadUnion2.ts, 18, 9))
+
+var o5 = { ...nullUnion, ...nullUnion };
+>o5 : Symbol(o5, Decl(spreadUnion2.ts, 18, 3), Decl(spreadUnion2.ts, 19, 3))
+>nullUnion : Symbol(nullUnion, Decl(spreadUnion2.ts, 2, 13))
+>nullUnion : Symbol(nullUnion, Decl(spreadUnion2.ts, 2, 13))
+
+var o6: { };
+>o6 : Symbol(o6, Decl(spreadUnion2.ts, 21, 3), Decl(spreadUnion2.ts, 22, 3), Decl(spreadUnion2.ts, 23, 3))
+
+var o6 = { ...nullAndUndefinedUnion, ...nullAndUndefinedUnion };
+>o6 : Symbol(o6, Decl(spreadUnion2.ts, 21, 3), Decl(spreadUnion2.ts, 22, 3), Decl(spreadUnion2.ts, 23, 3))
+>nullAndUndefinedUnion : Symbol(nullAndUndefinedUnion, Decl(spreadUnion2.ts, 3, 13))
+>nullAndUndefinedUnion : Symbol(nullAndUndefinedUnion, Decl(spreadUnion2.ts, 3, 13))
+
+var o6 = { ...nullAndUndefinedUnion };
+>o6 : Symbol(o6, Decl(spreadUnion2.ts, 21, 3), Decl(spreadUnion2.ts, 22, 3), Decl(spreadUnion2.ts, 23, 3))
+>nullAndUndefinedUnion : Symbol(nullAndUndefinedUnion, Decl(spreadUnion2.ts, 3, 13))
+

tests/baselines/reference/spreadUnion2.types

@@ -0,0 +1,84 @@
+=== tests/cases/compiler/spreadUnion2.ts ===
+
+declare const undefinedUnion: { a: number } | undefined;
+>undefinedUnion : { a: number; } | undefined
+>a : number
+
+declare const nullUnion: { b: number } | null;
+>nullUnion : { b: number; } | null
+>b : number
+>null : null
+
+declare const nullAndUndefinedUnion: null | undefined;
+>nullAndUndefinedUnion : null | undefined
+>null : null
+
+var o1: { a: number };
+>o1 : { a: number; }
+>a : number
+
+var o1 = { ...undefinedUnion };
+>o1 : { a: number; }
+>{ ...undefinedUnion } : { a: number; }
+>undefinedUnion : { a: number; } | undefined
+
+var o2: { b: number };
+>o2 : { b: number; }
+>b : number
+
+var o2 = { ...nullUnion };
+>o2 : { b: number; }
+>{ ...nullUnion } : { b: number; }
+>nullUnion : { b: number; } | null
+
+var o3: { a: number, b: number };
+>o3 : { a: number; b: number; }
+>a : number
+>b : number
+
+var o3 = { ...undefinedUnion, ...nullUnion };
+>o3 : { a: number; b: number; }
+>{ ...undefinedUnion, ...nullUnion } : { b: number; a: number; }
+>undefinedUnion : { a: number; } | undefined
+>nullUnion : { b: number; } | null
+
+var o3 = { ...nullUnion, ...undefinedUnion };
+>o3 : { a: number; b: number; }
+>{ ...nullUnion, ...undefinedUnion } : { a: number; b: number; }
+>nullUnion : { b: number; } | null
+>undefinedUnion : { a: number; } | undefined
+
+var o4: { a: number };
+>o4 : { a: number; }
+>a : number
+
+var o4 = { ...undefinedUnion, ...undefinedUnion };
+>o4 : { a: number; }
+>{ ...undefinedUnion, ...undefinedUnion } : { a: number; }
+>undefinedUnion : { a: number; } | undefined
+>undefinedUnion : { a: number; } | undefined
+
+var o5: { b: number };
+>o5 : { b: number; }
+>b : number
+
+var o5 = { ...nullUnion, ...nullUnion };
+>o5 : { b: number; }
+>{ ...nullUnion, ...nullUnion } : { b: number; }
+>nullUnion : { b: number; } | null
+>nullUnion : { b: number; } | null
+
+var o6: { };
+>o6 : {}
+
+var o6 = { ...nullAndUndefinedUnion, ...nullAndUndefinedUnion };
+>o6 : {}
+>{ ...nullAndUndefinedUnion, ...nullAndUndefinedUnion } : {}
+>nullAndUndefinedUnion : null | undefined
+>nullAndUndefinedUnion : null | undefined
+
+var o6 = { ...nullAndUndefinedUnion };
+>o6 : {}
+>{ ...nullAndUndefinedUnion } : {}
+>nullAndUndefinedUnion : null | undefined
+

tests/baselines/reference/unionTypeWithLeadingOperator.js

@@ -0,0 +1,10 @@
+//// [unionTypeWithLeadingOperator.ts]
+type A = | string;
+type B =
+  | { type: "INCREMENT" }
+  | { type: "DECREMENT" };
+
+type C = [| 0 | 1, | "foo" | "bar"];
+
+
+//// [unionTypeWithLeadingOperator.js]

tests/baselines/reference/unionTypeWithLeadingOperator.symbols

@@ -0,0 +1,16 @@
+=== tests/cases/compiler/unionTypeWithLeadingOperator.ts ===
+type A = | string;
+>A : Symbol(A, Decl(unionTypeWithLeadingOperator.ts, 0, 0))
+
+type B =
+>B : Symbol(B, Decl(unionTypeWithLeadingOperator.ts, 0, 18))
+
+  | { type: "INCREMENT" }
+>type : Symbol(type, Decl(unionTypeWithLeadingOperator.ts, 2, 5))
+
+  | { type: "DECREMENT" };
+>type : Symbol(type, Decl(unionTypeWithLeadingOperator.ts, 3, 5))
+
+type C = [| 0 | 1, | "foo" | "bar"];
+>C : Symbol(C, Decl(unionTypeWithLeadingOperator.ts, 3, 26))
+

tests/baselines/reference/unionTypeWithLeadingOperator.types

@@ -0,0 +1,16 @@
+=== tests/cases/compiler/unionTypeWithLeadingOperator.ts ===
+type A = | string;
+>A : string
+
+type B =
+>B : B
+
+  | { type: "INCREMENT" }
+>type : "INCREMENT"
+
+  | { type: "DECREMENT" };
+>type : "DECREMENT"
+
+type C = [| 0 | 1, | "foo" | "bar"];
+>C : [0 | 1, "foo" | "bar"]
+

tests/baselines/reference/useObjectValuesAndEntries1.types

@@ -22,38 +22,38 @@ for (var x of Object.values(o)) {
 }
 
 var entries = Object.entries(o);  // <-- entries: ['a' | 'b', number][]
->entries : ["a" | "b", number][]
->Object.entries(o) : ["a" | "b", number][]
->Object.entries : { <T extends { [key: string]: any; }, K extends keyof T>(o: T): [keyof T, T[K]][]; (o: any): [string, any][]; }
+>entries : [string, number][]
+>Object.entries(o) : [string, number][]
+>Object.entries : { <T>(o: { [s: string]: T; }): [string, T][]; (o: any): [string, any][]; }
 >Object : ObjectConstructor
->entries : { <T extends { [key: string]: any; }, K extends keyof T>(o: T): [keyof T, T[K]][]; (o: any): [string, any][]; }
+>entries : { <T>(o: { [s: string]: T; }): [string, T][]; (o: any): [string, any][]; }
 >o : { a: number; b: number; }
 
 var entries1 = Object.entries(1); // <-- entries: [string, any][]
 >entries1 : [string, any][]
 >Object.entries(1) : [string, any][]
->Object.entries : { <T extends { [key: string]: any; }, K extends keyof T>(o: T): [keyof T, T[K]][]; (o: any): [string, any][]; }
+>Object.entries : { <T>(o: { [s: string]: T; }): [string, T][]; (o: any): [string, any][]; }
 >Object : ObjectConstructor
->entries : { <T extends { [key: string]: any; }, K extends keyof T>(o: T): [keyof T, T[K]][]; (o: any): [string, any][]; }
+>entries : { <T>(o: { [s: string]: T; }): [string, T][]; (o: any): [string, any][]; }
 >1 : 1
 
 var entries2 = Object.entries({a: true, b: 2}) // ['a' | 'b', number | boolean][]
->entries2 : ["a" | "b", number | boolean][]
->Object.entries({a: true, b: 2}) : ["a" | "b", number | boolean][]
->Object.entries : { <T extends { [key: string]: any; }, K extends keyof T>(o: T): [keyof T, T[K]][]; (o: any): [string, any][]; }
+>entries2 : [string, number | boolean][]
+>Object.entries({a: true, b: 2}) : [string, number | boolean][]
+>Object.entries : { <T>(o: { [s: string]: T; }): [string, T][]; (o: any): [string, any][]; }
 >Object : ObjectConstructor
->entries : { <T extends { [key: string]: any; }, K extends keyof T>(o: T): [keyof T, T[K]][]; (o: any): [string, any][]; }
->{a: true, b: 2} : { a: true; b: number; }
+>entries : { <T>(o: { [s: string]: T; }): [string, T][]; (o: any): [string, any][]; }
+>{a: true, b: 2} : { a: true; b: 2; }
 >a : boolean
 >true : true
 >b : number
 >2 : 2
 
 var entries3 = Object.entries({}) // [never, any][]
->entries3 : [never, any][]
->Object.entries({}) : [never, any][]
->Object.entries : { <T extends { [key: string]: any; }, K extends keyof T>(o: T): [keyof T, T[K]][]; (o: any): [string, any][]; }
+>entries3 : [string, {}][]
+>Object.entries({}) : [string, {}][]
+>Object.entries : { <T>(o: { [s: string]: T; }): [string, T][]; (o: any): [string, any][]; }
 >Object : ObjectConstructor
->entries : { <T extends { [key: string]: any; }, K extends keyof T>(o: T): [keyof T, T[K]][]; (o: any): [string, any][]; }
+>entries : { <T>(o: { [s: string]: T; }): [string, T][]; (o: any): [string, any][]; }
 >{} : {}
 

tests/baselines/reference/useObjectValuesAndEntries4.types

@@ -22,10 +22,10 @@ for (var x of Object.values(o)) {
 }
 
 var entries = Object.entries(o);
->entries : ["a" | "b", number][]
->Object.entries(o) : ["a" | "b", number][]
->Object.entries : { <T extends { [key: string]: any; }, K extends keyof T>(o: T): [keyof T, T[K]][]; (o: any): [string, any][]; }
+>entries : [string, number][]
+>Object.entries(o) : [string, number][]
+>Object.entries : { <T>(o: { [s: string]: T; }): [string, T][]; (o: any): [string, any][]; }
 >Object : ObjectConstructor
->entries : { <T extends { [key: string]: any; }, K extends keyof T>(o: T): [keyof T, T[K]][]; (o: any): [string, any][]; }
+>entries : { <T>(o: { [s: string]: T; }): [string, T][]; (o: any): [string, any][]; }
 >o : { a: number; b: number; }
 

tests/cases/compiler/declarationEmitIndexTypeNotFound.ts

@@ -0,0 +1,5 @@
+// @declaration: true
+
+export interface Test {
+    [index: TypeNotFound]: any;
+}

tests/cases/compiler/decoratorWithUnderscoreMethod.ts

@@ -0,0 +1,18 @@
+// @noemithelpers: true
+// @experimentaldecorators: true
+
+declare var console : { log(arg: string): void };
+function dec(): Function {
+    return function (target: any, propKey: string, descr: PropertyDescriptor): void {
+        console.log(target[propKey]);
+        //logs undefined
+        //propKey has three underscores as prefix, but the method has only two underscores
+    };
+}
+
+class A {
+    @dec()
+    private __foo(bar: string): void {
+        // do something with bar
+    }
+}

tests/cases/compiler/exhaustiveSwitchWithWideningLiteralTypes.ts

@@ -0,0 +1,18 @@
+// @strictNullChecks: true
+
+// Repro from #12529
+
+class A {
+    readonly kind = "A"; // (property) A.kind: "A"
+}
+
+class B {
+    readonly kind = "B"; // (property) B.kind: "B"
+}
+
+function f(value: A | B): number {
+    switch(value.kind) {
+        case "A": return 0;
+        case "B": return 1;
+    }
+}

tests/cases/compiler/intersectionTypeNormalization.ts

@@ -57,4 +57,49 @@ function getValueAsString(value: IntersectionFail): string {
         return '' + value.num;
     }
     return value.str;
+}
+
+// Repro from #12535
+
+namespace enums {
+    export const enum A {
+        a1,
+        a2,
+        a3,
+       // ... elements omitted for the sake of clarity
+        a75,
+        a76,
+        a77,
+    }
+    export const enum B {
+        b1,
+        b2,
+       // ... elements omitted for the sake of clarity
+        b86,
+        b87,
+    }
+    export const enum C {
+        c1,
+        c2,
+       // ... elements omitted for the sake of clarity
+        c210,
+        c211,
+    }
+    export type Genre = A | B | C;
+}
+
+type Foo = {
+    genreId: enums.Genre;
+};
+
+type Bar = {
+    genreId: enums.Genre;
+};
+
+type FooBar = Foo & Bar;
+
+function foo(so: any) {
+    const val = so as FooBar;
+    const isGenre = val.genreId;
+    return isGenre;
 }

tests/cases/compiler/intersectionTypeWithLeadingOperator.ts

@@ -0,0 +1,6 @@
+type A = & string;
+type B =
+  & { foo: string }
+  & { bar: number };
+
+type C = [& { foo: 1 } & { bar: 2 }, & { foo: 3 } & { bar: 4 }];

tests/cases/compiler/restIntersection.ts

@@ -0,0 +1,4 @@
+var intersection: { x: number, y: number } & { w: string, z: string };
+
+var rest1: { y: number, w: string, z: string };
+var {x, ...rest1 } = intersection;

tests/cases/compiler/restInvalidArgumentType.ts

@@ -0,0 +1,59 @@
+enum E { v1, v2 };
+
+function f<T extends { b: string }>(p1: T, p2: T[]) {
+    var t: T;
+
+    var i: T["b"];
+    var k: keyof T;
+
+    var mapped_generic: {[P in keyof T]: T[P]};
+    var mapped: {[P in "b"]: T[P]};
+
+    var union_generic: T | { a: number };
+    var union_primitive: { a: number } | number;
+
+    var intersection_generic: T & { a: number };
+    var intersection_premitive: { a: number } | string;
+
+    var num: number;
+    var str: number;
+
+    var u: undefined;
+    var n: null;
+
+    var a: any;
+
+    var literal_string: "string";
+    var literal_number: 42;
+
+    var e: E;
+
+    var {...r1} = p1;   // Error, generic type paramterre
+    var {...r2} = p2;   // OK
+    var {...r3} = t;   // Error, generic type paramter
+
+    var {...r4} = i;   // Error, index access
+    var {...r5} = k;   // Error, index
+
+    var {...r6} = mapped_generic; // Error, generic mapped object type
+    var {...r7} = mapped;  // OK, non-generic mapped type
+
+    var {...r8} = union_generic;  // Error, union with generic type parameter
+    var {...r9} = union_primitive;  // Error, union with generic type parameter
+
+    var {...r10} = intersection_generic;  // Error, intersection with generic type parameter
+    var {...r11} = intersection_premitive;  // Error, intersection with generic type parameter
+
+    var {...r12} = num;  // Error
+    var {...r13} = str;  // Error
+
+    var {...r14} = u;  // OK
+    var {...r15} = n;  // OK
+
+    var {...r16} = a;  // OK
+
+    var {...r17} = literal_string;  // Error
+    var {...r18} = literal_number;  // Error
+
+    var {...r19} = e;  // Error, enum
+}

tests/cases/compiler/restUnion.ts

@@ -0,0 +1,14 @@
+var union: { a: number, c: boolean } | { a: string, b: string };
+
+var rest1: { c: boolean } | { b: string };
+var {a, ...rest1 } = union;
+
+
+var undefinedUnion: { n: number } | undefined;
+var rest2: {};
+var {n, ...rest2 } = undefinedUnion;
+
+
+var nullUnion: { n: number } | null;
+var rest3: {};
+var {n, ...rest3 } = nullUnion;

tests/cases/compiler/restUnion2.ts

@@ -0,0 +1,19 @@
+// @strictNullChecks: true
+
+declare const undefinedUnion: { n: number } | undefined;
+var rest2: { n: number };
+var {...rest2 } = undefinedUnion;
+
+
+declare const nullUnion: { n: number } | null;
+var rest3: { n: number };
+var {...rest3 } = nullUnion;
+
+
+declare const nullAndUndefinedUnion: null | undefined;
+var rest4: { };
+var {...rest4 } = nullAndUndefinedUnion;
+
+declare const unionWithIntersection: ({ n: number } & { s: string }) & undefined | null;
+var rest5: { n: number, s: string };
+var {...rest5 } = unionWithIntersection;

tests/cases/compiler/spreadIntersection.ts

@@ -0,0 +1,7 @@
+var intersection: { a: number } & { b: string };
+
+var o1: { a: number, b: string };
+var o1 = { ...intersection };
+
+var o2: { a: number, b: string, c: boolean };
+var o2 = { ...intersection, c: false };

tests/cases/compiler/spreadInvalidArgumentType.ts

@@ -0,0 +1,59 @@
+enum E { v1, v2 };
+
+function f<T extends { b: string }>(p1: T, p2: T[]) {
+    var t: T;
+
+    var i: T["b"];
+    var k: keyof T;
+
+    var mapped_generic: {[P in keyof T]: T[P]};
+    var mapped: {[P in "b"]: T[P]};
+
+    var union_generic: T | { a: number };
+    var union_primitive: { a: number } | number;
+
+    var intersection_generic: T & { a: number };
+    var intersection_premitive: { a: number } | string;
+
+    var num: number;
+    var str: number;
+
+    var u: undefined;
+    var n: null;
+
+    var a: any;
+
+    var literal_string: "string";
+    var literal_number: 42;
+
+    var e: E;
+
+    var o1 = { ...p1 };   // Error, generic type paramterre
+    var o2 = { ...p2 };   // OK
+    var o3 = { ...t };   // Error, generic type paramter
+
+    var o4 = { ...i };   // Error, index access
+    var o5 = { ...k };   // Error, index
+
+    var o6 = { ...mapped_generic }; // Error, generic mapped object type
+    var o7 = { ...mapped };  // OK, non-generic mapped type
+
+    var o8 = { ...union_generic };  // Error, union with generic type parameter
+    var o9 = { ...union_primitive };  // Error, union with generic type parameter
+
+    var o10 = { ...intersection_generic };  // Error, intersection with generic type parameter
+    var o11 = { ...intersection_premitive };  // Error, intersection with generic type parameter
+
+    var o12 = { ...num };  // Error
+    var o13 = { ...str };  // Error
+
+    var o14 = { ...u };  // OK
+    var o15 = { ...n };  // OK
+
+    var o16 = { ...a };  // OK
+
+    var o17 = { ...literal_string };  // Error
+    var o18 = { ...literal_number };  // Error
+
+    var o19 = { ...e };  // Error, enum
+}

tests/cases/compiler/spreadUnion.ts

@@ -0,0 +1,10 @@
+var union: { a: number } | { b: string };
+
+var o3: { a: number } | { b: string };
+var o3 =  { ...union };
+
+var o4: { a: boolean } | { b: string , a: boolean};
+var o4 =  { ...union, a: false };
+
+var o5: { a: number } | { b: string } | { a: number, b: string };
+var o5 =  { ...union, ...union };