extractMethod: Support renameLocation (#18050)

* extractMethod: Support renameLocation

* Add tslint disable

* Properly analyze list of changes to always get a correct rename location

* Update test

* Ensure name is really unique

* Improvements to test code

* Respond to PR comments

src/harness/fourslash.ts

@@ -2758,11 +2758,11 @@ namespace FourSlash {
             }
         }
 
-        private getSelection() {
-            return ({
+        private getSelection(): ts.TextRange {
+            return {
                 pos: this.currentCaretPosition,
                 end: this.selectionEnd === -1 ? this.currentCaretPosition : this.selectionEnd
-            });
+            };
         }
 
         public verifyRefactorAvailable(negative: boolean, name: string, actionName?: string) {
@@ -2803,7 +2803,7 @@ namespace FourSlash {
             }
         }
 
-        public applyRefactor({ refactorName, actionName, actionDescription }: FourSlashInterface.ApplyRefactorOptions) {
+        public applyRefactor({ refactorName, actionName, actionDescription, newContent: newContentWithRenameMarker }: FourSlashInterface.ApplyRefactorOptions) {
             const range = this.getSelection();
             const refactors = this.languageService.getApplicableRefactors(this.activeFile.fileName, range);
             const refactor = refactors.find(r => r.name === refactorName);
@@ -2823,6 +2823,35 @@ namespace FourSlash {
             for (const edit of editInfo.edits) {
                 this.applyEdits(edit.fileName, edit.textChanges, /*isFormattingEdit*/ false);
             }
+
+            const { renamePosition, newContent } = parseNewContent();
+
+            this.verifyCurrentFileContent(newContent);
+
+            if (renamePosition === undefined) {
+                if (editInfo.renameLocation !== undefined) {
+                    this.raiseError(`Did not expect a rename location, got ${editInfo.renameLocation}`);
+                }
+            }
+            else {
+                // TODO: test editInfo.renameFilename value
+                assert.isDefined(editInfo.renameFilename);
+                if (renamePosition !== editInfo.renameLocation) {
+                    this.raiseError(`Expected rename position of ${renamePosition}, but got ${editInfo.renameLocation}`);
+                }
+            }
+
+            function parseNewContent(): { renamePosition: number | undefined, newContent: string } {
+                const renamePosition = newContentWithRenameMarker.indexOf("/*RENAME*/");
+                if (renamePosition === -1) {
+                    return { renamePosition: undefined, newContent: newContentWithRenameMarker };
+                }
+                else {
+                    const newContent = newContentWithRenameMarker.slice(0, renamePosition) + newContentWithRenameMarker.slice(renamePosition + "/*RENAME*/".length);
+                    return { renamePosition, newContent };
+                }
+            }
+
         }
 
         public verifyFileAfterApplyingRefactorAtMarker(
@@ -4319,6 +4348,7 @@ namespace FourSlashInterface {
         refactorName: string;
         actionName: string;
         actionDescription: string;
+        newContent: string;
     }
 
     export interface CompletionsAtOptions {

src/harness/unittests/extractMethods.ts

@@ -745,9 +745,12 @@ function M3() { }`);
                 data.push(`// ==ORIGINAL==`);
                 data.push(sourceFile.text);
                 for (const r of results) {
-                    const changes = refactor.extractMethod.getPossibleExtractions(result.targetRange, context, results.indexOf(r))[0].changes;
+                    const { renameLocation, edits } = refactor.extractMethod.getExtractionAtIndex(result.targetRange, context, results.indexOf(r));
+                    assert.lengthOf(edits, 1);
                     data.push(`// ==SCOPE::${r.scopeDescription}==`);
-                    data.push(textChanges.applyChanges(sourceFile.text, changes[0].textChanges));
+                    const newText = textChanges.applyChanges(sourceFile.text, edits[0].textChanges);
+                    const newTextWithRename = newText.slice(0, renameLocation) + "/*RENAME*/" + newText.slice(renameLocation);
+                    data.push(newTextWithRename);
                 }
                 return data.join(newLineCharacter);
             });

src/server/client.ts

@@ -586,9 +586,7 @@ namespace ts.server {
             const response = this.processResponse<protocol.GetEditsForRefactorResponse>(request);
 
             if (!response.body) {
-                return {
-                    edits: []
-                };
+                return { edits: [], renameFilename: undefined, renameLocation: undefined };
             }
 
             const edits: FileTextChanges[] = this.convertCodeEditsToTextChanges(response.body.edits);

src/services/refactors/convertFunctionToEs6Class.ts

@@ -97,7 +97,9 @@ namespace ts.refactor.convertFunctionToES6Class {
         }
 
         return {
-            edits: changeTracker.getChanges()
+            edits: changeTracker.getChanges(),
+            renameFilename: undefined,
+            renameLocation: undefined,
         };
 
         function deleteNode(node: Node, inList = false) {

src/services/refactors/extractMethod.ts

@@ -31,16 +31,16 @@ namespace ts.refactor.extractMethod {
         const usedNames: Map<boolean> = createMap();
 
         let i = 0;
-        for (const extr of extractions) {
+        for (const { scopeDescription, errors } of extractions) {
             // Skip these since we don't have a way to report errors yet
-            if (extr.errors && extr.errors.length) {
+            if (errors.length) {
                 continue;
             }
 
             // Don't issue refactorings with duplicated names.
             // Scopes come back in "innermost first" order, so extractions will
             // preferentially go into nearer scopes
-            const description = formatStringFromArgs(Diagnostics.Extract_to_0.message, [extr.scopeDescription]);
+            const description = formatStringFromArgs(Diagnostics.Extract_to_0.message, [scopeDescription]);
             if (!usedNames.has(description)) {
                 usedNames.set(description, true);
                 actions.push({
@@ -75,10 +75,7 @@ namespace ts.refactor.extractMethod {
         const index = +parsedIndexMatch[1];
         Debug.assert(isFinite(index), "Expected to parse a finite number from the scope index");
 
-        const extractions = getPossibleExtractions(targetRange, context, index);
-        // Scope is no longer valid from when the user issued the refactor (??)
-        Debug.assert(extractions !== undefined, "The extraction went missing? How?");
-        return ({ edits: extractions[0].changes });
+        return getExtractionAtIndex(targetRange, context, index);
     }
 
     // Move these into diagnostic messages if they become user-facing
@@ -102,7 +99,7 @@ namespace ts.refactor.extractMethod {
         export const CannotExtractAmbientBlock = createMessage("Cannot extract code from ambient contexts");
     }
 
-    export enum RangeFacts {
+    enum RangeFacts {
         None = 0,
         HasReturn = 1 << 0,
         IsGenerator = 1 << 1,
@@ -117,7 +114,7 @@ namespace ts.refactor.extractMethod {
     /**
      * Represents an expression or a list of statements that should be extracted with some extra information
      */
-    export interface TargetRange {
+    interface TargetRange {
         readonly range: Expression | Statement[];
         readonly facts: RangeFacts;
         /**
@@ -130,7 +127,7 @@ namespace ts.refactor.extractMethod {
     /**
      * Result of 'getRangeToExtract' operation: contains either a range or a list of errors
      */
-    export type RangeToExtract = {
+    type RangeToExtract = {
         readonly targetRange?: never;
         readonly errors: ReadonlyArray<Diagnostic>;
     } | {
@@ -141,18 +138,7 @@ namespace ts.refactor.extractMethod {
     /*
      * Scopes that can store newly extracted method
      */
-    export type Scope = FunctionLikeDeclaration | SourceFile | ModuleBlock | ClassLikeDeclaration;
-
-    /**
-     * Result of 'extractRange' operation for a specific scope.
-     * Stores either a list of changes that should be applied to extract a range or a list of errors
-     */
-    export interface ExtractResultForScope {
-        readonly scope: Scope;
-        readonly scopeDescription: string;
-        readonly changes?: FileTextChanges[];
-        readonly errors?: Diagnostic[];
-    }
+    type Scope = FunctionLikeDeclaration | SourceFile | ModuleBlock | ClassLikeDeclaration;
 
     /**
      * getRangeToExtract takes a span inside a text file and returns either an expression or an array
@@ -160,6 +146,7 @@ namespace ts.refactor.extractMethod {
      * process may fail, in which case a set of errors is returned instead (these are currently
      * not shown to the user, but can be used by us diagnostically)
      */
+    // exported only for tests
     export function getRangeToExtract(sourceFile: SourceFile, span: TextSpan): RangeToExtract {
         const length = span.length || 0;
         // Walk up starting from the the start position until we find a non-SourceFile node that subsumes the selected span.
@@ -458,7 +445,7 @@ namespace ts.refactor.extractMethod {
      * you may be able to extract into a class method *or* local closure *or* namespace function,
      * depending on what's in the extracted body.
      */
-    export function collectEnclosingScopes(range: TargetRange): Scope[] | undefined {
+    function collectEnclosingScopes(range: TargetRange): Scope[] | undefined {
         let current: Node = isReadonlyArray(range.range) ? firstOrUndefined(range.range) : range.range;
         if (range.facts & RangeFacts.UsesThis) {
             // if range uses this as keyword or as type inside the class then it can only be extracted to a method of the containing class
@@ -494,12 +481,32 @@ namespace ts.refactor.extractMethod {
         return scopes;
     }
 
+    // exported only for tests
+    export function getExtractionAtIndex(targetRange: TargetRange, context: RefactorContext, requestedChangesIndex: number): RefactorEditInfo {
+        const { scopes, readsAndWrites: { target, usagesPerScope, errorsPerScope } } = getPossibleExtractionsWorker(targetRange, context);
+        Debug.assert(!errorsPerScope[requestedChangesIndex].length, "The extraction went missing? How?");
+        context.cancellationToken.throwIfCancellationRequested();
+        return extractFunctionInScope(target, scopes[requestedChangesIndex], usagesPerScope[requestedChangesIndex], targetRange, context);
+    }
+
+    interface PossibleExtraction {
+        readonly scopeDescription: string;
+        readonly errors: ReadonlyArray<Diagnostic>;
+    }
     /**
      * Given a piece of text to extract ('targetRange'), computes a list of possible extractions.
      * Each returned ExtractResultForScope corresponds to a possible target scope and is either a set of changes
      * or an error explaining why we can't extract into that scope.
      */
-    export function getPossibleExtractions(targetRange: TargetRange, context: RefactorContext, requestedChangesIndex: number = undefined): ReadonlyArray<ExtractResultForScope> | undefined {
+    // exported only for tests
+    export function getPossibleExtractions(targetRange: TargetRange, context: RefactorContext): ReadonlyArray<PossibleExtraction> | undefined {
+        const { scopes, readsAndWrites: { errorsPerScope } } = getPossibleExtractionsWorker(targetRange, context);
+        // Need the inner type annotation to avoid https://github.com/Microsoft/TypeScript/issues/7547
+        return scopes.map((scope, i): PossibleExtraction =>
+            ({ scopeDescription: getDescriptionForScope(scope), errors: errorsPerScope[i] }));
+    }
+
+    function getPossibleExtractionsWorker(targetRange: TargetRange, context: RefactorContext): { readonly scopes: Scope[], readonly readsAndWrites: ReadsAndWrites } {
         const { file: sourceFile } = context;
 
         if (targetRange === undefined) {
@@ -512,35 +519,14 @@ namespace ts.refactor.extractMethod {
         }
 
         const enclosingTextRange = getEnclosingTextRange(targetRange, sourceFile);
-        const { target, usagesPerScope, errorsPerScope } = collectReadsAndWrites(
+        const readsAndWrites = collectReadsAndWrites(
             targetRange,
             scopes,
             enclosingTextRange,
             sourceFile,
             context.program.getTypeChecker(),
             context.cancellationToken);
-
-        context.cancellationToken.throwIfCancellationRequested();
-
-        if (requestedChangesIndex !== undefined) {
-            if (errorsPerScope[requestedChangesIndex].length) {
-                return undefined;
-            }
-            return [extractFunctionInScope(target, scopes[requestedChangesIndex], usagesPerScope[requestedChangesIndex], targetRange, context)];
-        }
-        else {
-            return scopes.map((scope, i) => {
-                const errors = errorsPerScope[i];
-                if (errors.length) {
-                    return {
-                        scope,
-                        scopeDescription: getDescriptionForScope(scope),
-                        errors
-                    };
-                }
-                return { scope, scopeDescription: getDescriptionForScope(scope) };
-            });
-        }
+        return { scopes, readsAndWrites };
     }
 
     function getDescriptionForScope(scope: Scope): string {
@@ -583,34 +569,33 @@ namespace ts.refactor.extractMethod {
             : scope.externalModuleIndicator ? "module scope" : "global scope";
     }
 
-    function getUniqueName(isNameOkay: (name: string) => boolean) {
+    function getUniqueName(fileText: string): string {
         let functionNameText = "newFunction";
-        if (isNameOkay(functionNameText)) {
-            return functionNameText;
-        }
-        let i = 1;
-        while (!isNameOkay(functionNameText = `newFunction_${i}`)) {
-            i++;
+        for (let i = 1; fileText.indexOf(functionNameText) !== -1; i++) {
+            functionNameText = `newFunction_${i}`;
         }
         return functionNameText;
     }
 
-    export function extractFunctionInScope(
+    /**
+     * Result of 'extractRange' operation for a specific scope.
+     * Stores either a list of changes that should be applied to extract a range or a list of errors
+     */
+    function extractFunctionInScope(
         node: Statement | Expression | Block,
         scope: Scope,
         { usages: usagesInScope, typeParameterUsages, substitutions }: ScopeUsages,
         range: TargetRange,
-        context: RefactorContext): ExtractResultForScope {
+        context: RefactorContext): RefactorEditInfo {
 
         const checker = context.program.getTypeChecker();
 
         // Make a unique name for the extracted function
         const file = scope.getSourceFile();
-        const functionNameText: string = getUniqueName(n => !file.identifiers.has(n));
+        const functionNameText = getUniqueName(file.text);
         const isJS = isInJavaScriptFile(scope);
 
-        const functionName = createIdentifier(functionNameText as string);
-        const functionReference = createIdentifier(functionNameText as string);
+        const functionName = createIdentifier(functionNameText);
 
         let returnType: TypeNode = undefined;
         const parameters: ParameterDeclaration[] = [];
@@ -660,7 +645,7 @@ namespace ts.refactor.extractMethod {
             returnType = checker.typeToTypeNode(contextualType);
         }
 
-        const { body, returnValueProperty } = transformFunctionBody(node);
+        const { body, returnValueProperty } = transformFunctionBody(node, writes, substitutions, !!(range.facts & RangeFacts.HasReturn));
         let newFunction: MethodDeclaration | FunctionDeclaration;
 
         if (isClassLike(scope)) {
@@ -709,8 +694,10 @@ namespace ts.refactor.extractMethod {
 
         const newNodes: Node[] = [];
         // replace range with function call
+        const called = getCalledExpression(scope, range, functionNameText);
+
         let call: Expression = createCall(
-            isClassLike(scope) ? createPropertyAccess(range.facts & RangeFacts.InStaticRegion ? createIdentifier(scope.name.getText()) : createThis(), functionReference) : functionReference,
+            called,
             callTypeArguments, // Note that no attempt is made to take advantage of type argument inference
             callArguments);
         if (range.facts & RangeFacts.IsGenerator) {
@@ -779,147 +766,174 @@ namespace ts.refactor.extractMethod {
             changeTracker.replaceNodeWithNodes(context.file, range.range, newNodes, { nodeSeparator: context.newLineCharacter });
         }
 
-        return {
-            scope,
-            scopeDescription: getDescriptionForScope(scope),
-            changes: changeTracker.getChanges()
-        };
+        const edits = changeTracker.getChanges();
+        const renameRange = isReadonlyArray(range.range) ? range.range[0] : range.range;
 
-        function getFirstDeclaration(type: Type): Declaration | undefined {
-            let firstDeclaration = undefined;
+        const renameFilename = renameRange.getSourceFile().fileName;
+        const renameLocation = getRenameLocation(edits, renameFilename, functionNameText);
+        return { renameFilename, renameLocation, edits };
+    }
 
-            const symbol = type.symbol;
-            if (symbol && symbol.declarations) {
-                for (const declaration of symbol.declarations) {
-                    if (firstDeclaration === undefined || declaration.pos < firstDeclaration.pos) {
-                        firstDeclaration = declaration;
-                    }
+    function getRenameLocation(edits: ReadonlyArray<FileTextChanges>, renameFilename: string, functionNameText: string): number {
+        let delta = 0;
+        for (const { fileName, textChanges } of edits) {
+            Debug.assert(fileName === renameFilename);
+            for (const change of textChanges) {
+                const { span, newText } = change;
+                // TODO(acasey): We are assuming that the call expression comes before the function declaration,
+                // because we want the new cursor to be on the call expression,
+                // which is closer to where the user was before extracting the function.
+                const index = newText.indexOf(functionNameText);
+                if (index !== -1) {
+                    return span.start + delta + index;
+                }
+                delta += newText.length - span.length;
+            }
+        }
+        throw new Error(); // Didn't find the text we inserted?
+    }
+
+    function getFirstDeclaration(type: Type): Declaration | undefined {
+        let firstDeclaration = undefined;
+
+        const symbol = type.symbol;
+        if (symbol && symbol.declarations) {
+            for (const declaration of symbol.declarations) {
+                if (firstDeclaration === undefined || declaration.pos < firstDeclaration.pos) {
+                    firstDeclaration = declaration;
                 }
             }
-
-            return firstDeclaration;
         }
 
-        function compareTypesByDeclarationOrder(
-            {type: type1, declaration: declaration1}: {type: Type, declaration?: Declaration},
-            {type: type2, declaration: declaration2}: {type: Type, declaration?: Declaration}) {
+        return firstDeclaration;
+    }
 
-            if (declaration1) {
-                if (declaration2) {
-                    const positionDiff = declaration1.pos - declaration2.pos;
-                    if (positionDiff !== 0) {
-                        return positionDiff;
-                    }
+    function compareTypesByDeclarationOrder(
+        {type: type1, declaration: declaration1}: {type: Type, declaration?: Declaration},
+        {type: type2, declaration: declaration2}: {type: Type, declaration?: Declaration}) {
+
+        if (declaration1) {
+            if (declaration2) {
+                const positionDiff = declaration1.pos - declaration2.pos;
+                if (positionDiff !== 0) {
+                    return positionDiff;
                 }
-                else {
-                    return 1; // Sort undeclared type parameters to the front.
-                }
-            }
-            else if (declaration2) {
-                return -1; // Sort undeclared type parameters to the front.
-            }
-
-            const name1 = type1.symbol ? type1.symbol.getName() : "";
-            const name2 = type2.symbol ? type2.symbol.getName() : "";
-            const nameDiff = compareStrings(name1, name2);
-            if (nameDiff !== 0) {
-                return nameDiff;
-            }
-
-            // IDs are guaranteed to be unique, so this ensures a total ordering.
-            return type1.id - type2.id;
-        }
-
-        function getPropertyAssignmentsForWrites(writes: UsageEntry[]) {
-            return writes.map(w => createShorthandPropertyAssignment(w.symbol.name));
-        }
-
-        function generateReturnValueProperty() {
-            return "__return";
-        }
-
-        function getStatementsOrClassElements(scope: Scope): ReadonlyArray<Statement> | ReadonlyArray<ClassElement> {
-            if (isFunctionLike(scope)) {
-                const body = scope.body;
-                if (isBlock(body)) {
-                    return body.statements;
-                }
-            }
-            else if (isModuleBlock(scope) || isSourceFile(scope)) {
-                return scope.statements;
-            }
-            else if (isClassLike(scope)) {
-                return scope.members;
             }
             else {
-                assertTypeIsNever(scope);
-            }
-
-            return emptyArray;
-        }
-
-        /**
-         * If `scope` contains a function after `minPos`, then return the first such function.
-         * Otherwise, return `undefined`.
-         */
-        function getNodeToInsertBefore(minPos: number, scope: Scope): Node | undefined {
-            const children = getStatementsOrClassElements(scope);
-            for (const child of children) {
-                if (child.pos >= minPos && isFunctionLike(child) && !isConstructorDeclaration(child)) {
-                    return child;
-                }
+                return 1; // Sort undeclared type parameters to the front.
             }
         }
+        else if (declaration2) {
+            return -1; // Sort undeclared type parameters to the front.
+        }
 
-        function transformFunctionBody(body: Node) {
-            if (isBlock(body) && !writes && substitutions.size === 0) {
-                // already block, no writes to propagate back, no substitutions - can use node as is
-                return { body: createBlock(body.statements, /*multLine*/ true), returnValueProperty: undefined };
-            }
-            let returnValueProperty: string;
-            const statements = createNodeArray(isBlock(body) ? body.statements.slice(0) : [isStatement(body) ? body : createReturn(<Expression>body)]);
-            // rewrite body if either there are writes that should be propagated back via return statements or there are substitutions
-            if (writes || substitutions.size) {
-                const rewrittenStatements = visitNodes(statements, visitor).slice();
-                if (writes && !(range.facts & RangeFacts.HasReturn) && isStatement(body)) {
-                    // add return at the end to propagate writes back in case if control flow falls out of the function body
-                    // it is ok to know that range has at least one return since it we only allow unconditional returns
-                    const assignments = getPropertyAssignmentsForWrites(writes);
-                    if (assignments.length === 1) {
-                        rewrittenStatements.push(createReturn(assignments[0].name));
-                    }
-                    else {
-                        rewrittenStatements.push(createReturn(createObjectLiteral(assignments)));
-                    }
-                }
-                return { body: createBlock(rewrittenStatements, /*multiLine*/ true), returnValueProperty };
-            }
-            else {
-                return { body: createBlock(statements, /*multiLine*/ true), returnValueProperty: undefined };
-            }
+        const name1 = type1.symbol ? type1.symbol.getName() : "";
+        const name2 = type2.symbol ? type2.symbol.getName() : "";
+        const nameDiff = compareStrings(name1, name2);
+        if (nameDiff !== 0) {
+            return nameDiff;
+        }
 
-            function visitor(node: Node): VisitResult<Node> {
-                if (node.kind === SyntaxKind.ReturnStatement && writes) {
-                    const assignments: ObjectLiteralElementLike[] = getPropertyAssignmentsForWrites(writes);
-                    if ((<ReturnStatement>node).expression) {
-                        if (!returnValueProperty) {
-                            returnValueProperty = generateReturnValueProperty();
-                        }
-                        assignments.unshift(createPropertyAssignment(returnValueProperty, visitNode((<ReturnStatement>node).expression, visitor)));
-                    }
-                    if (assignments.length === 1) {
-                        return createReturn(assignments[0].name as Expression);
-                    }
-                    else {
-                        return createReturn(createObjectLiteral(assignments));
-                    }
+        // IDs are guaranteed to be unique, so this ensures a total ordering.
+        return type1.id - type2.id;
+    }
+
+    function getCalledExpression(scope: Node, range: TargetRange, functionNameText: string): Expression {
+        const functionReference = createIdentifier(functionNameText);
+        if (isClassLike(scope)) {
+            const lhs = range.facts & RangeFacts.InStaticRegion ? createIdentifier(scope.name.text) : createThis();
+            return createPropertyAccess(lhs, functionReference);
+        }
+        else {
+            return functionReference;
+        }
+    }
+
+    function transformFunctionBody(body: Node, writes: ReadonlyArray<UsageEntry>, substitutions: ReadonlyMap<Node>, hasReturn: boolean): { body: Block, returnValueProperty: string } {
+        if (isBlock(body) && !writes && substitutions.size === 0) {
+            // already block, no writes to propagate back, no substitutions - can use node as is
+            return { body: createBlock(body.statements, /*multLine*/ true), returnValueProperty: undefined };
+        }
+        let returnValueProperty: string;
+        const statements = createNodeArray(isBlock(body) ? body.statements.slice(0) : [isStatement(body) ? body : createReturn(<Expression>body)]);
+        // rewrite body if either there are writes that should be propagated back via return statements or there are substitutions
+        if (writes || substitutions.size) {
+            const rewrittenStatements = visitNodes(statements, visitor).slice();
+            if (writes && !hasReturn && isStatement(body)) {
+                // add return at the end to propagate writes back in case if control flow falls out of the function body
+                // it is ok to know that range has at least one return since it we only allow unconditional returns
+                const assignments = getPropertyAssignmentsForWrites(writes);
+                if (assignments.length === 1) {
+                    rewrittenStatements.push(createReturn(assignments[0].name));
                 }
                 else {
-                    const substitution = substitutions.get(getNodeId(node).toString());
-                    return substitution || visitEachChild(node, visitor, nullTransformationContext);
+                    rewrittenStatements.push(createReturn(createObjectLiteral(assignments)));
                 }
             }
+            return { body: createBlock(rewrittenStatements, /*multiLine*/ true), returnValueProperty };
         }
+        else {
+            return { body: createBlock(statements, /*multiLine*/ true), returnValueProperty: undefined };
+        }
+
+        function visitor(node: Node): VisitResult<Node> {
+            if (node.kind === SyntaxKind.ReturnStatement && writes) {
+                const assignments: ObjectLiteralElementLike[] = getPropertyAssignmentsForWrites(writes);
+                if ((<ReturnStatement>node).expression) {
+                    if (!returnValueProperty) {
+                        returnValueProperty = "__return";
+                    }
+                    assignments.unshift(createPropertyAssignment(returnValueProperty, visitNode((<ReturnStatement>node).expression, visitor)));
+                }
+                if (assignments.length === 1) {
+                    return createReturn(assignments[0].name as Expression);
+                }
+                else {
+                    return createReturn(createObjectLiteral(assignments));
+                }
+            }
+            else {
+                const substitution = substitutions.get(getNodeId(node).toString());
+                return substitution || visitEachChild(node, visitor, nullTransformationContext);
+            }
+        }
+    }
+
+    function getStatementsOrClassElements(scope: Scope): ReadonlyArray<Statement> | ReadonlyArray<ClassElement> {
+        if (isFunctionLike(scope)) {
+            const body = scope.body;
+            if (isBlock(body)) {
+                return body.statements;
+            }
+        }
+        else if (isModuleBlock(scope) || isSourceFile(scope)) {
+            return scope.statements;
+        }
+        else if (isClassLike(scope)) {
+            return scope.members;
+        }
+        else {
+            assertTypeIsNever(scope);
+        }
+
+        return emptyArray;
+    }
+
+    /**
+     * If `scope` contains a function after `minPos`, then return the first such function.
+     * Otherwise, return `undefined`.
+     */
+    function getNodeToInsertBefore(minPos: number, scope: Scope): Node | undefined {
+        const children = getStatementsOrClassElements(scope);
+        for (const child of children) {
+            if (child.pos >= minPos && isFunctionLike(child) && !isConstructorDeclaration(child)) {
+                return child;
+            }
+        }
+    }
+
+    function getPropertyAssignmentsForWrites(writes: ReadonlyArray<UsageEntry>): ShorthandPropertyAssignment[] {
+        return writes.map(w => createShorthandPropertyAssignment(w.symbol.name));
     }
 
     function isReadonlyArray(v: any): v is ReadonlyArray<any> {
@@ -948,25 +962,30 @@ namespace ts.refactor.extractMethod {
         Write = 2
     }
 
-    export interface UsageEntry {
+    interface UsageEntry {
         readonly usage: Usage;
         readonly symbol: Symbol;
         readonly node: Node;
     }
 
-    export interface ScopeUsages {
-        usages: Map<UsageEntry>;
-        typeParameterUsages: Map<TypeParameter>; // Key is type ID
-        substitutions: Map<Node>;
+    interface ScopeUsages {
+        readonly usages: Map<UsageEntry>;
+        readonly typeParameterUsages: Map<TypeParameter>; // Key is type ID
+        readonly substitutions: Map<Node>;
     }
 
+    interface ReadsAndWrites {
+        readonly target: Expression | Block;
+        readonly usagesPerScope: ReadonlyArray<ScopeUsages>;
+        readonly errorsPerScope: ReadonlyArray<ReadonlyArray<Diagnostic>>;
+    }
     function collectReadsAndWrites(
         targetRange: TargetRange,
         scopes: Scope[],
         enclosingTextRange: TextRange,
         sourceFile: SourceFile,
         checker: TypeChecker,
-        cancellationToken: CancellationToken) {
+        cancellationToken: CancellationToken): ReadsAndWrites {
 
         const allTypeParameterUsages = createMap<TypeParameter>(); // Key is type ID
         const usagesPerScope: ScopeUsages[] = [];

src/services/types.ts

@@ -414,8 +414,8 @@ namespace ts {
      */
     export interface RefactorEditInfo {
         edits: FileTextChanges[];
-        renameFilename?: string;
-        renameLocation?: number;
+        renameFilename: string | undefined;
+        renameLocation: number | undefined;
     }
 
     export interface TextInsertion {