Merge branch 'master' into emitHelper

src/compiler/binder.ts

@@ -1139,8 +1139,8 @@ namespace ts {
             }
             else if (node.kind === SyntaxKind.ArrayLiteralExpression) {
                 for (const e of (<ArrayLiteralExpression>node).elements) {
-                    if (e.kind === SyntaxKind.SpreadElementExpression) {
-                        bindAssignmentTargetFlow((<SpreadElementExpression>e).expression);
+                    if (e.kind === SyntaxKind.SpreadElement) {
+                        bindAssignmentTargetFlow((<SpreadElement>e).expression);
                     }
                     else {
                         bindDestructuringTargetFlow(e);
@@ -1155,6 +1155,9 @@ namespace ts {
                     else if (p.kind === SyntaxKind.ShorthandPropertyAssignment) {
                         bindAssignmentTargetFlow((<ShorthandPropertyAssignment>p).name);
                     }
+                    else if (p.kind === SyntaxKind.SpreadAssignment) {
+                        bindAssignmentTargetFlow((<SpreadAssignment>p).expression);
+                    }
                 }
             }
         }
@@ -1305,6 +1308,7 @@ namespace ts {
                 case SyntaxKind.JSDocFunctionType:
                 case SyntaxKind.ModuleDeclaration:
                 case SyntaxKind.TypeAliasDeclaration:
+                case SyntaxKind.MappedType:
                     return ContainerFlags.IsContainer | ContainerFlags.HasLocals;
 
                 case SyntaxKind.SourceFile:
@@ -1424,6 +1428,7 @@ namespace ts {
                 case SyntaxKind.ArrowFunction:
                 case SyntaxKind.JSDocFunctionType:
                 case SyntaxKind.TypeAliasDeclaration:
+                case SyntaxKind.MappedType:
                     // All the children of these container types are never visible through another
                     // symbol (i.e. through another symbol's 'exports' or 'members').  Instead,
                     // they're only accessed 'lexically' (i.e. from code that exists underneath
@@ -1550,7 +1555,7 @@ namespace ts {
                 const seen = createMap<ElementKind>();
 
                 for (const prop of node.properties) {
-                    if (prop.name.kind !== SyntaxKind.Identifier) {
+                    if (prop.kind === SyntaxKind.SpreadAssignment || prop.name.kind !== SyntaxKind.Identifier) {
                         continue;
                     }
 
@@ -1916,6 +1921,9 @@ 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:
@@ -1929,8 +1937,21 @@ namespace ts {
                 case SyntaxKind.EnumMember:
                     return bindPropertyOrMethodOrAccessor(<Declaration>node, SymbolFlags.EnumMember, SymbolFlags.EnumMemberExcludes);
 
+                case SyntaxKind.SpreadAssignment:
                 case SyntaxKind.JsxSpreadAttribute:
-                    emitFlags |= NodeFlags.HasJsxSpreadAttributes;
+                    let root = container;
+                    let hasRest = false;
+                    while (root.parent) {
+                        if (root.kind === SyntaxKind.ObjectLiteralExpression &&
+                            root.parent.kind === SyntaxKind.BinaryExpression &&
+                            (root.parent as BinaryExpression).operatorToken.kind === SyntaxKind.EqualsToken &&
+                            (root.parent as BinaryExpression).left === root) {
+                            hasRest = true;
+                            break;
+                        }
+                        root = root.parent;
+                    }
+                    emitFlags |= hasRest ? NodeFlags.HasRestAttribute : NodeFlags.HasSpreadAttribute;
                     return;
 
                 case SyntaxKind.CallSignature:
@@ -1958,9 +1979,10 @@ namespace ts {
                 case SyntaxKind.JSDocFunctionType:
                     return bindFunctionOrConstructorType(<SignatureDeclaration>node);
                 case SyntaxKind.TypeLiteral:
+                case SyntaxKind.MappedType:
                 case SyntaxKind.JSDocTypeLiteral:
                 case SyntaxKind.JSDocRecordType:
-                    return bindAnonymousDeclaration(<TypeLiteralNode>node, SymbolFlags.TypeLiteral, "__type");
+                    return bindAnonymousDeclaration(<Declaration>node, SymbolFlags.TypeLiteral, "__type");
                 case SyntaxKind.ObjectLiteralExpression:
                     return bindObjectLiteralExpression(<ObjectLiteralExpression>node);
                 case SyntaxKind.FunctionExpression:
@@ -2495,9 +2517,9 @@ namespace ts {
             transformFlags |= TransformFlags.AssertTypeScript;
         }
 
-        if (subtreeFlags & TransformFlags.ContainsSpreadElementExpression
+        if (subtreeFlags & TransformFlags.ContainsSpreadExpression
             || isSuperOrSuperProperty(expression, expressionKind)) {
-            // If the this node contains a SpreadElementExpression, or is a super call, then it is an ES6
+            // If the this node contains a SpreadExpression, or is a super call, then it is an ES6
             // node.
             transformFlags |= TransformFlags.AssertES2015;
         }
@@ -2526,7 +2548,7 @@ namespace ts {
         if (node.typeArguments) {
             transformFlags |= TransformFlags.AssertTypeScript;
         }
-        if (subtreeFlags & TransformFlags.ContainsSpreadElementExpression) {
+        if (subtreeFlags & TransformFlags.ContainsSpreadExpression) {
             // If the this node contains a SpreadElementExpression then it is an ES6
             // node.
             transformFlags |= TransformFlags.AssertES2015;
@@ -2541,10 +2563,13 @@ namespace ts {
         const operatorTokenKind = node.operatorToken.kind;
         const leftKind = node.left.kind;
 
-        if (operatorTokenKind === SyntaxKind.EqualsToken
-            && (leftKind === SyntaxKind.ObjectLiteralExpression
-                || leftKind === SyntaxKind.ArrayLiteralExpression)) {
-            // Destructuring assignments are ES6 syntax.
+        if (operatorTokenKind === SyntaxKind.EqualsToken && leftKind === SyntaxKind.ObjectLiteralExpression) {
+            // Destructuring object assignments with are ES2015 syntax
+            // and possibly ESNext if they contain rest
+            transformFlags |= TransformFlags.AssertESNext | TransformFlags.AssertES2015 | TransformFlags.AssertDestructuringAssignment;
+        }
+        else if (operatorTokenKind === SyntaxKind.EqualsToken && leftKind === SyntaxKind.ArrayLiteralExpression) {
+            // Destructuring assignments are ES2015 syntax.
             transformFlags |= TransformFlags.AssertES2015 | TransformFlags.AssertDestructuringAssignment;
         }
         else if (operatorTokenKind === SyntaxKind.AsteriskAsteriskToken
@@ -2578,6 +2603,11 @@ namespace ts {
             transformFlags |= TransformFlags.AssertTypeScript | TransformFlags.ContainsParameterPropertyAssignments;
         }
 
+        // parameters with object rest destructuring are ES Next syntax
+        if (subtreeFlags & TransformFlags.ContainsSpreadExpression) {
+            transformFlags |= TransformFlags.AssertESNext;
+        }
+
         // If a parameter has an initializer, a binding pattern or a dotDotDot token, then
         // it is ES6 syntax and its container must emit default value assignments or parameter destructuring downlevel.
         if (subtreeFlags & TransformFlags.ContainsBindingPattern || initializer || dotDotDotToken) {
@@ -2811,6 +2841,11 @@ namespace ts {
                 transformFlags |= TransformFlags.AssertES2017;
             }
 
+            // function declarations with object rest destructuring are ES Next syntax
+            if (subtreeFlags & TransformFlags.ContainsSpreadExpression) {
+                transformFlags |= TransformFlags.AssertESNext;
+            }
+
             // If a FunctionDeclaration's subtree has marked the container as needing to capture the
             // lexical this, or the function contains parameters with initializers, then this node is
             // ES6 syntax.
@@ -2848,6 +2883,12 @@ namespace ts {
             transformFlags |= TransformFlags.AssertES2017;
         }
 
+        // function expressions with object rest destructuring are ES Next syntax
+        if (subtreeFlags & TransformFlags.ContainsSpreadExpression) {
+            transformFlags |= TransformFlags.AssertESNext;
+        }
+
+
         // If a FunctionExpression's subtree has marked the container as needing to capture the
         // lexical this, or the function contains parameters with initializers, then this node is
         // ES6 syntax.
@@ -2885,6 +2926,11 @@ namespace ts {
             transformFlags |= TransformFlags.AssertES2017;
         }
 
+        // arrow functions with object rest destructuring are ES Next syntax
+        if (subtreeFlags & TransformFlags.ContainsSpreadExpression) {
+            transformFlags |= TransformFlags.AssertESNext;
+        }
+
         // If an ArrowFunction contains a lexical this, its container must capture the lexical this.
         if (subtreeFlags & TransformFlags.ContainsLexicalThis) {
             transformFlags |= TransformFlags.ContainsCapturedLexicalThis;
@@ -2913,8 +2959,13 @@ namespace ts {
         let transformFlags = subtreeFlags;
         const nameKind = node.name.kind;
 
-        // A VariableDeclaration with a binding pattern is ES6 syntax.
-        if (nameKind === SyntaxKind.ObjectBindingPattern || nameKind === SyntaxKind.ArrayBindingPattern) {
+        // A VariableDeclaration with an object binding pattern is ES2015 syntax
+        // and possibly ESNext syntax if it contains an object binding pattern
+        if (nameKind === SyntaxKind.ObjectBindingPattern) {
+            transformFlags |= TransformFlags.AssertESNext | TransformFlags.AssertES2015 | TransformFlags.ContainsBindingPattern;
+        }
+        // A VariableDeclaration with an object binding pattern is ES2015 syntax.
+        else if (nameKind === SyntaxKind.ArrayBindingPattern) {
             transformFlags |= TransformFlags.AssertES2015 | TransformFlags.ContainsBindingPattern;
         }
 
@@ -3055,6 +3106,10 @@ namespace ts {
                 transformFlags |= TransformFlags.AssertJsx;
                 break;
 
+            case SyntaxKind.ForOfStatement:
+                // for-of might be ESNext if it has a rest destructuring
+                transformFlags |= TransformFlags.AssertESNext;
+                // FALLTHROUGH
             case SyntaxKind.NoSubstitutionTemplateLiteral:
             case SyntaxKind.TemplateHead:
             case SyntaxKind.TemplateMiddle:
@@ -3062,7 +3117,6 @@ namespace ts {
             case SyntaxKind.TemplateExpression:
             case SyntaxKind.TaggedTemplateExpression:
             case SyntaxKind.ShorthandPropertyAssignment:
-            case SyntaxKind.ForOfStatement:
             case SyntaxKind.StaticKeyword:
                 // These nodes are ES6 syntax.
                 transformFlags |= TransformFlags.AssertES2015;
@@ -3102,6 +3156,7 @@ namespace ts {
             case SyntaxKind.ThisType:
             case SyntaxKind.TypeOperator:
             case SyntaxKind.IndexedAccessType:
+            case SyntaxKind.MappedType:
             case SyntaxKind.LiteralType:
                 // Types and signatures are TypeScript syntax, and exclude all other facts.
                 transformFlags = TransformFlags.AssertTypeScript;
@@ -3126,11 +3181,18 @@ namespace ts {
                 }
                 break;
 
-            case SyntaxKind.SpreadElementExpression:
-                // This node is ES6 syntax, but is handled by a containing node.
-                transformFlags |= TransformFlags.ContainsSpreadElementExpression;
+            case SyntaxKind.SpreadElement:
+            case SyntaxKind.SpreadAssignment:
+                // This node is ES6 or ES next syntax, but is handled by a containing node.
+                transformFlags |= TransformFlags.ContainsSpreadExpression;
                 break;
 
+            case SyntaxKind.BindingElement:
+                if ((node as BindingElement).dotDotDotToken) {
+                    // this node is ES2015 or ES next syntax, but is handled by a containing node.
+                    transformFlags |= TransformFlags.ContainsSpreadExpression;
+                }
+
             case SyntaxKind.SuperKeyword:
                 // This node is ES6 syntax.
                 transformFlags |= TransformFlags.AssertES2015;
@@ -3143,8 +3205,13 @@ namespace ts {
 
             case SyntaxKind.ObjectBindingPattern:
             case SyntaxKind.ArrayBindingPattern:
-                // These nodes are ES6 syntax.
-                transformFlags |= TransformFlags.AssertES2015 | TransformFlags.ContainsBindingPattern;
+                // These nodes are ES2015 or ES Next syntax.
+                if (subtreeFlags & TransformFlags.ContainsSpreadExpression) {
+                    transformFlags |= TransformFlags.AssertESNext | TransformFlags.ContainsBindingPattern;
+                }
+                else {
+                    transformFlags |= TransformFlags.AssertES2015 | TransformFlags.ContainsBindingPattern;
+                }
                 break;
 
             case SyntaxKind.Decorator:
@@ -3166,13 +3233,19 @@ namespace ts {
                     transformFlags |= TransformFlags.ContainsLexicalThis;
                 }
 
+                if (subtreeFlags & TransformFlags.ContainsSpreadExpression) {
+                    // If an ObjectLiteralExpression contains a spread element, then it
+                    // is an ES next node.
+                    transformFlags |= TransformFlags.AssertESNext;
+                }
+
                 break;
 
             case SyntaxKind.ArrayLiteralExpression:
             case SyntaxKind.NewExpression:
                 excludeFlags = TransformFlags.ArrayLiteralOrCallOrNewExcludes;
-                if (subtreeFlags & TransformFlags.ContainsSpreadElementExpression) {
-                    // If the this node contains a SpreadElementExpression, then it is an ES6
+                if (subtreeFlags & TransformFlags.ContainsSpreadExpression) {
+                    // If the this node contains a SpreadExpression, then it is an ES6
                     // node.
                     transformFlags |= TransformFlags.AssertES2015;
                 }

src/compiler/commandLineParser.ts

@@ -77,6 +77,11 @@ namespace ts {
             type: "string",
             description: Diagnostics.Specify_the_object_invoked_for_createElement_and_spread_when_targeting_react_JSX_emit
         },
+        {
+            name: "jsxFactory",
+            type: "string",
+            description: Diagnostics.Specify_the_JSX_factory_function_to_use_when_targeting_react_JSX_emit_e_g_React_createElement_or_h
+        },
         {
             name: "listFiles",
             type: "boolean",
@@ -265,6 +270,7 @@ namespace ts {
                 "es2015": ScriptTarget.ES2015,
                 "es2016": ScriptTarget.ES2016,
                 "es2017": ScriptTarget.ES2017,
+                "esnext": ScriptTarget.ESNext,
             }),
             description: Diagnostics.Specify_ECMAScript_target_version_Colon_ES3_default_ES5_or_ES2015,
             paramType: Diagnostics.VERSION,
@@ -428,7 +434,8 @@ namespace ts {
                     "es2015.symbol.wellknown": "lib.es2015.symbol.wellknown.d.ts",
                     "es2016.array.include": "lib.es2016.array.include.d.ts",
                     "es2017.object": "lib.es2017.object.d.ts",
-                    "es2017.sharedmemory": "lib.es2017.sharedmemory.d.ts"
+                    "es2017.sharedmemory": "lib.es2017.sharedmemory.d.ts",
+                    "es2017.string": "lib.es2017.string.d.ts",
                 }),
             },
             description: Diagnostics.Specify_library_files_to_be_included_in_the_compilation_Colon

src/compiler/core.ts

@@ -1,6 +1,11 @@
 /// <reference path="types.ts"/>
 /// <reference path="performance.ts" />
 
+namespace ts {
+    /** The version of the TypeScript compiler release */
+    export const version = "2.2.0";
+}
+
 /* @internal */
 namespace ts {
     /**
@@ -2231,6 +2236,13 @@ namespace ts {
      * Path must have a valid extension.
      */
     export function extensionFromPath(path: string): Extension {
+        const ext = tryGetExtensionFromPath(path);
+        if (ext !== undefined) {
+            return ext;
+        }
+        Debug.fail(`File ${path} has unknown extension.`);
+    }
+    export function tryGetExtensionFromPath(path: string): Extension | undefined {
         if (fileExtensionIs(path, ".d.ts")) {
             return Extension.Dts;
         }
@@ -2246,7 +2258,5 @@ namespace ts {
         if (fileExtensionIs(path, ".jsx")) {
             return Extension.Jsx;
         }
-        Debug.fail(`File ${path} has unknown extension.`);
-        return Extension.Js;
     }
 }

src/compiler/declarationEmitter.ts

@@ -416,7 +416,9 @@ namespace ts {
                 case SyntaxKind.TypeOperator:
                     return emitTypeOperator(<TypeOperatorNode>type);
                 case SyntaxKind.IndexedAccessType:
-                    return emitPropertyAccessType(<IndexedAccessTypeNode>type);
+                    return emitIndexedAccessType(<IndexedAccessTypeNode>type);
+                case SyntaxKind.MappedType:
+                    return emitMappedType(<MappedTypeNode>type);
                 case SyntaxKind.FunctionType:
                 case SyntaxKind.ConstructorType:
                     return emitSignatureDeclarationWithJsDocComments(<FunctionOrConstructorTypeNode>type);
@@ -516,13 +518,39 @@ namespace ts {
                 emitType(type.type);
             }
 
-            function emitPropertyAccessType(node: IndexedAccessTypeNode) {
+            function emitIndexedAccessType(node: IndexedAccessTypeNode) {
                 emitType(node.objectType);
                 write("[");
                 emitType(node.indexType);
                 write("]");
             }
 
+            function emitMappedType(node: MappedTypeNode) {
+                const prevEnclosingDeclaration = enclosingDeclaration;
+                enclosingDeclaration = node;
+                write("{");
+                writeLine();
+                increaseIndent();
+                if (node.readonlyToken) {
+                    write("readonly ");
+                }
+                write("[");
+                writeEntityName(node.typeParameter.name);
+                write(" in ");
+                emitType(node.typeParameter.constraint);
+                write("]");
+                if (node.questionToken) {
+                    write("?");
+                }
+                write(": ");
+                emitType(node.type);
+                write(";");
+                writeLine();
+                decreaseIndent();
+                write("}");
+                enclosingDeclaration = prevEnclosingDeclaration;
+            }
+
             function emitTypeLiteral(type: TypeLiteralNode) {
                 write("{");
                 if (type.members.length) {

src/compiler/diagnosticMessages.json

@@ -1455,7 +1455,7 @@
         "category": "Error",
         "code": 2461
     },
-    "A rest element must be last in an array destructuring pattern": {
+    "A rest element must be last in a destructuring pattern": {
         "category": "Error",
         "code": 2462
     },
@@ -1983,6 +1983,18 @@
         "category": "Error",
         "code": 2697
     },
+    "Spread types may only be created from object types.": {
+        "category": "Error",
+        "code": 2698
+    },
+    "Rest types may only be created from object types.": {
+        "category": "Error",
+        "code": 2700
+    },
+    "An object rest element must be an identifier.": {
+        "category": "Error",
+        "code": 2701
+    },
 
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",
@@ -2381,6 +2393,10 @@
         "category": "Error",
         "code": 5066
     },
+    "Invalid value for 'jsxFactory'. '{0}' is not a valid identifier or qualified-name.": {
+        "category": "Error",
+        "code": 5067
+    },
     "Concatenate and emit output to single file.": {
         "category": "Message",
         "code": 6001
@@ -2897,6 +2913,10 @@
         "category": "Message",
         "code": 6145
     },
+    "Specify the JSX factory function to use when targeting 'react' JSX emit, e.g. 'React.createElement' or 'h'.": {
+        "category": "Message",
+        "code": 6146
+    },
     "Variable '{0}' implicitly has an '{1}' type.": {
         "category": "Error",
         "code": 7005
@@ -3069,6 +3089,10 @@
         "category": "Error",
         "code": 9003
     },
+    "Language service is disabled.": {
+        "category": "Error",
+        "code": 9004
+    },
     "JSX attributes must only be assigned a non-empty 'expression'.": {
         "category": "Error",
         "code": 17000
@@ -3162,5 +3186,9 @@
     "Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig": {
         "category": "Error",
         "code": 90009
+    },
+    "Type '{0}' is not assignable to type '{1}'. Two different types with this name exist, but they are unrelated.": {
+        "category": "Error",
+        "code": 90010
     }
 }

src/compiler/emitter.ts

@@ -421,7 +421,9 @@ namespace ts {
                 case SyntaxKind.TypeOperator:
                     return emitTypeOperator(<TypeOperatorNode>node);
                 case SyntaxKind.IndexedAccessType:
-                    return emitPropertyAccessType(<IndexedAccessTypeNode>node);
+                    return emitIndexedAccessType(<IndexedAccessTypeNode>node);
+                case SyntaxKind.MappedType:
+                    return emitMappedType(<MappedTypeNode>node);
                 case SyntaxKind.LiteralType:
                     return emitLiteralType(<LiteralTypeNode>node);
 
@@ -556,6 +558,8 @@ namespace ts {
                     return emitPropertyAssignment(<PropertyAssignment>node);
                 case SyntaxKind.ShorthandPropertyAssignment:
                     return emitShorthandPropertyAssignment(<ShorthandPropertyAssignment>node);
+                case SyntaxKind.SpreadAssignment:
+                    return emitSpreadAssignment(node as SpreadAssignment);
 
                 // Enum
                 case SyntaxKind.EnumMember:
@@ -646,8 +650,8 @@ namespace ts {
                     return emitTemplateExpression(<TemplateExpression>node);
                 case SyntaxKind.YieldExpression:
                     return emitYieldExpression(<YieldExpression>node);
-                case SyntaxKind.SpreadElementExpression:
-                    return emitSpreadElementExpression(<SpreadElementExpression>node);
+                case SyntaxKind.SpreadElement:
+                    return emitSpreadExpression(<SpreadElement>node);
                 case SyntaxKind.ClassExpression:
                     return emitClassExpression(<ClassExpression>node);
                 case SyntaxKind.OmittedExpression:
@@ -919,13 +923,36 @@ namespace ts {
             emit(node.type);
         }
 
-        function emitPropertyAccessType(node: IndexedAccessTypeNode) {
+        function emitIndexedAccessType(node: IndexedAccessTypeNode) {
             emit(node.objectType);
             write("[");
             emit(node.indexType);
             write("]");
         }
 
+        function emitMappedType(node: MappedTypeNode) {
+            write("{");
+            writeLine();
+            increaseIndent();
+            if (node.readonlyToken) {
+                write("readonly ");
+            }
+            write("[");
+            emit(node.typeParameter.name);
+            write(" in ");
+            emit(node.typeParameter.constraint);
+            write("]");
+            if (node.questionToken) {
+                write("?");
+            }
+            write(": ");
+            emit(node.type);
+            write(";");
+            writeLine();
+            decreaseIndent();
+            write("}");
+        }
+
         function emitLiteralType(node: LiteralTypeNode) {
             emitExpression(node.literal);
         }
@@ -1195,7 +1222,7 @@ namespace ts {
             emitExpressionWithPrefix(" ", node.expression);
         }
 
-        function emitSpreadElementExpression(node: SpreadElementExpression) {
+        function emitSpreadExpression(node: SpreadElement) {
             write("...");
             emitExpression(node.expression);
         }
@@ -1923,6 +1950,13 @@ namespace ts {
             }
         }
 
+        function emitSpreadAssignment(node: SpreadAssignment) {
+            if (node.expression) {
+                write("...");
+                emitExpression(node.expression);
+            }
+        }
+
         //
         // Enum
         //

src/compiler/factory.ts

@@ -692,12 +692,12 @@ namespace ts {
     }
 
     export function createSpread(expression: Expression, location?: TextRange) {
-        const node = <SpreadElementExpression>createNode(SyntaxKind.SpreadElementExpression, location);
+        const node = <SpreadElement>createNode(SyntaxKind.SpreadElement, location);
         node.expression = parenthesizeExpressionForList(expression);
         return node;
     }
 
-    export function updateSpread(node: SpreadElementExpression, expression: Expression) {
+    export function updateSpread(node: SpreadElement, expression: Expression) {
         if (node.expression !== expression) {
             return updateNode(createSpread(expression, node), node);
         }
@@ -1399,14 +1399,27 @@ namespace ts {
         return node;
     }
 
-    export function updateShorthandPropertyAssignment(node: ShorthandPropertyAssignment, name: Identifier, objectAssignmentInitializer: Expression) {
+    export function createSpreadAssignment(expression: Expression, location?: TextRange) {
+        const node = <SpreadAssignment>createNode(SyntaxKind.SpreadAssignment, location);
+        node.expression = expression !== undefined ? parenthesizeExpressionForList(expression) : undefined;
+        return node;
+    }
+
+   export function updateShorthandPropertyAssignment(node: ShorthandPropertyAssignment, name: Identifier, objectAssignmentInitializer: Expression) {
         if (node.name !== name || node.objectAssignmentInitializer !== objectAssignmentInitializer) {
             return updateNode(createShorthandPropertyAssignment(name, objectAssignmentInitializer, node), node);
         }
         return node;
     }
 
-    // Top-level nodes
+    export function updateSpreadAssignment(node: SpreadAssignment, expression: Expression) {
+        if (node.expression !== expression) {
+            return updateNode(createSpreadAssignment(expression, node), node);
+        }
+        return node;
+    }
+
+   // Top-level nodes
 
     export function updateSourceFileNode(node: SourceFile, statements: Statement[]) {
         if (node.statements !== statements) {
@@ -1640,7 +1653,34 @@ namespace ts {
         return react;
     }
 
-    export function createReactCreateElement(reactNamespace: string, tagName: Expression, props: Expression, children: Expression[], parentElement: JsxOpeningLikeElement, location: TextRange): LeftHandSideExpression {
+    function createJsxFactoryExpressionFromEntityName(jsxFactory: EntityName, parent: JsxOpeningLikeElement): Expression {
+        if (isQualifiedName(jsxFactory)) {
+            return createPropertyAccess(
+                createJsxFactoryExpressionFromEntityName(
+                    jsxFactory.left,
+                    parent
+                ),
+                setEmitFlags(
+                    getMutableClone(jsxFactory.right),
+                    EmitFlags.NoSourceMap
+                )
+            );
+        }
+        else {
+            return createReactNamespace(jsxFactory.text, parent);
+        }
+    }
+
+    function createJsxFactoryExpression(jsxFactoryEntity: EntityName, reactNamespace: string, parent: JsxOpeningLikeElement): Expression {
+        return jsxFactoryEntity ?
+            createJsxFactoryExpressionFromEntityName(jsxFactoryEntity, parent) :
+            createPropertyAccess(
+                createReactNamespace(reactNamespace, parent),
+                "createElement"
+            );
+    }
+
+    export function createExpressionForJsxElement(jsxFactoryEntity: EntityName, reactNamespace: string, tagName: Expression, props: Expression, children: Expression[], parentElement: JsxOpeningLikeElement, location: TextRange): LeftHandSideExpression {
         const argumentsList = [tagName];
         if (props) {
             argumentsList.push(props);
@@ -1663,10 +1703,7 @@ namespace ts {
         }
 
         return createCall(
-            createPropertyAccess(
-                createReactNamespace(reactNamespace, parentElement),
-                "createElement"
-            ),
+            createJsxFactoryExpression(jsxFactoryEntity, reactNamespace, parentElement),
             /*typeArguments*/ undefined,
             argumentsList,
             location
@@ -2927,6 +2964,545 @@ namespace ts {
         return tryGetModuleNameFromFile(resolver.getExternalModuleFileFromDeclaration(declaration), host, compilerOptions);
     }
 
+    /**
+     * Transforms the body of a function-like node.
+     *
+     * @param node A function-like node.
+     */
+    export function transformFunctionBody(node: FunctionLikeDeclaration,
+                                          visitor: (node: Node) => VisitResult<Node>,
+                                          currentSourceFile: SourceFile,
+                                          context: TransformationContext,
+                                          enableSubstitutionsForCapturedThis: () => void,
+                                          convertObjectRest?: boolean) {
+        let multiLine = false; // indicates whether the block *must* be emitted as multiple lines
+        let singleLine = false; // indicates whether the block *may* be emitted as a single line
+        let statementsLocation: TextRange;
+        let closeBraceLocation: TextRange;
+
+        const statements: Statement[] = [];
+        const body = node.body;
+        let statementOffset: number;
+
+        context.resumeLexicalEnvironment();
+        if (isBlock(body)) {
+            // ensureUseStrict is false because no new prologue-directive should be added.
+            // addPrologueDirectives will simply put already-existing directives at the beginning of the target statement-array
+            statementOffset = addPrologueDirectives(statements, body.statements, /*ensureUseStrict*/ false, visitor);
+        }
+
+        addCaptureThisForNodeIfNeeded(statements, node, enableSubstitutionsForCapturedThis);
+        addDefaultValueAssignmentsIfNeeded(context, statements, node, visitor, convertObjectRest);
+        addRestParameterIfNeeded(statements, node, /*inConstructorWithSynthesizedSuper*/ false);
+
+        // If we added any generated statements, this must be a multi-line block.
+        if (!multiLine && statements.length > 0) {
+            multiLine = true;
+        }
+
+        if (isBlock(body)) {
+            statementsLocation = body.statements;
+            addRange(statements, visitNodes(body.statements, visitor, isStatement, statementOffset));
+
+            // If the original body was a multi-line block, this must be a multi-line block.
+            if (!multiLine && body.multiLine) {
+                multiLine = true;
+            }
+        }
+        else {
+            Debug.assert(node.kind === SyntaxKind.ArrowFunction);
+
+            // To align with the old emitter, we use a synthetic end position on the location
+            // for the statement list we synthesize when we down-level an arrow function with
+            // an expression function body. This prevents both comments and source maps from
+            // being emitted for the end position only.
+            statementsLocation = moveRangeEnd(body, -1);
+
+            const equalsGreaterThanToken = (<ArrowFunction>node).equalsGreaterThanToken;
+            if (!nodeIsSynthesized(equalsGreaterThanToken) && !nodeIsSynthesized(body)) {
+                if (rangeEndIsOnSameLineAsRangeStart(equalsGreaterThanToken, body, currentSourceFile)) {
+                    singleLine = true;
+                }
+                else {
+                    multiLine = true;
+                }
+            }
+
+            const expression = visitNode(body, visitor, isExpression);
+            const returnStatement = createReturn(expression, /*location*/ body);
+            setEmitFlags(returnStatement, EmitFlags.NoTokenSourceMaps | EmitFlags.NoTrailingSourceMap | EmitFlags.NoTrailingComments);
+            statements.push(returnStatement);
+
+            // To align with the source map emit for the old emitter, we set a custom
+            // source map location for the close brace.
+            closeBraceLocation = body;
+        }
+
+        const lexicalEnvironment = context.endLexicalEnvironment();
+        addRange(statements, lexicalEnvironment);
+
+        // If we added any final generated statements, this must be a multi-line block
+        if (!multiLine && lexicalEnvironment && lexicalEnvironment.length) {
+            multiLine = true;
+        }
+
+        const block = createBlock(createNodeArray(statements, statementsLocation), node.body, multiLine);
+        if (!multiLine && singleLine) {
+            setEmitFlags(block, EmitFlags.SingleLine);
+        }
+
+        if (closeBraceLocation) {
+            setTokenSourceMapRange(block, SyntaxKind.CloseBraceToken, closeBraceLocation);
+        }
+
+        setOriginalNode(block, node.body);
+        return block;
+    }
+
+    /**
+     * Adds a statement to capture the `this` of a function declaration if it is needed.
+     *
+     * @param statements The statements for the new function body.
+     * @param node A node.
+     */
+    export function addCaptureThisForNodeIfNeeded(statements: Statement[], node: Node, enableSubstitutionsForCapturedThis: () => void): void {
+        if (node.transformFlags & TransformFlags.ContainsCapturedLexicalThis && node.kind !== SyntaxKind.ArrowFunction) {
+            captureThisForNode(statements, node, createThis(), enableSubstitutionsForCapturedThis);
+        }
+    }
+
+    export function captureThisForNode(statements: Statement[], node: Node, initializer: Expression | undefined, enableSubstitutionsForCapturedThis?: () => void, originalStatement?: Statement): void {
+        if (enableSubstitutionsForCapturedThis) {
+            enableSubstitutionsForCapturedThis();
+        }
+        const captureThisStatement = createVariableStatement(
+            /*modifiers*/ undefined,
+            createVariableDeclarationList([
+                createVariableDeclaration(
+                    "_this",
+                    /*type*/ undefined,
+                    initializer
+                )
+            ]),
+            originalStatement
+        );
+
+        setEmitFlags(captureThisStatement, EmitFlags.NoComments | EmitFlags.CustomPrologue);
+        setSourceMapRange(captureThisStatement, node);
+        statements.push(captureThisStatement);
+    }
+
+    /**
+     * Gets a value indicating whether we need to add default value assignments for a
+     * function-like node.
+     *
+     * @param node A function-like node.
+     */
+    function shouldAddDefaultValueAssignments(node: FunctionLikeDeclaration): boolean {
+        return (node.transformFlags & TransformFlags.ContainsDefaultValueAssignments) !== 0;
+    }
+
+    /**
+     * Adds statements to the body of a function-like node if it contains parameters with
+     * binding patterns or initializers.
+     *
+     * @param statements The statements for the new function body.
+     * @param node A function-like node.
+     */
+    export function addDefaultValueAssignmentsIfNeeded(context: TransformationContext,
+                                                       statements: Statement[],
+                                                       node: FunctionLikeDeclaration,
+                                                       visitor: (node: Node) => VisitResult<Node>,
+                                                       convertObjectRest: boolean): void {
+        if (!shouldAddDefaultValueAssignments(node)) {
+            return;
+        }
+
+        for (const parameter of node.parameters) {
+            const { name, initializer, dotDotDotToken } = parameter;
+
+            // A rest parameter cannot have a binding pattern or an initializer,
+            // so let's just ignore it.
+            if (dotDotDotToken) {
+                continue;
+            }
+
+            if (isBindingPattern(name)) {
+                addDefaultValueAssignmentForBindingPattern(context, statements, parameter, name, initializer, visitor, convertObjectRest);
+            }
+            else if (initializer) {
+                addDefaultValueAssignmentForInitializer(statements, parameter, name, initializer, visitor);
+            }
+        }
+    }
+
+    /**
+     * Adds statements to the body of a function-like node for parameters with binding patterns
+     *
+     * @param statements The statements for the new function body.
+     * @param parameter The parameter for the function.
+     * @param name The name of the parameter.
+     * @param initializer The initializer for the parameter.
+     */
+    function addDefaultValueAssignmentForBindingPattern(context: TransformationContext,
+                                                        statements: Statement[],
+                                                        parameter: ParameterDeclaration,
+                                                        name: BindingPattern, initializer: Expression,
+                                                        visitor: (node: Node) => VisitResult<Node>,
+                                                        convertObjectRest: boolean): void {
+        const temp = getGeneratedNameForNode(parameter);
+
+        // In cases where a binding pattern is simply '[]' or '{}',
+        // we usually don't want to emit a var declaration; however, in the presence
+        // of an initializer, we must emit that expression to preserve side effects.
+        if (name.elements.length > 0) {
+            statements.push(
+                setEmitFlags(
+                    createVariableStatement(
+                        /*modifiers*/ undefined,
+                        createVariableDeclarationList(
+                            flattenParameterDestructuring(context, parameter, temp, visitor, convertObjectRest)
+                        )
+                    ),
+                    EmitFlags.CustomPrologue
+                )
+            );
+        }
+        else if (initializer) {
+            statements.push(
+                setEmitFlags(
+                    createStatement(
+                        createAssignment(
+                            temp,
+                            visitNode(initializer, visitor, isExpression)
+                        )
+                    ),
+                    EmitFlags.CustomPrologue
+                )
+            );
+        }
+    }
+
+    /**
+     * Adds statements to the body of a function-like node for parameters with initializers.
+     *
+     * @param statements The statements for the new function body.
+     * @param parameter The parameter for the function.
+     * @param name The name of the parameter.
+     * @param initializer The initializer for the parameter.
+     */
+    function addDefaultValueAssignmentForInitializer(statements: Statement[],
+                                                     parameter: ParameterDeclaration,
+                                                     name: Identifier,
+                                                     initializer: Expression,
+                                                     visitor: (node: Node) => VisitResult<Node>): void {
+        initializer = visitNode(initializer, visitor, isExpression);
+        const statement = createIf(
+            createStrictEquality(
+                getSynthesizedClone(name),
+                createVoidZero()
+            ),
+            setEmitFlags(
+                createBlock([
+                    createStatement(
+                        createAssignment(
+                            setEmitFlags(getMutableClone(name), EmitFlags.NoSourceMap),
+                            setEmitFlags(initializer, EmitFlags.NoSourceMap | getEmitFlags(initializer)),
+                            /*location*/ parameter
+                        )
+                    )
+                ], /*location*/ parameter),
+                EmitFlags.SingleLine | EmitFlags.NoTrailingSourceMap | EmitFlags.NoTokenSourceMaps
+            ),
+            /*elseStatement*/ undefined,
+            /*location*/ parameter
+        );
+        statement.startsOnNewLine = true;
+        setEmitFlags(statement, EmitFlags.NoTokenSourceMaps | EmitFlags.NoTrailingSourceMap | EmitFlags.CustomPrologue);
+        statements.push(statement);
+    }
+
+    /**
+     * Gets a value indicating whether we need to add statements to handle a rest parameter.
+     *
+     * @param node A ParameterDeclaration node.
+     * @param inConstructorWithSynthesizedSuper A value indicating whether the parameter is
+     *                                          part of a constructor declaration with a
+     *                                          synthesized call to `super`
+     */
+    function shouldAddRestParameter(node: ParameterDeclaration, inConstructorWithSynthesizedSuper: boolean) {
+        return node && node.dotDotDotToken && node.name.kind === SyntaxKind.Identifier && !inConstructorWithSynthesizedSuper;
+    }
+
+    /**
+     * Adds statements to the body of a function-like node if it contains a rest parameter.
+     *
+     * @param statements The statements for the new function body.
+     * @param node A function-like node.
+     * @param inConstructorWithSynthesizedSuper A value indicating whether the parameter is
+     *                                          part of a constructor declaration with a
+     *                                          synthesized call to `super`
+     */
+    export function addRestParameterIfNeeded(statements: Statement[], node: FunctionLikeDeclaration, inConstructorWithSynthesizedSuper: boolean): void {
+        const parameter = lastOrUndefined(node.parameters);
+        if (!shouldAddRestParameter(parameter, inConstructorWithSynthesizedSuper)) {
+            return;
+        }
+
+        // `declarationName` is the name of the local declaration for the parameter.
+        const declarationName = getMutableClone(<Identifier>parameter.name);
+        setEmitFlags(declarationName, EmitFlags.NoSourceMap);
+
+        // `expressionName` is the name of the parameter used in expressions.
+        const expressionName = getSynthesizedClone(<Identifier>parameter.name);
+        const restIndex = node.parameters.length - 1;
+        const temp = createLoopVariable();
+
+        // var param = [];
+        statements.push(
+            setEmitFlags(
+                createVariableStatement(
+                    /*modifiers*/ undefined,
+                    createVariableDeclarationList([
+                        createVariableDeclaration(
+                            declarationName,
+                            /*type*/ undefined,
+                            createArrayLiteral([])
+                        )
+                    ]),
+                    /*location*/ parameter
+                ),
+                EmitFlags.CustomPrologue
+            )
+        );
+
+        // for (var _i = restIndex; _i < arguments.length; _i++) {
+        //   param[_i - restIndex] = arguments[_i];
+        // }
+        const forStatement = createFor(
+            createVariableDeclarationList([
+                createVariableDeclaration(temp, /*type*/ undefined, createLiteral(restIndex))
+            ], /*location*/ parameter),
+            createLessThan(
+                temp,
+                createPropertyAccess(createIdentifier("arguments"), "length"),
+                /*location*/ parameter
+            ),
+            createPostfixIncrement(temp, /*location*/ parameter),
+            createBlock([
+                startOnNewLine(
+                    createStatement(
+                        createAssignment(
+                            createElementAccess(
+                                expressionName,
+                                createSubtract(temp, createLiteral(restIndex))
+                            ),
+                            createElementAccess(createIdentifier("arguments"), temp)
+                        ),
+                        /*location*/ parameter
+                    )
+                )
+            ])
+        );
+
+        setEmitFlags(forStatement, EmitFlags.CustomPrologue);
+        startOnNewLine(forStatement);
+        statements.push(forStatement);
+    }
+
+
+
+
+    export function convertForOf(node: ForOfStatement, convertedLoopBodyStatements: Statement[],
+                                 visitor: (node: Node) => VisitResult<Node>,
+                                 enableSubstitutionsForBlockScopedBindings: () => void,
+                                 context: TransformationContext,
+                                 convertObjectRest?: boolean): ForStatement | ForOfStatement {
+        // The following ES6 code:
+        //
+        //    for (let v of expr) { }
+        //
+        // should be emitted as
+        //
+        //    for (var _i = 0, _a = expr; _i < _a.length; _i++) {
+        //        var v = _a[_i];
+        //    }
+        //
+        // where _a and _i are temps emitted to capture the RHS and the counter,
+        // respectively.
+        // When the left hand side is an expression instead of a let declaration,
+        // the "let v" is not emitted.
+        // When the left hand side is a let/const, the v is renamed if there is
+        // another v in scope.
+        // Note that all assignments to the LHS are emitted in the body, including
+        // all destructuring.
+        // Note also that because an extra statement is needed to assign to the LHS,
+        // for-of bodies are always emitted as blocks.
+
+        const expression = visitNode(node.expression, visitor, isExpression);
+        const initializer = node.initializer;
+        const statements: Statement[] = [];
+
+        // In the case where the user wrote an identifier as the RHS, like this:
+        //
+        //     for (let v of arr) { }
+        //
+        // we don't want to emit a temporary variable for the RHS, just use it directly.
+        const counter = convertObjectRest ? undefined : createLoopVariable();
+        const rhsReference = expression.kind === SyntaxKind.Identifier
+            ? createUniqueName((<Identifier>expression).text)
+            : createTempVariable(/*recordTempVariable*/ undefined);
+        const elementAccess = convertObjectRest ? rhsReference : createElementAccess(rhsReference, counter);
+
+        // Initialize LHS
+        // var v = _a[_i];
+        if (isVariableDeclarationList(initializer)) {
+            if (initializer.flags & NodeFlags.BlockScoped) {
+                enableSubstitutionsForBlockScopedBindings();
+            }
+
+            const firstOriginalDeclaration = firstOrUndefined(initializer.declarations);
+            if (firstOriginalDeclaration && isBindingPattern(firstOriginalDeclaration.name)) {
+                // This works whether the declaration is a var, let, or const.
+                // It will use rhsIterationValue _a[_i] as the initializer.
+                const declarations = flattenVariableDestructuring(
+                    context,
+                    firstOriginalDeclaration,
+                    elementAccess,
+                    visitor,
+                    /*recordTempVariable*/ undefined,
+                    convertObjectRest
+                );
+
+                const declarationList = createVariableDeclarationList(declarations, /*location*/ initializer);
+                setOriginalNode(declarationList, initializer);
+
+                // Adjust the source map range for the first declaration to align with the old
+                // emitter.
+                const firstDeclaration = declarations[0];
+                const lastDeclaration = lastOrUndefined(declarations);
+                setSourceMapRange(declarationList, createRange(firstDeclaration.pos, lastDeclaration.end));
+
+                statements.push(
+                    createVariableStatement(
+                        /*modifiers*/ undefined,
+                        declarationList
+                    )
+                );
+            }
+            else {
+                // The following call does not include the initializer, so we have
+                // to emit it separately.
+                statements.push(
+                    createVariableStatement(
+                        /*modifiers*/ undefined,
+                        setOriginalNode(
+                            createVariableDeclarationList([
+                                createVariableDeclaration(
+                                    firstOriginalDeclaration ? firstOriginalDeclaration.name : createTempVariable(/*recordTempVariable*/ undefined),
+                                    /*type*/ undefined,
+                                    createElementAccess(rhsReference, counter)
+                                )
+                            ], /*location*/ moveRangePos(initializer, -1)),
+                            initializer
+                        ),
+                        /*location*/ moveRangeEnd(initializer, -1)
+                    )
+                );
+            }
+        }
+        else {
+            // Initializer is an expression. Emit the expression in the body, so that it's
+            // evaluated on every iteration.
+            const assignment = createAssignment(initializer, elementAccess);
+            if (isDestructuringAssignment(assignment)) {
+                // This is a destructuring pattern, so we flatten the destructuring instead.
+                statements.push(
+                    createStatement(
+                        flattenDestructuringAssignment(
+                            context,
+                            assignment,
+                            /*needsValue*/ false,
+                            context.hoistVariableDeclaration,
+                            visitor,
+                            convertObjectRest
+                        )
+                    )
+                );
+            }
+            else {
+                // Currently there is not way to check that assignment is binary expression of destructing assignment
+                // so we have to cast never type to binaryExpression
+                (<BinaryExpression>assignment).end = initializer.end;
+                statements.push(createStatement(assignment, /*location*/ moveRangeEnd(initializer, -1)));
+            }
+        }
+
+        let bodyLocation: TextRange;
+        let statementsLocation: TextRange;
+        if (convertedLoopBodyStatements) {
+            addRange(statements, convertedLoopBodyStatements);
+        }
+        else {
+            const statement = visitNode(node.statement, visitor, isStatement);
+            if (isBlock(statement)) {
+                addRange(statements, statement.statements);
+                bodyLocation = statement;
+                statementsLocation = statement.statements;
+            }
+            else {
+                statements.push(statement);
+            }
+        }
+
+        // The old emitter does not emit source maps for the expression
+        setEmitFlags(expression, EmitFlags.NoSourceMap | getEmitFlags(expression));
+
+        // The old emitter does not emit source maps for the block.
+        // We add the location to preserve comments.
+        const body = createBlock(
+            createNodeArray(statements, /*location*/ statementsLocation),
+            /*location*/ bodyLocation
+        );
+
+        setEmitFlags(body, EmitFlags.NoSourceMap | EmitFlags.NoTokenSourceMaps);
+
+        let forStatement: ForStatement | ForOfStatement;
+        if (convertObjectRest) {
+            forStatement = createForOf(
+                createVariableDeclarationList([
+                    createVariableDeclaration(rhsReference, /*type*/ undefined, /*initializer*/ undefined, /*location*/ node.expression)
+                ], /*location*/ node.expression),
+                node.expression,
+                body,
+                /*location*/ node
+            );
+        }
+        else {
+            forStatement = createFor(
+                setEmitFlags(
+                    createVariableDeclarationList([
+                        createVariableDeclaration(counter, /*type*/ undefined, createLiteral(0), /*location*/ moveRangePos(node.expression, -1)),
+                        createVariableDeclaration(rhsReference, /*type*/ undefined, expression, /*location*/ node.expression)
+                    ], /*location*/ node.expression),
+                    EmitFlags.NoHoisting
+                ),
+                createLessThan(
+                    counter,
+                    createPropertyAccess(rhsReference, "length"),
+                    /*location*/ node.expression
+                ),
+                createPostfixIncrement(counter, /*location*/ node.expression),
+                body,
+                /*location*/ node
+            );
+        }
+
+        // Disable trailing source maps for the OpenParenToken to align source map emit with the old emitter.
+        setEmitFlags(forStatement, EmitFlags.NoTokenTrailingSourceMaps);
+        return forStatement;
+    }
+
     export interface ExternalModuleInfo {
         externalImports: (ImportDeclaration | ImportEqualsDeclaration | ExportDeclaration)[]; // imports of other external modules
         externalHelpersImportDeclaration: ImportDeclaration | undefined; // import of external helpers

src/compiler/moduleNameResolver.ts

@@ -14,6 +14,11 @@ namespace ts {
         return compilerOptions.traceResolution && host.trace !== undefined;
     }
 
+    /** Array that is only intended to be pushed to, never read. */
+    interface Push<T> {
+        push(value: T): void;
+    }
+
     /**
      * Result of trying to resolve a module.
      * At least one of `ts` and `js` should be defined, or the whole thing should be `undefined`.
@@ -62,8 +67,7 @@ namespace ts {
 
     interface ModuleResolutionState {
         host: ModuleResolutionHost;
-        // We only use this subset of the compiler options.
-        compilerOptions: { rootDirs?: string[], baseUrl?: string, paths?: MapLike<string[]> };
+        compilerOptions: CompilerOptions;
         traceEnabled: boolean;
     }
 
@@ -128,7 +132,9 @@ namespace ts {
             currentDirectory = host.getCurrentDirectory();
         }
 
-        return currentDirectory !== undefined && getDefaultTypeRoots(currentDirectory, host);
+        if (currentDirectory !== undefined) {
+            return getDefaultTypeRoots(currentDirectory, host);
+        }
     }
 
     /**
@@ -142,20 +148,12 @@ namespace ts {
         }
 
         let typeRoots: string[];
-
-        while (true) {
-            const atTypes = combinePaths(currentDirectory, nodeModulesAtTypes);
+        forEachAncestorDirectory(currentDirectory, directory => {
+            const atTypes = combinePaths(directory, nodeModulesAtTypes);
             if (host.directoryExists(atTypes)) {
                 (typeRoots || (typeRoots = [])).push(atTypes);
             }
-
-            const parent = getDirectoryPath(currentDirectory);
-            if (parent === currentDirectory) {
-                break;
-            }
-            currentDirectory = parent;
-        }
-
+        });
         return typeRoots;
     }
     const nodeModulesAtTypes = combinePaths("node_modules", "@types");
@@ -195,63 +193,66 @@ namespace ts {
 
         const failedLookupLocations: string[] = [];
 
-        // Check primary library paths
-        if (typeRoots && typeRoots.length) {
+        let resolved = primaryLookup();
+        let primary = true;
+        if (!resolved) {
+            resolved = secondaryLookup();
+            primary = false;
+        }
+
+        let resolvedTypeReferenceDirective: ResolvedTypeReferenceDirective | undefined;
+        if (resolved) {
+            resolved = realpath(resolved, host, traceEnabled);
             if (traceEnabled) {
-                trace(host, Diagnostics.Resolving_with_primary_search_path_0, typeRoots.join(", "));
+                trace(host, Diagnostics.Type_reference_directive_0_was_successfully_resolved_to_1_primary_Colon_2, typeReferenceDirectiveName, resolved, primary);
             }
-            for (const typeRoot of typeRoots) {
-                const candidate = combinePaths(typeRoot, typeReferenceDirectiveName);
-                const candidateDirectory = getDirectoryPath(candidate);
+            resolvedTypeReferenceDirective = { primary, resolvedFileName: resolved };
+        }
 
-                const resolved = resolvedTypeScriptOnly(
-                    loadNodeModuleFromDirectory(Extensions.DtsOnly, candidate, failedLookupLocations,
-                        !directoryProbablyExists(candidateDirectory, host), moduleResolutionState));
+        return { resolvedTypeReferenceDirective, failedLookupLocations };
 
-                if (resolved) {
-                    if (traceEnabled) {
-                        trace(host, Diagnostics.Type_reference_directive_0_was_successfully_resolved_to_1_primary_Colon_2, typeReferenceDirectiveName, resolved, true);
-                    }
-                    return {
-                        resolvedTypeReferenceDirective: { primary: true, resolvedFileName: resolved },
-                        failedLookupLocations
-                    };
+        function primaryLookup(): string | undefined {
+            // Check primary library paths
+            if (typeRoots && typeRoots.length) {
+                if (traceEnabled) {
+                    trace(host, Diagnostics.Resolving_with_primary_search_path_0, typeRoots.join(", "));
+                }
+                return forEach(typeRoots, typeRoot => {
+                    const candidate = combinePaths(typeRoot, typeReferenceDirectiveName);
+                    const candidateDirectory = getDirectoryPath(candidate);
+                    return resolvedTypeScriptOnly(
+                        loadNodeModuleFromDirectory(Extensions.DtsOnly, candidate, failedLookupLocations,
+                            !directoryProbablyExists(candidateDirectory, host), moduleResolutionState));
+                });
+            }
+            else {
+                if (traceEnabled) {
+                    trace(host, Diagnostics.Root_directory_cannot_be_determined_skipping_primary_search_paths);
                 }
             }
         }
-        else {
-            if (traceEnabled) {
-                trace(host, Diagnostics.Root_directory_cannot_be_determined_skipping_primary_search_paths);
-            }
-        }
 
-        let resolvedFile: string;
-        const initialLocationForSecondaryLookup = containingFile && getDirectoryPath(containingFile);
+        function secondaryLookup(): string | undefined {
+            let resolvedFile: string;
+            const initialLocationForSecondaryLookup = containingFile && getDirectoryPath(containingFile);
 
-        if (initialLocationForSecondaryLookup !== undefined) {
-            // check secondary locations
-            if (traceEnabled) {
-                trace(host, Diagnostics.Looking_up_in_node_modules_folder_initial_location_0, initialLocationForSecondaryLookup);
-            }
-            resolvedFile = resolvedTypeScriptOnly(loadModuleFromNodeModules(Extensions.DtsOnly, typeReferenceDirectiveName, initialLocationForSecondaryLookup, failedLookupLocations, moduleResolutionState, /*checkOneLevel*/ false));
-            if (traceEnabled) {
-                if (resolvedFile) {
-                    trace(host, Diagnostics.Type_reference_directive_0_was_successfully_resolved_to_1_primary_Colon_2, typeReferenceDirectiveName, resolvedFile, false);
+            if (initialLocationForSecondaryLookup !== undefined) {
+                // check secondary locations
+                if (traceEnabled) {
+                    trace(host, Diagnostics.Looking_up_in_node_modules_folder_initial_location_0, initialLocationForSecondaryLookup);
                 }
-                else {
+                resolvedFile = resolvedTypeScriptOnly(loadModuleFromNodeModules(Extensions.DtsOnly, typeReferenceDirectiveName, initialLocationForSecondaryLookup, failedLookupLocations, moduleResolutionState));
+                if (!resolvedFile && traceEnabled) {
                     trace(host, Diagnostics.Type_reference_directive_0_was_not_resolved, typeReferenceDirectiveName);
                 }
+                return resolvedFile;
+            }
+            else {
+                if (traceEnabled) {
+                    trace(host, Diagnostics.Containing_file_is_not_specified_and_root_directory_cannot_be_determined_skipping_lookup_in_node_modules_folder);
+                }
             }
         }
-        else {
-            if (traceEnabled) {
-                trace(host, Diagnostics.Containing_file_is_not_specified_and_root_directory_cannot_be_determined_skipping_lookup_in_node_modules_folder);
-            }
-        }
-        return {
-            resolvedTypeReferenceDirective: resolvedFile ? { primary: false, resolvedFileName: resolvedFile } : undefined,
-            failedLookupLocations
-        };
     }
 
     /**
@@ -341,7 +342,7 @@ namespace ts {
      * 'typings' entry or file 'index' with some supported extension
      * - Classic loader will only try to interpret '/a/b/c' as file.
      */
-    type ResolutionKindSpecificLoader = (extensions: Extensions, candidate: string, failedLookupLocations: string[], onlyRecordFailures: boolean, state: ModuleResolutionState) => Resolved | undefined;
+    type ResolutionKindSpecificLoader = (extensions: Extensions, candidate: string, failedLookupLocations: Push<string>, onlyRecordFailures: boolean, state: ModuleResolutionState) => Resolved | undefined;
 
     /**
      * Any module resolution kind can be augmented with optional settings: 'baseUrl', 'paths' and 'rootDirs' - they are used to
@@ -404,7 +405,7 @@ namespace ts {
      * entries in 'rootDirs', use them to build absolute path out of (*) and try to resolve module from this location.
      */
     function tryLoadModuleUsingOptionalResolutionSettings(extensions: Extensions, moduleName: string, containingDirectory: string, loader: ResolutionKindSpecificLoader,
-        failedLookupLocations: string[], state: ModuleResolutionState): Resolved | undefined {
+        failedLookupLocations: Push<string>, state: ModuleResolutionState): Resolved | undefined {
 
         if (moduleHasNonRelativeName(moduleName)) {
             return tryLoadModuleUsingBaseUrl(extensions, moduleName, loader, failedLookupLocations, state);
@@ -415,7 +416,7 @@ namespace ts {
     }
 
     function tryLoadModuleUsingRootDirs(extensions: Extensions, moduleName: string, containingDirectory: string, loader: ResolutionKindSpecificLoader,
-        failedLookupLocations: string[], state: ModuleResolutionState): Resolved | undefined {
+        failedLookupLocations: Push<string>, state: ModuleResolutionState): Resolved | undefined {
 
         if (!state.compilerOptions.rootDirs) {
             return undefined;
@@ -491,7 +492,7 @@ namespace ts {
         return undefined;
     }
 
-    function tryLoadModuleUsingBaseUrl(extensions: Extensions, moduleName: string, loader: ResolutionKindSpecificLoader, failedLookupLocations: string[], state: ModuleResolutionState): Resolved | undefined {
+    function tryLoadModuleUsingBaseUrl(extensions: Extensions, moduleName: string, loader: ResolutionKindSpecificLoader, failedLookupLocations: Push<string>, state: ModuleResolutionState): Resolved | undefined {
         if (!state.compilerOptions.baseUrl) {
             return undefined;
         }
@@ -514,18 +515,21 @@ namespace ts {
             if (state.traceEnabled) {
                 trace(state.host, Diagnostics.Module_name_0_matched_pattern_1, moduleName, matchedPatternText);
             }
-            for (const subst of state.compilerOptions.paths[matchedPatternText]) {
+            return forEach(state.compilerOptions.paths[matchedPatternText], subst => {
                 const path = matchedStar ? subst.replace("*", matchedStar) : subst;
                 const candidate = normalizePath(combinePaths(state.compilerOptions.baseUrl, path));
                 if (state.traceEnabled) {
                     trace(state.host, Diagnostics.Trying_substitution_0_candidate_module_location_Colon_1, subst, path);
                 }
-                const resolved = loader(extensions, candidate, failedLookupLocations, !directoryProbablyExists(getDirectoryPath(candidate), state.host), state);
-                if (resolved) {
-                    return resolved;
+                // A path mapping may have a ".ts" extension; in contrast to an import, which should omit it.
+                const tsExtension = tryGetExtensionFromPath(candidate);
+                if (tsExtension !== undefined) {
+                    const path = tryFile(candidate, failedLookupLocations, /*onlyRecordFailures*/false, state);
+                    return path && { path, extension: tsExtension };
                 }
-            }
-            return undefined;
+
+                return loader(extensions, candidate, failedLookupLocations, !directoryProbablyExists(getDirectoryPath(candidate), state.host), state);
+            });
         }
         else {
             const candidate = normalizePath(combinePaths(state.compilerOptions.baseUrl, moduleName));
@@ -548,7 +552,7 @@ namespace ts {
         const result = tryResolve(Extensions.TypeScript) || tryResolve(Extensions.JavaScript);
         if (result) {
             const { resolved, isExternalLibraryImport } = result;
-            return createResolvedModuleWithFailedLookupLocations(resolved && resolvedWithRealpath(resolved, host, traceEnabled), isExternalLibraryImport, failedLookupLocations);
+            return createResolvedModuleWithFailedLookupLocations(resolved, isExternalLibraryImport, failedLookupLocations);
         }
         return { resolvedModule: undefined, failedLookupLocations };
 
@@ -562,8 +566,9 @@ namespace ts {
                 if (traceEnabled) {
                     trace(host, Diagnostics.Loading_module_0_from_node_modules_folder, moduleName);
                 }
-                const resolved = loadModuleFromNodeModules(extensions, moduleName, containingDirectory, failedLookupLocations, state, /*checkOneLevel*/ false);
-                return resolved && { resolved, isExternalLibraryImport: true };
+                const resolved = loadModuleFromNodeModules(extensions, moduleName, containingDirectory, failedLookupLocations, state);
+                // For node_modules lookups, get the real path so that multiple accesses to an `npm link`-ed module do not create duplicate files.
+                return resolved && { resolved: { path: realpath(resolved.path, host, traceEnabled), extension: resolved.extension }, isExternalLibraryImport: true };
             }
             else {
                 const candidate = normalizePath(combinePaths(containingDirectory, moduleName));
@@ -573,19 +578,19 @@ namespace ts {
         }
     }
 
-    function resolvedWithRealpath(resolved: Resolved, host: ModuleResolutionHost, traceEnabled: boolean): Resolved {
+    function realpath(path: string, host: ModuleResolutionHost, traceEnabled: boolean): string {
         if (!host.realpath) {
-            return resolved;
+            return path;
         }
 
-        const real = normalizePath(host.realpath(resolved.path));
+        const real = normalizePath(host.realpath(path));
         if (traceEnabled) {
-            trace(host, Diagnostics.Resolving_real_path_for_0_result_1, resolved.path, real);
+            trace(host, Diagnostics.Resolving_real_path_for_0_result_1, path, real);
         }
-        return { path: real, extension: resolved.extension };
+        return real;
     }
 
-    function nodeLoadModuleByRelativeName(extensions: Extensions, candidate: string, failedLookupLocations: string[], onlyRecordFailures: boolean, state: ModuleResolutionState): Resolved | undefined {
+    function nodeLoadModuleByRelativeName(extensions: Extensions, candidate: string, failedLookupLocations: Push<string>, onlyRecordFailures: boolean, state: ModuleResolutionState): Resolved | undefined {
         if (state.traceEnabled) {
             trace(state.host, Diagnostics.Loading_module_as_file_Slash_folder_candidate_module_location_0, candidate);
         }
@@ -604,7 +609,7 @@ namespace ts {
      * @param {boolean} onlyRecordFailures - if true then function won't try to actually load files but instead record all attempts as failures. This flag is necessary
      * in cases when we know upfront that all load attempts will fail (because containing folder does not exists) however we still need to record all failed lookup locations.
      */
-    function loadModuleFromFile(extensions: Extensions, candidate: string, failedLookupLocations: string[], onlyRecordFailures: boolean, state: ModuleResolutionState): Resolved | undefined {
+    function loadModuleFromFile(extensions: Extensions, candidate: string, failedLookupLocations: Push<string>, onlyRecordFailures: boolean, state: ModuleResolutionState): Resolved | undefined {
         // First, try adding an extension. An import of "foo" could be matched by a file "foo.ts", or "foo.js" by "foo.js.ts"
         const resolvedByAddingExtension = tryAddingExtensions(candidate, extensions, failedLookupLocations, onlyRecordFailures, state);
         if (resolvedByAddingExtension) {
@@ -624,7 +629,7 @@ namespace ts {
     }
 
     /** Try to return an existing file that adds one of the `extensions` to `candidate`. */
-    function tryAddingExtensions(candidate: string, extensions: Extensions, failedLookupLocations: string[], onlyRecordFailures: boolean, state: ModuleResolutionState): Resolved | undefined {
+    function tryAddingExtensions(candidate: string, extensions: Extensions, failedLookupLocations: Push<string>, onlyRecordFailures: boolean, state: ModuleResolutionState): Resolved | undefined {
         if (!onlyRecordFailures) {
             // check if containing folder exists - if it doesn't then just record failures for all supported extensions without disk probing
             const directory = getDirectoryPath(candidate);
@@ -649,7 +654,7 @@ namespace ts {
     }
 
     /** Return the file if it exists. */
-    function tryFile(fileName: string, failedLookupLocation: string[], onlyRecordFailures: boolean, state: ModuleResolutionState): string | undefined {
+    function tryFile(fileName: string, failedLookupLocations: Push<string>, onlyRecordFailures: boolean, state: ModuleResolutionState): string | undefined {
         if (!onlyRecordFailures && state.host.fileExists(fileName)) {
             if (state.traceEnabled) {
                 trace(state.host, Diagnostics.File_0_exist_use_it_as_a_name_resolution_result, fileName);
@@ -660,12 +665,12 @@ namespace ts {
             if (state.traceEnabled) {
                 trace(state.host, Diagnostics.File_0_does_not_exist, fileName);
             }
-            failedLookupLocation.push(fileName);
+            failedLookupLocations.push(fileName);
             return undefined;
         }
     }
 
-    function loadNodeModuleFromDirectory(extensions: Extensions, candidate: string, failedLookupLocation: string[], onlyRecordFailures: boolean, state: ModuleResolutionState): Resolved | undefined {
+    function loadNodeModuleFromDirectory(extensions: Extensions, candidate: string, failedLookupLocations: Push<string>, onlyRecordFailures: boolean, state: ModuleResolutionState): Resolved | undefined {
         const packageJsonPath = pathToPackageJson(candidate);
         const directoryExists = !onlyRecordFailures && directoryProbablyExists(candidate, state.host);
 
@@ -677,12 +682,12 @@ namespace ts {
             if (typesFile) {
                 const onlyRecordFailures = !directoryProbablyExists(getDirectoryPath(typesFile), state.host);
                 // A package.json "typings" may specify an exact filename, or may choose to omit an extension.
-                const fromFile = tryFile(typesFile, failedLookupLocation, onlyRecordFailures, state);
+                const fromFile = tryFile(typesFile, failedLookupLocations, onlyRecordFailures, state);
                 if (fromFile) {
                     // Note: this would allow a package.json to specify a ".js" file as typings. Maybe that should be forbidden.
                     return resolvedFromAnyFile(fromFile);
                 }
-                const x = tryAddingExtensions(typesFile, Extensions.TypeScript, failedLookupLocation, onlyRecordFailures, state);
+                const x = tryAddingExtensions(typesFile, Extensions.TypeScript, failedLookupLocations, onlyRecordFailures, state);
                 if (x) {
                     return x;
                 }
@@ -698,17 +703,17 @@ namespace ts {
                 trace(state.host, Diagnostics.File_0_does_not_exist, packageJsonPath);
             }
             // record package json as one of failed lookup locations - in the future if this file will appear it will invalidate resolution results
-            failedLookupLocation.push(packageJsonPath);
+            failedLookupLocations.push(packageJsonPath);
         }
 
-        return loadModuleFromFile(extensions, combinePaths(candidate, "index"), failedLookupLocation, !directoryExists, state);
+        return loadModuleFromFile(extensions, combinePaths(candidate, "index"), failedLookupLocations, !directoryExists, state);
     }
 
     function pathToPackageJson(directory: string): string {
         return combinePaths(directory, "package.json");
     }
 
-    function loadModuleFromNodeModulesFolder(extensions: Extensions, moduleName: string, directory: string, failedLookupLocations: string[], state: ModuleResolutionState): Resolved | undefined {
+    function loadModuleFromNodeModulesFolder(extensions: Extensions, moduleName: string, directory: string, failedLookupLocations: Push<string>, state: ModuleResolutionState): Resolved | undefined {
         const nodeModulesFolder = combinePaths(directory, "node_modules");
         const nodeModulesFolderExists = directoryProbablyExists(nodeModulesFolder, state.host);
         const candidate = normalizePath(combinePaths(nodeModulesFolder, moduleName));
@@ -717,34 +722,30 @@ namespace ts {
             loadNodeModuleFromDirectory(extensions, candidate, failedLookupLocations, !nodeModulesFolderExists, state);
     }
 
-    function loadModuleFromNodeModules(extensions: Extensions, moduleName: string, directory: string, failedLookupLocations: string[], state: ModuleResolutionState, checkOneLevel: boolean): Resolved | undefined {
-        return loadModuleFromNodeModulesWorker(extensions, moduleName, directory, failedLookupLocations, state, checkOneLevel, /*typesOnly*/ false);
+    function loadModuleFromNodeModules(extensions: Extensions, moduleName: string, directory: string, failedLookupLocations: Push<string>, state: ModuleResolutionState): Resolved | undefined {
+        return loadModuleFromNodeModulesWorker(extensions, moduleName, directory, failedLookupLocations, state, /*typesOnly*/ false);
     }
-    function loadModuleFromNodeModulesAtTypes(moduleName: string, directory: string, failedLookupLocations: string[], state: ModuleResolutionState): Resolved | undefined {
-        return loadModuleFromNodeModulesWorker(Extensions.TypeScript, moduleName, directory, failedLookupLocations, state, /*checkOneLevel*/ false, /*typesOnly*/ true);
+    function loadModuleFromNodeModulesAtTypes(moduleName: string, directory: string, failedLookupLocations: Push<string>, state: ModuleResolutionState): Resolved | undefined {
+        // Extensions parameter here doesn't actually matter, because typesOnly ensures we're just doing @types lookup, which is always DtsOnly.
+        return loadModuleFromNodeModulesWorker(Extensions.DtsOnly, moduleName, directory, failedLookupLocations, state, /*typesOnly*/ true);
     }
 
-    function loadModuleFromNodeModulesWorker(extensions: Extensions, moduleName: string, directory: string, failedLookupLocations: string[], state: ModuleResolutionState, checkOneLevel: boolean, typesOnly: boolean): Resolved | undefined {
-        directory = normalizeSlashes(directory);
-        while (true) {
-            if (getBaseFileName(directory) !== "node_modules") {
-                const resolved = tryInDirectory();
-                if (resolved) {
-                    return resolved;
-                }
+    function loadModuleFromNodeModulesWorker(extensions: Extensions, moduleName: string, directory: string, failedLookupLocations: Push<string>, state: ModuleResolutionState, typesOnly: boolean): Resolved | undefined {
+        return forEachAncestorDirectory(normalizeSlashes(directory), ancestorDirectory => {
+            if (getBaseFileName(ancestorDirectory) !== "node_modules") {
+                return loadModuleFromNodeModulesOneLevel(extensions, moduleName, ancestorDirectory, failedLookupLocations, state, typesOnly);
             }
+        });
+    }
 
-            const parentPath = getDirectoryPath(directory);
-            if (parentPath === directory || checkOneLevel) {
-                return undefined;
-            }
-
-            directory = parentPath;
+    /** Load a module from a single node_modules directory, but not from any ancestors' node_modules directories. */
+    function loadModuleFromNodeModulesOneLevel(extensions: Extensions, moduleName: string, directory: string, failedLookupLocations: Push<string>, state: ModuleResolutionState, typesOnly = false): Resolved | undefined {
+        const packageResult = typesOnly ? undefined : loadModuleFromNodeModulesFolder(extensions, moduleName, directory, failedLookupLocations, state);
+        if (packageResult) {
+            return packageResult;
         }
-
-        function tryInDirectory(): Resolved | undefined {
-            const packageResult = typesOnly ? undefined : loadModuleFromNodeModulesFolder(extensions, moduleName, directory, failedLookupLocations, state);
-            return packageResult || loadModuleFromNodeModulesFolder(extensions, combinePaths("@types", moduleName), directory, failedLookupLocations, state);
+        if (extensions !== Extensions.JavaScript) {
+            return loadModuleFromNodeModulesFolder(Extensions.DtsOnly, combinePaths("@types", moduleName), directory, failedLookupLocations, state);
         }
     }
 
@@ -764,7 +765,11 @@ namespace ts {
             }
 
             if (moduleHasNonRelativeName(moduleName)) {
-                const resolved = loadModuleFromAncestorDirectories(extensions, moduleName, containingDirectory, failedLookupLocations, state);
+                // Climb up parent directories looking for a module.
+                const resolved = forEachAncestorDirectory(containingDirectory, directory => {
+                    const searchName = normalizePath(combinePaths(directory, moduleName));
+                    return loadModuleFromFile(extensions, searchName, failedLookupLocations, /*onlyRecordFailures*/ false, state);
+                });
                 if (resolved) {
                     return resolved;
                 }
@@ -780,22 +785,6 @@ namespace ts {
         }
     }
 
-    /** Climb up parent directories looking for a module. */
-    function loadModuleFromAncestorDirectories(extensions: Extensions, moduleName: string, containingDirectory: string, failedLookupLocations: string[], state: ModuleResolutionState): Resolved | undefined {
-        while (true) {
-            const searchName = normalizePath(combinePaths(containingDirectory, moduleName));
-            const referencedSourceFile = loadModuleFromFile(extensions, searchName, failedLookupLocations, /*onlyRecordFailures*/ false, state);
-            if (referencedSourceFile) {
-                return referencedSourceFile;
-            }
-            const parentPath = getDirectoryPath(containingDirectory);
-            if (parentPath === containingDirectory) {
-                return undefined;
-            }
-            containingDirectory = parentPath;
-        }
-    }
-
     /**
      * LSHost may load a module from a global cache of typings.
      * This is the minumum code needed to expose that functionality; the rest is in LSHost.
@@ -808,8 +797,24 @@ namespace ts {
         }
         const state: ModuleResolutionState = { compilerOptions, host, traceEnabled };
         const failedLookupLocations: string[] = [];
-        const resolved = loadModuleFromNodeModules(Extensions.TypeScript, moduleName, globalCache, failedLookupLocations, state, /*checkOneLevel*/ true) ||
-            loadModuleFromNodeModules(Extensions.JavaScript, moduleName, globalCache, failedLookupLocations, state, /*checkOneLevel*/ true);
+        const resolved = loadModuleFromNodeModulesOneLevel(Extensions.DtsOnly, moduleName, globalCache, failedLookupLocations, state);
         return createResolvedModuleWithFailedLookupLocations(resolved, /*isExternalLibraryImport*/ true, failedLookupLocations);
     }
+
+    /** Calls `callback` on `directory` and every ancestor directory it has, returning the first defined result. */
+    function forEachAncestorDirectory<T>(directory: string, callback: (directory: string) => T | undefined): T | undefined {
+        while (true) {
+            const result = callback(directory);
+            if (result !== undefined) {
+                return result;
+            }
+
+            const parentPath = getDirectoryPath(directory);
+            if (parentPath === directory) {
+                return undefined;
+            }
+
+            directory = parentPath;
+        }
+    }
 }

src/compiler/parser.ts

@@ -74,6 +74,8 @@ namespace ts {
                     visitNode(cbNode, (<ShorthandPropertyAssignment>node).questionToken) ||
                     visitNode(cbNode, (<ShorthandPropertyAssignment>node).equalsToken) ||
                     visitNode(cbNode, (<ShorthandPropertyAssignment>node).objectAssignmentInitializer);
+            case SyntaxKind.SpreadAssignment:
+                return visitNode(cbNode, (<SpreadAssignment>node).expression);
             case SyntaxKind.Parameter:
             case SyntaxKind.PropertyDeclaration:
             case SyntaxKind.PropertySignature:
@@ -139,6 +141,11 @@ namespace ts {
             case SyntaxKind.IndexedAccessType:
                 return visitNode(cbNode, (<IndexedAccessTypeNode>node).objectType) ||
                     visitNode(cbNode, (<IndexedAccessTypeNode>node).indexType);
+            case SyntaxKind.MappedType:
+                return visitNode(cbNode, (<MappedTypeNode>node).readonlyToken) ||
+                    visitNode(cbNode, (<MappedTypeNode>node).typeParameter) ||
+                    visitNode(cbNode, (<MappedTypeNode>node).questionToken) ||
+                    visitNode(cbNode, (<MappedTypeNode>node).type);
             case SyntaxKind.LiteralType:
                 return visitNode(cbNode, (<LiteralTypeNode>node).literal);
             case SyntaxKind.ObjectBindingPattern:
@@ -197,8 +204,8 @@ namespace ts {
                     visitNode(cbNode, (<ConditionalExpression>node).whenTrue) ||
                     visitNode(cbNode, (<ConditionalExpression>node).colonToken) ||
                     visitNode(cbNode, (<ConditionalExpression>node).whenFalse);
-            case SyntaxKind.SpreadElementExpression:
-                return visitNode(cbNode, (<SpreadElementExpression>node).expression);
+            case SyntaxKind.SpreadElement:
+                return visitNode(cbNode, (<SpreadElement>node).expression);
             case SyntaxKind.Block:
             case SyntaxKind.ModuleBlock:
                 return visitNodes(cbNodes, (<Block>node).statements);
@@ -438,6 +445,10 @@ namespace ts {
         return result;
     }
 
+    export function parseIsolatedEntityName(text: string, languageVersion: ScriptTarget): EntityName {
+        return Parser.parseIsolatedEntityName(text, languageVersion);
+    }
+
     export function isExternalModule(file: SourceFile): boolean {
         return file.externalModuleIndicator !== undefined;
     }
@@ -589,6 +600,16 @@ namespace ts {
             return result;
         }
 
+        export function parseIsolatedEntityName(content: string, languageVersion: ScriptTarget): EntityName {
+            initializeState(content, languageVersion, /*syntaxCursor*/ undefined, ScriptKind.JS);
+            // Prime the scanner.
+            nextToken();
+            const entityName = parseEntityName(/*allowReservedWords*/ true);
+            const isInvalid = token() === SyntaxKind.EndOfFileToken && !parseDiagnostics.length;
+            clearState();
+            return isInvalid ? entityName : undefined;
+        }
+
         function getLanguageVariant(scriptKind: ScriptKind) {
             // .tsx and .jsx files are treated as jsx language variant.
             return scriptKind === ScriptKind.TSX || scriptKind === ScriptKind.JSX || scriptKind === ScriptKind.JS ? LanguageVariant.JSX : LanguageVariant.Standard;
@@ -1269,9 +1290,11 @@ namespace ts {
                     // which would be a candidate for improved error reporting.
                     return token() === SyntaxKind.OpenBracketToken || isLiteralPropertyName();
                 case ParsingContext.ObjectLiteralMembers:
-                    return token() === SyntaxKind.OpenBracketToken || token() === SyntaxKind.AsteriskToken || isLiteralPropertyName();
+                    return token() === SyntaxKind.OpenBracketToken || token() === SyntaxKind.AsteriskToken || token() === SyntaxKind.DotDotDotToken || isLiteralPropertyName();
+                case ParsingContext.RestProperties:
+                    return isLiteralPropertyName();
                 case ParsingContext.ObjectBindingElements:
-                    return token() === SyntaxKind.OpenBracketToken || isLiteralPropertyName();
+                    return token() === SyntaxKind.OpenBracketToken || token() === SyntaxKind.DotDotDotToken || isLiteralPropertyName();
                 case ParsingContext.HeritageClauseElement:
                     // If we see { } then only consume it as an expression if it is followed by , or {
                     // That way we won't consume the body of a class in its heritage clause.
@@ -1398,6 +1421,7 @@ namespace ts {
                 case ParsingContext.ArrayBindingElements:
                     return token() === SyntaxKind.CloseBracketToken;
                 case ParsingContext.Parameters:
+                case ParsingContext.RestProperties:
                     // Tokens other than ')' and ']' (the latter for index signatures) are here for better error recovery
                     return token() === SyntaxKind.CloseParenToken || token() === SyntaxKind.CloseBracketToken /*|| token === SyntaxKind.OpenBraceToken*/;
                 case ParsingContext.TypeArguments:
@@ -1583,6 +1607,9 @@ namespace ts {
                 case ParsingContext.Parameters:
                     return isReusableParameter(node);
 
+                case ParsingContext.RestProperties:
+                    return false;
+
                 // Any other lists we do not care about reusing nodes in.  But feel free to add if
                 // you can do so safely.  Danger areas involve nodes that may involve speculative
                 // parsing.  If speculative parsing is involved with the node, then the range the
@@ -1780,6 +1807,7 @@ namespace ts {
                 case ParsingContext.BlockStatements: return Diagnostics.Declaration_or_statement_expected;
                 case ParsingContext.SwitchClauses: return Diagnostics.case_or_default_expected;
                 case ParsingContext.SwitchClauseStatements: return Diagnostics.Statement_expected;
+                case ParsingContext.RestProperties: // fallthrough
                 case ParsingContext.TypeMembers: return Diagnostics.Property_or_signature_expected;
                 case ParsingContext.ClassMembers: return Diagnostics.Unexpected_token_A_constructor_method_accessor_or_property_was_expected;
                 case ParsingContext.EnumMembers: return Diagnostics.Enum_member_expected;
@@ -2399,6 +2427,36 @@ namespace ts {
             return members;
         }
 
+        function isStartOfMappedType() {
+            nextToken();
+            if (token() === SyntaxKind.ReadonlyKeyword) {
+                nextToken();
+            }
+            return token() === SyntaxKind.OpenBracketToken && nextTokenIsIdentifier() && nextToken() === SyntaxKind.InKeyword;
+        }
+
+        function parseMappedTypeParameter() {
+            const node = <TypeParameterDeclaration>createNode(SyntaxKind.TypeParameter);
+            node.name = parseIdentifier();
+            parseExpected(SyntaxKind.InKeyword);
+            node.constraint = parseType();
+            return finishNode(node);
+        }
+
+        function parseMappedType() {
+            const node = <MappedTypeNode>createNode(SyntaxKind.MappedType);
+            parseExpected(SyntaxKind.OpenBraceToken);
+            node.readonlyToken = parseOptionalToken(SyntaxKind.ReadonlyKeyword);
+            parseExpected(SyntaxKind.OpenBracketToken);
+            node.typeParameter = parseMappedTypeParameter();
+            parseExpected(SyntaxKind.CloseBracketToken);
+            node.questionToken = parseOptionalToken(SyntaxKind.QuestionToken);
+            node.type = parseTypeAnnotation();
+            parseSemicolon();
+            parseExpected(SyntaxKind.CloseBraceToken);
+            return finishNode(node);
+        }
+
         function parseTupleType(): TupleTypeNode {
             const node = <TupleTypeNode>createNode(SyntaxKind.TupleType);
             node.elementTypes = parseBracketedList(ParsingContext.TupleElementTypes, parseType, SyntaxKind.OpenBracketToken, SyntaxKind.CloseBracketToken);
@@ -2472,7 +2530,7 @@ namespace ts {
                 case SyntaxKind.TypeOfKeyword:
                     return parseTypeQuery();
                 case SyntaxKind.OpenBraceToken:
-                    return parseTypeLiteral();
+                    return lookAhead(isStartOfMappedType) ? parseMappedType() : parseTypeLiteral();
                 case SyntaxKind.OpenBracketToken:
                     return parseTupleType();
                 case SyntaxKind.OpenParenToken:
@@ -4122,7 +4180,7 @@ namespace ts {
         }
 
         function parseSpreadElement(): Expression {
-            const node = <SpreadElementExpression>createNode(SyntaxKind.SpreadElementExpression);
+            const node = <SpreadElement>createNode(SyntaxKind.SpreadElement);
             parseExpected(SyntaxKind.DotDotDotToken);
             node.expression = parseAssignmentExpressionOrHigher();
             return finishNode(node);
@@ -4162,6 +4220,12 @@ namespace ts {
 
         function parseObjectLiteralElement(): ObjectLiteralElementLike {
             const fullStart = scanner.getStartPos();
+            const dotDotDotToken = parseOptionalToken(SyntaxKind.DotDotDotToken);
+            if (dotDotDotToken) {
+                const spreadElement = <SpreadAssignment>createNode(SyntaxKind.SpreadAssignment, fullStart);
+                spreadElement.expression = parseAssignmentExpressionOrHigher();
+                return addJSDocComment(finishNode(spreadElement));
+            }
             const decorators = parseDecorators();
             const modifiers = parseModifiers();
 
@@ -4865,6 +4929,7 @@ namespace ts {
 
         function parseObjectBindingElement(): BindingElement {
             const node = <BindingElement>createNode(SyntaxKind.BindingElement);
+            node.dotDotDotToken = parseOptionalToken(SyntaxKind.DotDotDotToken);
             const tokenIsIdentifier = isIdentifier();
             const propertyName = parsePropertyName();
             if (tokenIsIdentifier && token() !== SyntaxKind.ColonToken) {
@@ -5809,6 +5874,7 @@ namespace ts {
             JsxChildren,               // Things between opening and closing JSX tags
             ArrayLiteralMembers,       // Members in array literal
             Parameters,                // Parameters in parameter list
+            RestProperties,            // Property names in a rest type list
             TypeParameters,            // Type parameters in type parameter list
             TypeArguments,             // Type arguments in type argument list
             TupleElementTypes,         // Element types in tuple element type list
@@ -6238,6 +6304,7 @@ namespace ts {
                     }
                     if (token() === SyntaxKind.NewLineTrivia) {
                         state = JSDocState.BeginningOfLine;
+                        indent = 0;
                         nextJSDocToken();
                     }
                     while (token() !== SyntaxKind.EndOfFileToken) {

src/compiler/program.ts

@@ -3,10 +3,6 @@
 /// <reference path="core.ts" />
 
 namespace ts {
-    /** The version of the TypeScript compiler release */
-
-    export const version = "2.1.0";
-
     const emptyArray: any[] = [];
 
     export function findConfigFile(searchPath: string, fileExists: (fileName: string) => boolean, configName = "tsconfig.json"): string {
@@ -431,13 +427,14 @@ namespace ts {
         return program;
 
         function getCommonSourceDirectory() {
-            if (typeof commonSourceDirectory === "undefined") {
-                if (options.rootDir && checkSourceFilesBelongToPath(files, options.rootDir)) {
+            if (commonSourceDirectory === undefined) {
+                const emittedFiles = filterSourceFilesInDirectory(files, isSourceFileFromExternalLibrary);
+                if (options.rootDir && checkSourceFilesBelongToPath(emittedFiles, options.rootDir)) {
                     // If a rootDir is specified and is valid use it as the commonSourceDirectory
                     commonSourceDirectory = getNormalizedAbsolutePath(options.rootDir, currentDirectory);
                 }
                 else {
-                    commonSourceDirectory = computeCommonSourceDirectory(files);
+                    commonSourceDirectory = computeCommonSourceDirectory(emittedFiles);
                 }
                 if (commonSourceDirectory && commonSourceDirectory[commonSourceDirectory.length - 1] !== directorySeparator) {
                     // Make sure directory path ends with directory separator so this string can directly
@@ -476,7 +473,7 @@ namespace ts {
                 return resolveModuleNamesWorker(moduleNames, containingFile);
             }
 
-            // at this point we know that either 
+            // at this point we know that either
             // - file has local declarations for ambient modules
             // OR
             // - old program state is available
@@ -670,7 +667,7 @@ namespace ts {
             }
 
             const modifiedFilePaths = modifiedSourceFiles.map(f => f.newFile.path);
-            // try to verify results of module resolution 
+            // try to verify results of module resolution
             for (const { oldFile: oldSourceFile, newFile: newSourceFile } of modifiedSourceFiles) {
                 const newSourceFilePath = getNormalizedAbsolutePath(newSourceFile.fileName, currentDirectory);
                 if (resolveModuleNamesWorker) {
@@ -908,48 +905,24 @@ namespace ts {
         function getJavaScriptSyntacticDiagnosticsForFile(sourceFile: SourceFile): Diagnostic[] {
             return runWithCancellationToken(() => {
                 const diagnostics: Diagnostic[] = [];
+                let parent: Node = sourceFile;
                 walk(sourceFile);
 
                 return diagnostics;
 
-                function walk(node: Node): boolean {
-                    if (!node) {
-                        return false;
-                    }
+                function walk(node: Node) {
+                    // Return directly from the case if the given node doesnt want to visit each child
+                    // Otherwise break to visit each child
 
-                    switch (node.kind) {
-                        case SyntaxKind.ImportEqualsDeclaration:
-                            diagnostics.push(createDiagnosticForNode(node, Diagnostics.import_can_only_be_used_in_a_ts_file));
-                            return true;
-                        case SyntaxKind.ExportAssignment:
-                            if ((<ExportAssignment>node).isExportEquals) {
-                                diagnostics.push(createDiagnosticForNode(node, Diagnostics.export_can_only_be_used_in_a_ts_file));
-                                return true;
+                    switch (parent.kind) {
+                        case SyntaxKind.Parameter:
+                        case SyntaxKind.PropertyDeclaration:
+                            if ((<ParameterDeclaration | PropertyDeclaration>parent).questionToken === node) {
+                                diagnostics.push(createDiagnosticForNode(node, Diagnostics._0_can_only_be_used_in_a_ts_file, "?"));
+                                return;
                             }
-                            break;
-                        case SyntaxKind.ClassDeclaration:
-                            let classDeclaration = <ClassDeclaration>node;
-                            if (checkModifiers(classDeclaration.modifiers) ||
-                                checkTypeParameters(classDeclaration.typeParameters)) {
-                                return true;
-                            }
-                            break;
-                        case SyntaxKind.HeritageClause:
-                            let heritageClause = <HeritageClause>node;
-                            if (heritageClause.token === SyntaxKind.ImplementsKeyword) {
-                                diagnostics.push(createDiagnosticForNode(node, Diagnostics.implements_clauses_can_only_be_used_in_a_ts_file));
-                                return true;
-                            }
-                            break;
-                        case SyntaxKind.InterfaceDeclaration:
-                            diagnostics.push(createDiagnosticForNode(node, Diagnostics.interface_declarations_can_only_be_used_in_a_ts_file));
-                            return true;
-                        case SyntaxKind.ModuleDeclaration:
-                            diagnostics.push(createDiagnosticForNode(node, Diagnostics.module_declarations_can_only_be_used_in_a_ts_file));
-                            return true;
-                        case SyntaxKind.TypeAliasDeclaration:
-                            diagnostics.push(createDiagnosticForNode(node, Diagnostics.type_aliases_can_only_be_used_in_a_ts_file));
-                            return true;
+
+                        // Pass through
                         case SyntaxKind.MethodDeclaration:
                         case SyntaxKind.MethodSignature:
                         case SyntaxKind.Constructor:
@@ -959,124 +932,151 @@ namespace ts {
                         case SyntaxKind.FunctionDeclaration:
                         case SyntaxKind.ArrowFunction:
                         case SyntaxKind.FunctionDeclaration:
-                            const functionDeclaration = <FunctionLikeDeclaration>node;
-                            if (checkModifiers(functionDeclaration.modifiers) ||
-                                checkTypeParameters(functionDeclaration.typeParameters) ||
-                                checkTypeAnnotation(functionDeclaration.type)) {
-                                return true;
-                            }
-                            break;
-                        case SyntaxKind.VariableStatement:
-                            const variableStatement = <VariableStatement>node;
-                            if (checkModifiers(variableStatement.modifiers)) {
-                                return true;
-                            }
-                            break;
                         case SyntaxKind.VariableDeclaration:
-                            const variableDeclaration = <VariableDeclaration>node;
-                            if (checkTypeAnnotation(variableDeclaration.type)) {
-                                return true;
+                            // type annotation
+                            if ((<FunctionLikeDeclaration | VariableDeclaration | ParameterDeclaration | PropertyDeclaration>parent).type === node) {
+                                diagnostics.push(createDiagnosticForNode(node, Diagnostics.types_can_only_be_used_in_a_ts_file));
+                                return;
+                            }
+                    }
+
+                    switch (node.kind) {
+                        case SyntaxKind.ImportEqualsDeclaration:
+                            diagnostics.push(createDiagnosticForNode(node, Diagnostics.import_can_only_be_used_in_a_ts_file));
+                            return;
+                        case SyntaxKind.ExportAssignment:
+                            if ((<ExportAssignment>node).isExportEquals) {
+                                diagnostics.push(createDiagnosticForNode(node, Diagnostics.export_can_only_be_used_in_a_ts_file));
+                                return;
+                            }
+                            break;
+                        case SyntaxKind.HeritageClause:
+                            let heritageClause = <HeritageClause>node;
+                            if (heritageClause.token === SyntaxKind.ImplementsKeyword) {
+                                diagnostics.push(createDiagnosticForNode(node, Diagnostics.implements_clauses_can_only_be_used_in_a_ts_file));
+                                return;
+                            }
+                            break;
+                        case SyntaxKind.InterfaceDeclaration:
+                            diagnostics.push(createDiagnosticForNode(node, Diagnostics.interface_declarations_can_only_be_used_in_a_ts_file));
+                            return;
+                        case SyntaxKind.ModuleDeclaration:
+                            diagnostics.push(createDiagnosticForNode(node, Diagnostics.module_declarations_can_only_be_used_in_a_ts_file));
+                            return;
+                        case SyntaxKind.TypeAliasDeclaration:
+                            diagnostics.push(createDiagnosticForNode(node, Diagnostics.type_aliases_can_only_be_used_in_a_ts_file));
+                            return;
+                        case SyntaxKind.EnumDeclaration:
+                            diagnostics.push(createDiagnosticForNode(node, Diagnostics.enum_declarations_can_only_be_used_in_a_ts_file));
+                            return;
+                        case SyntaxKind.TypeAssertionExpression:
+                            let typeAssertionExpression = <TypeAssertion>node;
+                            diagnostics.push(createDiagnosticForNode(typeAssertionExpression.type, Diagnostics.type_assertion_expressions_can_only_be_used_in_a_ts_file));
+                            return;
+                    }
+
+                    const prevParent = parent;
+                    parent = node;
+                    forEachChild(node, walk, walkArray);
+                    parent = prevParent;
+                }
+
+                function walkArray(nodes: NodeArray<Node>) {
+                    if (parent.decorators === nodes && !options.experimentalDecorators) {
+                        diagnostics.push(createDiagnosticForNode(parent, 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));
+                    }
+
+                    switch (parent.kind) {
+                        case SyntaxKind.ClassDeclaration:
+                        case SyntaxKind.MethodDeclaration:
+                        case SyntaxKind.MethodSignature:
+                        case SyntaxKind.Constructor:
+                        case SyntaxKind.GetAccessor:
+                        case SyntaxKind.SetAccessor:
+                        case SyntaxKind.FunctionExpression:
+                        case SyntaxKind.FunctionDeclaration:
+                        case SyntaxKind.ArrowFunction:
+                        case SyntaxKind.FunctionDeclaration:
+                            // Check type parameters
+                            if (nodes === (<ClassDeclaration | FunctionLikeDeclaration>parent).typeParameters) {
+                                diagnostics.push(createDiagnosticForNodeArray(nodes, Diagnostics.type_parameter_declarations_can_only_be_used_in_a_ts_file));
+                                return;
+                            }
+                            // pass through
+                        case SyntaxKind.VariableStatement:
+                            // Check modifiers
+                            if (nodes === (<ClassDeclaration | FunctionLikeDeclaration | VariableStatement>parent).modifiers) {
+                                return checkModifiers(<NodeArray<Modifier>>nodes, parent.kind === SyntaxKind.VariableStatement);
+                            }
+                            break;
+                        case SyntaxKind.PropertyDeclaration:
+                            // Check modifiers of property declaration
+                            if (nodes === (<PropertyDeclaration>parent).modifiers) {
+                                for (const modifier of <NodeArray<Modifier>>nodes) {
+                                    if (modifier.kind !== SyntaxKind.StaticKeyword) {
+                                        diagnostics.push(createDiagnosticForNode(modifier, Diagnostics._0_can_only_be_used_in_a_ts_file, tokenToString(modifier.kind)));
+                                    }
+                                }
+                                return;
+                            }
+                            break;
+                        case SyntaxKind.Parameter:
+                            // Check modifiers of parameter declaration
+                            if (nodes === (<ParameterDeclaration>parent).modifiers) {
+                                diagnostics.push(createDiagnosticForNodeArray(nodes, Diagnostics.parameter_modifiers_can_only_be_used_in_a_ts_file));
+                                return;
                             }
                             break;
                         case SyntaxKind.CallExpression:
                         case SyntaxKind.NewExpression:
-                            const expression = <CallExpression>node;
-                            if (expression.typeArguments && expression.typeArguments.length > 0) {
-                                const start = expression.typeArguments.pos;
-                                diagnostics.push(createFileDiagnostic(sourceFile, start, expression.typeArguments.end - start,
-                                    Diagnostics.type_arguments_can_only_be_used_in_a_ts_file));
-                                return true;
+                        case SyntaxKind.ExpressionWithTypeArguments:
+                            // Check type arguments
+                            if (nodes === (<CallExpression | NewExpression | ExpressionWithTypeArguments>parent).typeArguments) {
+                                diagnostics.push(createDiagnosticForNodeArray(nodes, Diagnostics.type_arguments_can_only_be_used_in_a_ts_file));
+                                return;
                             }
                             break;
-                        case SyntaxKind.Parameter:
-                            const parameter = <ParameterDeclaration>node;
-                            if (parameter.modifiers) {
-                                const start = parameter.modifiers.pos;
-                                diagnostics.push(createFileDiagnostic(sourceFile, start, parameter.modifiers.end - start,
-                                    Diagnostics.parameter_modifiers_can_only_be_used_in_a_ts_file));
-                                return true;
-                            }
-                            if (parameter.questionToken) {
-                                diagnostics.push(createDiagnosticForNode(parameter.questionToken, Diagnostics._0_can_only_be_used_in_a_ts_file, "?"));
-                                return true;
-                            }
-                            if (parameter.type) {
-                                diagnostics.push(createDiagnosticForNode(parameter.type, Diagnostics.types_can_only_be_used_in_a_ts_file));
-                                return true;
-                            }
-                            break;
-                        case SyntaxKind.PropertyDeclaration:
-                            const propertyDeclaration = <PropertyDeclaration>node;
-                            if (propertyDeclaration.modifiers) {
-                                for (const modifier of propertyDeclaration.modifiers) {
-                                    if (modifier.kind !== SyntaxKind.StaticKeyword) {
-                                        diagnostics.push(createDiagnosticForNode(modifier, Diagnostics._0_can_only_be_used_in_a_ts_file, tokenToString(modifier.kind)));
-                                        return true;
-                                    }
+                    }
+
+                    for (const node of nodes) {
+                        walk(node);
+                    }
+                }
+
+                function checkModifiers(modifiers: NodeArray<Modifier>, isConstValid: boolean) {
+                    for (const modifier of modifiers) {
+                        switch (modifier.kind) {
+                            case SyntaxKind.ConstKeyword:
+                                if (isConstValid) {
+                                    continue;
                                 }
-                            }
-                            if (checkTypeAnnotation((<PropertyDeclaration>node).type)) {
-                                return true;
-                            }
-                            break;
-                        case SyntaxKind.EnumDeclaration:
-                            diagnostics.push(createDiagnosticForNode(node, Diagnostics.enum_declarations_can_only_be_used_in_a_ts_file));
-                            return true;
-                        case SyntaxKind.TypeAssertionExpression:
-                            let typeAssertionExpression = <TypeAssertion>node;
-                            diagnostics.push(createDiagnosticForNode(typeAssertionExpression.type, Diagnostics.type_assertion_expressions_can_only_be_used_in_a_ts_file));
-                            return true;
-                        case SyntaxKind.Decorator:
-                            if (!options.experimentalDecorators) {
-                                diagnostics.push(createDiagnosticForNode(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));
-                            }
-                            return true;
-                    }
+                                // Fallthrough to report error
+                            case SyntaxKind.PublicKeyword:
+                            case SyntaxKind.PrivateKeyword:
+                            case SyntaxKind.ProtectedKeyword:
+                            case SyntaxKind.ReadonlyKeyword:
+                            case SyntaxKind.DeclareKeyword:
+                            case SyntaxKind.AbstractKeyword:
+                                diagnostics.push(createDiagnosticForNode(modifier, Diagnostics._0_can_only_be_used_in_a_ts_file, tokenToString(modifier.kind)));
+                                break;
 
-                    return forEachChild(node, walk);
-                }
-
-                function checkTypeParameters(typeParameters: NodeArray<TypeParameterDeclaration>): boolean {
-                    if (typeParameters) {
-                        const start = typeParameters.pos;
-                        diagnostics.push(createFileDiagnostic(sourceFile, start, typeParameters.end - start, Diagnostics.type_parameter_declarations_can_only_be_used_in_a_ts_file));
-                        return true;
-                    }
-                    return false;
-                }
-
-                function checkTypeAnnotation(type: TypeNode): boolean {
-                    if (type) {
-                        diagnostics.push(createDiagnosticForNode(type, Diagnostics.types_can_only_be_used_in_a_ts_file));
-                        return true;
-                    }
-
-                    return false;
-                }
-
-                function checkModifiers(modifiers: NodeArray<Modifier>): boolean {
-                    if (modifiers) {
-                        for (const modifier of modifiers) {
-                            switch (modifier.kind) {
-                                case SyntaxKind.PublicKeyword:
-                                case SyntaxKind.PrivateKeyword:
-                                case SyntaxKind.ProtectedKeyword:
-                                case SyntaxKind.ReadonlyKeyword:
-                                case SyntaxKind.DeclareKeyword:
-                                    diagnostics.push(createDiagnosticForNode(modifier, Diagnostics._0_can_only_be_used_in_a_ts_file, tokenToString(modifier.kind)));
-                                    return true;
-
-                                // These are all legal modifiers.
-                                case SyntaxKind.StaticKeyword:
-                                case SyntaxKind.ExportKeyword:
-                                case SyntaxKind.ConstKeyword:
-                                case SyntaxKind.DefaultKeyword:
-                                case SyntaxKind.AbstractKeyword:
-                            }
+                            // These are all legal modifiers.
+                            case SyntaxKind.StaticKeyword:
+                            case SyntaxKind.ExportKeyword:
+                            case SyntaxKind.DefaultKeyword:
                         }
                     }
+                }
 
-                    return false;
+                function createDiagnosticForNodeArray(nodes: NodeArray<Node>, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number): Diagnostic {
+                    const start = nodes.pos;
+                    return createFileDiagnostic(sourceFile, start, nodes.end - start, message, arg0, arg1, arg2);
+                }
+
+                // Since these are syntactic diagnostics, parent might not have been set
+                // this means the sourceFile cannot be infered from the node
+                function createDiagnosticForNode(node: Node, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number): Diagnostic {
+                    return createDiagnosticForNodeInSourceFile(sourceFile, node, message, arg0, arg1, arg2);
                 }
             });
         }
@@ -1140,9 +1140,14 @@ namespace ts {
             if (options.importHelpers
                 && (options.isolatedModules || isExternalModuleFile)
                 && !file.isDeclarationFile) {
-                const externalHelpersModuleReference = <StringLiteral>createNode(SyntaxKind.StringLiteral);
+                // synthesize 'import "tslib"' declaration
+                const externalHelpersModuleReference = <StringLiteral>createSynthesizedNode(SyntaxKind.StringLiteral);
                 externalHelpersModuleReference.text = externalHelpersModuleNameText;
-                externalHelpersModuleReference.parent = file;
+                const importDecl = createSynthesizedNode(SyntaxKind.ImportDeclaration);
+
+                importDecl.parent = file;
+                externalHelpersModuleReference.parent = importDecl;
+
                 imports = [externalHelpersModuleReference];
             }
 
@@ -1395,14 +1400,17 @@ namespace ts {
                     // If we already resolved to this file, it must have been a secondary reference. Check file contents
                     // for sameness and possibly issue an error
                     if (previousResolution) {
-                        const otherFileText = host.readFile(resolvedTypeReferenceDirective.resolvedFileName);
-                        if (otherFileText !== getSourceFile(previousResolution.resolvedFileName).text) {
-                            fileProcessingDiagnostics.add(createDiagnostic(refFile, refPos, refEnd,
-                                Diagnostics.Conflicting_definitions_for_0_found_at_1_and_2_Consider_installing_a_specific_version_of_this_library_to_resolve_the_conflict,
-                                typeReferenceDirective,
-                                resolvedTypeReferenceDirective.resolvedFileName,
-                                previousResolution.resolvedFileName
-                            ));
+                        // Don't bother reading the file again if it's the same file.
+                        if (resolvedTypeReferenceDirective.resolvedFileName !== previousResolution.resolvedFileName) {
+                            const otherFileText = host.readFile(resolvedTypeReferenceDirective.resolvedFileName);
+                            if (otherFileText !== getSourceFile(previousResolution.resolvedFileName).text) {
+                                fileProcessingDiagnostics.add(createDiagnostic(refFile, refPos, refEnd,
+                                    Diagnostics.Conflicting_definitions_for_0_found_at_1_and_2_Consider_installing_a_specific_version_of_this_library_to_resolve_the_conflict,
+                                    typeReferenceDirective,
+                                    resolvedTypeReferenceDirective.resolvedFileName,
+                                    previousResolution.resolvedFileName
+                                ));
+                            }
                         }
                         // don't overwrite previous resolution result
                         saveResolution = false;
@@ -1439,7 +1447,9 @@ namespace ts {
             collectExternalModuleReferences(file);
             if (file.imports.length || file.moduleAugmentations.length) {
                 file.resolvedModules = createMap<ResolvedModuleFull>();
-                const moduleNames = map(concatenate(file.imports, file.moduleAugmentations), getTextOfLiteral);
+                // Because global augmentation doesn't have string literal name, we can check for global augmentation as such.
+                const nonGlobalAugmentation = filter(file.moduleAugmentations, (moduleAugmentation) => moduleAugmentation.kind === SyntaxKind.StringLiteral);
+                const moduleNames = map(concatenate(file.imports, nonGlobalAugmentation), getTextOfLiteral);
                 const resolutions = resolveModuleNamesReusingOldState(moduleNames, getNormalizedAbsolutePath(file.fileName, currentDirectory), file);
                 Debug.assert(resolutions.length === moduleNames.length);
                 for (let i = 0; i < moduleNames.length; i++) {
@@ -1670,7 +1680,15 @@ namespace ts {
                 programDiagnostics.add(createCompilerDiagnostic(Diagnostics.Option_0_cannot_be_specified_without_specifying_option_1, "emitDecoratorMetadata", "experimentalDecorators"));
             }
 
-            if (options.reactNamespace && !isIdentifierText(options.reactNamespace, languageVersion)) {
+            if (options.jsxFactory) {
+                if (options.reactNamespace) {
+                    programDiagnostics.add(createCompilerDiagnostic(Diagnostics.Option_0_cannot_be_specified_with_option_1, "reactNamespace", "jsxFactory"));
+                }
+                if (!parseIsolatedEntityName(options.jsxFactory, languageVersion)) {
+                    programDiagnostics.add(createCompilerDiagnostic(Diagnostics.Invalid_value_for_jsxFactory_0_is_not_a_valid_identifier_or_qualified_name, options.jsxFactory));
+                }
+            }
+            else if (options.reactNamespace && !isIdentifierText(options.reactNamespace, languageVersion)) {
                 programDiagnostics.add(createCompilerDiagnostic(Diagnostics.Invalid_value_for_reactNamespace_0_is_not_a_valid_identifier, options.reactNamespace));
             }
 
@@ -1690,18 +1708,13 @@ namespace ts {
                     const emitFilePath = toPath(emitFileName, currentDirectory, getCanonicalFileName);
                     // Report error if the output overwrites input file
                     if (filesByName.contains(emitFilePath)) {
-                        if (options.noEmitOverwritenFiles && !options.out && !options.outDir && !options.outFile) {
-                            blockEmittingOfFile(emitFileName);
-                        }
-                        else {
-                            let chain: DiagnosticMessageChain;
-                            if (!options.configFilePath) {
-                                // The program is from either an inferred project or an external project
-                                chain = chainDiagnosticMessages(/*details*/ undefined, Diagnostics.Adding_a_tsconfig_json_file_will_help_organize_projects_that_contain_both_TypeScript_and_JavaScript_files_Learn_more_at_https_Colon_Slash_Slashaka_ms_Slashtsconfig);
-                            }
-                            chain = chainDiagnosticMessages(chain, Diagnostics.Cannot_write_file_0_because_it_would_overwrite_input_file, emitFileName);
-                            blockEmittingOfFile(emitFileName, createCompilerDiagnosticFromMessageChain(chain));
+                        let chain: DiagnosticMessageChain;
+                        if (!options.configFilePath) {
+                            // The program is from either an inferred project or an external project
+                            chain = chainDiagnosticMessages(/*details*/ undefined, Diagnostics.Adding_a_tsconfig_json_file_will_help_organize_projects_that_contain_both_TypeScript_and_JavaScript_files_Learn_more_at_https_Colon_Slash_Slashaka_ms_Slashtsconfig);
                         }
+                        chain = chainDiagnosticMessages(chain, Diagnostics.Cannot_write_file_0_because_it_would_overwrite_input_file, emitFileName);
+                        blockEmittingOfFile(emitFileName, createCompilerDiagnosticFromMessageChain(chain));
                     }
 
                     // Report error if multiple files write into same file
@@ -1716,11 +1729,9 @@ namespace ts {
             }
         }
 
-        function blockEmittingOfFile(emitFileName: string, diag?: Diagnostic) {
+        function blockEmittingOfFile(emitFileName: string, diag: Diagnostic) {
             hasEmitBlockingDiagnostics.set(toPath(emitFileName, currentDirectory, getCanonicalFileName), true);
-            if (diag) {
-                programDiagnostics.add(diag);
-            }
+            programDiagnostics.add(diag);
         }
     }
 

src/compiler/transformer.ts

@@ -1,6 +1,7 @@
 /// <reference path="visitor.ts" />
 /// <reference path="transformers/ts.ts" />
 /// <reference path="transformers/jsx.ts" />
+/// <reference path="transformers/esnext.ts" />
 /// <reference path="transformers/es2017.ts" />
 /// <reference path="transformers/es2016.ts" />
 /// <reference path="transformers/es2015.ts" />
@@ -38,6 +39,10 @@ namespace ts {
             transformers.push(transformJsx);
         }
 
+        if (languageVersion < ScriptTarget.ESNext) {
+            transformers.push(transformESNext);
+        }
+
         if (languageVersion < ScriptTarget.ES2017) {
             transformers.push(transformES2017);
         }

src/compiler/transformers/destructuring.ts

@@ -17,7 +17,8 @@ namespace ts {
         node: BinaryExpression,
         needsValue: boolean,
         recordTempVariable: (node: Identifier) => void,
-        visitor?: (node: Node) => VisitResult<Node>): Expression {
+        visitor?: (node: Node) => VisitResult<Node>,
+        transformRest?: boolean): Expression {
 
         if (isEmptyObjectLiteralOrArrayLiteral(node.left)) {
             const right = node.right;
@@ -51,7 +52,7 @@ namespace ts {
             location = value;
         }
 
-        flattenDestructuring(node, value, location, emitAssignment, emitTempVariableAssignment, visitor);
+        flattenDestructuring(context, node, value, location, emitAssignment, emitTempVariableAssignment, recordTempVariable, emitRestAssignment, transformRest, visitor);
 
         if (needsValue) {
             expressions.push(value);
@@ -61,7 +62,7 @@ namespace ts {
         aggregateTransformFlags(expression);
         return expression;
 
-        function emitAssignment(name: Identifier, value: Expression, location: TextRange) {
+        function emitAssignment(name: Identifier | ObjectLiteralExpression, value: Expression, location: TextRange) {
             const expression = createAssignment(name, value, location);
 
             // NOTE: this completely disables source maps, but aligns with the behavior of
@@ -77,6 +78,10 @@ namespace ts {
             emitAssignment(name, value, location);
             return name;
         }
+
+        function emitRestAssignment(elements: ObjectLiteralElementLike[], value: Expression, location: TextRange) {
+            emitAssignment(createObjectLiteral(elements), value, location);
+        }
     }
 
     /**
@@ -87,16 +92,18 @@ namespace ts {
      * @param visitor An optional visitor to use to visit expressions.
      */
     export function flattenParameterDestructuring(
+        context: TransformationContext,
         node: ParameterDeclaration,
         value: Expression,
-        visitor?: (node: Node) => VisitResult<Node>) {
+        visitor?: (node: Node) => VisitResult<Node>,
+        transformRest?: boolean) {
         const declarations: VariableDeclaration[] = [];
 
-        flattenDestructuring(node, value, node, emitAssignment, emitTempVariableAssignment, visitor);
+        flattenDestructuring(context, node, value, node, emitAssignment, emitTempVariableAssignment, noop, emitRestAssignment, transformRest, visitor);
 
         return declarations;
 
-        function emitAssignment(name: Identifier, value: Expression, location: TextRange) {
+        function emitAssignment(name: Identifier | BindingPattern, value: Expression, location: TextRange) {
             const declaration = createVariableDeclaration(name, /*type*/ undefined, value, location);
 
             // NOTE: this completely disables source maps, but aligns with the behavior of
@@ -112,6 +119,10 @@ namespace ts {
             emitAssignment(name, value, location);
             return name;
         }
+
+        function emitRestAssignment(elements: BindingElement[], value: Expression, location: TextRange) {
+            emitAssignment(createObjectBindingPattern(elements), value, location);
+        }
     }
 
     /**
@@ -122,18 +133,20 @@ namespace ts {
      * @param visitor An optional visitor to use to visit expressions.
      */
     export function flattenVariableDestructuring(
+        context: TransformationContext,
         node: VariableDeclaration,
         value?: Expression,
         visitor?: (node: Node) => VisitResult<Node>,
-        recordTempVariable?: (node: Identifier) => void) {
+        recordTempVariable?: (node: Identifier) => void,
+        transformRest?: boolean) {
         const declarations: VariableDeclaration[] = [];
 
         let pendingAssignments: Expression[];
-        flattenDestructuring(node, value, node, emitAssignment, emitTempVariableAssignment, visitor);
+        flattenDestructuring(context, node, value, node, emitAssignment, emitTempVariableAssignment, recordTempVariable, emitRestAssignment, transformRest, visitor);
 
         return declarations;
 
-        function emitAssignment(name: Identifier, value: Expression, location: TextRange, original: Node) {
+        function emitAssignment(name: Identifier | BindingPattern, value: Expression, location: TextRange, original: Node) {
             if (pendingAssignments) {
                 pendingAssignments.push(value);
                 value = inlineExpressions(pendingAssignments);
@@ -167,6 +180,10 @@ namespace ts {
             }
             return name;
         }
+
+        function emitRestAssignment(elements: BindingElement[], value: Expression, location: TextRange, original: Node) {
+            emitAssignment(createObjectBindingPattern(elements), value, location, original);
+        }
     }
 
     /**
@@ -179,6 +196,7 @@ namespace ts {
      * @param visitor An optional visitor to use to visit expressions.
      */
     export function flattenVariableDestructuringToExpression(
+        context: TransformationContext,
         node: VariableDeclaration,
         recordTempVariable: (name: Identifier) => void,
         createAssignmentCallback?: (name: Identifier, value: Expression, location?: TextRange) => Expression,
@@ -186,15 +204,17 @@ namespace ts {
 
         const pendingAssignments: Expression[] = [];
 
-        flattenDestructuring(node, /*value*/ undefined, node, emitAssignment, emitTempVariableAssignment, visitor);
+        flattenDestructuring(context, node, /*value*/ undefined, node, emitAssignment, emitTempVariableAssignment, noop, emitRestAssignment, /*transformRest*/ false, visitor);
 
         const expression = inlineExpressions(pendingAssignments);
         aggregateTransformFlags(expression);
         return expression;
 
-        function emitAssignment(name: Identifier, value: Expression, location: TextRange, original: Node) {
+        function emitAssignment(name: Identifier | ObjectLiteralExpression, value: Expression, location: TextRange, original: Node) {
             const expression = createAssignmentCallback
-                ? createAssignmentCallback(name, value, location)
+                ? createAssignmentCallback(name.kind === SyntaxKind.Identifier ? name : emitTempVariableAssignment(name, location),
+                                           value,
+                                           location)
                 : createAssignment(name, value, location);
 
             emitPendingAssignment(expression, original);
@@ -206,6 +226,10 @@ namespace ts {
             return name;
         }
 
+        function emitRestAssignment(elements: ObjectLiteralElementLike[], value: Expression, location: TextRange, original: Node) {
+            emitAssignment(createObjectLiteral(elements), value, location, original);
+        }
+
         function emitPendingAssignment(expression: Expression, original: Node) {
             expression.original = original;
 
@@ -218,11 +242,15 @@ namespace ts {
     }
 
     function flattenDestructuring(
+        context: TransformationContext,
         root: VariableDeclaration | ParameterDeclaration | BindingElement | BinaryExpression,
         value: Expression,
         location: TextRange,
         emitAssignment: (name: Identifier, value: Expression, location: TextRange, original: Node) => void,
         emitTempVariableAssignment: (value: Expression, location: TextRange) => Identifier,
+        recordTempVariable: (node: Identifier) => void,
+        emitRestAssignment: (elements: (ObjectLiteralElementLike[] | BindingElement[]), value: Expression, location: TextRange, original: Node) => void,
+        transformRest: boolean,
         visitor?: (node: Node) => VisitResult<Node>) {
         if (value && visitor) {
             value = visitNode(value, visitor, isExpression);
@@ -280,27 +308,102 @@ namespace ts {
             if (properties.length !== 1) {
                 // For anything but a single element destructuring we need to generate a temporary
                 // to ensure value is evaluated exactly once.
-                // When doing so we want to hightlight the passed in source map node since thats the one needing this temp assignment
+                // When doing so we want to highlight the passed in source map node since that's the one needing this temp assignment
                 value = ensureIdentifier(value, /*reuseIdentifierExpressions*/ true, location, emitTempVariableAssignment);
             }
 
-            for (const p of properties) {
+            let bindingElements: ObjectLiteralElementLike[] = [];
+            let computedTempVariables: Expression[];
+            for (let i = 0; i < properties.length; i++) {
+                const p = properties[i];
                 if (p.kind === SyntaxKind.PropertyAssignment || p.kind === SyntaxKind.ShorthandPropertyAssignment) {
-                    const propName = <Identifier | LiteralExpression>(<PropertyAssignment>p).name;
-                    const target = p.kind === SyntaxKind.ShorthandPropertyAssignment ? <ShorthandPropertyAssignment>p : (<PropertyAssignment>p).initializer || propName;
-                    // Assignment for target = value.propName should highligh whole property, hence use p as source map node
-                    emitDestructuringAssignment(target, createDestructuringPropertyAccess(value, propName), p);
+                    if (!transformRest ||
+                        p.transformFlags & TransformFlags.ContainsSpreadExpression ||
+                        (p.kind === SyntaxKind.PropertyAssignment && p.initializer.transformFlags & TransformFlags.ContainsSpreadExpression) ||
+                        isComputedPropertyName(p.name)) {
+                        if (bindingElements.length) {
+                            emitRestAssignment(bindingElements, value, location, target);
+                            bindingElements = [];
+                        }
+                        const propName = <Identifier | LiteralExpression>(<PropertyAssignment>p).name;
+                        const bindingTarget = p.kind === SyntaxKind.ShorthandPropertyAssignment ? <ShorthandPropertyAssignment>p : (<PropertyAssignment>p).initializer || propName;
+                        // Assignment for bindingTarget = value.propName should highlight whole property, hence use p as source map node
+                        const propAccess = createDestructuringPropertyAccess(value, propName);
+                        if (isComputedPropertyName(propName)) {
+                            computedTempVariables = append(computedTempVariables, (propAccess as ElementAccessExpression).argumentExpression);
+                        }
+                        emitDestructuringAssignment(bindingTarget, propAccess, p);
+                    }
+                    else {
+                        bindingElements.push(p);
+                    }
                 }
+                else if (i === properties.length - 1 &&
+                         p.kind === SyntaxKind.SpreadAssignment &&
+                         p.expression.kind === SyntaxKind.Identifier) {
+                    if (bindingElements.length) {
+                        emitRestAssignment(bindingElements, value, location, target);
+                        bindingElements = [];
+                    }
+                    const propName = (p as SpreadAssignment).expression as Identifier;
+                    const restCall = createRestCall(context, value, target.properties, p => p.name, target, computedTempVariables);
+                    emitDestructuringAssignment(propName, restCall, p);
+                }
+            }
+            if (bindingElements.length) {
+                emitRestAssignment(bindingElements, value, location, target);
+                bindingElements = [];
             }
         }
 
         function emitArrayLiteralAssignment(target: ArrayLiteralExpression, value: Expression, location: TextRange) {
+            if (transformRest) {
+                emitESNextArrayLiteralAssignment(target, value, location);
+            }
+            else {
+                emitES2015ArrayLiteralAssignment(target, value, location);
+            }
+        }
+
+        function emitESNextArrayLiteralAssignment(target: ArrayLiteralExpression, value: Expression, location: TextRange) {
             const elements = target.elements;
             const numElements = elements.length;
             if (numElements !== 1) {
                 // For anything but a single element destructuring we need to generate a temporary
                 // to ensure value is evaluated exactly once.
-                // When doing so we want to hightlight the passed in source map node since thats the one needing this temp assignment
+                // When doing so we want to highlight the passed-in source map node since thats the one needing this temp assignment
+                value = ensureIdentifier(value, /*reuseIdentifierExpressions*/ true, location, emitTempVariableAssignment);
+            }
+
+            const expressions: Expression[] = [];
+            const spreadContainingExpressions: [Expression, Identifier][] = [];
+            for (let i = 0; i < numElements; i++) {
+                const e = elements[i];
+                if (e.kind === SyntaxKind.OmittedExpression) {
+                    continue;
+                }
+                if (e.transformFlags & TransformFlags.ContainsSpreadExpression && i < numElements - 1) {
+                    const tmp = createTempVariable(recordTempVariable);
+                    spreadContainingExpressions.push([e, tmp]);
+                    expressions.push(tmp);
+                }
+                else {
+                    expressions.push(e);
+                }
+            }
+            emitAssignment(updateArrayLiteral(target, expressions) as any as Identifier, value, undefined, undefined);
+            for (const [e, tmp] of spreadContainingExpressions) {
+                emitDestructuringAssignment(e, tmp, e);
+            }
+        }
+
+        function emitES2015ArrayLiteralAssignment(target: ArrayLiteralExpression, value: Expression, location: TextRange) {
+            const elements = target.elements;
+            const numElements = elements.length;
+            if (numElements !== 1) {
+                // For anything but a single element destructuring we need to generate a temporary
+                // to ensure value is evaluated exactly once.
+                // When doing so we want to highlight the passed-in source map node since thats the one needing this temp assignment
                 value = ensureIdentifier(value, /*reuseIdentifierExpressions*/ true, location, emitTempVariableAssignment);
             }
 
@@ -308,11 +411,11 @@ namespace ts {
                 const e = elements[i];
                 if (e.kind !== SyntaxKind.OmittedExpression) {
                     // Assignment for target = value.propName should highligh whole property, hence use e as source map node
-                    if (e.kind !== SyntaxKind.SpreadElementExpression) {
+                    if (e.kind !== SyntaxKind.SpreadElement) {
                         emitDestructuringAssignment(e, createElementAccess(value, createLiteral(i)), e);
                     }
                     else if (i === numElements - 1) {
-                        emitDestructuringAssignment((<SpreadElementExpression>e).expression, createArraySlice(value, i), e);
+                        emitDestructuringAssignment((<SpreadElement>e).expression, createArraySlice(value, i), e);
                     }
                 }
             }
@@ -321,7 +424,10 @@ namespace ts {
         function emitBindingElement(target: VariableDeclaration | ParameterDeclaration | BindingElement, value: Expression) {
             // Any temporary assignments needed to emit target = value should point to target
             const initializer = visitor ? visitNode(target.initializer, visitor, isExpression) : target.initializer;
-            if (initializer) {
+            if (transformRest) {
+                value = value || initializer;
+            }
+            else if (initializer) {
                 // Combine value and initializer
                 value = value ? createDefaultValueCheck(value, initializer, target) : initializer;
             }
@@ -331,9 +437,11 @@ namespace ts {
             }
 
             const name = target.name;
-            if (isBindingPattern(name)) {
-                const elements = name.elements;
-                const numElements = elements.length;
+            if (!isBindingPattern(name)) {
+                emitAssignment(name, value, target, target);
+            }
+            else {
+                const numElements = name.elements.length;
                 if (numElements !== 1) {
                     // For anything other than a single-element destructuring we need to generate a temporary
                     // to ensure value is evaluated exactly once. Additionally, if we have zero elements
@@ -341,29 +449,113 @@ namespace ts {
                     // so in that case, we'll intentionally create that temporary.
                     value = ensureIdentifier(value, /*reuseIdentifierExpressions*/ numElements !== 0, target, emitTempVariableAssignment);
                 }
-                for (let i = 0; i < numElements; i++) {
-                    const element = elements[i];
-                    if (isOmittedExpression(element)) {
-                        continue;
-                    }
-                    else if (name.kind === SyntaxKind.ObjectBindingPattern) {
-                        // Rewrite element to a declaration with an initializer that fetches property
-                        const propName = element.propertyName || <Identifier>element.name;
-                        emitBindingElement(element, createDestructuringPropertyAccess(value, propName));
-                    }
-                    else {
-                        if (!element.dotDotDotToken) {
-                            // Rewrite element to a declaration that accesses array element at index i
-                            emitBindingElement(element, createElementAccess(value, i));
-                        }
-                        else if (i === numElements - 1) {
-                            emitBindingElement(element, createArraySlice(value, i));
-                        }
-                    }
+                if (name.kind === SyntaxKind.ArrayBindingPattern) {
+                    emitArrayBindingElement(name as ArrayBindingPattern, value);
+                }
+                else {
+                    emitObjectBindingElement(target, value);
                 }
             }
+        }
+
+        function emitArrayBindingElement(name: ArrayBindingPattern, value: Expression) {
+            if (transformRest) {
+                emitESNextArrayBindingElement(name, value);
+            }
             else {
-                emitAssignment(name, value, target, target);
+                emitES2015ArrayBindingElement(name, value);
+            }
+        }
+
+        function emitES2015ArrayBindingElement(name: ArrayBindingPattern, value: Expression) {
+            const elements = name.elements;
+            const numElements = elements.length;
+            for (let i = 0; i < numElements; i++) {
+                const element = elements[i];
+                if (isOmittedExpression(element)) {
+                    continue;
+                }
+                if (!element.dotDotDotToken) {
+                    // Rewrite element to a declaration that accesses array element at index i
+                    emitBindingElement(element, createElementAccess(value, i));
+                }
+                else if (i === numElements - 1) {
+                    emitBindingElement(element, createArraySlice(value, i));
+                }
+            }
+        }
+
+        function emitESNextArrayBindingElement(name: ArrayBindingPattern, value: Expression) {
+            const elements = name.elements;
+            const numElements = elements.length;
+            const bindingElements: BindingElement[] = [];
+            const spreadContainingElements: BindingElement[] = [];
+            for (let i = 0; i < numElements; i++) {
+                const element = elements[i];
+                if (isOmittedExpression(element)) {
+                    continue;
+                }
+                if (element.transformFlags & TransformFlags.ContainsSpreadExpression && i < numElements - 1) {
+                    spreadContainingElements.push(element);
+                    bindingElements.push(createBindingElement(undefined, undefined, getGeneratedNameForNode(element), undefined, value));
+                }
+                else {
+                    bindingElements.push(element);
+                }
+            }
+            emitAssignment(updateArrayBindingPattern(name, bindingElements) as any as Identifier, value, undefined, undefined);
+            for (const element of spreadContainingElements) {
+                emitBindingElement(element, getGeneratedNameForNode(element));
+            }
+        }
+
+        function emitObjectBindingElement(target: VariableDeclaration | ParameterDeclaration | BindingElement, value: Expression) {
+            const name = target.name as BindingPattern;
+            const elements = name.elements;
+            const numElements = elements.length;
+            let bindingElements: BindingElement[] = [];
+            let computedTempVariables: Expression[];
+            for (let i = 0; i < numElements; i++) {
+                const element = elements[i];
+                if (isOmittedExpression(element)) {
+                    continue;
+                }
+                if (i === numElements - 1 && element.dotDotDotToken) {
+                    if (bindingElements.length) {
+                        emitRestAssignment(bindingElements, value, target, target);
+                        bindingElements = [];
+                    }
+                    const restCall = createRestCall(context,
+                                                    value,
+                                                    elements, // name.elements,
+                                                    element => (element as BindingElement).propertyName || <Identifier>(element as BindingElement).name,
+                                                    name,
+                                                    computedTempVariables);
+                    emitBindingElement(element, restCall);
+                }
+                else if (transformRest &&
+                         !(element.transformFlags & TransformFlags.ContainsSpreadExpression) &&
+                         !isComputedPropertyName(element.propertyName || element.name)) {
+                    // do not emit until we have a complete bundle of ES2015 syntax
+                    bindingElements.push(element);
+                }
+                else {
+                    if (bindingElements.length) {
+                        emitRestAssignment(bindingElements, value, target, target);
+                        bindingElements = [];
+                    }
+                    // Rewrite element to a declaration with an initializer that fetches property
+                    const propName = element.propertyName || <Identifier>element.name;
+                    const propAccess = createDestructuringPropertyAccess(value, propName);
+                    if (isComputedPropertyName(propName)) {
+                        computedTempVariables = append(computedTempVariables, (propAccess as ElementAccessExpression).argumentExpression);
+                    }
+                    emitBindingElement(element, propAccess);
+                }
+            }
+            if (bindingElements.length) {
+                emitRestAssignment(bindingElements, value, target, target);
+                bindingElements = [];
             }
         }
 
@@ -440,4 +632,49 @@ namespace ts {
             return emitTempVariableAssignment(value, location);
         }
     }
+
+    const restHelper: EmitHelper = {
+        name: "typescript:rest",
+        scoped: false,
+        text: `
+            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")
+                    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;
+            };`
+    };
+
+    /** Given value: o, propName: p, pattern: { a, b, ...p } from the original statement
+     * `{ a, b, ...p } = o`, create `p = __rest(o, ["a", "b"]);`*/
+    function createRestCall<T extends Node>(context: TransformationContext, value: Expression, elements: T[], getPropertyName: (element: T) => PropertyName, location: TextRange, computedTempVariables: Expression[]): Expression {
+        context.requestEmitHelper(restHelper);
+        const propertyNames: Expression[] = [];
+        for (let i = 0; i < elements.length - 1; i++) {
+            const element = elements[i];
+            if (isOmittedExpression(element)) {
+                continue;
+            }
+            if (isComputedPropertyName(getPropertyName(element))) {
+                // get the temp name and put that in there instead, like `_tmp + ""`
+                const temp = computedTempVariables.shift();
+                propertyNames.push(createConditional(createBinary(createTypeOf(temp),
+                                                                    SyntaxKind.EqualsEqualsEqualsToken,
+                                                                    createLiteral("symbol")),
+                                                        createToken(SyntaxKind.QuestionToken),
+                                                        temp,
+                                                        createToken(SyntaxKind.ColonToken),
+                                                        createBinary(temp, SyntaxKind.PlusToken, createLiteral(""))));
+            }
+            else {
+                const propName = getTextOfPropertyName(getPropertyName(element));
+                propertyNames.push(createLiteral(propName, location));
+            }
+        }
+        const args = createSynthesizedNodeArray([value, createArrayLiteral(propertyNames, location)]);
+        return createCall(getHelperName("__rest"), /*typeArguments*/ undefined, args);
+    }
 }

src/compiler/transformers/es2015.ts

@@ -464,8 +464,8 @@ namespace ts {
                 case SyntaxKind.YieldExpression:
                     return visitYieldExpression(<YieldExpression>node);
 
-                case SyntaxKind.SpreadElementExpression:
-                    return visitSpreadElementExpression(<SpreadElementExpression>node);
+                case SyntaxKind.SpreadElement:
+                    return visitSpreadElement(<SpreadElement>node);
 
                 case SyntaxKind.SuperKeyword:
                     return visitSuperKeyword();
@@ -490,7 +490,7 @@ namespace ts {
             const statements: Statement[] = [];
             startLexicalEnvironment();
             const statementOffset = addPrologueDirectives(statements, node.statements, /*ensureUseStrict*/ false, visitor);
-            addCaptureThisForNodeIfNeeded(statements, node);
+            addCaptureThisForNodeIfNeeded(statements, node, enableSubstitutionsForCapturedThis);
             addRange(statements, visitNodes(node.statements, visitor, isStatement, statementOffset));
             addRange(statements, endLexicalEnvironment());
             return updateSourceFileNode(
@@ -876,7 +876,7 @@ namespace ts {
             }
 
             if (constructor) {
-                addDefaultValueAssignmentsIfNeeded(statements, constructor);
+                addDefaultValueAssignmentsIfNeeded(context, statements, constructor, visitor, /*convertObjectRest*/ false);
                 addRestParameterIfNeeded(statements, constructor, hasSynthesizedSuper);
                 Debug.assert(statementOffset >= 0, "statementOffset not initialized correctly!");
 
@@ -969,7 +969,7 @@ namespace ts {
             // If this isn't a derived class, just capture 'this' for arrow functions if necessary.
             if (!hasExtendsClause) {
                 if (ctor) {
-                    addCaptureThisForNodeIfNeeded(statements, ctor);
+                    addCaptureThisForNodeIfNeeded(statements, ctor, enableSubstitutionsForCapturedThis);
                 }
                 return SuperCaptureResult.NoReplacement;
             }
@@ -986,7 +986,7 @@ namespace ts {
             // for something like property initializers.
             // Create a captured '_this' variable and assume it will subsequently be used.
             if (hasSynthesizedSuper) {
-                captureThisForNode(statements, ctor, createDefaultSuperCallOrThis());
+                captureThisForNode(statements, ctor, createDefaultSuperCallOrThis(), enableSubstitutionsForCapturedThis);
                 enableSubstitutionsForCapturedThis();
                 return SuperCaptureResult.ReplaceSuperCapture;
             }
@@ -1026,12 +1026,25 @@ namespace ts {
 
             // Return the result if we have an immediate super() call on the last statement.
             if (superCallExpression && statementOffset === ctorStatements.length - 1) {
-                statements.push(createReturn(superCallExpression));
+                const returnStatement = createReturn(superCallExpression);
+
+                if (superCallExpression.kind !== SyntaxKind.BinaryExpression
+                    || (superCallExpression as BinaryExpression).left.kind !== SyntaxKind.CallExpression) {
+                    Debug.fail("Assumed generated super call would have form 'super.call(...) || this'.");
+                }
+
+                // Shift comments from the original super call to the return statement.
+                setCommentRange(returnStatement, getCommentRange(
+                    setEmitFlags(
+                        (superCallExpression as BinaryExpression).left,
+                        EmitFlags.NoComments)));
+
+                statements.push(returnStatement);
                 return SuperCaptureResult.ReplaceWithReturn;
             }
 
             // Perform the capture.
-            captureThisForNode(statements, ctor, superCallExpression, firstStatement);
+            captureThisForNode(statements, ctor, superCallExpression, enableSubstitutionsForCapturedThis, firstStatement);
 
             // If we're actually replacing the original statement, we need to signal this to the caller.
             if (superCallExpression) {
@@ -1100,242 +1113,6 @@ namespace ts {
             }
         }
 
-        /**
-         * Gets a value indicating whether we need to add default value assignments for a
-         * function-like node.
-         *
-         * @param node A function-like node.
-         */
-        function shouldAddDefaultValueAssignments(node: FunctionLikeDeclaration): boolean {
-            return (node.transformFlags & TransformFlags.ContainsDefaultValueAssignments) !== 0;
-        }
-
-        /**
-         * Adds statements to the body of a function-like node if it contains parameters with
-         * binding patterns or initializers.
-         *
-         * @param statements The statements for the new function body.
-         * @param node A function-like node.
-         */
-        function addDefaultValueAssignmentsIfNeeded(statements: Statement[], node: FunctionLikeDeclaration): void {
-            if (!shouldAddDefaultValueAssignments(node)) {
-                return;
-            }
-
-            for (const parameter of node.parameters) {
-                const { name, initializer, dotDotDotToken } = parameter;
-
-                // A rest parameter cannot have a binding pattern or an initializer,
-                // so let's just ignore it.
-                if (dotDotDotToken) {
-                    continue;
-                }
-
-                if (isBindingPattern(name)) {
-                    addDefaultValueAssignmentForBindingPattern(statements, parameter, name, initializer);
-                }
-                else if (initializer) {
-                    addDefaultValueAssignmentForInitializer(statements, parameter, name, initializer);
-                }
-            }
-        }
-
-        /**
-         * Adds statements to the body of a function-like node for parameters with binding patterns
-         *
-         * @param statements The statements for the new function body.
-         * @param parameter The parameter for the function.
-         * @param name The name of the parameter.
-         * @param initializer The initializer for the parameter.
-         */
-        function addDefaultValueAssignmentForBindingPattern(statements: Statement[], parameter: ParameterDeclaration, name: BindingPattern, initializer: Expression): void {
-            const temp = getGeneratedNameForNode(parameter);
-
-            // In cases where a binding pattern is simply '[]' or '{}',
-            // we usually don't want to emit a var declaration; however, in the presence
-            // of an initializer, we must emit that expression to preserve side effects.
-            if (name.elements.length > 0) {
-                statements.push(
-                    setEmitFlags(
-                        createVariableStatement(
-                            /*modifiers*/ undefined,
-                            createVariableDeclarationList(
-                                flattenParameterDestructuring(parameter, temp, visitor)
-                            )
-                        ),
-                        EmitFlags.CustomPrologue
-                    )
-                );
-            }
-            else if (initializer) {
-                statements.push(
-                    setEmitFlags(
-                        createStatement(
-                            createAssignment(
-                                temp,
-                                visitNode(initializer, visitor, isExpression)
-                            )
-                        ),
-                        EmitFlags.CustomPrologue
-                    )
-                );
-            }
-        }
-
-        /**
-         * Adds statements to the body of a function-like node for parameters with initializers.
-         *
-         * @param statements The statements for the new function body.
-         * @param parameter The parameter for the function.
-         * @param name The name of the parameter.
-         * @param initializer The initializer for the parameter.
-         */
-        function addDefaultValueAssignmentForInitializer(statements: Statement[], parameter: ParameterDeclaration, name: Identifier, initializer: Expression): void {
-            initializer = visitNode(initializer, visitor, isExpression);
-            const statement = createIf(
-                createStrictEquality(
-                    getSynthesizedClone(name),
-                    createVoidZero()
-                ),
-                setEmitFlags(
-                    createBlock([
-                        createStatement(
-                            createAssignment(
-                                setEmitFlags(getMutableClone(name), EmitFlags.NoSourceMap),
-                                setEmitFlags(initializer, EmitFlags.NoSourceMap | getEmitFlags(initializer)),
-                                /*location*/ parameter
-                            )
-                        )
-                    ], /*location*/ parameter),
-                    EmitFlags.SingleLine | EmitFlags.NoTrailingSourceMap | EmitFlags.NoTokenSourceMaps
-                ),
-                /*elseStatement*/ undefined,
-                /*location*/ parameter
-            );
-            statement.startsOnNewLine = true;
-            setEmitFlags(statement, EmitFlags.NoTokenSourceMaps | EmitFlags.NoTrailingSourceMap | EmitFlags.CustomPrologue);
-            statements.push(statement);
-        }
-
-        /**
-         * Gets a value indicating whether we need to add statements to handle a rest parameter.
-         *
-         * @param node A ParameterDeclaration node.
-         * @param inConstructorWithSynthesizedSuper A value indicating whether the parameter is
-         *                                          part of a constructor declaration with a
-         *                                          synthesized call to `super`
-         */
-        function shouldAddRestParameter(node: ParameterDeclaration, inConstructorWithSynthesizedSuper: boolean) {
-            return node && node.dotDotDotToken && node.name.kind === SyntaxKind.Identifier && !inConstructorWithSynthesizedSuper;
-        }
-
-        /**
-         * Adds statements to the body of a function-like node if it contains a rest parameter.
-         *
-         * @param statements The statements for the new function body.
-         * @param node A function-like node.
-         * @param inConstructorWithSynthesizedSuper A value indicating whether the parameter is
-         *                                          part of a constructor declaration with a
-         *                                          synthesized call to `super`
-         */
-        function addRestParameterIfNeeded(statements: Statement[], node: FunctionLikeDeclaration, inConstructorWithSynthesizedSuper: boolean): void {
-            const parameter = lastOrUndefined(node.parameters);
-            if (!shouldAddRestParameter(parameter, inConstructorWithSynthesizedSuper)) {
-                return;
-            }
-
-            // `declarationName` is the name of the local declaration for the parameter.
-            const declarationName = getMutableClone(<Identifier>parameter.name);
-            setEmitFlags(declarationName, EmitFlags.NoSourceMap);
-
-            // `expressionName` is the name of the parameter used in expressions.
-            const expressionName = getSynthesizedClone(<Identifier>parameter.name);
-            const restIndex = node.parameters.length - 1;
-            const temp = createLoopVariable();
-
-            // var param = [];
-            statements.push(
-                setEmitFlags(
-                    createVariableStatement(
-                        /*modifiers*/ undefined,
-                        createVariableDeclarationList([
-                            createVariableDeclaration(
-                                declarationName,
-                                /*type*/ undefined,
-                                createArrayLiteral([])
-                            )
-                        ]),
-                        /*location*/ parameter
-                    ),
-                    EmitFlags.CustomPrologue
-                )
-            );
-
-            // for (var _i = restIndex; _i < arguments.length; _i++) {
-            //   param[_i - restIndex] = arguments[_i];
-            // }
-            const forStatement = createFor(
-                createVariableDeclarationList([
-                    createVariableDeclaration(temp, /*type*/ undefined, createLiteral(restIndex))
-                ], /*location*/ parameter),
-                createLessThan(
-                    temp,
-                    createPropertyAccess(createIdentifier("arguments"), "length"),
-                    /*location*/ parameter
-                ),
-                createPostfixIncrement(temp, /*location*/ parameter),
-                createBlock([
-                    startOnNewLine(
-                        createStatement(
-                            createAssignment(
-                                createElementAccess(
-                                    expressionName,
-                                    createSubtract(temp, createLiteral(restIndex))
-                                ),
-                                createElementAccess(createIdentifier("arguments"), temp)
-                            ),
-                            /*location*/ parameter
-                        )
-                    )
-                ])
-            );
-
-            setEmitFlags(forStatement, EmitFlags.CustomPrologue);
-            startOnNewLine(forStatement);
-            statements.push(forStatement);
-        }
-
-        /**
-         * Adds a statement to capture the `this` of a function declaration if it is needed.
-         *
-         * @param statements The statements for the new function body.
-         * @param node A node.
-         */
-        function addCaptureThisForNodeIfNeeded(statements: Statement[], node: Node): void {
-            if (node.transformFlags & TransformFlags.ContainsCapturedLexicalThis && node.kind !== SyntaxKind.ArrowFunction) {
-                captureThisForNode(statements, node, createThis());
-            }
-        }
-
-        function captureThisForNode(statements: Statement[], node: Node, initializer: Expression | undefined, originalStatement?: Statement): void {
-            enableSubstitutionsForCapturedThis();
-            const captureThisStatement = createVariableStatement(
-                /*modifiers*/ undefined,
-                createVariableDeclarationList([
-                    createVariableDeclaration(
-                        "_this",
-                        /*type*/ undefined,
-                        initializer
-                    )
-                ]),
-                originalStatement
-            );
-
-            setEmitFlags(captureThisStatement, EmitFlags.NoComments | EmitFlags.CustomPrologue);
-            setSourceMapRange(captureThisStatement, node);
-            statements.push(captureThisStatement);
-        }
-
         /**
          * Adds statements to the class body function for a class to define the members of the
          * class.
@@ -1503,7 +1280,7 @@ namespace ts {
                 /*typeParameters*/ undefined,
                 visitParameterList(node.parameters, visitor, context),
                 /*type*/ undefined,
-                transformFunctionBody(node),
+                transformFunctionBody(node, visitor, currentSourceFile, context, enableSubstitutionsForCapturedThis),
                 node
             );
             setOriginalNode(func, node);
@@ -1525,7 +1302,7 @@ namespace ts {
                 visitParameterList(node.parameters, visitor, context),
                 /*type*/ undefined,
                 node.transformFlags & TransformFlags.ES2015
-                    ? transformFunctionBody(node)
+                    ? transformFunctionBody(node, visitor, currentSourceFile, context, enableSubstitutionsForCapturedThis)
                     : visitFunctionBody(node.body, visitor, context)
             );
         }
@@ -1545,7 +1322,7 @@ namespace ts {
                 visitParameterList(node.parameters, visitor, context),
                 /*type*/ undefined,
                 node.transformFlags & TransformFlags.ES2015
-                    ? transformFunctionBody(node)
+                    ? transformFunctionBody(node, visitor, currentSourceFile, context, enableSubstitutionsForCapturedThis)
                     : visitFunctionBody(node.body, visitor, context)
             );
         }
@@ -1571,7 +1348,7 @@ namespace ts {
                     /*typeParameters*/ undefined,
                     visitParameterList(node.parameters, visitor, context),
                     /*type*/ undefined,
-                    saveStateAndInvoke(node, transformFunctionBody),
+                    saveStateAndInvoke(node, node => transformFunctionBody(node, visitor, currentSourceFile, context, enableSubstitutionsForCapturedThis)),
                     location
                 ),
                 /*original*/ node
@@ -1581,102 +1358,6 @@ namespace ts {
             return expression;
         }
 
-        /**
-         * Transforms the body of a function-like node.
-         *
-         * @param node A function-like node.
-         */
-        function transformFunctionBody(node: FunctionLikeDeclaration) {
-            let multiLine = false; // indicates whether the block *must* be emitted as multiple lines
-            let singleLine = false; // indicates whether the block *may* be emitted as a single line
-            let statementsLocation: TextRange;
-            let closeBraceLocation: TextRange;
-
-            const statements: Statement[] = [];
-            const body = node.body;
-            let statementOffset: number;
-
-            resumeLexicalEnvironment();
-
-            if (isBlock(body)) {
-                // ensureUseStrict is false because no new prologue-directive should be added.
-                // addPrologueDirectives will simply put already-existing directives at the beginning of the target statement-array
-                statementOffset = addPrologueDirectives(statements, body.statements, /*ensureUseStrict*/ false, visitor);
-            }
-
-            addCaptureThisForNodeIfNeeded(statements, node);
-            addDefaultValueAssignmentsIfNeeded(statements, node);
-            addRestParameterIfNeeded(statements, node, /*inConstructorWithSynthesizedSuper*/ false);
-
-            // If we added any generated statements, this must be a multi-line block.
-            if (!multiLine && statements.length > 0) {
-                multiLine = true;
-            }
-
-            if (isBlock(body)) {
-                statementsLocation = body.statements;
-                addRange(statements, visitNodes(body.statements, visitor, isStatement, statementOffset));
-
-                // If the original body was a multi-line block, this must be a multi-line block.
-                if (!multiLine && body.multiLine) {
-                    multiLine = true;
-                }
-            }
-            else {
-                Debug.assert(node.kind === SyntaxKind.ArrowFunction);
-
-                // To align with the old emitter, we use a synthetic end position on the location
-                // for the statement list we synthesize when we down-level an arrow function with
-                // an expression function body. This prevents both comments and source maps from
-                // being emitted for the end position only.
-                statementsLocation = moveRangeEnd(body, -1);
-
-                const equalsGreaterThanToken = (<ArrowFunction>node).equalsGreaterThanToken;
-                if (!nodeIsSynthesized(equalsGreaterThanToken) && !nodeIsSynthesized(body)) {
-                    if (rangeEndIsOnSameLineAsRangeStart(equalsGreaterThanToken, body, currentSourceFile)) {
-                        singleLine = true;
-                    }
-                    else {
-                        multiLine = true;
-                    }
-                }
-
-                const expression = visitNode(body, visitor, isExpression);
-                const returnStatement = createReturn(expression, /*location*/ body);
-                setEmitFlags(returnStatement, EmitFlags.NoTokenSourceMaps | EmitFlags.NoTrailingSourceMap | EmitFlags.NoTrailingComments);
-                statements.push(returnStatement);
-
-                // To align with the source map emit for the old emitter, we set a custom
-                // source map location for the close brace.
-                closeBraceLocation = body;
-            }
-
-            const declarations = endLexicalEnvironment();
-            addRange(statements, declarations);
-
-            // If we added any final generated statements, this must be a multi-line block
-            if (!multiLine && declarations && declarations.length) {
-                multiLine = true;
-            }
-
-            const block = createBlock(
-                createNodeArray(statements, statementsLocation),
-                node.body,
-                multiLine);
-
-            setOriginalNode(block, node.body);
-
-            if (!multiLine && singleLine) {
-                setEmitFlags(block, EmitFlags.SingleLine);
-            }
-
-            if (closeBraceLocation) {
-                setTokenSourceMapRange(block, SyntaxKind.CloseBraceToken, closeBraceLocation);
-            }
-
-            return block;
-        }
-
         /**
          * Visits an ExpressionStatement that contains a destructuring assignment.
          *
@@ -1752,7 +1433,7 @@ namespace ts {
                     if (decl.initializer) {
                         let assignment: Expression;
                         if (isBindingPattern(decl.name)) {
-                            assignment = flattenVariableDestructuringToExpression(decl, hoistVariableDeclaration, /*createAssignmentCallback*/ undefined, visitor);
+                            assignment = flattenVariableDestructuringToExpression(context, decl, hoistVariableDeclaration, /*createAssignmentCallback*/ undefined, visitor);
                         }
                         else {
                             assignment = createBinary(<Identifier>decl.name, SyntaxKind.EqualsToken, visitNode(decl.initializer, visitor, isExpression));
@@ -1905,7 +1586,7 @@ namespace ts {
             if (isBindingPattern(node.name)) {
                 const recordTempVariablesInLine = !enclosingVariableStatement
                     || !hasModifier(enclosingVariableStatement, ModifierFlags.Export);
-                return flattenVariableDestructuring(node, /*value*/ undefined, visitor,
+                return flattenVariableDestructuring(context, node, /*value*/ undefined, visitor,
                     recordTempVariablesInLine ? undefined : hoistVariableDeclaration);
             }
 
@@ -1961,171 +1642,7 @@ namespace ts {
         }
 
         function convertForOfToFor(node: ForOfStatement, convertedLoopBodyStatements: Statement[]): ForStatement {
-            // The following ES6 code:
-            //
-            //    for (let v of expr) { }
-            //
-            // should be emitted as
-            //
-            //    for (var _i = 0, _a = expr; _i < _a.length; _i++) {
-            //        var v = _a[_i];
-            //    }
-            //
-            // where _a and _i are temps emitted to capture the RHS and the counter,
-            // respectively.
-            // When the left hand side is an expression instead of a let declaration,
-            // the "let v" is not emitted.
-            // When the left hand side is a let/const, the v is renamed if there is
-            // another v in scope.
-            // Note that all assignments to the LHS are emitted in the body, including
-            // all destructuring.
-            // Note also that because an extra statement is needed to assign to the LHS,
-            // for-of bodies are always emitted as blocks.
-
-            const expression = visitNode(node.expression, visitor, isExpression);
-            const initializer = node.initializer;
-            const statements: Statement[] = [];
-
-            // In the case where the user wrote an identifier as the RHS, like this:
-            //
-            //     for (let v of arr) { }
-            //
-            // we don't want to emit a temporary variable for the RHS, just use it directly.
-            const counter = createLoopVariable();
-            const rhsReference = expression.kind === SyntaxKind.Identifier
-                ? createUniqueName((<Identifier>expression).text)
-                : createTempVariable(/*recordTempVariable*/ undefined);
-
-            // Initialize LHS
-            // var v = _a[_i];
-            if (isVariableDeclarationList(initializer)) {
-                if (initializer.flags & NodeFlags.BlockScoped) {
-                    enableSubstitutionsForBlockScopedBindings();
-                }
-
-                const firstOriginalDeclaration = firstOrUndefined(initializer.declarations);
-                if (firstOriginalDeclaration && isBindingPattern(firstOriginalDeclaration.name)) {
-                    // This works whether the declaration is a var, let, or const.
-                    // It will use rhsIterationValue _a[_i] as the initializer.
-                    const declarations = flattenVariableDestructuring(
-                        firstOriginalDeclaration,
-                        createElementAccess(rhsReference, counter),
-                        visitor
-                    );
-
-                    const declarationList = createVariableDeclarationList(declarations, /*location*/ initializer);
-                    setOriginalNode(declarationList, initializer);
-
-                    // Adjust the source map range for the first declaration to align with the old
-                    // emitter.
-                    const firstDeclaration = declarations[0];
-                    const lastDeclaration = lastOrUndefined(declarations);
-                    setSourceMapRange(declarationList, createRange(firstDeclaration.pos, lastDeclaration.end));
-
-                    statements.push(
-                        createVariableStatement(
-                            /*modifiers*/ undefined,
-                            declarationList
-                        )
-                    );
-                }
-                else {
-                    // The following call does not include the initializer, so we have
-                    // to emit it separately.
-                    statements.push(
-                        createVariableStatement(
-                            /*modifiers*/ undefined,
-                            setOriginalNode(
-                                createVariableDeclarationList([
-                                    createVariableDeclaration(
-                                        firstOriginalDeclaration ? firstOriginalDeclaration.name : createTempVariable(/*recordTempVariable*/ undefined),
-                                        /*type*/ undefined,
-                                        createElementAccess(rhsReference, counter)
-                                    )
-                                ], /*location*/ moveRangePos(initializer, -1)),
-                                initializer
-                            ),
-                            /*location*/ moveRangeEnd(initializer, -1)
-                        )
-                    );
-                }
-            }
-            else {
-                // Initializer is an expression. Emit the expression in the body, so that it's
-                // evaluated on every iteration.
-                const assignment = createAssignment(initializer, createElementAccess(rhsReference, counter));
-                if (isDestructuringAssignment(assignment)) {
-                    // This is a destructuring pattern, so we flatten the destructuring instead.
-                    statements.push(
-                        createStatement(
-                            flattenDestructuringAssignment(
-                                context,
-                                assignment,
-                                /*needsValue*/ false,
-                                hoistVariableDeclaration,
-                                visitor
-                            )
-                        )
-                    );
-                }
-                else {
-                    // Currently there is not way to check that assignment is binary expression of destructing assignment
-                    // so we have to cast never type to binaryExpression
-                    (<BinaryExpression>assignment).end = initializer.end;
-                    statements.push(createStatement(assignment, /*location*/ moveRangeEnd(initializer, -1)));
-                }
-            }
-
-            let bodyLocation: TextRange;
-            let statementsLocation: TextRange;
-            if (convertedLoopBodyStatements) {
-                addRange(statements, convertedLoopBodyStatements);
-            }
-            else {
-                const statement = visitNode(node.statement, visitor, isStatement);
-                if (isBlock(statement)) {
-                    addRange(statements, statement.statements);
-                    bodyLocation = statement;
-                    statementsLocation = statement.statements;
-                }
-                else {
-                    statements.push(statement);
-                }
-            }
-
-            // The old emitter does not emit source maps for the expression
-            setEmitFlags(expression, EmitFlags.NoSourceMap | getEmitFlags(expression));
-
-            // The old emitter does not emit source maps for the block.
-            // We add the location to preserve comments.
-            const body = createBlock(
-                createNodeArray(statements, /*location*/ statementsLocation),
-                /*location*/ bodyLocation
-            );
-
-            setEmitFlags(body, EmitFlags.NoSourceMap | EmitFlags.NoTokenSourceMaps);
-
-            const forStatement = createFor(
-                setEmitFlags(
-                    createVariableDeclarationList([
-                        createVariableDeclaration(counter, /*type*/ undefined, createLiteral(0), /*location*/ moveRangePos(node.expression, -1)),
-                        createVariableDeclaration(rhsReference, /*type*/ undefined, expression, /*location*/ node.expression)
-                    ], /*location*/ node.expression),
-                    EmitFlags.NoHoisting
-                ),
-                createLessThan(
-                    counter,
-                    createPropertyAccess(rhsReference, "length"),
-                    /*location*/ node.expression
-                ),
-                createPostfixIncrement(counter, /*location*/ node.expression),
-                body,
-                /*location*/ node
-            );
-
-            // Disable trailing source maps for the OpenParenToken to align source map emit with the old emitter.
-            setEmitFlags(forStatement, EmitFlags.NoTokenTrailingSourceMaps);
-            return forStatement;
+            return <ForStatement>convertForOf(node, convertedLoopBodyStatements, visitor, enableSubstitutionsForBlockScopedBindings, context, /*transformRest*/ false);
         }
 
         /**
@@ -2699,7 +2216,7 @@ namespace ts {
             const temp = createTempVariable(undefined);
             const newVariableDeclaration = createVariableDeclaration(temp, undefined, undefined, node.variableDeclaration);
 
-            const vars = flattenVariableDestructuring(node.variableDeclaration, temp, visitor);
+            const vars = flattenVariableDestructuring(context, node.variableDeclaration, temp, visitor);
             const list = createVariableDeclarationList(vars, /*location*/node.variableDeclaration, /*flags*/node.variableDeclaration.flags);
             const destructure = createVariableStatement(undefined, list);
 
@@ -2786,7 +2303,7 @@ namespace ts {
                 setEmitFlags(thisArg, EmitFlags.NoSubstitution);
             }
             let resultingCall: CallExpression | BinaryExpression;
-            if (node.transformFlags & TransformFlags.ContainsSpreadElementExpression) {
+            if (node.transformFlags & TransformFlags.ContainsSpreadExpression) {
                 // [source]
                 //      f(...a, b)
                 //      x.m(...a, b)
@@ -2848,7 +2365,7 @@ namespace ts {
          */
         function visitNewExpression(node: NewExpression): LeftHandSideExpression {
             // We are here because we contain a SpreadElementExpression.
-            Debug.assert((node.transformFlags & TransformFlags.ContainsSpreadElementExpression) !== 0);
+            Debug.assert((node.transformFlags & TransformFlags.ContainsSpreadExpression) !== 0);
 
             // [source]
             //      new C(...a)
@@ -2869,7 +2386,7 @@ namespace ts {
         }
 
         /**
-         * Transforms an array of Expression nodes that contains a SpreadElementExpression.
+         * Transforms an array of Expression nodes that contains a SpreadExpression.
          *
          * @param elements The array of Expression nodes.
          * @param needsUniqueCopy A value indicating whether to ensure that the result is a fresh array.
@@ -2886,14 +2403,14 @@ namespace ts {
             // expressions into an array literal.
             const numElements = elements.length;
             const segments = flatten(
-                spanMap(elements, partitionSpreadElement, (partition, visitPartition, _start, end) =>
+                spanMap(elements, partitionSpread, (partition, visitPartition, _start, end) =>
                     visitPartition(partition, multiLine, hasTrailingComma && end === numElements)
                 )
             );
 
             if (segments.length === 1) {
                 const firstElement = elements[0];
-                return needsUniqueCopy && isSpreadElementExpression(firstElement) && firstElement.expression.kind !== SyntaxKind.ArrayLiteralExpression
+                return needsUniqueCopy && isSpreadExpression(firstElement) && firstElement.expression.kind !== SyntaxKind.ArrayLiteralExpression
                     ? createArraySlice(segments[0])
                     : segments[0];
             }
@@ -2902,17 +2419,17 @@ namespace ts {
             return createArrayConcat(segments.shift(), segments);
         }
 
-        function partitionSpreadElement(node: Expression) {
-            return isSpreadElementExpression(node)
-                ? visitSpanOfSpreadElements
-                : visitSpanOfNonSpreadElements;
+        function partitionSpread(node: Expression) {
+            return isSpreadExpression(node)
+                ? visitSpanOfSpreads
+                : visitSpanOfNonSpreads;
         }
 
-        function visitSpanOfSpreadElements(chunk: Expression[]): VisitResult<Expression> {
-            return map(chunk, visitExpressionOfSpreadElement);
+        function visitSpanOfSpreads(chunk: Expression[]): VisitResult<Expression> {
+            return map(chunk, visitExpressionOfSpread);
         }
 
-        function visitSpanOfNonSpreadElements(chunk: Expression[], multiLine: boolean, hasTrailingComma: boolean): VisitResult<Expression> {
+        function visitSpanOfNonSpreads(chunk: Expression[], multiLine: boolean, hasTrailingComma: boolean): VisitResult<Expression> {
             return createArrayLiteral(
                 visitNodes(createNodeArray(chunk, /*location*/ undefined, hasTrailingComma), visitor, isExpression),
                 /*location*/ undefined,
@@ -2920,16 +2437,16 @@ namespace ts {
             );
         }
 
-        function visitSpreadElementExpression(node: SpreadElementExpression) {
+        function visitSpreadElement(node: SpreadElement) {
             return visitNode(node.expression, visitor, isExpression);
         }
 
         /**
-         * Transforms the expression of a SpreadElementExpression node.
+         * Transforms the expression of a SpreadExpression node.
          *
-         * @param node A SpreadElementExpression node.
+         * @param node A SpreadExpression node.
          */
-        function visitExpressionOfSpreadElement(node: SpreadElementExpression) {
+        function visitExpressionOfSpread(node: SpreadElement) {
             return visitNode(node.expression, visitor, isExpression);
         }
 
@@ -3291,11 +2808,11 @@ namespace ts {
             }
 
             const callArgument = singleOrUndefined((<CallExpression>statementExpression).arguments);
-            if (!callArgument || !nodeIsSynthesized(callArgument) || callArgument.kind !== SyntaxKind.SpreadElementExpression) {
+            if (!callArgument || !nodeIsSynthesized(callArgument) || callArgument.kind !== SyntaxKind.SpreadElement) {
                 return false;
             }
 
-            const expression = (<SpreadElementExpression>callArgument).expression;
+            const expression = (<SpreadElement>callArgument).expression;
             return isIdentifier(expression) && expression.text === "arguments";
         }
     }

src/compiler/transformers/es2016.ts

@@ -32,7 +32,6 @@ namespace ts {
             switch (node.kind) {
                 case SyntaxKind.BinaryExpression:
                     return visitBinaryExpression(<BinaryExpression>node);
-
                 default:
                     Debug.failBadSyntaxKind(node);
                     return visitEachChild(node, visitor, context);

src/compiler/transformers/esnext.ts

@@ -0,0 +1,301 @@
+/// <reference path="../factory.ts" />
+/// <reference path="../visitor.ts" />
+
+/*@internal*/
+namespace ts {
+    export function transformESNext(context: TransformationContext) {
+        const {
+            hoistVariableDeclaration,
+        } = context;
+        let currentSourceFile: SourceFile;
+        return transformSourceFile;
+
+        function transformSourceFile(node: SourceFile) {
+            currentSourceFile = node;
+
+            const visited = visitEachChild(node, visitor, context);
+            addEmitHelpers(visited, context.readEmitHelpers());
+            return visited;
+        }
+
+        function visitor(node: Node): VisitResult<Node> {
+            if (node.transformFlags & TransformFlags.ESNext) {
+                return visitorWorker(node);
+            }
+            else if (node.transformFlags & TransformFlags.ContainsESNext) {
+                return visitEachChild(node, visitor, context);
+            }
+            else {
+                return node;
+            }
+        }
+
+        function visitorWorker(node: Node): VisitResult<Node> {
+            switch (node.kind) {
+                case SyntaxKind.ObjectLiteralExpression:
+                    return visitObjectLiteralExpression(node as ObjectLiteralExpression);
+                case SyntaxKind.BinaryExpression:
+                    return visitBinaryExpression(node as BinaryExpression);
+                case SyntaxKind.VariableDeclaration:
+                    return visitVariableDeclaration(node as VariableDeclaration);
+                case SyntaxKind.ForOfStatement:
+                    return visitForOfStatement(node as ForOfStatement);
+                case SyntaxKind.ObjectBindingPattern:
+                case SyntaxKind.ArrayBindingPattern:
+                    return node;
+                case SyntaxKind.FunctionDeclaration:
+                    return visitFunctionDeclaration(node as FunctionDeclaration);
+                case SyntaxKind.FunctionExpression:
+                    return visitFunctionExpression(node as FunctionExpression);
+                case SyntaxKind.ArrowFunction:
+                    return visitArrowFunction(node as ArrowFunction);
+                case SyntaxKind.Parameter:
+                    return visitParameter(node as ParameterDeclaration);
+                default:
+                    Debug.failBadSyntaxKind(node);
+                    return visitEachChild(node, visitor, context);
+            }
+        }
+
+        function chunkObjectLiteralElements(elements: ObjectLiteralElement[]): Expression[] {
+            let chunkObject: (ShorthandPropertyAssignment | PropertyAssignment)[];
+            const objects: Expression[] = [];
+            for (const e of elements) {
+                if (e.kind === SyntaxKind.SpreadAssignment) {
+                    if (chunkObject) {
+                        objects.push(createObjectLiteral(chunkObject));
+                        chunkObject = undefined;
+                    }
+                    const target = (e as SpreadAssignment).expression;
+                    objects.push(visitNode(target, visitor, isExpression));
+                }
+                else {
+                    if (!chunkObject) {
+                        chunkObject = [];
+                    }
+                    if (e.kind === SyntaxKind.PropertyAssignment) {
+                        const p = e as PropertyAssignment;
+                        chunkObject.push(createPropertyAssignment(p.name, visitNode(p.initializer, visitor, isExpression)));
+                    }
+                    else {
+                        chunkObject.push(e as ShorthandPropertyAssignment);
+                    }
+                }
+            }
+            if (chunkObject) {
+                objects.push(createObjectLiteral(chunkObject));
+            }
+
+            return objects;
+        }
+
+        function visitObjectLiteralExpression(node: ObjectLiteralExpression): Expression {
+            // spread elements emit like so:
+            // non-spread elements are chunked together into object literals, and then all are passed to __assign:
+            //     { a, ...o, b } => __assign({a}, o, {b});
+            // If the first element is a spread element, then the first argument to __assign is {}:
+            //     { ...o, a, b, ...o2 } => __assign({}, o, {a, b}, o2)
+            if (forEach(node.properties, p => p.kind === SyntaxKind.SpreadAssignment)) {
+                const objects = chunkObjectLiteralElements(node.properties);
+                if (objects.length && objects[0].kind !== SyntaxKind.ObjectLiteralExpression) {
+                    objects.unshift(createObjectLiteral());
+                }
+                return createAssignHelper(context, objects);
+            }
+            return visitEachChild(node, visitor, context);
+        }
+
+        /**
+         * Visits a BinaryExpression that contains a destructuring assignment.
+         *
+         * @param node A BinaryExpression node.
+         */
+        function visitBinaryExpression(node: BinaryExpression): Expression {
+            if (isDestructuringAssignment(node) && node.left.transformFlags & TransformFlags.AssertESNext) {
+                return flattenDestructuringAssignment(context, node, /*needsDestructuringValue*/ true, hoistVariableDeclaration, visitor, /*transformRest*/ true);
+            }
+
+            return visitEachChild(node, visitor, context);
+        }
+
+        /**
+         * Visits a VariableDeclaration node with a binding pattern.
+         *
+         * @param node A VariableDeclaration node.
+         */
+        function visitVariableDeclaration(node: VariableDeclaration): VisitResult<VariableDeclaration> {
+            // If we are here it is because the name contains a binding pattern with a rest somewhere in it.
+            if (isBindingPattern(node.name) && node.name.transformFlags & TransformFlags.AssertESNext) {
+                const result = flattenVariableDestructuring(context, node, /*value*/ undefined, visitor, /*recordTempVariable*/ undefined, /*transformRest*/ true);
+                return result;
+            }
+
+            return visitEachChild(node, visitor, context);
+        }
+
+        /**
+         * Visits a ForOfStatement and converts it into a ES2015-compatible ForOfStatement.
+         *
+         * @param node A ForOfStatement.
+         */
+        function visitForOfStatement(node: ForOfStatement): VisitResult<Statement> {
+            // The following ESNext code:
+            //
+            //    for (let { x, y, ...rest } of expr) { }
+            //
+            // should be emitted as
+            //
+            //    for (var _a of expr) {
+            //        let { x, y } = _a, rest = __rest(_a, ["x", "y"]);
+            //    }
+            //
+            // where _a is a temp emitted to capture the RHS.
+            // When the left hand side is an expression instead of a let declaration,
+            // the `let` before the `{ x, y }` is not emitted.
+            // When the left hand side is a let/const, the v is renamed if there is
+            // another v in scope.
+            // Note that all assignments to the LHS are emitted in the body, including
+            // all destructuring.
+            // Note also that because an extra statement is needed to assign to the LHS,
+            // for-of bodies are always emitted as blocks.
+
+            // for (<init> of <expression>) <statement>
+            // where <init> is [let] variabledeclarationlist | expression
+            const initializer = node.initializer;
+            if (!isRestBindingPattern(initializer) && !isRestAssignment(initializer)) {
+                return visitEachChild(node, visitor, context);
+            }
+
+            return convertForOf(node, undefined, visitor, noop, context, /*transformRest*/ true);
+        }
+
+        function isRestBindingPattern(initializer: ForInitializer) {
+            if (isVariableDeclarationList(initializer)) {
+                const declaration = firstOrUndefined(initializer.declarations);
+                return declaration && declaration.name &&
+                    declaration.name.kind === SyntaxKind.ObjectBindingPattern &&
+                    !!(declaration.name.transformFlags & TransformFlags.ContainsSpreadExpression);
+            }
+            return false;
+        }
+
+        function isRestAssignment(initializer: ForInitializer) {
+            return initializer.kind === SyntaxKind.ObjectLiteralExpression &&
+                initializer.transformFlags & TransformFlags.ContainsSpreadExpression;
+        }
+
+        function visitParameter(node: ParameterDeclaration): ParameterDeclaration {
+            if (isObjectRestParameter(node)) {
+                // Binding patterns are converted into a generated name and are
+                // evaluated inside the function body.
+                return setOriginalNode(
+                    createParameter(
+                        /*decorators*/ undefined,
+                        /*modifiers*/ undefined,
+                        /*dotDotDotToken*/ undefined,
+                        getGeneratedNameForNode(node),
+                        /*questionToken*/ undefined,
+                        /*type*/ undefined,
+                        node.initializer,
+                        /*location*/ node
+                    ),
+                    /*original*/ node
+                );
+            }
+            else {
+                return node;
+            }
+        }
+
+        function isObjectRestParameter(node: ParameterDeclaration) {
+            return node.name &&
+                node.name.kind === SyntaxKind.ObjectBindingPattern &&
+                !!(node.name.transformFlags & TransformFlags.ContainsSpreadExpression);
+        }
+
+        function visitFunctionDeclaration(node: FunctionDeclaration): FunctionDeclaration {
+            const hasRest = forEach(node.parameters, isObjectRestParameter);
+            return setOriginalNode(
+                createFunctionDeclaration(
+                    /*decorators*/ undefined,
+                    node.modifiers,
+                    node.asteriskToken,
+                    node.name,
+                    /*typeParameters*/ undefined,
+                    visitParameterList(node.parameters, visitor, context),
+                    /*type*/ undefined,
+                    hasRest ?
+                        transformFunctionBody(node, visitor, currentSourceFile, context, noop, /*convertObjectRest*/ true) as Block :
+                        visitFunctionBody(node.body, visitor, context),
+                    /*location*/ node
+                ),
+                /*original*/ node);
+        }
+
+        function visitArrowFunction(node: ArrowFunction) {
+            const hasRest = forEach(node.parameters, isObjectRestParameter);
+            const func = setOriginalNode(
+                createArrowFunction(
+                    node.modifiers,
+                    /*typeParameters*/ undefined,
+                    visitParameterList(node.parameters, visitor, context),
+                    /*type*/ undefined,
+                    node.equalsGreaterThanToken,
+                    hasRest ?
+                        transformFunctionBody(node, visitor, currentSourceFile, context, noop, /*convertObjectRest*/ true) as Block :
+                        visitFunctionBody(node.body, visitor, context),
+                    /*location*/ node
+                ),
+                /*original*/ node
+            );
+            setEmitFlags(func, EmitFlags.CapturesThis);
+            return func;
+        }
+
+        function visitFunctionExpression(node: FunctionExpression): Expression {
+            const hasRest = forEach(node.parameters, isObjectRestParameter);
+            return setOriginalNode(
+                createFunctionExpression(
+                    node.modifiers,
+                    node.asteriskToken,
+                    name,
+                    /*typeParameters*/ undefined,
+                    visitParameterList(node.parameters, visitor, context),
+                    /*type*/ undefined,
+                    hasRest ?
+                        transformFunctionBody(node, visitor, currentSourceFile, context, noop, /*convertObjectRest*/ true) as Block :
+                        visitFunctionBody(node.body, visitor, context),
+                    /*location*/ node
+                ),
+                /*original*/ node
+            );
+        }
+    }
+
+    const assignHelper: EmitHelper = {
+        name: "typescript:assign",
+        scoped: false,
+        priority: 1,
+        text: `
+            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];
+                    if (typeof Object.getOwnPropertySymbols === "function")
+                        for (var i = 0, p = Object.getOwnPropertySymbols(s); i < p.length; i++)
+                            t[p[i]] = s[p[i]];
+                }
+                return t;
+            };`
+    };
+
+    export function createAssignHelper(context: TransformationContext, attributesSegments: Expression[]) {
+        context.requestEmitHelper(assignHelper);
+        return createCall(
+            getHelperName("__assign"),
+            /*typeArguments*/ undefined,
+            attributesSegments
+        );
+    }
+}

src/compiler/transformers/jsx.ts

@@ -1,5 +1,6 @@
 /// <reference path="../factory.ts" />
 /// <reference path="../visitor.ts" />
+/// <reference path="./esnext.ts" />
 
 /*@internal*/
 namespace ts {
@@ -117,7 +118,8 @@ namespace ts {
                 }
             }
 
-            const element = createReactCreateElement(
+            const element = createExpressionForJsxElement(
+                context.getEmitResolver().getJsxFactoryEntity(),
                 compilerOptions.reactNamespace,
                 tagName,
                 objectProperties,
@@ -534,28 +536,4 @@ namespace ts {
         "hearts": 0x2665,
         "diams": 0x2666
     });
-
-    function createAssignHelper(context: TransformationContext, attributesSegments: Expression[]) {
-        context.requestEmitHelper(assignHelper);
-        return createCall(
-            getHelperName("__assign"),
-            /*typeArguments*/ undefined,
-            attributesSegments
-        );
-    }
-
-    const assignHelper: EmitHelper = {
-        name: "typescript:assign",
-        scoped: false,
-        priority: 1,
-        text: `
-            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;
-            };`
-    };
 }

src/compiler/transformers/module/module.ts

@@ -759,6 +759,7 @@ namespace ts {
         function transformInitializedVariable(node: VariableDeclaration): Expression {
             if (isBindingPattern(node.name)) {
                 return flattenVariableDestructuringToExpression(
+                    context,
                     node,
                     hoistVariableDeclaration,
                     createExportExpression

src/compiler/transformers/module/system.ts

@@ -818,7 +818,7 @@ namespace ts {
         function transformInitializedVariable(node: VariableDeclaration, isExportedDeclaration: boolean): Expression {
             const createAssignment = isExportedDeclaration ? createExportedVariableAssignment : createNonExportedVariableAssignment;
             return isBindingPattern(node.name)
-                ? flattenVariableDestructuringToExpression(node, hoistVariableDeclaration, createAssignment, destructuringVisitor)
+                ? flattenVariableDestructuringToExpression(context, node, hoistVariableDeclaration, createAssignment, destructuringVisitor)
                 : createAssignment(node.name, visitNode(node.initializer, destructuringVisitor, isExpression));
         }
 
@@ -1484,7 +1484,7 @@ namespace ts {
             if (isAssignmentExpression(node)) {
                 return hasExportedReferenceInDestructuringTarget(node.left);
             }
-            else if (isSpreadElementExpression(node)) {
+            else if (isSpreadExpression(node)) {
                 return hasExportedReferenceInDestructuringTarget(node.expression);
             }
             else if (isObjectLiteralExpression(node)) {

src/compiler/transformers/ts.ts

@@ -330,6 +330,7 @@ namespace ts {
                 case SyntaxKind.ThisType:
                 case SyntaxKind.TypeOperator:
                 case SyntaxKind.IndexedAccessType:
+                case SyntaxKind.MappedType:
                 case SyntaxKind.LiteralType:
                     // TypeScript type nodes are elided.
 
@@ -470,9 +471,10 @@ namespace ts {
         }
 
         function visitSourceFile(node: SourceFile) {
+            const alwaysStrict = compilerOptions.alwaysStrict && !(isExternalModule(node) && moduleKind === ModuleKind.ES2015);
             return updateSourceFileNode(
                 node,
-                visitLexicalEnvironment(node.statements, sourceElementVisitor, context, /*start*/ 0, compilerOptions.alwaysStrict));
+                visitLexicalEnvironment(node.statements, sourceElementVisitor, context, /*start*/ 0, alwaysStrict));
         }
 
         /**
@@ -1748,6 +1750,7 @@ namespace ts {
                 case SyntaxKind.TypeQuery:
                 case SyntaxKind.TypeOperator:
                 case SyntaxKind.IndexedAccessType:
+                case SyntaxKind.MappedType:
                 case SyntaxKind.TypeLiteral:
                 case SyntaxKind.AnyKeyword:
                 case SyntaxKind.ThisType:
@@ -2247,6 +2250,7 @@ namespace ts {
             const name = node.name;
             if (isBindingPattern(name)) {
                 return flattenVariableDestructuringToExpression(
+                    context,
                     node,
                     hoistVariableDeclaration,
                     createNamespaceExportExpression,
@@ -3351,7 +3355,6 @@ namespace ts {
         );
     }
 
-
     const decorateHelper: EmitHelper = {
         name: "typescript:decorate",
         scoped: false,

src/compiler/tsconfig.json

@@ -27,6 +27,7 @@
         "visitor.ts",
         "transformers/ts.ts",
         "transformers/jsx.ts",
+        "transformers/esnext.ts",
         "transformers/es2017.ts",
         "transformers/es2016.ts",
         "transformers/es2015.ts",

src/compiler/types.ts

@@ -219,6 +219,7 @@ namespace ts {
         ThisType,
         TypeOperator,
         IndexedAccessType,
+        MappedType,
         LiteralType,
         // Binding patterns
         ObjectBindingPattern,
@@ -246,7 +247,7 @@ namespace ts {
         ConditionalExpression,
         TemplateExpression,
         YieldExpression,
-        SpreadElementExpression,
+        SpreadElement,
         ClassExpression,
         OmittedExpression,
         ExpressionWithTypeArguments,
@@ -320,6 +321,7 @@ namespace ts {
         // Property assignments
         PropertyAssignment,
         ShorthandPropertyAssignment,
+        SpreadAssignment,
 
         // Enum
         EnumMember,
@@ -419,20 +421,21 @@ namespace ts {
         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)
-        HasJsxSpreadAttributes = 1 << 14, // If the file as JSX spread attributes (initialized by binding)
-        DisallowInContext =  1 << 15, // If node was parsed in a context where 'in-expressions' are not allowed
-        YieldContext =       1 << 16, // If node was parsed in the 'yield' context created when parsing a generator
-        DecoratorContext =   1 << 17, // If node was parsed as part of a decorator
-        AwaitContext =       1 << 18, // If node was parsed in the 'await' context created when parsing an async function
-        ThisNodeHasError =   1 << 19, // If the parser encountered an error when parsing the code that created this node
-        JavaScriptFile =     1 << 20, // If node was parsed in a JavaScript
-        ThisNodeOrAnySubNodesHasError = 1 << 21, // If this node or any of its children had an error
-        HasAggregatedChildData = 1 << 22, // If we've computed data from children and cached it in this node
+        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
 
         BlockScoped = Let | Const,
 
         ReachabilityCheckFlags = HasImplicitReturn | HasExplicitReturn,
-        EmitHelperFlags = HasClassExtends | HasDecorators | HasParamDecorators | HasAsyncFunctions | HasJsxSpreadAttributes,
+        EmitHelperFlags = HasClassExtends | HasDecorators | HasParamDecorators | HasAsyncFunctions | HasSpreadAttribute | HasRestAttribute,
         ReachabilityAndEmitFlags = ReachabilityCheckFlags | EmitHelperFlags,
 
         // Parsing context flags
@@ -455,7 +458,6 @@ namespace ts {
         Async =              1 << 8,  // Property/Method/Function
         Default =            1 << 9,  // Function/Class (export default declaration)
         Const =              1 << 11, // Variable declaration
-
         HasComputedFlags =   1 << 29, // Modifier flags have been computed
 
         AccessibilityModifier = Public | Private | Protected,
@@ -520,6 +522,7 @@ namespace ts {
     export type EqualsGreaterThanToken = Token<SyntaxKind.EqualsGreaterThanToken>;
     export type EndOfFileToken = Token<SyntaxKind.EndOfFileToken>;
     export type AtToken = Token<SyntaxKind.AtToken>;
+    export type ReadonlyToken = Token<SyntaxKind.ReadonlyKeyword>;
 
     export type Modifier
         = Token<SyntaxKind.AbstractKeyword>
@@ -650,7 +653,7 @@ namespace ts {
     export interface BindingElement extends Declaration {
         kind: SyntaxKind.BindingElement;
         propertyName?: PropertyName;        // Binding property name (in object binding pattern)
-        dotDotDotToken?: DotDotDotToken;              // Present on rest binding element
+        dotDotDotToken?: DotDotDotToken;    // Present on rest element (in object binding pattern)
         name: BindingName;                  // Declared binding element name
         initializer?: Expression;           // Optional initializer
     }
@@ -676,7 +679,7 @@ namespace ts {
         name?: PropertyName;
     }
 
-    export type ObjectLiteralElementLike = PropertyAssignment | ShorthandPropertyAssignment | MethodDeclaration | AccessorDeclaration;
+    export type ObjectLiteralElementLike = PropertyAssignment | ShorthandPropertyAssignment | MethodDeclaration | AccessorDeclaration | SpreadAssignment;
 
     export interface PropertyAssignment extends ObjectLiteralElement {
         kind: SyntaxKind.PropertyAssignment;
@@ -695,6 +698,11 @@ namespace ts {
         objectAssignmentInitializer?: Expression;
     }
 
+    export interface SpreadAssignment extends ObjectLiteralElement {
+        kind: SyntaxKind.SpreadAssignment;
+        expression: Expression;
+    }
+
     // SyntaxKind.VariableDeclaration
     // SyntaxKind.Parameter
     // SyntaxKind.BindingElement
@@ -898,6 +906,14 @@ namespace ts {
         indexType: TypeNode;
     }
 
+    export interface MappedTypeNode extends TypeNode, Declaration {
+        kind: SyntaxKind.MappedType;
+        readonlyToken?: ReadonlyToken;
+        typeParameter: TypeParameterDeclaration;
+        questionToken?: QuestionToken;
+        type?: TypeNode;
+    }
+
     export interface LiteralTypeNode extends TypeNode {
         kind: SyntaxKind.LiteralType;
         literal: Expression;
@@ -1280,8 +1296,8 @@ namespace ts {
         multiLine?: boolean;
     }
 
-    export interface SpreadElementExpression extends Expression {
-        kind: SyntaxKind.SpreadElementExpression;
+    export interface SpreadElement extends Expression {
+        kind: SyntaxKind.SpreadElement;
         expression: Expression;
     }
 
@@ -2395,6 +2411,12 @@ namespace ts {
         CannotBeNamed
     }
 
+    /* @internal */
+    export const enum SyntheticSymbolKind {
+        UnionOrIntersection,
+        Spread
+    }
+
     export const enum TypePredicateKind {
         This,
         Identifier
@@ -2487,6 +2509,7 @@ namespace ts {
         getTypeReferenceDirectivesForSymbol(symbol: Symbol, meaning?: SymbolFlags): string[];
         isLiteralConstDeclaration(node: VariableDeclaration | PropertyDeclaration | PropertySignature | ParameterDeclaration): boolean;
         writeLiteralConstValue(node: VariableDeclaration | PropertyDeclaration | PropertySignature | ParameterDeclaration, writer: SymbolWriter): void;
+        getJsxFactoryEntity(): EntityName;
     }
 
     export const enum SymbolFlags {
@@ -2502,7 +2525,7 @@ namespace ts {
         RegularEnum             = 0x00000100,  // Enum
         ValueModule             = 0x00000200,  // Instantiated module
         NamespaceModule         = 0x00000400,  // Uninstantiated module
-        TypeLiteral             = 0x00000800,  // Type Literal
+        TypeLiteral             = 0x00000800,  // Type Literal or mapped type
         ObjectLiteral           = 0x00001000,  // Object Literal
         Method                  = 0x00002000,  // Method
         Constructor             = 0x00004000,  // Constructor
@@ -2606,7 +2629,9 @@ namespace ts {
         instantiations?: Map<Type>;         // Instantiations of generic type alias (undefined if non-generic)
         mapper?: TypeMapper;                // Type mapper for instantiation alias
         referenced?: boolean;               // True if alias symbol has been referenced as a value
-        containingType?: UnionOrIntersectionType; // Containing union or intersection type for synthetic property
+        containingType?: UnionOrIntersectionType;  // Containing union or intersection type for synthetic property
+        leftSpread?: Symbol;                // Left source for synthetic spread property
+        rightSpread?: Symbol;               // Right source for synthetic spread property
         hasNonUniformType?: boolean;        // True if constituents have non-uniform types
         isPartial?: boolean;                // True if syntheric property of union type occurs in some but not all constituents
         isDiscriminantProperty?: boolean;   // True if discriminant synthetic property
@@ -2667,6 +2692,7 @@ namespace ts {
         resolvedSignature?: Signature;    // Cached signature of signature node or call expression
         resolvedSymbol?: Symbol;          // Cached name resolution result
         resolvedIndexInfo?: IndexInfo;    // Cached indexing info resolution result
+        maybeTypePredicate?: boolean;     // Cached check whether call expression might reference a type predicate 
         enumMemberValue?: number;         // Constant value of enum member
         isVisible?: boolean;              // Is this node visible
         hasReportedStatementInAmbientContext?: boolean;  // Cache boolean if we report statements in ambient context
@@ -2778,10 +2804,11 @@ namespace ts {
         Reference        = 1 << 2,  // Generic type reference
         Tuple            = 1 << 3,  // Synthesized generic tuple type
         Anonymous        = 1 << 4,  // Anonymous
-        Instantiated     = 1 << 5,  // Instantiated anonymous type
-        ObjectLiteral    = 1 << 6,  // Originates in an object literal
-        EvolvingArray    = 1 << 7,  // Evolving array type
-        ObjectLiteralPatternWithComputedProperties = 1 << 8,  // Object literal pattern with computed properties
+        Mapped           = 1 << 5,  // Mapped
+        Instantiated     = 1 << 6,  // Instantiated anonymous or mapped type
+        ObjectLiteral    = 1 << 7,  // Originates in an object literal
+        EvolvingArray    = 1 << 8,  // Evolving array type
+        ObjectLiteralPatternWithComputedProperties = 1 << 9,  // Object literal pattern with computed properties
         ClassOrInterface = Class | Interface
     }
 
@@ -2850,6 +2877,15 @@ namespace ts {
         mapper?: TypeMapper;     // Instantiation mapper
     }
 
+    /* @internal */
+    export interface MappedType extends ObjectType {
+        declaration: MappedTypeNode;
+        typeParameter?: TypeParameter;
+        constraintType?: Type;
+        templateType?: Type;
+        mapper?: TypeMapper;  // Instantiation mapper
+    }
+
     export interface EvolvingArrayType extends ObjectType {
         elementType: Type;      // Element expressions of evolving array type
         finalArrayType?: Type;  // Final array type of evolving array type
@@ -3074,7 +3110,7 @@ namespace ts {
         moduleResolution?: ModuleResolutionKind;
         newLine?: NewLineKind;
         noEmit?: boolean;
-        /*@internal*/noEmitOverwritenFiles?: boolean;
+        /*@internal*/noEmitForJsFiles?: boolean;
         noEmitHelpers?: boolean;
         noEmitOnError?: boolean;
         noErrorTruncation?: boolean;
@@ -3095,6 +3131,7 @@ namespace ts {
         project?: string;
         /* @internal */ pretty?: DiagnosticStyle;
         reactNamespace?: string;
+        jsxFactory?: string;
         removeComments?: boolean;
         rootDir?: string;
         rootDirs?: string[];
@@ -3177,7 +3214,8 @@ namespace ts {
         ES2015 = 2,
         ES2016 = 3,
         ES2017 = 4,
-        Latest = ES2017,
+        ESNext = 5,
+        Latest = ESNext,
     }
 
     export const enum LanguageVariant {
@@ -3492,32 +3530,34 @@ namespace ts {
         ContainsTypeScript = 1 << 1,
         Jsx = 1 << 2,
         ContainsJsx = 1 << 3,
-        ES2017 = 1 << 4,
-        ContainsES2017 = 1 << 5,
-        ES2016 = 1 << 6,
-        ContainsES2016 = 1 << 7,
-        ES2015 = 1 << 8,
-        ContainsES2015 = 1 << 9,
-        Generator = 1 << 10,
-        ContainsGenerator = 1 << 11,
-        DestructuringAssignment = 1 << 12,
-        ContainsDestructuringAssignment = 1 << 13,
+        ESNext = 1 << 4,
+        ContainsESNext = 1 << 5,
+        ES2017 = 1 << 6,
+        ContainsES2017 = 1 << 7,
+        ES2016 = 1 << 8,
+        ContainsES2016 = 1 << 9,
+        ES2015 = 1 << 10,
+        ContainsES2015 = 1 << 11,
+        Generator = 1 << 12,
+        ContainsGenerator = 1 << 13,
+        DestructuringAssignment = 1 << 14,
+        ContainsDestructuringAssignment = 1 << 15,
 
         // Markers
         // - Flags used to indicate that a subtree contains a specific transformation.
-        ContainsDecorators = 1 << 14,
-        ContainsPropertyInitializer = 1 << 15,
-        ContainsLexicalThis = 1 << 16,
-        ContainsCapturedLexicalThis = 1 << 17,
-        ContainsLexicalThisInComputedPropertyName = 1 << 18,
-        ContainsDefaultValueAssignments = 1 << 19,
-        ContainsParameterPropertyAssignments = 1 << 20,
-        ContainsSpreadElementExpression = 1 << 21,
-        ContainsComputedPropertyName = 1 << 22,
-        ContainsBlockScopedBinding = 1 << 23,
-        ContainsBindingPattern = 1 << 24,
-        ContainsYield = 1 << 25,
-        ContainsHoistedDeclarationOrCompletion = 1 << 26,
+        ContainsDecorators = 1 << 16,
+        ContainsPropertyInitializer = 1 << 17,
+        ContainsLexicalThis = 1 << 18,
+        ContainsCapturedLexicalThis = 1 << 19,
+        ContainsLexicalThisInComputedPropertyName = 1 << 20,
+        ContainsDefaultValueAssignments = 1 << 21,
+        ContainsParameterPropertyAssignments = 1 << 22,
+        ContainsSpreadExpression = 1 << 23,
+        ContainsComputedPropertyName = 1 << 24,
+        ContainsBlockScopedBinding = 1 << 25,
+        ContainsBindingPattern = 1 << 26,
+        ContainsYield = 1 << 27,
+        ContainsHoistedDeclarationOrCompletion = 1 << 28,
 
         HasComputedFlags = 1 << 29, // Transform flags have been computed.
 
@@ -3525,6 +3565,7 @@ namespace ts {
         // - Bitmasks that are used to assert facts about the syntax of a node and its subtree.
         AssertTypeScript = TypeScript | ContainsTypeScript,
         AssertJsx = Jsx | ContainsJsx,
+        AssertESNext = ESNext | ContainsESNext,
         AssertES2017 = ES2017 | ContainsES2017,
         AssertES2016 = ES2016 | ContainsES2016,
         AssertES2015 = ES2015 | ContainsES2015,
@@ -3534,7 +3575,7 @@ namespace ts {
         // Scope Exclusions
         // - Bitmasks that exclude flags from propagating out of a specific context
         //   into the subtree flags of their container.
-        NodeExcludes = TypeScript | Jsx | ES2017 | ES2016 | ES2015 | DestructuringAssignment | Generator | HasComputedFlags,
+        NodeExcludes = TypeScript | Jsx | ESNext | ES2017 | ES2016 | ES2015 | DestructuringAssignment | Generator | HasComputedFlags,
         ArrowFunctionExcludes = NodeExcludes | ContainsDecorators | ContainsDefaultValueAssignments | ContainsLexicalThis | ContainsParameterPropertyAssignments | ContainsBlockScopedBinding | ContainsYield | ContainsHoistedDeclarationOrCompletion,
         FunctionExcludes = NodeExcludes | ContainsDecorators | ContainsDefaultValueAssignments | ContainsCapturedLexicalThis | ContainsLexicalThis | ContainsParameterPropertyAssignments | ContainsBlockScopedBinding | ContainsYield | ContainsHoistedDeclarationOrCompletion,
         ConstructorExcludes = NodeExcludes | ContainsDefaultValueAssignments | ContainsLexicalThis | ContainsCapturedLexicalThis | ContainsBlockScopedBinding | ContainsYield | ContainsHoistedDeclarationOrCompletion,
@@ -3543,7 +3584,7 @@ namespace ts {
         ModuleExcludes = NodeExcludes | ContainsDecorators | ContainsLexicalThis | ContainsCapturedLexicalThis | ContainsBlockScopedBinding | ContainsHoistedDeclarationOrCompletion,
         TypeExcludes = ~ContainsTypeScript,
         ObjectLiteralExcludes = NodeExcludes | ContainsDecorators | ContainsComputedPropertyName | ContainsLexicalThisInComputedPropertyName,
-        ArrayLiteralOrCallOrNewExcludes = NodeExcludes | ContainsSpreadElementExpression,
+        ArrayLiteralOrCallOrNewExcludes = NodeExcludes | ContainsSpreadExpression,
         VariableDeclarationListExcludes = NodeExcludes | ContainsBindingPattern,
         ParameterExcludes = NodeExcludes | ContainsBindingPattern,
 

src/compiler/utilities.ts

@@ -177,7 +177,7 @@ namespace ts {
     export function nodePosToString(node: Node): string {
         const file = getSourceFileOfNode(node);
         const loc = getLineAndCharacterOfPosition(file, node.pos);
-        return `${ file.fileName }(${ loc.line + 1 },${ loc.character + 1 })`;
+        return `${file.fileName}(${loc.line + 1},${loc.character + 1})`;
     }
 
     export function getStartPosOfNode(node: Node): number {
@@ -424,7 +424,7 @@ namespace ts {
     }
 
     export function isBlockScope(node: Node, parentNode: Node) {
-        switch (node.kind)  {
+        switch (node.kind) {
             case SyntaxKind.SourceFile:
             case SyntaxKind.CaseBlock:
             case SyntaxKind.CatchClause:
@@ -470,6 +470,22 @@ namespace ts {
         return getFullWidth(name) === 0 ? "(Missing)" : getTextOfNode(name);
     }
 
+    export function getTextOfPropertyName(name: PropertyName): string {
+        switch (name.kind) {
+        case SyntaxKind.Identifier:
+            return (<Identifier>name).text;
+        case SyntaxKind.StringLiteral:
+        case SyntaxKind.NumericLiteral:
+            return (<LiteralExpression>name).text;
+        case SyntaxKind.ComputedPropertyName:
+            if (isStringOrNumericLiteral((<ComputedPropertyName>name).expression.kind)) {
+                return (<LiteralExpression>(<ComputedPropertyName>name).expression).text;
+            }
+        }
+
+        return undefined;
+    }
+
     export function entityNameToString(name: EntityNameOrEntityNameExpression): string {
         switch (name.kind) {
             case SyntaxKind.Identifier:
@@ -483,6 +499,10 @@ namespace ts {
 
     export function createDiagnosticForNode(node: Node, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number): Diagnostic {
         const sourceFile = getSourceFileOfNode(node);
+        return createDiagnosticForNodeInSourceFile(sourceFile, node, message, arg0, arg1, arg2);
+    }
+
+    export function createDiagnosticForNodeInSourceFile(sourceFile: SourceFile, node: Node, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number): Diagnostic {
         const span = getErrorSpanForNode(sourceFile, node);
         return createFileDiagnostic(sourceFile, span.start, span.length, message, arg0, arg1, arg2);
     }
@@ -610,9 +630,9 @@ namespace ts {
 
     export function getJsDocCommentsFromText(node: Node, text: string) {
         const commentRanges = (node.kind === SyntaxKind.Parameter ||
-                               node.kind === SyntaxKind.TypeParameter ||
-                               node.kind === SyntaxKind.FunctionExpression ||
-                               node.kind === SyntaxKind.ArrowFunction) ?
+            node.kind === SyntaxKind.TypeParameter ||
+            node.kind === SyntaxKind.FunctionExpression ||
+            node.kind === SyntaxKind.ArrowFunction) ?
             concatenate(getTrailingCommentRanges(text, node.pos), getLeadingCommentRanges(text, node.pos)) :
             getLeadingCommentRangesOfNodeFromText(node, text);
         return filter(commentRanges, isJsDocComment);
@@ -877,7 +897,7 @@ namespace ts {
     export function isObjectLiteralOrClassExpressionMethod(node: Node): node is MethodDeclaration {
         return node.kind === SyntaxKind.MethodDeclaration &&
             (node.parent.kind === SyntaxKind.ObjectLiteralExpression ||
-            node.parent.kind === SyntaxKind.ClassExpression);
+                node.parent.kind === SyntaxKind.ClassExpression);
     }
 
     export function isIdentifierTypePredicate(predicate: TypePredicate): predicate is IdentifierTypePredicate {
@@ -1099,8 +1119,8 @@ namespace ts {
                 // if the parameter's parent has a body and its grandparent is a class declaration, this is a valid target;
                 return (<FunctionLikeDeclaration>node.parent).body !== undefined
                     && (node.parent.kind === SyntaxKind.Constructor
-                    || node.parent.kind === SyntaxKind.MethodDeclaration
-                    || node.parent.kind === SyntaxKind.SetAccessor)
+                        || node.parent.kind === SyntaxKind.MethodDeclaration
+                        || node.parent.kind === SyntaxKind.SetAccessor)
                     && node.parent.parent.kind === SyntaxKind.ClassDeclaration;
         }
 
@@ -1165,7 +1185,7 @@ namespace ts {
             case SyntaxKind.PostfixUnaryExpression:
             case SyntaxKind.BinaryExpression:
             case SyntaxKind.ConditionalExpression:
-            case SyntaxKind.SpreadElementExpression:
+            case SyntaxKind.SpreadElement:
             case SyntaxKind.TemplateExpression:
             case SyntaxKind.NoSubstitutionTemplateLiteral:
             case SyntaxKind.OmittedExpression:
@@ -1228,6 +1248,7 @@ namespace ts {
                     case SyntaxKind.Decorator:
                     case SyntaxKind.JsxExpression:
                     case SyntaxKind.JsxSpreadAttribute:
+                    case SyntaxKind.SpreadAssignment:
                         return true;
                     case SyntaxKind.ExpressionWithTypeArguments:
                         return (<ExpressionWithTypeArguments>parent).expression === node && isExpressionWithTypeArgumentsInClassExtendsClause(parent);
@@ -1447,7 +1468,7 @@ namespace ts {
         }, tags => tags);
     }
 
-   function getJSDocs<T>(node: Node, checkParentVariableStatement: boolean, getDocs: (docs: JSDoc[]) => T[], getTags: (tags: JSDocTag[]) => T[]): T[] {
+    function getJSDocs<T>(node: Node, checkParentVariableStatement: boolean, getDocs: (docs: JSDoc[]) => T[], getTags: (tags: JSDocTag[]) => T[]): T[] {
         // TODO: Get rid of getJsDocComments and friends (note the lowercase 's' in Js)
         // TODO: A lot of this work should be cached, maybe. I guess it's only used in services right now...
         let result: T[] = undefined;
@@ -1468,8 +1489,8 @@ namespace ts {
 
             const variableStatementNode =
                 isInitializerOfVariableDeclarationInStatement ? node.parent.parent.parent :
-                isVariableOfVariableDeclarationStatement ? node.parent.parent :
-                undefined;
+                    isVariableOfVariableDeclarationStatement ? node.parent.parent :
+                        undefined;
             if (variableStatementNode) {
                 result = append(result, getJSDocs(variableStatementNode, checkParentVariableStatement, getDocs, getTags));
             }
@@ -1627,14 +1648,14 @@ namespace ts {
                     return (<ForInStatement | ForOfStatement>parent).initializer === node ? AssignmentKind.Definite : AssignmentKind.None;
                 case SyntaxKind.ParenthesizedExpression:
                 case SyntaxKind.ArrayLiteralExpression:
-                case SyntaxKind.SpreadElementExpression:
+                case SyntaxKind.SpreadElement:
                     node = parent;
                     break;
                 case SyntaxKind.ShorthandPropertyAssignment:
                     if ((<ShorthandPropertyAssignment>parent).name !== node) {
                         return AssignmentKind.None;
                     }
-                    // Fall through
+                // Fall through
                 case SyntaxKind.PropertyAssignment:
                     node = parent.parent;
                     break;
@@ -2213,7 +2234,7 @@ namespace ts {
             case SyntaxKind.YieldExpression:
                 return 2;
 
-            case SyntaxKind.SpreadElementExpression:
+            case SyntaxKind.SpreadElement:
                 return 1;
 
             default:
@@ -2537,22 +2558,39 @@ namespace ts {
         if (options.outFile || options.out) {
             const moduleKind = getEmitModuleKind(options);
             const moduleEmitEnabled = moduleKind === ModuleKind.AMD || moduleKind === ModuleKind.System;
-            const sourceFiles = host.getSourceFiles();
+            const sourceFiles = getAllEmittableSourceFiles();
             // Can emit only sources that are not declaration file and are either non module code or module with --module or --target es6 specified
             return filter(sourceFiles, moduleEmitEnabled ? isNonDeclarationFile : isBundleEmitNonExternalModule);
         }
         else {
-            const sourceFiles = targetSourceFile === undefined ? host.getSourceFiles() : [targetSourceFile];
-            return filter(sourceFiles, isNonDeclarationFile);
+            const sourceFiles = targetSourceFile === undefined ? getAllEmittableSourceFiles() : [targetSourceFile];
+            return filterSourceFilesInDirectory(sourceFiles, file => host.isSourceFileFromExternalLibrary(file));
         }
+
+        function getAllEmittableSourceFiles() {
+            return options.noEmitForJsFiles ? filter(host.getSourceFiles(), sourceFile => !isSourceFileJavaScript(sourceFile)) : host.getSourceFiles();
+        }
+    }
+
+    /** Don't call this for `--outFile`, just for `--outDir` or plain emit. */
+    export function filterSourceFilesInDirectory(sourceFiles: SourceFile[], isSourceFileFromExternalLibrary: (file: SourceFile) => boolean): SourceFile[] {
+        return filter(sourceFiles, file => shouldEmitInDirectory(file, isSourceFileFromExternalLibrary));
     }
 
     function isNonDeclarationFile(sourceFile: SourceFile) {
         return !isDeclarationFile(sourceFile);
     }
 
+    /**
+     * Whether a file should be emitted in a non-`--outFile` case.
+     * Don't emit if source file is a declaration file, or was located under node_modules
+     */
+    function shouldEmitInDirectory(sourceFile: SourceFile, isSourceFileFromExternalLibrary: (file: SourceFile) => boolean): boolean {
+        return isNonDeclarationFile(sourceFile) && !isSourceFileFromExternalLibrary(sourceFile);
+    }
+
     function isBundleEmitNonExternalModule(sourceFile: SourceFile) {
-        return !isDeclarationFile(sourceFile) && !isExternalModule(sourceFile);
+        return isNonDeclarationFile(sourceFile) && !isExternalModule(sourceFile);
     }
 
     /**
@@ -2576,7 +2614,7 @@ namespace ts {
         }
         else {
             for (const sourceFile of sourceFiles) {
-                 // Don't emit if source file is a declaration file, or was located under node_modules
+                // Don't emit if source file is a declaration file, or was located under node_modules
                 if (!isDeclarationFile(sourceFile) && !host.isSourceFileFromExternalLibrary(sourceFile)) {
                     onSingleFileEmit(host, sourceFile);
                 }
@@ -2638,10 +2676,9 @@ namespace ts {
             onBundledEmit(host);
         }
         else {
-            const sourceFiles = targetSourceFile === undefined ? host.getSourceFiles() : [targetSourceFile];
+            const sourceFiles = targetSourceFile === undefined ? getSourceFilesToEmit(host) : [targetSourceFile];
             for (const sourceFile of sourceFiles) {
-                // Don't emit if source file is a declaration file, or was located under node_modules
-                if (!isDeclarationFile(sourceFile) && !host.isSourceFileFromExternalLibrary(sourceFile)) {
+                if (shouldEmitInDirectory(sourceFile, file => host.isSourceFileFromExternalLibrary(file))) {
                     onSingleFileEmit(host, sourceFile);
                 }
             }
@@ -2676,11 +2713,11 @@ namespace ts {
         function onBundledEmit(host: EmitHost) {
             // Can emit only sources that are not declaration file and are either non module code or module with
             // --module or --target es6 specified. Files included by searching under node_modules are also not emitted.
-            const bundledSources = filter(host.getSourceFiles(),
+            const bundledSources = filter(getSourceFilesToEmit(host),
                 sourceFile => !isDeclarationFile(sourceFile) &&
-                              !host.isSourceFileFromExternalLibrary(sourceFile) &&
-                              (!isExternalModule(sourceFile) ||
-                               !!getEmitModuleKind(options)));
+                    !host.isSourceFileFromExternalLibrary(sourceFile) &&
+                    (!isExternalModule(sourceFile) ||
+                        !!getEmitModuleKind(options)));
             if (bundledSources.length) {
                 const jsFilePath = options.outFile || options.out;
                 const emitFileNames: EmitFileNames = {
@@ -2866,7 +2903,7 @@ namespace ts {
         writeComment: (text: string, lineMap: number[], writer: EmitTextWriter, commentPos: number, commentEnd: number, newLine: string) => void,
         node: TextRange, newLine: string, removeComments: boolean) {
         let leadingComments: CommentRange[];
-        let currentDetachedCommentInfo: {nodePos: number, detachedCommentEndPos: number};
+        let currentDetachedCommentInfo: { nodePos: number, detachedCommentEndPos: number };
         if (removeComments) {
             // removeComments is true, only reserve pinned comment at the top of file
             // For example:
@@ -3213,10 +3250,10 @@ namespace ts {
 
     function stringifyValue(value: any): string {
         return typeof value === "string" ? `"${escapeString(value)}"`
-             : typeof value === "number" ? isFinite(value) ? String(value) : "null"
-             : typeof value === "boolean" ? value ? "true" : "false"
-             : typeof value === "object" && value ? isArray(value) ? cycleCheck(stringifyArray, value) : cycleCheck(stringifyObject, value)
-             : /*fallback*/ "null";
+            : typeof value === "number" ? isFinite(value) ? String(value) : "null"
+                : typeof value === "boolean" ? value ? "true" : "false"
+                    : typeof value === "object" && value ? isArray(value) ? cycleCheck(stringifyArray, value) : cycleCheck(stringifyObject, value)
+                        : /*fallback*/ "null";
     }
 
     function cycleCheck(cb: (value: any) => string, value: any) {
@@ -3241,7 +3278,7 @@ namespace ts {
 
     function stringifyProperty(memo: string, value: any, key: string) {
         return value === undefined || typeof value === "function" || key === "__cycle" ? memo
-             : (memo ? memo + "," : memo) + `"${escapeString(key)}":${stringifyValue(value)}`;
+            : (memo ? memo + "," : memo) + `"${escapeString(key)}":${stringifyValue(value)}`;
     }
 
     const base64Digits = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
@@ -3486,7 +3523,7 @@ namespace ts {
      * @param token The token.
      */
     export function createTokenRange(pos: number, token: SyntaxKind): TextRange {
-        return createRange(pos,  pos + tokenToString(token).length);
+        return createRange(pos, pos + tokenToString(token).length);
     }
 
     export function rangeIsOnSingleLine(range: TextRange, sourceFile: SourceFile) {
@@ -3702,6 +3739,7 @@ namespace ts {
         const kind = node.kind;
         return kind === SyntaxKind.PropertyAssignment
             || kind === SyntaxKind.ShorthandPropertyAssignment
+            || kind === SyntaxKind.SpreadAssignment
             || kind === SyntaxKind.MethodDeclaration
             || kind === SyntaxKind.GetAccessor
             || kind === SyntaxKind.SetAccessor
@@ -3789,8 +3827,8 @@ namespace ts {
             || kind === SyntaxKind.NoSubstitutionTemplateLiteral;
     }
 
-    export function isSpreadElementExpression(node: Node): node is SpreadElementExpression {
-        return node.kind === SyntaxKind.SpreadElementExpression;
+    export function isSpreadExpression(node: Node): node is SpreadElement {
+        return node.kind === SyntaxKind.SpreadElement;
     }
 
     export function isExpressionWithTypeArguments(node: Node): node is ExpressionWithTypeArguments {
@@ -3849,7 +3887,7 @@ namespace ts {
             || kind === SyntaxKind.YieldExpression
             || kind === SyntaxKind.ArrowFunction
             || kind === SyntaxKind.BinaryExpression
-            || kind === SyntaxKind.SpreadElementExpression
+            || kind === SyntaxKind.SpreadElement
             || kind === SyntaxKind.AsExpression
             || kind === SyntaxKind.OmittedExpression
             || kind === SyntaxKind.RawExpression
@@ -4152,6 +4190,7 @@ namespace ts {
 namespace ts {
     export function getDefaultLibFileName(options: CompilerOptions): string {
         switch (options.target) {
+            case ScriptTarget.ESNext:
             case ScriptTarget.ES2017:
                 return "lib.es2017.d.ts";
             case ScriptTarget.ES2016:

src/compiler/visitor.ts

@@ -267,9 +267,9 @@ namespace ts {
             case SyntaxKind.VoidExpression:
             case SyntaxKind.AwaitExpression:
             case SyntaxKind.YieldExpression:
-            case SyntaxKind.SpreadElementExpression:
+            case SyntaxKind.SpreadElement:
             case SyntaxKind.NonNullExpression:
-                result = reduceNode((<ParenthesizedExpression | DeleteExpression | TypeOfExpression | VoidExpression | AwaitExpression | YieldExpression | SpreadElementExpression | NonNullExpression>node).expression, f, result);
+                result = reduceNode((<ParenthesizedExpression | DeleteExpression | TypeOfExpression | VoidExpression | AwaitExpression | YieldExpression | SpreadElement | NonNullExpression>node).expression, f, result);
                 break;
 
             case SyntaxKind.PrefixUnaryExpression:
@@ -510,6 +510,10 @@ namespace ts {
                 result = reduceNode((<ShorthandPropertyAssignment>node).objectAssignmentInitializer, f, result);
                 break;
 
+            case SyntaxKind.SpreadAssignment:
+                result = reduceNode((node as SpreadAssignment).expression, f, result);
+                break;
+
             // Top-level nodes
             case SyntaxKind.SourceFile:
                 result = reduceLeft((<SourceFile>node).statements, f, result);
@@ -907,9 +911,9 @@ namespace ts {
                 return updateYield(<YieldExpression>node,
                     visitNode((<YieldExpression>node).expression, visitor, isExpression));
 
-            case SyntaxKind.SpreadElementExpression:
-                return updateSpread(<SpreadElementExpression>node,
-                    visitNode((<SpreadElementExpression>node).expression, visitor, isExpression));
+            case SyntaxKind.SpreadElement:
+                return updateSpread(<SpreadElement>node,
+                    visitNode((<SpreadElement>node).expression, visitor, isExpression));
 
             case SyntaxKind.ClassExpression:
                 return updateClassExpression(<ClassExpression>node,
@@ -1160,7 +1164,11 @@ namespace ts {
                     visitNode((<ShorthandPropertyAssignment>node).name, visitor, isIdentifier),
                     visitNode((<ShorthandPropertyAssignment>node).objectAssignmentInitializer, visitor, isExpression));
 
-            // Top-level nodes
+            case SyntaxKind.SpreadAssignment:
+                return updateSpreadAssignment(node as SpreadAssignment,
+                    visitNode((node as SpreadAssignment).expression, visitor, isExpression));
+
+           // Top-level nodes
             case SyntaxKind.SourceFile:
                 context.startLexicalEnvironment();
                 return updateSourceFileNode(<SourceFile>node,