add support to convert lambda to function and vice-versa (#28250)

* add skeleton

* add getAvailableActions

* add working getEditsForAction

* add multi vardecl

* fix multi decl bug

* change refactor name

* add tests for ToAnon, ToArrow and available arrow

* add tests for ToNamed and available anon

* add tests for ReturnType and available Arrow as FnParam

* fix bug modifiers by toNamed

* add tests for modifiers

* fix for tslint error

* adapt one test case

* refactor getInfo getAvailableActions

* refactor small progress

* extract creation of block

* extract creation of funcDeclaration

* make guideline compliant

* apply feedback from pr

* add testcase and apply feedback from pr

* apply feedback from pr

* add newline

* rename testcases

* Make conditions more expressive

* fix for unnecessary duplication of comment

* apply feedback from pr

* update getAvailableActions

* check if functionExpression name is used

* add more testcases

* do not provide refactoring when it contains this
because this behaves differently in arrow than in function

* exclude nested functions and classes at containingThis check

* fix linting error

* fix line endings

Co-authored-by: BigAru <arooran@indikon.ch>
Co-authored-by: bigaru <bigaru@users.noreply.github.com>
Co-authored-by: Jesse Trinity <42591254+jessetrinity@users.noreply.github.com>
Co-authored-by: Jesse Trinity <jetrinit@microsoft.com>

src/compiler/diagnosticMessages.json

@@ -5717,6 +5717,22 @@
         "category": "Message",
         "code": 95121
     },
+    "Convert arrow function or function expression": {
+        "category": "Message",
+        "code": 95122
+    },
+    "Convert to anonymous function": {
+        "category": "Message",
+        "code": 95123
+    },
+    "Convert to named function": {
+        "category": "Message",
+        "code": 95124
+    },
+    "Convert to arrow function": {
+        "category": "Message",
+        "code": 95125
+    },
 
     "No value exists in scope for the shorthand property '{0}'. Either declare one or provide an initializer.": {
         "category": "Error",

src/services/refactors/convertArrowFunctionOrFunctionExpression.ts

@@ -0,0 +1,216 @@
+/* @internal */
+namespace ts.refactor.convertArrowFunctionOrFunctionExpression {
+    const refactorName = "Convert arrow function or function expression";
+    const refactorDescription = getLocaleSpecificMessage(Diagnostics.Convert_arrow_function_or_function_expression);
+
+    const toAnonymousFunctionActionName = "Convert to anonymous function";
+    const toNamedFunctionActionName = "Convert to named function";
+    const toArrowFunctionActionName = "Convert to arrow function";
+
+    const toAnonymousFunctionActionDescription = getLocaleSpecificMessage(Diagnostics.Convert_to_anonymous_function);
+    const toNamedFunctionActionDescription = getLocaleSpecificMessage(Diagnostics.Convert_to_named_function);
+    const toArrowFunctionActionDescription = getLocaleSpecificMessage(Diagnostics.Convert_to_arrow_function);
+
+    registerRefactor(refactorName, { getEditsForAction, getAvailableActions });
+
+    interface FunctionInfo {
+        readonly selectedVariableDeclaration: boolean;
+        readonly func: FunctionExpression | ArrowFunction;
+    }
+
+    interface VariableInfo {
+        readonly variableDeclaration: VariableDeclaration;
+        readonly variableDeclarationList: VariableDeclarationList;
+        readonly statement: VariableStatement;
+        readonly name: Identifier;
+    }
+
+    function getAvailableActions(context: RefactorContext): readonly ApplicableRefactorInfo[] {
+        const { file, startPosition, program } = context;
+        const info = getFunctionInfo(file, startPosition, program);
+
+        if (!info) return emptyArray;
+        const { selectedVariableDeclaration, func } = info;
+        const possibleActions: RefactorActionInfo[] = [];
+
+        if (selectedVariableDeclaration || (isArrowFunction(func) && isVariableDeclaration(func.parent))) {
+            possibleActions.push({
+                name: toNamedFunctionActionName,
+                description: toNamedFunctionActionDescription
+            });
+        }
+
+        if (!selectedVariableDeclaration && isArrowFunction(func)) {
+            possibleActions.push({
+                name: toAnonymousFunctionActionName,
+                description: toAnonymousFunctionActionDescription
+            });
+        }
+
+        if (isFunctionExpression(func)) {
+            possibleActions.push({
+                name: toArrowFunctionActionName,
+                description: toArrowFunctionActionDescription
+            });
+        }
+
+        return [{
+            name: refactorName,
+            description: refactorDescription,
+            actions: possibleActions
+        }];
+    }
+
+    function getEditsForAction(context: RefactorContext, actionName: string): RefactorEditInfo | undefined {
+        const { file, startPosition, program } = context;
+        const info = getFunctionInfo(file, startPosition, program);
+
+        if (!info) return undefined;
+        const { func } = info;
+        const edits: FileTextChanges[] = [];
+
+        switch (actionName) {
+            case toAnonymousFunctionActionName:
+                edits.push(...getEditInfoForConvertToAnonymousFunction(context, func));
+                break;
+
+            case toNamedFunctionActionName:
+                const variableInfo = getVariableInfo(func);
+                if (!variableInfo) return undefined;
+
+                edits.push(...getEditInfoForConvertToNamedFunction(context, func, variableInfo));
+                break;
+
+            case toArrowFunctionActionName:
+                if (!isFunctionExpression(func)) return undefined;
+                edits.push(...getEditInfoForConvertToArrowFunction(context, func));
+                break;
+
+            default:
+                return Debug.fail("invalid action");
+        }
+
+        return { renameFilename: undefined, renameLocation: undefined, edits };
+    }
+
+    function containingThis(node: Node): boolean {
+        let containsThis = false;
+        node.forEachChild(function checkThis(child) {
+
+            if (isThis(child)) {
+                containsThis = true;
+                return;
+            }
+
+            if (!isClassLike(child) && !isFunctionDeclaration(child) && !isFunctionExpression(child)) {
+                forEachChild(child, checkThis);
+            }
+        });
+
+        return containsThis;
+    }
+
+    function getFunctionInfo(file: SourceFile, startPosition: number, program: Program): FunctionInfo | undefined {
+        const token = getTokenAtPosition(file, startPosition);
+
+        const arrowFunc = getArrowFunctionFromVariableDeclaration(token.parent);
+        if (arrowFunc && !containingThis(arrowFunc.body)) return { selectedVariableDeclaration: true, func: arrowFunc };
+
+        const maybeFunc = getContainingFunction(token);
+        const typeChecker = program.getTypeChecker();
+
+        if (
+            maybeFunc &&
+            (isFunctionExpression(maybeFunc) || isArrowFunction(maybeFunc)) &&
+            !rangeContainsRange(maybeFunc.body, token) &&
+            !containingThis(maybeFunc.body)
+        ) {
+            if ((isFunctionExpression(maybeFunc) && maybeFunc.name && FindAllReferences.Core.isSymbolReferencedInFile(maybeFunc.name, typeChecker, file))) return undefined;
+            return { selectedVariableDeclaration: false, func: maybeFunc };
+        }
+
+        return undefined;
+    }
+
+    function isSingleVariableDeclaration(parent: Node): parent is VariableDeclarationList {
+        return isVariableDeclaration(parent) || (isVariableDeclarationList(parent) && parent.declarations.length === 1);
+    }
+
+    function getArrowFunctionFromVariableDeclaration(parent: Node): ArrowFunction | undefined {
+        if (!isSingleVariableDeclaration(parent)) return undefined;
+        const variableDeclaration = isVariableDeclaration(parent) ? parent : parent.declarations[0];
+
+        const initializer = variableDeclaration.initializer;
+        if (!initializer || !isArrowFunction(initializer)) return undefined;
+        return initializer;
+    }
+
+    function convertToBlock(body: ConciseBody): Block {
+        if (isExpression(body)) {
+            return createBlock([createReturn(body)], /* multiLine */ true);
+        }
+        else {
+            return body;
+        }
+    }
+
+    function getVariableInfo(func: FunctionExpression | ArrowFunction): VariableInfo | undefined {
+        const variableDeclaration = func.parent;
+        if (!isVariableDeclaration(variableDeclaration) || !isVariableDeclarationInVariableStatement(variableDeclaration)) return undefined;
+
+        const variableDeclarationList = variableDeclaration.parent;
+        const statement = variableDeclarationList.parent;
+        if (!isVariableDeclarationList(variableDeclarationList) || !isVariableStatement(statement) || !isIdentifier(variableDeclaration.name)) return undefined;
+
+        return { variableDeclaration, variableDeclarationList, statement, name: variableDeclaration.name };
+    }
+
+    function getEditInfoForConvertToAnonymousFunction(context: RefactorContext, func: FunctionExpression | ArrowFunction): FileTextChanges[] {
+        const { file } = context;
+        const body = convertToBlock(func.body);
+        const newNode = createFunctionExpression(func.modifiers, func.asteriskToken, /* name */ undefined, func.typeParameters, func.parameters, func.type, body);
+        return textChanges.ChangeTracker.with(context, t => t.replaceNode(file, func, newNode));
+    }
+
+    function getEditInfoForConvertToNamedFunction(context: RefactorContext, func: FunctionExpression | ArrowFunction, variableInfo: VariableInfo): FileTextChanges[] {
+        const { file } = context;
+        const body = convertToBlock(func.body);
+
+        const { variableDeclaration, variableDeclarationList, statement, name } = variableInfo;
+        suppressLeadingTrivia(statement);
+        const newNode = createFunctionDeclaration(func.decorators, statement.modifiers, func.asteriskToken, name, func.typeParameters, func.parameters, func.type, body);
+
+        if (variableDeclarationList.declarations.length === 1) {
+            return textChanges.ChangeTracker.with(context, t => t.replaceNode(file, statement, newNode));
+        }
+        else {
+            return textChanges.ChangeTracker.with(context, t => {
+                t.delete(file, variableDeclaration);
+                t.insertNodeAfter(file, statement, newNode);
+            });
+        }
+    }
+
+    function getEditInfoForConvertToArrowFunction(context: RefactorContext, func: FunctionExpression): FileTextChanges[] {
+        const { file } = context;
+        const statements = func.body.statements;
+        const head = statements[0];
+        let body: ConciseBody;
+
+        if (canBeConvertedToExpression(func.body, head)) {
+            body = head.expression!;
+            suppressLeadingAndTrailingTrivia(body);
+            copyComments(head, body);
+        }
+        else {
+            body = func.body;
+        }
+
+        const newNode = createArrowFunction(func.modifiers, func.typeParameters, func.parameters, func.type, createToken(SyntaxKind.EqualsGreaterThanToken), body);
+        return textChanges.ChangeTracker.with(context, t => t.replaceNode(file, func, newNode));
+    }
+
+    function canBeConvertedToExpression(body: Block, head: Statement): head is ReturnStatement {
+        return body.statements.length === 1 && ((isReturnStatement(head) && !!head.expression));
+    }
+}

src/services/tsconfig.json

@@ -113,6 +113,7 @@
         "refactors/addOrRemoveBracesToArrowFunction.ts",
         "refactors/convertParamsToDestructuredObject.ts",
         "refactors/convertStringOrTemplateLiteral.ts",
+        "refactors/convertArrowFunctionOrFunctionExpression.ts",
         "services.ts",
         "breakpoints.ts",
         "transform.ts",