grand unified theory of predicate types

src/compiler/checker.ts

@@ -123,8 +123,8 @@ namespace ts {
 
         const noConstraintType = createAnonymousType(undefined, emptySymbols, emptyArray, emptyArray, undefined, undefined);
 
-        const anySignature = createSignature(undefined, undefined, emptyArray, anyType, undefined, 0, /*hasRestParameter*/ false, /*hasStringLiterals*/ false);
-        const unknownSignature = createSignature(undefined, undefined, emptyArray, unknownType, undefined, 0, /*hasRestParameter*/ false, /*hasStringLiterals*/ false);
+        const anySignature = createSignature(undefined, undefined, emptyArray, anyType, 0, /*hasRestParameter*/ false, /*hasStringLiterals*/ false);
+        const unknownSignature = createSignature(undefined, undefined, emptyArray, unknownType, 0, /*hasRestParameter*/ false, /*hasStringLiterals*/ false);
 
         const globals: SymbolTable = {};
 
@@ -2074,15 +2074,7 @@ namespace ts {
                 }
                 writeSpace(writer);
 
-                let returnType: Type;
-                const predicate = signature.typePredicate;
-                if (predicate) {
-                    buildTypePredicateDisplay(writer, predicate);
-                    returnType = predicate.type;
-                }
-                else {
-                    returnType = getReturnTypeOfSignature(signature);
-                }
+                const returnType = getReturnTypeOfSignature(signature);
                 buildTypeDisplay(returnType, writer, enclosingDeclaration, flags, symbolStack);
             }
 
@@ -3378,13 +3370,12 @@ namespace ts {
         }
 
         function createSignature(declaration: SignatureDeclaration, typeParameters: TypeParameter[], parameters: Symbol[],
-            resolvedReturnType: Type, typePredicate: IdentifierTypePredicate | ThisTypePredicate, minArgumentCount: number, hasRestParameter: boolean, hasStringLiterals: boolean): Signature {
+            resolvedReturnType: Type, minArgumentCount: number, hasRestParameter: boolean, hasStringLiterals: boolean): Signature {
             const sig = new Signature(checker);
             sig.declaration = declaration;
             sig.typeParameters = typeParameters;
             sig.parameters = parameters;
             sig.resolvedReturnType = resolvedReturnType;
-            sig.typePredicate = typePredicate;
             sig.minArgumentCount = minArgumentCount;
             sig.hasRestParameter = hasRestParameter;
             sig.hasStringLiterals = hasStringLiterals;
@@ -3392,13 +3383,13 @@ namespace ts {
         }
 
         function cloneSignature(sig: Signature): Signature {
-            return createSignature(sig.declaration, sig.typeParameters, sig.parameters, sig.resolvedReturnType, sig.typePredicate,
+            return createSignature(sig.declaration, sig.typeParameters, sig.parameters, sig.resolvedReturnType,
                 sig.minArgumentCount, sig.hasRestParameter, sig.hasStringLiterals);
         }
 
         function getDefaultConstructSignatures(classType: InterfaceType): Signature[] {
             if (!hasClassBaseType(classType)) {
-                return [createSignature(undefined, classType.localTypeParameters, emptyArray, classType, undefined, 0, /*hasRestParameter*/ false, /*hasStringLiterals*/ false)];
+                return [createSignature(undefined, classType.localTypeParameters, emptyArray, classType, 0, /*hasRestParameter*/ false, /*hasStringLiterals*/ false)];
             }
             const baseConstructorType = getBaseConstructorTypeOfClass(classType);
             const baseSignatures = getSignaturesOfType(baseConstructorType, SignatureKind.Construct);
@@ -3924,15 +3915,11 @@ namespace ts {
                 }
 
                 let returnType: Type;
-                let typePredicate: IdentifierTypePredicate | ThisTypePredicate;
                 if (classType) {
                     returnType = classType;
                 }
                 else if (declaration.type) {
                     returnType = getTypeFromTypeNode(declaration.type);
-                    if (declaration.type.kind === SyntaxKind.TypePredicate) {
-                        typePredicate = createTypePredicateFromTypePredicateNode(declaration.type as TypePredicateNode);
-                    }
                 }
                 else {
                     // TypeScript 1.0 spec (April 2014):
@@ -3947,8 +3934,7 @@ namespace ts {
                     }
                 }
 
-                links.resolvedSignature = createSignature(declaration, typeParameters, parameters, returnType, typePredicate,
-                    minArgumentCount, hasRestParameter(declaration), hasStringLiterals);
+                links.resolvedSignature = createSignature(declaration, typeParameters, parameters, returnType, minArgumentCount, hasRestParameter(declaration), hasStringLiterals);
             }
             return links.resolvedSignature;
         }
@@ -4608,15 +4594,10 @@ namespace ts {
         }
 
         function getPredicateType(node: TypePredicateNode): Type {
-            if (!(node.parent.kind === SyntaxKind.PropertyDeclaration || node.parent.kind === SyntaxKind.PropertySignature || node.parent.kind === SyntaxKind.GetAccessor)) {
-                return booleanType;
-            }
-            else {
-                return createPredicateType(getSymbolOfNode(node), createTypePredicateFromTypePredicateNode(node) as ThisTypePredicate);
-            }
+            return createPredicateType(getSymbolOfNode(node), createTypePredicateFromTypePredicateNode(node));
         }
 
-        function createPredicateType(symbol: Symbol, predicate: ThisTypePredicate) {
+        function createPredicateType(symbol: Symbol, predicate: ThisTypePredicate | IdentifierTypePredicate) {
                 const type = createType(TypeFlags.Boolean | TypeFlags.PredicateType) as PredicateType;
                 type.symbol = symbol;
                 type.predicate = predicate;
@@ -4801,7 +4782,6 @@ namespace ts {
             const result = createSignature(signature.declaration, freshTypeParameters,
                 instantiateList(signature.parameters, mapper, instantiateSymbol),
                 instantiateType(signature.resolvedReturnType, mapper),
-                signature.typePredicate && cloneTypePredicate(signature.typePredicate, mapper),
                 signature.minArgumentCount, signature.hasRestParameter, signature.hasStringLiterals);
             result.target = signature;
             result.mapper = mapper;
@@ -4872,7 +4852,8 @@ namespace ts {
                     return getIntersectionType(instantiateList((<IntersectionType>type).types, mapper, instantiateType));
                 }
                 if (type.flags & TypeFlags.PredicateType) {
-                    return createPredicateType(type.symbol, {kind: TypePredicateKind.This, type: instantiateType((type as PredicateType).predicate.type, mapper)} as ThisTypePredicate);
+                    const predicate = (type as PredicateType).predicate;
+                    return createPredicateType(type.symbol, cloneTypePredicate(predicate, mapper));
                 }
             }
             return type;
@@ -5044,7 +5025,36 @@ namespace ts {
                 if (relation === assignableRelation) {
                     if (isTypeAny(source)) return Ternary.True;
                     if (source === numberType && target.flags & TypeFlags.Enum) return Ternary.True;
-                    if (source.flags & TypeFlags.Boolean && target.flags & TypeFlags.Boolean && (source.flags & TypeFlags.PredicateType || target.flags & TypeFlags.PredicateType)) return Ternary.True;
+                }
+                if (source.flags & TypeFlags.Boolean && target.flags & TypeFlags.Boolean) {
+                    if (source.flags & TypeFlags.PredicateType && target.flags & TypeFlags.PredicateType) {
+                        const sourcePredicate = source as PredicateType;
+                        const targetPredicate = target as PredicateType;
+                        if (sourcePredicate.predicate.kind !== targetPredicate.predicate.kind) {
+                            if (reportErrors) {
+                                reportError(Diagnostics.A_this_based_type_guard_is_not_assignable_to_a_parameter_based_type_guard);
+                                reportError(Diagnostics.Type_predicate_0_is_not_assignable_to_1, typeToString(source), typeToString(target));
+                            }
+                            return Ternary.False;
+                        }
+                        if (sourcePredicate.predicate.kind === TypePredicateKind.Identifier) {
+                            const sourceIdentifierPredicate = sourcePredicate.predicate as IdentifierTypePredicate;
+                            const targetIdentifierPredicate = targetPredicate.predicate as IdentifierTypePredicate;
+                            if (sourceIdentifierPredicate.parameterIndex !== targetIdentifierPredicate.parameterIndex) {
+                                if (reportErrors) {
+                                    reportError(Diagnostics.Parameter_0_is_not_in_the_same_position_as_parameter_1, sourceIdentifierPredicate.parameterName, targetIdentifierPredicate.parameterName);
+                                    reportError(Diagnostics.Type_predicate_0_is_not_assignable_to_1, typeToString(source), typeToString(target));
+                                }
+                                return Ternary.False;
+                            }
+                        }
+                        const related = isRelatedTo(sourcePredicate.predicate.type, targetPredicate.predicate.type, reportErrors, headMessage);
+                        if (related === Ternary.False && reportErrors) {
+                            reportError(Diagnostics.Type_predicate_0_is_not_assignable_to_1, typeToString(source), typeToString(target));
+                        }
+                        return related;
+                    }
+                    return Ternary.True;
                 }
 
                 if (source.flags & TypeFlags.FreshObjectLiteral) {
@@ -5619,65 +5629,6 @@ namespace ts {
                     result &= related;
                 }
 
-                if (source.typePredicate && target.typePredicate) {
-                    const sourcePredicate = source.typePredicate;
-                    const targetPredicate = target.typePredicate;
-                    if (source.typePredicate.kind !== target.typePredicate.kind) {
-                        if (reportErrors) {
-                            reportError(Diagnostics.A_this_based_type_guard_is_not_assignable_to_a_parameter_based_type_guard);
-                        }
-                        return Ternary.False;
-                    }
-                    if (!(isIdentifierTypePredicate(sourcePredicate) && isIdentifierTypePredicate(targetPredicate))) {
-                        if (!isTypeIdenticalTo(sourcePredicate.type, targetPredicate.type)) {
-                            if (reportErrors) {
-                                const sourceTypeText = typeToString(sourcePredicate.type);
-                                const targetTypeText = typeToString(targetPredicate.type);
-                                reportError(Diagnostics.Type_0_is_not_assignable_to_type_1,
-                                    sourceTypeText,
-                                    targetTypeText);
-                            }
-                            return Ternary.False;
-                        }
-                    }
-                    else {
-                        const hasDifferentParameterIndex = sourcePredicate.parameterIndex !== targetPredicate.parameterIndex;
-                        let hasDifferentTypes: boolean;
-                        if (hasDifferentParameterIndex ||
-                            (hasDifferentTypes = !isTypeIdenticalTo(sourcePredicate.type, targetPredicate.type))) {
-
-                            if (reportErrors) {
-                                const sourceParamText = sourcePredicate.parameterName;
-                                const targetParamText = targetPredicate.parameterName;
-                                const sourceTypeText = typeToString(sourcePredicate.type);
-                                const targetTypeText = typeToString(targetPredicate.type);
-
-                                if (hasDifferentParameterIndex) {
-                                    reportError(Diagnostics.Parameter_0_is_not_in_the_same_position_as_parameter_1,
-                                        sourceParamText,
-                                        targetParamText);
-                                }
-                                else if (hasDifferentTypes) {
-                                    reportError(Diagnostics.Type_0_is_not_assignable_to_type_1,
-                                        sourceTypeText,
-                                        targetTypeText);
-                                }
-
-                                reportError(Diagnostics.Type_predicate_0_is_not_assignable_to_1,
-                                    `${sourceParamText} is ${sourceTypeText}`,
-                                    `${targetParamText} is ${targetTypeText}`);
-                            }
-                            return Ternary.False;
-                        }
-                    }
-                }
-                else if (!source.typePredicate && target.typePredicate) {
-                    if (reportErrors) {
-                        reportError(Diagnostics.Signature_0_must_have_a_type_predicate, signatureToString(source));
-                    }
-                    return Ternary.False;
-                }
-
                 const targetReturnType = getReturnTypeOfSignature(target);
                 if (targetReturnType === voidType) return result;
                 const sourceReturnType = getReturnTypeOfSignature(source);
@@ -6239,6 +6190,11 @@ namespace ts {
                         inferFromTypes(sourceTypes[i], targetTypes[i]);
                     }
                 }
+                else if (source.flags & TypeFlags.PredicateType && target.flags & TypeFlags.PredicateType) {
+                    if ((source as PredicateType).predicate.kind === (target as PredicateType).predicate.kind) {
+                        inferFromTypes((source as PredicateType).predicate.type, (target as PredicateType).predicate.type);
+                    }
+                }
                 else if (source.flags & TypeFlags.Tuple && target.flags & TypeFlags.Tuple && (<TupleType>source).elementTypes.length === (<TupleType>target).elementTypes.length) {
                     // If source and target are tuples of the same size, infer from element types
                     const sourceTypes = (<TupleType>source).elementTypes;
@@ -6331,21 +6287,7 @@ namespace ts {
 
             function inferFromSignature(source: Signature, target: Signature) {
                 forEachMatchingParameterType(source, target, inferFromTypes);
-                if (source.typePredicate && target.typePredicate) {
-                    if (target.typePredicate.kind === source.typePredicate.kind) {
-                        if ((target.typePredicate.kind === TypePredicateKind.Identifier
-                            && (target.typePredicate as IdentifierTypePredicate).parameterIndex === (source.typePredicate as IdentifierTypePredicate).parameterIndex)
-                            || target.typePredicate.kind === TypePredicateKind.This) {
-                            // Return types from type predicates are treated as booleans. In order to infer types
-                            // from type predicates we would need to infer using the type within the type predicate
-                            // (i.e. 'Foo' from 'x is Foo').
-                            inferFromTypes(source.typePredicate.type, target.typePredicate.type);
-                        }
-                    }
-                }
-                else {
-                    inferFromTypes(getReturnTypeOfSignature(source), getReturnTypeOfSignature(target));
-                }
+                inferFromTypes(getReturnTypeOfSignature(source), getReturnTypeOfSignature(target));
             }
 
             function inferFromIndexTypes(source: Type, target: Type, sourceKind: IndexKind, targetKind: IndexKind) {
@@ -6791,11 +6733,12 @@ namespace ts {
                     return type;
                 }
                 const signature = getResolvedSignature(expr);
+                const predicateType = getReturnTypeOfSignature(signature);
 
-                if (!signature.typePredicate) {
+                if (!predicateType || !(predicateType.flags & TypeFlags.PredicateType)) {
                     return type;
                 }
-                const predicate = signature.typePredicate;
+                const predicate = (predicateType as PredicateType).predicate;
                 if (isIdentifierTypePredicate(predicate)) {
                     const callExpression = expr as CallExpression;
                     if (callExpression.arguments[predicate.parameterIndex] &&
@@ -6819,7 +6762,7 @@ namespace ts {
                     return type;
                 }
 
-                return narrowTypeByThisTypePredicate(type, (memberType as PredicateType).predicate, expr, assumeTrue);
+                return narrowTypeByThisTypePredicate(type, (memberType as PredicateType).predicate as ThisTypePredicate, expr, assumeTrue);
             }
 
             function narrowTypeByThisTypePredicate(type: Type, predicate: ThisTypePredicate, expression: Expression, assumeTrue: boolean): Type {
@@ -11119,8 +11062,12 @@ namespace ts {
 
             if (node.type) {
                 if (node.type.kind === SyntaxKind.TypePredicate) {
-                    const typePredicate = getSignatureFromDeclaration(node).typePredicate;
-                    const typePredicateNode = <TypePredicateNode>node.type;
+                    const returnType = getReturnTypeOfSignature(getSignatureFromDeclaration(node));
+                    if (!returnType || !(returnType.flags & TypeFlags.PredicateType)) {
+                        return;
+                    }
+                    const typePredicate = (returnType as PredicateType).predicate;
+                    const typePredicateNode = node.type as TypePredicateNode;
                     checkSourceElement(typePredicateNode);
                     if (isIdentifierTypePredicate(typePredicate)) {
                         if (typePredicate.parameterIndex >= 0) {
@@ -13126,7 +13073,7 @@ namespace ts {
                             error(node.expression, Diagnostics.Return_type_of_constructor_signature_must_be_assignable_to_the_instance_type_of_the_class);
                         }
                     }
-                    else if (func.type || isGetAccessorWithAnnotatatedSetAccessor(func) || signature.typePredicate) {
+                    else if (func.type || isGetAccessorWithAnnotatatedSetAccessor(func) || returnType.flags & TypeFlags.PredicateType) {
                         if (isAsyncFunctionLike(func)) {
                             const promisedType = getPromisedType(returnType);
                             const awaitedType = checkAwaitedType(exprType, node.expression, Diagnostics.Return_expression_in_async_function_does_not_have_a_valid_callable_then_member);

src/compiler/types.ts

@@ -2143,7 +2143,7 @@ namespace ts {
 
     // Predicate types (TypeFlags.Predicate)
     export interface PredicateType extends Type {
-        predicate: ThisTypePredicate;
+        predicate: ThisTypePredicate | IdentifierTypePredicate;
     }
 
     // String literal types (TypeFlags.StringLiteral)
@@ -2262,7 +2262,6 @@ namespace ts {
         declaration: SignatureDeclaration;  // Originating declaration
         typeParameters: TypeParameter[];    // Type parameters (undefined if non-generic)
         parameters: Symbol[];               // Parameters
-        typePredicate?: ThisTypePredicate | IdentifierTypePredicate;      // Type predicate
         /* @internal */
         resolvedReturnType: Type;           // Resolved return type
         /* @internal */

tests/baselines/reference/arrayBufferIsViewNarrowsType.types

@@ -4,7 +4,7 @@ var obj: Object;
 >Object : Object
 
 if (ArrayBuffer.isView(obj)) {
->ArrayBuffer.isView(obj) : boolean
+>ArrayBuffer.isView(obj) : arg is ArrayBufferView
 >ArrayBuffer.isView : (arg: any) => arg is ArrayBufferView
 >ArrayBuffer : ArrayBufferConstructor
 >isView : (arg: any) => arg is ArrayBufferView

tests/baselines/reference/isArray.types

@@ -4,7 +4,7 @@ var maybeArray: number | number[];
 
 
 if (Array.isArray(maybeArray)) {
->Array.isArray(maybeArray) : boolean
+>Array.isArray(maybeArray) : arg is any[]
 >Array.isArray : (arg: any) => arg is any[]
 >Array : ArrayConstructor
 >isArray : (arg: any) => arg is any[]

tests/baselines/reference/stringLiteralCheckedInIf02.types

@@ -31,7 +31,7 @@ function f(foo: T) {
 >T : ("a" | "b")[] | "a" | "b"
 
     if (isS(foo)) {
->isS(foo) : boolean
+>isS(foo) : t is "a" | "b"
 >isS : (t: ("a" | "b")[] | "a" | "b") => t is "a" | "b"
 >foo : ("a" | "b")[] | "a" | "b"
 

tests/baselines/reference/stringLiteralTypesAsTags01.errors.txt

@@ -1,10 +1,7 @@
-tests/cases/conformance/types/stringLiteral/stringLiteralTypesAsTags01.ts(18,10): error TS2382: Specialized overload signature is not assignable to any non-specialized signature.
-tests/cases/conformance/types/stringLiteral/stringLiteralTypesAsTags01.ts(19,10): error TS2382: Specialized overload signature is not assignable to any non-specialized signature.
-tests/cases/conformance/types/stringLiteral/stringLiteralTypesAsTags01.ts(20,10): error TS2394: Overload signature is not compatible with function implementation.
 tests/cases/conformance/types/stringLiteral/stringLiteralTypesAsTags01.ts(22,21): error TS2304: Cannot find name 'is'.
 
 
-==== tests/cases/conformance/types/stringLiteral/stringLiteralTypesAsTags01.ts (4 errors) ====
+==== tests/cases/conformance/types/stringLiteral/stringLiteralTypesAsTags01.ts (1 errors) ====
     
     type Kind = "A" | "B"
     
@@ -23,14 +20,8 @@ tests/cases/conformance/types/stringLiteral/stringLiteralTypesAsTags01.ts(22,21)
     }
     
     function hasKind(entity: Entity, kind: "A"): entity is A;
-             ~~~~~~~
-!!! error TS2382: Specialized overload signature is not assignable to any non-specialized signature.
     function hasKind(entity: Entity, kind: "B"): entity is B;
-             ~~~~~~~
-!!! error TS2382: Specialized overload signature is not assignable to any non-specialized signature.
     function hasKind(entity: Entity, kind: Kind): entity is Entity;
-             ~~~~~~~
-!!! error TS2394: Overload signature is not compatible with function implementation.
     function hasKind(entity: Entity, kind: Kind): boolean {
         return kind === is;
                         ~~

tests/baselines/reference/typeGuardFunction.types

@@ -54,7 +54,7 @@ var b: B;
 
 // Basic
 if (isC(a)) {
->isC(a) : boolean
+>isC(a) : p1 is C
 >isC : (p1: any) => p1 is C
 >a : A
 
@@ -70,7 +70,7 @@ var subType: C;
 >C : C
 
 if(isA(subType)) {
->isA(subType) : boolean
+>isA(subType) : p1 is A
 >isA : (p1: any) => p1 is A
 >subType : C
 
@@ -87,7 +87,7 @@ var union: A | B;
 >B : B
 
 if(isA(union)) {
->isA(union) : boolean
+>isA(union) : p1 is A
 >isA : (p1: any) => p1 is A
 >union : A | B
 
@@ -118,7 +118,7 @@ declare function isC_multipleParams(p1, p2): p1 is C;
 >C : C
 
 if (isC_multipleParams(a, 0)) {
->isC_multipleParams(a, 0) : boolean
+>isC_multipleParams(a, 0) : p1 is C
 >isC_multipleParams : (p1: any, p2: any) => p1 is C
 >a : A
 >0 : number
@@ -197,7 +197,7 @@ declare function acceptingBoolean(a: boolean);
 acceptingBoolean(isA(a));
 >acceptingBoolean(isA(a)) : any
 >acceptingBoolean : (a: boolean) => any
->isA(a) : boolean
+>isA(a) : p1 is A
 >isA : (p1: any) => p1 is A
 >a : A
 
@@ -223,8 +223,8 @@ let union2: C | B;
 let union3: boolean | B = isA(union2) || union2;
 >union3 : boolean | B
 >B : B
->isA(union2) || union2 : boolean | B
->isA(union2) : boolean
+>isA(union2) || union2 : p1 is A | B
+>isA(union2) : p1 is A
 >isA : (p1: any) => p1 is A
 >union2 : C | B
 >union2 : B

tests/baselines/reference/typeGuardFunctionErrors.errors.txt

@@ -1,4 +1,4 @@
-tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(15,12): error TS2322: Type 'string' is not assignable to type 'boolean'.
+tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(15,12): error TS2322: Type 'string' is not assignable to type 'x is A'.
 tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(22,33): error TS2304: Cannot find name 'x'.
 tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(26,33): error TS1225: Cannot find parameter 'x'.
 tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(30,10): error TS2391: Function implementation is missing or not immediately following the declaration.
@@ -16,8 +16,7 @@ tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(70,7):
 tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(75,46): error TS2345: Argument of type '(p1: any) => p1 is C' is not assignable to parameter of type '(p1: any) => p1 is B'.
   Type predicate 'p1 is C' is not assignable to 'p1 is B'.
     Type 'C' is not assignable to type 'B'.
-tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(79,1): error TS2322: Type '(p1: any, p2: any) => boolean' is not assignable to type '(p1: any, p2: any) => p1 is A'.
-  Signature '(p1: any, p2: any): boolean' must have a type predicate.
+      Property 'propB' is missing in type 'C'.
 tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(85,1): error TS2322: Type '(p1: any, p2: any) => p2 is A' is not assignable to type '(p1: any, p2: any) => p1 is A'.
   Type predicate 'p2 is A' is not assignable to 'p1 is A'.
     Parameter 'p2' is not in the same position as parameter 'p1'.
@@ -25,7 +24,6 @@ tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(91,1):
 tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(96,9): error TS1228: A type predicate is only allowed in return type position for functions and methods.
 tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(97,16): error TS1228: A type predicate is only allowed in return type position for functions and methods.
 tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(98,20): error TS1228: A type predicate is only allowed in return type position for functions and methods.
-tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(104,25): error TS1228: A type predicate is only allowed in return type position for functions and methods.
 tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(105,16): error TS2322: Type 'boolean' is not assignable to type 'D'.
   Property 'm1' is missing in type 'Boolean'.
 tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(105,16): error TS2409: Return type of constructor signature must be assignable to the instance type of the class
@@ -41,7 +39,7 @@ tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(133,34
 tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(137,39): error TS1230: A type predicate cannot reference element 'p1' in a binding pattern.
 
 
-==== tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts (34 errors) ====
+==== tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts (32 errors) ====
     
     class A {
         propA: number;
@@ -58,7 +56,7 @@ tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(137,39
     function hasANonBooleanReturnStatement(x): x is A {
         return '';
                ~~
-!!! error TS2322: Type 'string' is not assignable to type 'boolean'.
+!!! error TS2322: Type 'string' is not assignable to type 'x is A'.
     }
     
     function hasTypeGuardTypeInsideTypeGuardType(x): x is x is A {
@@ -150,13 +148,11 @@ tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(137,39
 !!! error TS2345: Argument of type '(p1: any) => p1 is C' is not assignable to parameter of type '(p1: any) => p1 is B'.
 !!! error TS2345:   Type predicate 'p1 is C' is not assignable to 'p1 is B'.
 !!! error TS2345:     Type 'C' is not assignable to type 'B'.
+!!! error TS2345:       Property 'propB' is missing in type 'C'.
     
     // Boolean not assignable to type guard
     var assign1: (p1, p2) => p1 is A;
     assign1 = function(p1, p2): boolean {
-    ~~~~~~~
-!!! error TS2322: Type '(p1: any, p2: any) => boolean' is not assignable to type '(p1: any, p2: any) => p1 is A'.
-!!! error TS2322:   Signature '(p1: any, p2: any): boolean' must have a type predicate.
         return true;
     };
     
@@ -194,8 +190,6 @@ tests/cases/conformance/expressions/typeGuards/typeGuardFunctionErrors.ts(137,39
     // Non-compatiable type predicate positions for signature declarations
     class D {
         constructor(p1: A): p1 is C {
-                            ~~~~~~~
-!!! error TS1228: A type predicate is only allowed in return type position for functions and methods.
             return true;
                    ~~~~
 !!! error TS2322: Type 'boolean' is not assignable to type 'D'.

tests/baselines/reference/typeGuardFunctionGenerics.types

@@ -100,7 +100,7 @@ let test1: boolean = funA(isB);
 >isB : (p1: any) => p1 is B
 
 if (funB(retC, a)) {
->funB(retC, a) : boolean
+>funB(retC, a) : p2 is C
 >funB : <T>(p1: (p1: any) => T, p2: any) => p2 is T
 >retC : (x: any) => C
 >a : A
@@ -118,7 +118,7 @@ let test2: B = funC(isB);
 >isB : (p1: any) => p1 is B
 
 if (funD(isC, a)) {
->funD(isC, a) : boolean
+>funD(isC, a) : p2 is C
 >funD : <T>(p1: (p1: any) => p1 is T, p2: any) => p2 is T
 >isC : (p1: any) => p1 is C
 >a : A

tests/baselines/reference/typeGuardFunctionOfFormThis.types

@@ -45,7 +45,7 @@ let a: RoyalGuard = new FollowerGuard();
 >FollowerGuard : typeof FollowerGuard
 
 if (a.isLeader()) {
->a.isLeader() : boolean
+>a.isLeader() : this is LeadGuard
 >a.isLeader : () => this is LeadGuard
 >a : RoyalGuard
 >isLeader : () => this is LeadGuard
@@ -57,7 +57,7 @@ if (a.isLeader()) {
 >lead : () => void
 }
 else if (a.isFollower()) {
->a.isFollower() : boolean
+>a.isFollower() : this is FollowerGuard
 >a.isFollower : () => this is FollowerGuard
 >a : RoyalGuard
 >isFollower : () => this is FollowerGuard
@@ -78,7 +78,7 @@ let b: GuardInterface;
 >GuardInterface : GuardInterface
 
 if (b.isLeader()) {
->b.isLeader() : boolean
+>b.isLeader() : this is LeadGuard
 >b.isLeader : () => this is LeadGuard
 >b : GuardInterface
 >isLeader : () => this is LeadGuard
@@ -90,7 +90,7 @@ if (b.isLeader()) {
 >lead : () => void
 }
 else if (b.isFollower()) {
->b.isFollower() : boolean
+>b.isFollower() : this is FollowerGuard
 >b.isFollower : () => this is FollowerGuard
 >b : GuardInterface
 >isFollower : () => this is FollowerGuard
@@ -103,8 +103,8 @@ else if (b.isFollower()) {
 }
 
 if (((a.isLeader)())) {
->((a.isLeader)()) : boolean
->(a.isLeader)() : boolean
+>((a.isLeader)()) : this is LeadGuard
+>(a.isLeader)() : this is LeadGuard
 >(a.isLeader) : () => this is LeadGuard
 >a.isLeader : () => this is LeadGuard
 >a : RoyalGuard
@@ -117,8 +117,8 @@ if (((a.isLeader)())) {
 >lead : () => void
 }
 else if (((a).isFollower())) {
->((a).isFollower()) : boolean
->(a).isFollower() : boolean
+>((a).isFollower()) : this is FollowerGuard
+>(a).isFollower() : this is FollowerGuard
 >(a).isFollower : () => this is FollowerGuard
 >(a) : RoyalGuard
 >a : RoyalGuard
@@ -132,8 +132,8 @@ else if (((a).isFollower())) {
 }
 
 if (((a["isLeader"])())) {
->((a["isLeader"])()) : boolean
->(a["isLeader"])() : boolean
+>((a["isLeader"])()) : this is LeadGuard
+>(a["isLeader"])() : this is LeadGuard
 >(a["isLeader"]) : () => this is LeadGuard
 >a["isLeader"] : () => this is LeadGuard
 >a : RoyalGuard
@@ -146,8 +146,8 @@ if (((a["isLeader"])())) {
 >lead : () => void
 }
 else if (((a)["isFollower"]())) {
->((a)["isFollower"]()) : boolean
->(a)["isFollower"]() : boolean
+>((a)["isFollower"]()) : this is FollowerGuard
+>(a)["isFollower"]() : this is FollowerGuard
 >(a)["isFollower"] : () => this is FollowerGuard
 >(a) : RoyalGuard
 >a : RoyalGuard
@@ -166,7 +166,7 @@ var holder2 = {a};
 >a : RoyalGuard
 
 if (holder2.a.isLeader()) {
->holder2.a.isLeader() : boolean
+>holder2.a.isLeader() : this is LeadGuard
 >holder2.a.isLeader : () => this is LeadGuard
 >holder2.a : RoyalGuard
 >holder2 : { a: RoyalGuard; }
@@ -232,7 +232,7 @@ let guard = new ArrowGuard();
 >ArrowGuard : typeof ArrowGuard
 
 if (guard.isElite()) {
->guard.isElite() : boolean
+>guard.isElite() : this is ArrowElite
 >guard.isElite : () => this is ArrowElite
 >guard : ArrowGuard
 >isElite : () => this is ArrowElite
@@ -244,7 +244,7 @@ if (guard.isElite()) {
 >defend : () => void
 }
 else if (guard.isMedic()) {
->guard.isMedic() : boolean
+>guard.isMedic() : this is ArrowMedic
 >guard.isMedic : () => this is ArrowMedic
 >guard : ArrowGuard
 >isMedic : () => this is ArrowMedic
@@ -297,7 +297,7 @@ let crate: Crate<{}>;
 >Crate : Crate<T>
 
 if (crate.isSundries()) {
->crate.isSundries() : boolean
+>crate.isSundries() : this is Crate<Sundries>
 >crate.isSundries : () => this is Crate<Sundries>
 >crate : Crate<{}>
 >isSundries : () => this is Crate<Sundries>
@@ -312,7 +312,7 @@ if (crate.isSundries()) {
 >true : boolean
 }
 else if (crate.isSupplies()) {
->crate.isSupplies() : boolean
+>crate.isSupplies() : this is Crate<Supplies>
 >crate.isSupplies : () => this is Crate<Supplies>
 >crate : Crate<{}>
 >isSupplies : () => this is Crate<Supplies>
@@ -405,7 +405,7 @@ a.isFollower = mimic.isFollower;
 >isFollower : () => this is MimicFollower
 
 if (mimic.isFollower()) {
->mimic.isFollower() : boolean
+>mimic.isFollower() : this is MimicFollower
 >mimic.isFollower : () => this is MimicFollower
 >mimic : MimicGuard
 >isFollower : () => this is MimicFollower

tests/baselines/reference/typeGuardFunctionOfFormThisErrors.errors.txt

@@ -1,11 +1,17 @@
 tests/cases/conformance/expressions/typeGuards/typeGuardFunctionOfFormThisErrors.ts(23,1): error TS2322: Type '() => this is LeadGuard' is not assignable to type '() => this is FollowerGuard'.
-  Type 'LeadGuard' is not assignable to type 'FollowerGuard'.
+  Type predicate 'this is LeadGuard' is not assignable to 'this is FollowerGuard'.
+    Type 'LeadGuard' is not assignable to type 'FollowerGuard'.
+      Property 'follow' is missing in type 'LeadGuard'.
 tests/cases/conformance/expressions/typeGuards/typeGuardFunctionOfFormThisErrors.ts(24,1): error TS2322: Type '() => this is FollowerGuard' is not assignable to type '() => this is LeadGuard'.
-  Type 'FollowerGuard' is not assignable to type 'LeadGuard'.
+  Type predicate 'this is FollowerGuard' is not assignable to 'this is LeadGuard'.
+    Type 'FollowerGuard' is not assignable to type 'LeadGuard'.
+      Property 'lead' is missing in type 'FollowerGuard'.
 tests/cases/conformance/expressions/typeGuards/typeGuardFunctionOfFormThisErrors.ts(26,1): error TS2322: Type '() => this is LeadGuard' is not assignable to type '() => this is FollowerGuard'.
-  Type 'LeadGuard' is not assignable to type 'FollowerGuard'.
+  Type predicate 'this is LeadGuard' is not assignable to 'this is FollowerGuard'.
+    Type 'LeadGuard' is not assignable to type 'FollowerGuard'.
 tests/cases/conformance/expressions/typeGuards/typeGuardFunctionOfFormThisErrors.ts(27,1): error TS2322: Type '() => this is FollowerGuard' is not assignable to type '() => this is LeadGuard'.
-  Type 'FollowerGuard' is not assignable to type 'LeadGuard'.
+  Type predicate 'this is FollowerGuard' is not assignable to 'this is LeadGuard'.
+    Type 'FollowerGuard' is not assignable to type 'LeadGuard'.
 tests/cases/conformance/expressions/typeGuards/typeGuardFunctionOfFormThisErrors.ts(29,32): error TS2526: A 'this' type is available only in a non-static member of a class or interface.
 tests/cases/conformance/expressions/typeGuards/typeGuardFunctionOfFormThisErrors.ts(55,7): error TS2339: Property 'follow' does not exist on type 'RoyalGuard'.
 tests/cases/conformance/expressions/typeGuards/typeGuardFunctionOfFormThisErrors.ts(58,7): error TS2339: Property 'lead' does not exist on type 'RoyalGuard'.
@@ -37,20 +43,26 @@ tests/cases/conformance/expressions/typeGuards/typeGuardFunctionOfFormThisErrors
     b.isFollower = b.isLeader;
     ~~~~~~~~~~~~
 !!! error TS2322: Type '() => this is LeadGuard' is not assignable to type '() => this is FollowerGuard'.
-!!! error TS2322:   Type 'LeadGuard' is not assignable to type 'FollowerGuard'.
+!!! error TS2322:   Type predicate 'this is LeadGuard' is not assignable to 'this is FollowerGuard'.
+!!! error TS2322:     Type 'LeadGuard' is not assignable to type 'FollowerGuard'.
+!!! error TS2322:       Property 'follow' is missing in type 'LeadGuard'.
     b.isLeader = b.isFollower;
     ~~~~~~~~~~
 !!! error TS2322: Type '() => this is FollowerGuard' is not assignable to type '() => this is LeadGuard'.
-!!! error TS2322:   Type 'FollowerGuard' is not assignable to type 'LeadGuard'.
+!!! error TS2322:   Type predicate 'this is FollowerGuard' is not assignable to 'this is LeadGuard'.
+!!! error TS2322:     Type 'FollowerGuard' is not assignable to type 'LeadGuard'.
+!!! error TS2322:       Property 'lead' is missing in type 'FollowerGuard'.
     
     a.isFollower = a.isLeader;
     ~~~~~~~~~~~~
 !!! error TS2322: Type '() => this is LeadGuard' is not assignable to type '() => this is FollowerGuard'.
-!!! error TS2322:   Type 'LeadGuard' is not assignable to type 'FollowerGuard'.
+!!! error TS2322:   Type predicate 'this is LeadGuard' is not assignable to 'this is FollowerGuard'.
+!!! error TS2322:     Type 'LeadGuard' is not assignable to type 'FollowerGuard'.
     a.isLeader = a.isFollower;
     ~~~~~~~~~~
 !!! error TS2322: Type '() => this is FollowerGuard' is not assignable to type '() => this is LeadGuard'.
-!!! error TS2322:   Type 'FollowerGuard' is not assignable to type 'LeadGuard'.
+!!! error TS2322:   Type predicate 'this is FollowerGuard' is not assignable to 'this is LeadGuard'.
+!!! error TS2322:     Type 'FollowerGuard' is not assignable to type 'LeadGuard'.
     
     function invalidGuard(c: any): this is number {
                                    ~~~~

tests/baselines/reference/typeGuardOfFormIsType.types

@@ -67,7 +67,7 @@ str = isC1(c1Orc2) && c1Orc2.p1; // C1
 >str = isC1(c1Orc2) && c1Orc2.p1 : string
 >str : string
 >isC1(c1Orc2) && c1Orc2.p1 : string
->isC1(c1Orc2) : boolean
+>isC1(c1Orc2) : x is C1
 >isC1 : (x: any) => x is C1
 >c1Orc2 : C1 | C2
 >c1Orc2.p1 : string
@@ -78,7 +78,7 @@ num = isC2(c1Orc2) && c1Orc2.p2; // C2
 >num = isC2(c1Orc2) && c1Orc2.p2 : number
 >num : number
 >isC2(c1Orc2) && c1Orc2.p2 : number
->isC2(c1Orc2) : boolean
+>isC2(c1Orc2) : x is C2
 >isC2 : (x: any) => x is C2
 >c1Orc2 : C1 | C2
 >c1Orc2.p2 : number
@@ -89,7 +89,7 @@ str = isD1(c1Orc2) && c1Orc2.p1; // D1
 >str = isD1(c1Orc2) && c1Orc2.p1 : string
 >str : string
 >isD1(c1Orc2) && c1Orc2.p1 : string
->isD1(c1Orc2) : boolean
+>isD1(c1Orc2) : x is D1
 >isD1 : (x: any) => x is D1
 >c1Orc2 : C1 | C2
 >c1Orc2.p1 : string
@@ -100,7 +100,7 @@ num = isD1(c1Orc2) && c1Orc2.p3; // D1
 >num = isD1(c1Orc2) && c1Orc2.p3 : number
 >num : number
 >isD1(c1Orc2) && c1Orc2.p3 : number
->isD1(c1Orc2) : boolean
+>isD1(c1Orc2) : x is D1
 >isD1 : (x: any) => x is D1
 >c1Orc2 : C1 | C2
 >c1Orc2.p3 : number
@@ -116,7 +116,7 @@ num = isC2(c2Ord1) && c2Ord1.p2; // C2
 >num = isC2(c2Ord1) && c2Ord1.p2 : number
 >num : number
 >isC2(c2Ord1) && c2Ord1.p2 : number
->isC2(c2Ord1) : boolean
+>isC2(c2Ord1) : x is C2
 >isC2 : (x: any) => x is C2
 >c2Ord1 : C2 | D1
 >c2Ord1.p2 : number
@@ -127,7 +127,7 @@ num = isD1(c2Ord1) && c2Ord1.p3; // D1
 >num = isD1(c2Ord1) && c2Ord1.p3 : number
 >num : number
 >isD1(c2Ord1) && c2Ord1.p3 : number
->isD1(c2Ord1) : boolean
+>isD1(c2Ord1) : x is D1
 >isD1 : (x: any) => x is D1
 >c2Ord1 : C2 | D1
 >c2Ord1.p3 : number
@@ -138,7 +138,7 @@ str = isD1(c2Ord1) && c2Ord1.p1; // D1
 >str = isD1(c2Ord1) && c2Ord1.p1 : string
 >str : string
 >isD1(c2Ord1) && c2Ord1.p1 : string
->isD1(c2Ord1) : boolean
+>isD1(c2Ord1) : x is D1
 >isD1 : (x: any) => x is D1
 >c2Ord1 : C2 | D1
 >c2Ord1.p1 : string
@@ -150,7 +150,7 @@ var r2: C2 | D1 = isC1(c2Ord1) && c2Ord1; // C2 | D1
 >C2 : C2
 >D1 : D1
 >isC1(c2Ord1) && c2Ord1 : D1
->isC1(c2Ord1) : boolean
+>isC1(c2Ord1) : x is C1
 >isC1 : (x: any) => x is C1
 >c2Ord1 : C2 | D1
 >c2Ord1 : D1

tests/baselines/reference/typeGuardOfFormIsTypeOnInterfaces.types

@@ -98,7 +98,7 @@ str = isC1(c1Orc2) && c1Orc2.p1; // C1
 >str = isC1(c1Orc2) && c1Orc2.p1 : string
 >str : string
 >isC1(c1Orc2) && c1Orc2.p1 : string
->isC1(c1Orc2) : boolean
+>isC1(c1Orc2) : x is C1
 >isC1 : (x: any) => x is C1
 >c1Orc2 : C1 | C2
 >c1Orc2.p1 : string
@@ -109,7 +109,7 @@ num = isC2(c1Orc2) && c1Orc2.p2; // C2
 >num = isC2(c1Orc2) && c1Orc2.p2 : number
 >num : number
 >isC2(c1Orc2) && c1Orc2.p2 : number
->isC2(c1Orc2) : boolean
+>isC2(c1Orc2) : x is C2
 >isC2 : (x: any) => x is C2
 >c1Orc2 : C1 | C2
 >c1Orc2.p2 : number
@@ -120,7 +120,7 @@ str = isD1(c1Orc2) && c1Orc2.p1; // D1
 >str = isD1(c1Orc2) && c1Orc2.p1 : string
 >str : string
 >isD1(c1Orc2) && c1Orc2.p1 : string
->isD1(c1Orc2) : boolean
+>isD1(c1Orc2) : x is D1
 >isD1 : (x: any) => x is D1
 >c1Orc2 : C1 | C2
 >c1Orc2.p1 : string
@@ -131,7 +131,7 @@ num = isD1(c1Orc2) && c1Orc2.p3; // D1
 >num = isD1(c1Orc2) && c1Orc2.p3 : number
 >num : number
 >isD1(c1Orc2) && c1Orc2.p3 : number
->isD1(c1Orc2) : boolean
+>isD1(c1Orc2) : x is D1
 >isD1 : (x: any) => x is D1
 >c1Orc2 : C1 | C2
 >c1Orc2.p3 : number
@@ -147,7 +147,7 @@ num = isC2(c2Ord1) && c2Ord1.p2; // C2
 >num = isC2(c2Ord1) && c2Ord1.p2 : number
 >num : number
 >isC2(c2Ord1) && c2Ord1.p2 : number
->isC2(c2Ord1) : boolean
+>isC2(c2Ord1) : x is C2
 >isC2 : (x: any) => x is C2
 >c2Ord1 : C2 | D1
 >c2Ord1.p2 : number
@@ -158,7 +158,7 @@ num = isD1(c2Ord1) && c2Ord1.p3; // D1
 >num = isD1(c2Ord1) && c2Ord1.p3 : number
 >num : number
 >isD1(c2Ord1) && c2Ord1.p3 : number
->isD1(c2Ord1) : boolean
+>isD1(c2Ord1) : x is D1
 >isD1 : (x: any) => x is D1
 >c2Ord1 : C2 | D1
 >c2Ord1.p3 : number
@@ -169,7 +169,7 @@ str = isD1(c2Ord1) && c2Ord1.p1; // D1
 >str = isD1(c2Ord1) && c2Ord1.p1 : string
 >str : string
 >isD1(c2Ord1) && c2Ord1.p1 : string
->isD1(c2Ord1) : boolean
+>isD1(c2Ord1) : x is D1
 >isD1 : (x: any) => x is D1
 >c2Ord1 : C2 | D1
 >c2Ord1.p1 : string
@@ -181,7 +181,7 @@ var r2: C2 | D1 = isC1(c2Ord1) && c2Ord1; // C2 | D1
 >C2 : C2
 >D1 : D1
 >isC1(c2Ord1) && c2Ord1 : D1
->isC1(c2Ord1) : boolean
+>isC1(c2Ord1) : x is C1
 >isC1 : (x: any) => x is C1
 >c2Ord1 : C2 | D1
 >c2Ord1 : D1

tests/baselines/reference/typeGuardOfFormThisMember.js

@@ -2,6 +2,7 @@
 // There's a 'File' class in the stdlib, wrap with a namespace to avoid collision
 namespace Test {
 	export class FileSystemObject {
+		isFSO: this is FileSystemObject;
 		get isFile(): this is File {
 			return this instanceof File;
 		}
@@ -27,8 +28,8 @@ namespace Test {
 
 	let file: FileSystemObject = new File("foo/bar.txt", "foo");
 	file.isNetworked = false;
-	file.isNetworked = file.isDirectory;
-	file.isFile = file.isNetworked;
+	file.isFSO = file.isFile;
+	file.isFile = true;
 	let x = file.isFile;
 	if (file.isFile) {
 		file.content;
@@ -133,8 +134,8 @@ var Test;
     Test.Directory = Directory;
     var file = new File("foo/bar.txt", "foo");
     file.isNetworked = false;
-    file.isNetworked = file.isDirectory;
-    file.isFile = file.isNetworked;
+    file.isFSO = file.isFile;
+    file.isFile = true;
     var x = file.isFile;
     if (file.isFile) {
         file.content;
@@ -167,6 +168,7 @@ var Test;
 declare namespace Test {
     class FileSystemObject {
         path: string;
+        isFSO: this is FileSystemObject;
         isFile: this is File;
         isDirectory: this is Directory;
         isNetworked: this is (Networked & this);

tests/baselines/reference/typeGuardOfFormThisMember.symbols

@@ -6,234 +6,235 @@ namespace Test {
 	export class FileSystemObject {
 >FileSystemObject : Symbol(FileSystemObject, Decl(typeGuardOfFormThisMember.ts, 1, 16))
 
+		isFSO: this is FileSystemObject;
+>isFSO : Symbol(isFSO, Decl(typeGuardOfFormThisMember.ts, 2, 32))
+>FileSystemObject : Symbol(FileSystemObject, Decl(typeGuardOfFormThisMember.ts, 1, 16))
+
 		get isFile(): this is File {
->isFile : Symbol(isFile, Decl(typeGuardOfFormThisMember.ts, 2, 32), Decl(typeGuardOfFormThisMember.ts, 5, 3))
->File : Symbol(File, Decl(typeGuardOfFormThisMember.ts, 14, 2))
+>isFile : Symbol(isFile, Decl(typeGuardOfFormThisMember.ts, 3, 34), Decl(typeGuardOfFormThisMember.ts, 6, 3))
+>File : Symbol(File, Decl(typeGuardOfFormThisMember.ts, 15, 2))
 
 			return this instanceof File;
 >this : Symbol(FileSystemObject, Decl(typeGuardOfFormThisMember.ts, 1, 16))
->File : Symbol(File, Decl(typeGuardOfFormThisMember.ts, 14, 2))
+>File : Symbol(File, Decl(typeGuardOfFormThisMember.ts, 15, 2))
 		}
 		set isFile(param) {
->isFile : Symbol(isFile, Decl(typeGuardOfFormThisMember.ts, 2, 32), Decl(typeGuardOfFormThisMember.ts, 5, 3))
->param : Symbol(param, Decl(typeGuardOfFormThisMember.ts, 6, 13))
+>isFile : Symbol(isFile, Decl(typeGuardOfFormThisMember.ts, 3, 34), Decl(typeGuardOfFormThisMember.ts, 6, 3))
+>param : Symbol(param, Decl(typeGuardOfFormThisMember.ts, 7, 13))
 
 			// noop
 		}
 		get isDirectory(): this is Directory {
->isDirectory : Symbol(isDirectory, Decl(typeGuardOfFormThisMember.ts, 8, 3))
->Directory : Symbol(Directory, Decl(typeGuardOfFormThisMember.ts, 18, 2))
+>isDirectory : Symbol(isDirectory, Decl(typeGuardOfFormThisMember.ts, 9, 3))
+>Directory : Symbol(Directory, Decl(typeGuardOfFormThisMember.ts, 19, 2))
 
 			return this instanceof Directory;
 >this : Symbol(FileSystemObject, Decl(typeGuardOfFormThisMember.ts, 1, 16))
->Directory : Symbol(Directory, Decl(typeGuardOfFormThisMember.ts, 18, 2))
+>Directory : Symbol(Directory, Decl(typeGuardOfFormThisMember.ts, 19, 2))
 		}
 		isNetworked: this is (Networked & this);
->isNetworked : Symbol(isNetworked, Decl(typeGuardOfFormThisMember.ts, 11, 3))
->Networked : Symbol(Networked, Decl(typeGuardOfFormThisMember.ts, 21, 2))
+>isNetworked : Symbol(isNetworked, Decl(typeGuardOfFormThisMember.ts, 12, 3))
+>Networked : Symbol(Networked, Decl(typeGuardOfFormThisMember.ts, 22, 2))
 
 		constructor(public path: string) {}
->path : Symbol(path, Decl(typeGuardOfFormThisMember.ts, 13, 14))
+>path : Symbol(path, Decl(typeGuardOfFormThisMember.ts, 14, 14))
 	}
 
 	export class File extends FileSystemObject {
->File : Symbol(File, Decl(typeGuardOfFormThisMember.ts, 14, 2))
+>File : Symbol(File, Decl(typeGuardOfFormThisMember.ts, 15, 2))
 >FileSystemObject : Symbol(FileSystemObject, Decl(typeGuardOfFormThisMember.ts, 1, 16))
 
 		constructor(path: string, public content: string) { super(path); }
->path : Symbol(path, Decl(typeGuardOfFormThisMember.ts, 17, 14))
->content : Symbol(content, Decl(typeGuardOfFormThisMember.ts, 17, 27))
+>path : Symbol(path, Decl(typeGuardOfFormThisMember.ts, 18, 14))
+>content : Symbol(content, Decl(typeGuardOfFormThisMember.ts, 18, 27))
 >super : Symbol(FileSystemObject, Decl(typeGuardOfFormThisMember.ts, 1, 16))
->path : Symbol(path, Decl(typeGuardOfFormThisMember.ts, 17, 14))
+>path : Symbol(path, Decl(typeGuardOfFormThisMember.ts, 18, 14))
 	}
 	export class Directory extends FileSystemObject {
->Directory : Symbol(Directory, Decl(typeGuardOfFormThisMember.ts, 18, 2))
+>Directory : Symbol(Directory, Decl(typeGuardOfFormThisMember.ts, 19, 2))
 >FileSystemObject : Symbol(FileSystemObject, Decl(typeGuardOfFormThisMember.ts, 1, 16))
 
 		children: FileSystemObject[];
->children : Symbol(children, Decl(typeGuardOfFormThisMember.ts, 19, 50))
+>children : Symbol(children, Decl(typeGuardOfFormThisMember.ts, 20, 50))
 >FileSystemObject : Symbol(FileSystemObject, Decl(typeGuardOfFormThisMember.ts, 1, 16))
 	}
 	export interface Networked {
->Networked : Symbol(Networked, Decl(typeGuardOfFormThisMember.ts, 21, 2))
+>Networked : Symbol(Networked, Decl(typeGuardOfFormThisMember.ts, 22, 2))
 
 		host: string;
->host : Symbol(host, Decl(typeGuardOfFormThisMember.ts, 22, 29))
+>host : Symbol(host, Decl(typeGuardOfFormThisMember.ts, 23, 29))
 	}
 
 	let file: FileSystemObject = new File("foo/bar.txt", "foo");
->file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 26, 4))
+>file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 27, 4))
 >FileSystemObject : Symbol(FileSystemObject, Decl(typeGuardOfFormThisMember.ts, 1, 16))
->File : Symbol(File, Decl(typeGuardOfFormThisMember.ts, 14, 2))
+>File : Symbol(File, Decl(typeGuardOfFormThisMember.ts, 15, 2))
 
 	file.isNetworked = false;
->file.isNetworked : Symbol(FileSystemObject.isNetworked, Decl(typeGuardOfFormThisMember.ts, 11, 3))
->file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 26, 4))
->isNetworked : Symbol(FileSystemObject.isNetworked, Decl(typeGuardOfFormThisMember.ts, 11, 3))
+>file.isNetworked : Symbol(FileSystemObject.isNetworked, Decl(typeGuardOfFormThisMember.ts, 12, 3))
+>file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 27, 4))
+>isNetworked : Symbol(FileSystemObject.isNetworked, Decl(typeGuardOfFormThisMember.ts, 12, 3))
 
-	file.isNetworked = file.isDirectory;
->file.isNetworked : Symbol(FileSystemObject.isNetworked, Decl(typeGuardOfFormThisMember.ts, 11, 3))
->file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 26, 4))
->isNetworked : Symbol(FileSystemObject.isNetworked, Decl(typeGuardOfFormThisMember.ts, 11, 3))
->file.isDirectory : Symbol(FileSystemObject.isDirectory, Decl(typeGuardOfFormThisMember.ts, 8, 3))
->file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 26, 4))
->isDirectory : Symbol(FileSystemObject.isDirectory, Decl(typeGuardOfFormThisMember.ts, 8, 3))
+	file.isFSO = file.isFile;
+>file.isFSO : Symbol(FileSystemObject.isFSO, Decl(typeGuardOfFormThisMember.ts, 2, 32))
+>file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 27, 4))
+>isFSO : Symbol(FileSystemObject.isFSO, Decl(typeGuardOfFormThisMember.ts, 2, 32))
+>file.isFile : Symbol(FileSystemObject.isFile, Decl(typeGuardOfFormThisMember.ts, 3, 34), Decl(typeGuardOfFormThisMember.ts, 6, 3))
+>file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 27, 4))
+>isFile : Symbol(FileSystemObject.isFile, Decl(typeGuardOfFormThisMember.ts, 3, 34), Decl(typeGuardOfFormThisMember.ts, 6, 3))
 
-	file.isFile = file.isNetworked;
->file.isFile : Symbol(FileSystemObject.isFile, Decl(typeGuardOfFormThisMember.ts, 2, 32), Decl(typeGuardOfFormThisMember.ts, 5, 3))
->file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 26, 4))
->isFile : Symbol(FileSystemObject.isFile, Decl(typeGuardOfFormThisMember.ts, 2, 32), Decl(typeGuardOfFormThisMember.ts, 5, 3))
->file.isNetworked : Symbol(FileSystemObject.isNetworked, Decl(typeGuardOfFormThisMember.ts, 11, 3))
->file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 26, 4))
->isNetworked : Symbol(FileSystemObject.isNetworked, Decl(typeGuardOfFormThisMember.ts, 11, 3))
+	file.isFile = true;
+>file.isFile : Symbol(FileSystemObject.isFile, Decl(typeGuardOfFormThisMember.ts, 3, 34), Decl(typeGuardOfFormThisMember.ts, 6, 3))
+>file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 27, 4))
+>isFile : Symbol(FileSystemObject.isFile, Decl(typeGuardOfFormThisMember.ts, 3, 34), Decl(typeGuardOfFormThisMember.ts, 6, 3))
 
 	let x = file.isFile;
->x : Symbol(x, Decl(typeGuardOfFormThisMember.ts, 30, 4))
->file.isFile : Symbol(FileSystemObject.isFile, Decl(typeGuardOfFormThisMember.ts, 2, 32), Decl(typeGuardOfFormThisMember.ts, 5, 3))
->file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 26, 4))
->isFile : Symbol(FileSystemObject.isFile, Decl(typeGuardOfFormThisMember.ts, 2, 32), Decl(typeGuardOfFormThisMember.ts, 5, 3))
+>x : Symbol(x, Decl(typeGuardOfFormThisMember.ts, 31, 4))
+>file.isFile : Symbol(FileSystemObject.isFile, Decl(typeGuardOfFormThisMember.ts, 3, 34), Decl(typeGuardOfFormThisMember.ts, 6, 3))
+>file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 27, 4))
+>isFile : Symbol(FileSystemObject.isFile, Decl(typeGuardOfFormThisMember.ts, 3, 34), Decl(typeGuardOfFormThisMember.ts, 6, 3))
 
 	if (file.isFile) {
->file.isFile : Symbol(FileSystemObject.isFile, Decl(typeGuardOfFormThisMember.ts, 2, 32), Decl(typeGuardOfFormThisMember.ts, 5, 3))
->file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 26, 4))
->isFile : Symbol(FileSystemObject.isFile, Decl(typeGuardOfFormThisMember.ts, 2, 32), Decl(typeGuardOfFormThisMember.ts, 5, 3))
+>file.isFile : Symbol(FileSystemObject.isFile, Decl(typeGuardOfFormThisMember.ts, 3, 34), Decl(typeGuardOfFormThisMember.ts, 6, 3))
+>file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 27, 4))
+>isFile : Symbol(FileSystemObject.isFile, Decl(typeGuardOfFormThisMember.ts, 3, 34), Decl(typeGuardOfFormThisMember.ts, 6, 3))
 
 		file.content;
->file.content : Symbol(File.content, Decl(typeGuardOfFormThisMember.ts, 17, 27))
->file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 26, 4))
->content : Symbol(File.content, Decl(typeGuardOfFormThisMember.ts, 17, 27))
+>file.content : Symbol(File.content, Decl(typeGuardOfFormThisMember.ts, 18, 27))
+>file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 27, 4))
+>content : Symbol(File.content, Decl(typeGuardOfFormThisMember.ts, 18, 27))
 
 		if (file.isNetworked) {
->file.isNetworked : Symbol(FileSystemObject.isNetworked, Decl(typeGuardOfFormThisMember.ts, 11, 3))
->file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 26, 4))
->isNetworked : Symbol(FileSystemObject.isNetworked, Decl(typeGuardOfFormThisMember.ts, 11, 3))
+>file.isNetworked : Symbol(FileSystemObject.isNetworked, Decl(typeGuardOfFormThisMember.ts, 12, 3))
+>file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 27, 4))
+>isNetworked : Symbol(FileSystemObject.isNetworked, Decl(typeGuardOfFormThisMember.ts, 12, 3))
 
 			file.host;
->file.host : Symbol(Networked.host, Decl(typeGuardOfFormThisMember.ts, 22, 29))
->file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 26, 4))
->host : Symbol(Networked.host, Decl(typeGuardOfFormThisMember.ts, 22, 29))
+>file.host : Symbol(Networked.host, Decl(typeGuardOfFormThisMember.ts, 23, 29))
+>file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 27, 4))
+>host : Symbol(Networked.host, Decl(typeGuardOfFormThisMember.ts, 23, 29))
 
 			file.content;
->file.content : Symbol(File.content, Decl(typeGuardOfFormThisMember.ts, 17, 27))
->file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 26, 4))
->content : Symbol(File.content, Decl(typeGuardOfFormThisMember.ts, 17, 27))
+>file.content : Symbol(File.content, Decl(typeGuardOfFormThisMember.ts, 18, 27))
+>file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 27, 4))
+>content : Symbol(File.content, Decl(typeGuardOfFormThisMember.ts, 18, 27))
 		}
 	}
 	else if (file.isDirectory) {
->file.isDirectory : Symbol(FileSystemObject.isDirectory, Decl(typeGuardOfFormThisMember.ts, 8, 3))
->file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 26, 4))
->isDirectory : Symbol(FileSystemObject.isDirectory, Decl(typeGuardOfFormThisMember.ts, 8, 3))
+>file.isDirectory : Symbol(FileSystemObject.isDirectory, Decl(typeGuardOfFormThisMember.ts, 9, 3))
+>file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 27, 4))
+>isDirectory : Symbol(FileSystemObject.isDirectory, Decl(typeGuardOfFormThisMember.ts, 9, 3))
 
 		file.children;
->file.children : Symbol(Directory.children, Decl(typeGuardOfFormThisMember.ts, 19, 50))
->file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 26, 4))
->children : Symbol(Directory.children, Decl(typeGuardOfFormThisMember.ts, 19, 50))
+>file.children : Symbol(Directory.children, Decl(typeGuardOfFormThisMember.ts, 20, 50))
+>file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 27, 4))
+>children : Symbol(Directory.children, Decl(typeGuardOfFormThisMember.ts, 20, 50))
 	}
 	else if (file.isNetworked) {
->file.isNetworked : Symbol(FileSystemObject.isNetworked, Decl(typeGuardOfFormThisMember.ts, 11, 3))
->file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 26, 4))
->isNetworked : Symbol(FileSystemObject.isNetworked, Decl(typeGuardOfFormThisMember.ts, 11, 3))
+>file.isNetworked : Symbol(FileSystemObject.isNetworked, Decl(typeGuardOfFormThisMember.ts, 12, 3))
+>file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 27, 4))
+>isNetworked : Symbol(FileSystemObject.isNetworked, Decl(typeGuardOfFormThisMember.ts, 12, 3))
 
 		file.host;
->file.host : Symbol(Networked.host, Decl(typeGuardOfFormThisMember.ts, 22, 29))
->file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 26, 4))
->host : Symbol(Networked.host, Decl(typeGuardOfFormThisMember.ts, 22, 29))
+>file.host : Symbol(Networked.host, Decl(typeGuardOfFormThisMember.ts, 23, 29))
+>file : Symbol(file, Decl(typeGuardOfFormThisMember.ts, 27, 4))
+>host : Symbol(Networked.host, Decl(typeGuardOfFormThisMember.ts, 23, 29))
 	}
 	
 	interface GenericLeadGuard<T> extends GenericGuard<T> {
->GenericLeadGuard : Symbol(GenericLeadGuard, Decl(typeGuardOfFormThisMember.ts, 43, 2))
->T : Symbol(T, Decl(typeGuardOfFormThisMember.ts, 45, 28))
->GenericGuard : Symbol(GenericGuard, Decl(typeGuardOfFormThisMember.ts, 51, 2))
->T : Symbol(T, Decl(typeGuardOfFormThisMember.ts, 45, 28))
+>GenericLeadGuard : Symbol(GenericLeadGuard, Decl(typeGuardOfFormThisMember.ts, 44, 2))
+>T : Symbol(T, Decl(typeGuardOfFormThisMember.ts, 46, 28))
+>GenericGuard : Symbol(GenericGuard, Decl(typeGuardOfFormThisMember.ts, 52, 2))
+>T : Symbol(T, Decl(typeGuardOfFormThisMember.ts, 46, 28))
 
 		lead(): void;
->lead : Symbol(lead, Decl(typeGuardOfFormThisMember.ts, 45, 56))
+>lead : Symbol(lead, Decl(typeGuardOfFormThisMember.ts, 46, 56))
 	}
 	
 	interface GenericFollowerGuard<T> extends GenericGuard<T> {
->GenericFollowerGuard : Symbol(GenericFollowerGuard, Decl(typeGuardOfFormThisMember.ts, 47, 2))
->T : Symbol(T, Decl(typeGuardOfFormThisMember.ts, 49, 32))
->GenericGuard : Symbol(GenericGuard, Decl(typeGuardOfFormThisMember.ts, 51, 2))
->T : Symbol(T, Decl(typeGuardOfFormThisMember.ts, 49, 32))
+>GenericFollowerGuard : Symbol(GenericFollowerGuard, Decl(typeGuardOfFormThisMember.ts, 48, 2))
+>T : Symbol(T, Decl(typeGuardOfFormThisMember.ts, 50, 32))
+>GenericGuard : Symbol(GenericGuard, Decl(typeGuardOfFormThisMember.ts, 52, 2))
+>T : Symbol(T, Decl(typeGuardOfFormThisMember.ts, 50, 32))
 
 		follow(): void;
->follow : Symbol(follow, Decl(typeGuardOfFormThisMember.ts, 49, 60))
+>follow : Symbol(follow, Decl(typeGuardOfFormThisMember.ts, 50, 60))
 	}
 	
 	interface GenericGuard<T> {
->GenericGuard : Symbol(GenericGuard, Decl(typeGuardOfFormThisMember.ts, 51, 2))
->T : Symbol(T, Decl(typeGuardOfFormThisMember.ts, 53, 24))
+>GenericGuard : Symbol(GenericGuard, Decl(typeGuardOfFormThisMember.ts, 52, 2))
+>T : Symbol(T, Decl(typeGuardOfFormThisMember.ts, 54, 24))
 
 		target: T;
->target : Symbol(target, Decl(typeGuardOfFormThisMember.ts, 53, 28))
->T : Symbol(T, Decl(typeGuardOfFormThisMember.ts, 53, 24))
+>target : Symbol(target, Decl(typeGuardOfFormThisMember.ts, 54, 28))
+>T : Symbol(T, Decl(typeGuardOfFormThisMember.ts, 54, 24))
 
 		isLeader: this is (GenericLeadGuard<T>);
->isLeader : Symbol(isLeader, Decl(typeGuardOfFormThisMember.ts, 54, 12))
->GenericLeadGuard : Symbol(GenericLeadGuard, Decl(typeGuardOfFormThisMember.ts, 43, 2))
->T : Symbol(T, Decl(typeGuardOfFormThisMember.ts, 53, 24))
+>isLeader : Symbol(isLeader, Decl(typeGuardOfFormThisMember.ts, 55, 12))
+>GenericLeadGuard : Symbol(GenericLeadGuard, Decl(typeGuardOfFormThisMember.ts, 44, 2))
+>T : Symbol(T, Decl(typeGuardOfFormThisMember.ts, 54, 24))
 
 		isFollower: this is GenericFollowerGuard<T>;
->isFollower : Symbol(isFollower, Decl(typeGuardOfFormThisMember.ts, 55, 42))
->GenericFollowerGuard : Symbol(GenericFollowerGuard, Decl(typeGuardOfFormThisMember.ts, 47, 2))
->T : Symbol(T, Decl(typeGuardOfFormThisMember.ts, 53, 24))
+>isFollower : Symbol(isFollower, Decl(typeGuardOfFormThisMember.ts, 56, 42))
+>GenericFollowerGuard : Symbol(GenericFollowerGuard, Decl(typeGuardOfFormThisMember.ts, 48, 2))
+>T : Symbol(T, Decl(typeGuardOfFormThisMember.ts, 54, 24))
 	}
 
 	let guard: GenericGuard<File>;
->guard : Symbol(guard, Decl(typeGuardOfFormThisMember.ts, 59, 4))
->GenericGuard : Symbol(GenericGuard, Decl(typeGuardOfFormThisMember.ts, 51, 2))
->File : Symbol(File, Decl(typeGuardOfFormThisMember.ts, 14, 2))
+>guard : Symbol(guard, Decl(typeGuardOfFormThisMember.ts, 60, 4))
+>GenericGuard : Symbol(GenericGuard, Decl(typeGuardOfFormThisMember.ts, 52, 2))
+>File : Symbol(File, Decl(typeGuardOfFormThisMember.ts, 15, 2))
 
 	if (guard.isLeader) {
->guard.isLeader : Symbol(GenericGuard.isLeader, Decl(typeGuardOfFormThisMember.ts, 54, 12))
->guard : Symbol(guard, Decl(typeGuardOfFormThisMember.ts, 59, 4))
->isLeader : Symbol(GenericGuard.isLeader, Decl(typeGuardOfFormThisMember.ts, 54, 12))
+>guard.isLeader : Symbol(GenericGuard.isLeader, Decl(typeGuardOfFormThisMember.ts, 55, 12))
+>guard : Symbol(guard, Decl(typeGuardOfFormThisMember.ts, 60, 4))
+>isLeader : Symbol(GenericGuard.isLeader, Decl(typeGuardOfFormThisMember.ts, 55, 12))
 
 		guard.lead();
->guard.lead : Symbol(GenericLeadGuard.lead, Decl(typeGuardOfFormThisMember.ts, 45, 56))
->guard : Symbol(guard, Decl(typeGuardOfFormThisMember.ts, 59, 4))
->lead : Symbol(GenericLeadGuard.lead, Decl(typeGuardOfFormThisMember.ts, 45, 56))
+>guard.lead : Symbol(GenericLeadGuard.lead, Decl(typeGuardOfFormThisMember.ts, 46, 56))
+>guard : Symbol(guard, Decl(typeGuardOfFormThisMember.ts, 60, 4))
+>lead : Symbol(GenericLeadGuard.lead, Decl(typeGuardOfFormThisMember.ts, 46, 56))
 	}
 	else if (guard.isFollower) {
->guard.isFollower : Symbol(GenericGuard.isFollower, Decl(typeGuardOfFormThisMember.ts, 55, 42))
->guard : Symbol(guard, Decl(typeGuardOfFormThisMember.ts, 59, 4))
->isFollower : Symbol(GenericGuard.isFollower, Decl(typeGuardOfFormThisMember.ts, 55, 42))
+>guard.isFollower : Symbol(GenericGuard.isFollower, Decl(typeGuardOfFormThisMember.ts, 56, 42))
+>guard : Symbol(guard, Decl(typeGuardOfFormThisMember.ts, 60, 4))
+>isFollower : Symbol(GenericGuard.isFollower, Decl(typeGuardOfFormThisMember.ts, 56, 42))
 
 		guard.follow();
->guard.follow : Symbol(GenericFollowerGuard.follow, Decl(typeGuardOfFormThisMember.ts, 49, 60))
->guard : Symbol(guard, Decl(typeGuardOfFormThisMember.ts, 59, 4))
->follow : Symbol(GenericFollowerGuard.follow, Decl(typeGuardOfFormThisMember.ts, 49, 60))
+>guard.follow : Symbol(GenericFollowerGuard.follow, Decl(typeGuardOfFormThisMember.ts, 50, 60))
+>guard : Symbol(guard, Decl(typeGuardOfFormThisMember.ts, 60, 4))
+>follow : Symbol(GenericFollowerGuard.follow, Decl(typeGuardOfFormThisMember.ts, 50, 60))
 	}
 
 	interface SpecificGuard {
->SpecificGuard : Symbol(SpecificGuard, Decl(typeGuardOfFormThisMember.ts, 65, 2))
+>SpecificGuard : Symbol(SpecificGuard, Decl(typeGuardOfFormThisMember.ts, 66, 2))
 
 		isMoreSpecific: this is MoreSpecificGuard;
->isMoreSpecific : Symbol(isMoreSpecific, Decl(typeGuardOfFormThisMember.ts, 67, 26))
->MoreSpecificGuard : Symbol(MoreSpecificGuard, Decl(typeGuardOfFormThisMember.ts, 69, 2))
+>isMoreSpecific : Symbol(isMoreSpecific, Decl(typeGuardOfFormThisMember.ts, 68, 26))
+>MoreSpecificGuard : Symbol(MoreSpecificGuard, Decl(typeGuardOfFormThisMember.ts, 70, 2))
 	}
 
 	interface MoreSpecificGuard extends SpecificGuard {
->MoreSpecificGuard : Symbol(MoreSpecificGuard, Decl(typeGuardOfFormThisMember.ts, 69, 2))
->SpecificGuard : Symbol(SpecificGuard, Decl(typeGuardOfFormThisMember.ts, 65, 2))
+>MoreSpecificGuard : Symbol(MoreSpecificGuard, Decl(typeGuardOfFormThisMember.ts, 70, 2))
+>SpecificGuard : Symbol(SpecificGuard, Decl(typeGuardOfFormThisMember.ts, 66, 2))
 
 		do(): void;
->do : Symbol(do, Decl(typeGuardOfFormThisMember.ts, 71, 52))
+>do : Symbol(do, Decl(typeGuardOfFormThisMember.ts, 72, 52))
 	}
 
 	let general: SpecificGuard;
->general : Symbol(general, Decl(typeGuardOfFormThisMember.ts, 75, 4))
->SpecificGuard : Symbol(SpecificGuard, Decl(typeGuardOfFormThisMember.ts, 65, 2))
+>general : Symbol(general, Decl(typeGuardOfFormThisMember.ts, 76, 4))
+>SpecificGuard : Symbol(SpecificGuard, Decl(typeGuardOfFormThisMember.ts, 66, 2))
 
 	if (general.isMoreSpecific) {
->general.isMoreSpecific : Symbol(SpecificGuard.isMoreSpecific, Decl(typeGuardOfFormThisMember.ts, 67, 26))
->general : Symbol(general, Decl(typeGuardOfFormThisMember.ts, 75, 4))
->isMoreSpecific : Symbol(SpecificGuard.isMoreSpecific, Decl(typeGuardOfFormThisMember.ts, 67, 26))
+>general.isMoreSpecific : Symbol(SpecificGuard.isMoreSpecific, Decl(typeGuardOfFormThisMember.ts, 68, 26))
+>general : Symbol(general, Decl(typeGuardOfFormThisMember.ts, 76, 4))
+>isMoreSpecific : Symbol(SpecificGuard.isMoreSpecific, Decl(typeGuardOfFormThisMember.ts, 68, 26))
 
 		general.do();
->general.do : Symbol(MoreSpecificGuard.do, Decl(typeGuardOfFormThisMember.ts, 71, 52))
->general : Symbol(general, Decl(typeGuardOfFormThisMember.ts, 75, 4))
->do : Symbol(MoreSpecificGuard.do, Decl(typeGuardOfFormThisMember.ts, 71, 52))
+>general.do : Symbol(MoreSpecificGuard.do, Decl(typeGuardOfFormThisMember.ts, 72, 52))
+>general : Symbol(general, Decl(typeGuardOfFormThisMember.ts, 76, 4))
+>do : Symbol(MoreSpecificGuard.do, Decl(typeGuardOfFormThisMember.ts, 72, 52))
 	}
 }
 

tests/baselines/reference/typeGuardOfFormThisMember.types

@@ -6,6 +6,10 @@ namespace Test {
 	export class FileSystemObject {
 >FileSystemObject : FileSystemObject
 
+		isFSO: this is FileSystemObject;
+>isFSO : this is FileSystemObject
+>FileSystemObject : FileSystemObject
+
 		get isFile(): this is File {
 >isFile : this is File
 >File : File
@@ -79,23 +83,21 @@ namespace Test {
 >isNetworked : this is Networked & FileSystemObject
 >false : boolean
 
-	file.isNetworked = file.isDirectory;
->file.isNetworked = file.isDirectory : this is Directory
->file.isNetworked : this is Networked & FileSystemObject
+	file.isFSO = file.isFile;
+>file.isFSO = file.isFile : this is File
+>file.isFSO : this is FileSystemObject
 >file : FileSystemObject
->isNetworked : this is Networked & FileSystemObject
->file.isDirectory : this is Directory
->file : FileSystemObject
->isDirectory : this is Directory
-
-	file.isFile = file.isNetworked;
->file.isFile = file.isNetworked : this is Networked & FileSystemObject
+>isFSO : this is FileSystemObject
 >file.isFile : this is File
 >file : FileSystemObject
 >isFile : this is File
->file.isNetworked : this is Networked & FileSystemObject
+
+	file.isFile = true;
+>file.isFile = true : boolean
+>file.isFile : this is File
 >file : FileSystemObject
->isNetworked : this is Networked & FileSystemObject
+>isFile : this is File
+>true : boolean
 
 	let x = file.isFile;
 >x : boolean

tests/baselines/reference/typeGuardOfFormThisMemberErrors.errors.txt

@@ -0,0 +1,51 @@
+tests/cases/conformance/expressions/typeGuards/typeGuardOfFormThisMemberErrors.ts(29,2): error TS1226: Type predicate 'this is File' is not assignable to 'this is Networked & FileSystemObject'.
+  Type 'File' is not assignable to type 'Networked & FileSystemObject'.
+    Type 'File' is not assignable to type 'Networked'.
+      Property 'host' is missing in type 'File'.
+tests/cases/conformance/expressions/typeGuards/typeGuardOfFormThisMemberErrors.ts(31,2): error TS1226: Type predicate 'this is FileSystemObject' is not assignable to 'this is File'.
+  Type 'FileSystemObject' is not assignable to type 'File'.
+    Property 'content' is missing in type 'FileSystemObject'.
+
+
+==== tests/cases/conformance/expressions/typeGuards/typeGuardOfFormThisMemberErrors.ts (2 errors) ====
+    // There's a 'File' class in the stdlib, wrap with a namespace to avoid collision
+    namespace Test {
+    	export class FileSystemObject {
+    		isFSO: this is FileSystemObject;
+    		get isFile(): this is File {
+    			return this instanceof File;
+    		}
+    		set isFile(param) {
+    			// noop
+    		}
+    		get isDirectory(): this is Directory {
+    			return this instanceof Directory;
+    		}
+    		isNetworked: this is (Networked & this);
+    		constructor(public path: string) {}
+    	}
+    
+    	export class File extends FileSystemObject {
+    		constructor(path: string, public content: string) { super(path); }
+    	}
+    	export class Directory extends FileSystemObject {
+    		children: FileSystemObject[];
+    	}
+    	export interface Networked {
+    		host: string;
+    	}
+    
+    	let file: FileSystemObject = new File("foo/bar.txt", "foo");
+    	file.isNetworked = file.isFile;
+    	~~~~~~~~~~~~~~~~
+!!! error TS1226: Type predicate 'this is File' is not assignable to 'this is Networked & FileSystemObject'.
+!!! error TS1226:   Type 'File' is not assignable to type 'Networked & FileSystemObject'.
+!!! error TS1226:     Type 'File' is not assignable to type 'Networked'.
+!!! error TS1226:       Property 'host' is missing in type 'File'.
+    	file.isFSO = file.isNetworked;
+    	file.isFile = file.isFSO;
+    	~~~~~~~~~~~
+!!! error TS1226: Type predicate 'this is FileSystemObject' is not assignable to 'this is File'.
+!!! error TS1226:   Type 'FileSystemObject' is not assignable to type 'File'.
+!!! error TS1226:     Property 'content' is missing in type 'FileSystemObject'.
+    }

tests/baselines/reference/typeGuardOfFormThisMemberErrors.js

@@ -0,0 +1,112 @@
+//// [typeGuardOfFormThisMemberErrors.ts]
+// There's a 'File' class in the stdlib, wrap with a namespace to avoid collision
+namespace Test {
+	export class FileSystemObject {
+		isFSO: this is FileSystemObject;
+		get isFile(): this is File {
+			return this instanceof File;
+		}
+		set isFile(param) {
+			// noop
+		}
+		get isDirectory(): this is Directory {
+			return this instanceof Directory;
+		}
+		isNetworked: this is (Networked & this);
+		constructor(public path: string) {}
+	}
+
+	export class File extends FileSystemObject {
+		constructor(path: string, public content: string) { super(path); }
+	}
+	export class Directory extends FileSystemObject {
+		children: FileSystemObject[];
+	}
+	export interface Networked {
+		host: string;
+	}
+
+	let file: FileSystemObject = new File("foo/bar.txt", "foo");
+	file.isNetworked = file.isFile;
+	file.isFSO = file.isNetworked;
+	file.isFile = file.isFSO;
+}
+
+//// [typeGuardOfFormThisMemberErrors.js]
+var __extends = (this && this.__extends) || function (d, b) {
+    for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p];
+    function __() { this.constructor = d; }
+    d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
+};
+// There's a 'File' class in the stdlib, wrap with a namespace to avoid collision
+var Test;
+(function (Test) {
+    var FileSystemObject = (function () {
+        function FileSystemObject(path) {
+            this.path = path;
+        }
+        Object.defineProperty(FileSystemObject.prototype, "isFile", {
+            get: function () {
+                return this instanceof File;
+            },
+            set: function (param) {
+                // noop
+            },
+            enumerable: true,
+            configurable: true
+        });
+        Object.defineProperty(FileSystemObject.prototype, "isDirectory", {
+            get: function () {
+                return this instanceof Directory;
+            },
+            enumerable: true,
+            configurable: true
+        });
+        return FileSystemObject;
+    })();
+    Test.FileSystemObject = FileSystemObject;
+    var File = (function (_super) {
+        __extends(File, _super);
+        function File(path, content) {
+            _super.call(this, path);
+            this.content = content;
+        }
+        return File;
+    })(FileSystemObject);
+    Test.File = File;
+    var Directory = (function (_super) {
+        __extends(Directory, _super);
+        function Directory() {
+            _super.apply(this, arguments);
+        }
+        return Directory;
+    })(FileSystemObject);
+    Test.Directory = Directory;
+    var file = new File("foo/bar.txt", "foo");
+    file.isNetworked = file.isFile;
+    file.isFSO = file.isNetworked;
+    file.isFile = file.isFSO;
+})(Test || (Test = {}));
+
+
+//// [typeGuardOfFormThisMemberErrors.d.ts]
+declare namespace Test {
+    class FileSystemObject {
+        path: string;
+        isFSO: this is FileSystemObject;
+        isFile: this is File;
+        isDirectory: this is Directory;
+        isNetworked: this is (Networked & this);
+        constructor(path: string);
+    }
+    class File extends FileSystemObject {
+        content: string;
+        constructor(path: string, content: string);
+    }
+    class Directory extends FileSystemObject {
+        children: FileSystemObject[];
+    }
+    interface Networked {
+        host: string;
+    }
+}

tests/baselines/reference/unionAndIntersectionInference1.types

@@ -110,7 +110,7 @@ function foo1<a>(value: void|a): void {
 >a : a
 
     if (isVoid(value)) {
->isVoid(value) : boolean
+>isVoid(value) : value is void
 >isVoid : <a>(value: void | a) => value is void
 >value : void | a
 
@@ -130,7 +130,7 @@ function baz1<a>(value: void|a): void {
 >a : a
 
       if (isNonVoid(value)) {
->isNonVoid(value) : boolean
+>isNonVoid(value) : value is {}
 >isNonVoid : <a>(value: void | a) => value is a
 >value : void | a
 

tests/cases/conformance/expressions/typeGuards/typeGuardOfFormThisMember.ts

@@ -3,6 +3,7 @@
 // There's a 'File' class in the stdlib, wrap with a namespace to avoid collision
 namespace Test {
 	export class FileSystemObject {
+		isFSO: this is FileSystemObject;
 		get isFile(): this is File {
 			return this instanceof File;
 		}
@@ -28,8 +29,8 @@ namespace Test {
 
 	let file: FileSystemObject = new File("foo/bar.txt", "foo");
 	file.isNetworked = false;
-	file.isNetworked = file.isDirectory;
-	file.isFile = file.isNetworked;
+	file.isFSO = file.isFile;
+	file.isFile = true;
 	let x = file.isFile;
 	if (file.isFile) {
 		file.content;

tests/cases/conformance/expressions/typeGuards/typeGuardOfFormThisMemberErrors.ts

@@ -0,0 +1,34 @@
+// @target: es5
+// @declaration: true
+// There's a 'File' class in the stdlib, wrap with a namespace to avoid collision
+namespace Test {
+	export class FileSystemObject {
+		isFSO: this is FileSystemObject;
+		get isFile(): this is File {
+			return this instanceof File;
+		}
+		set isFile(param) {
+			// noop
+		}
+		get isDirectory(): this is Directory {
+			return this instanceof Directory;
+		}
+		isNetworked: this is (Networked & this);
+		constructor(public path: string) {}
+	}
+
+	export class File extends FileSystemObject {
+		constructor(path: string, public content: string) { super(path); }
+	}
+	export class Directory extends FileSystemObject {
+		children: FileSystemObject[];
+	}
+	export interface Networked {
+		host: string;
+	}
+
+	let file: FileSystemObject = new File("foo/bar.txt", "foo");
+	file.isNetworked = file.isFile;
+	file.isFSO = file.isNetworked;
+	file.isFile = file.isFSO;
+}