Quick fix for functions lacking return expressions

src/compiler/checker.ts

@@ -315,6 +315,7 @@ namespace ts {
             isArrayLikeType,
             isTypeInvalidDueToUnionDiscriminant,
             getAllPossiblePropertiesOfTypes,
+            isTypeAssignableTo,
             getSuggestionForNonexistentProperty: (node, type) => getSuggestionForNonexistentProperty(node, type),
             getSuggestionForNonexistentSymbol: (location, name, meaning) => getSuggestionForNonexistentSymbol(location, escapeLeadingUnderscores(name), meaning),
             getSuggestionForNonexistentExport: (node, target) => getSuggestionForNonexistentExport(node, target),

src/compiler/diagnosticMessages.json

@@ -4954,5 +4954,25 @@
     "No value exists in scope for the shorthand property '{0}'. Either declare one or provide an initializer." :{
         "category": "Error",
         "code": 18004
+    },
+    "Add a return statement": {
+        "category": "Message",
+        "code": 95077
+    },
+    "Remove block body braces": {
+        "category": "Message",
+        "code": 95078
+    },
+    "Replace braces with parentheses": {
+        "category": "Message",
+        "code": 95079
+    },
+    "Wrap this block with parentheses": {
+        "category": "Message",
+        "code": 95080
+    },
+    "Surmise all return value": {
+        "category": "Message",
+        "code": 95081
     }
 }

src/compiler/types.ts

@@ -3261,6 +3261,7 @@ namespace ts {
          * e.g. it specifies `kind: "a"` and obj has `kind: "b"`.
          */
         /* @internal */ isTypeInvalidDueToUnionDiscriminant(contextualType: Type, obj: ObjectLiteralExpression | JsxAttributes): boolean;
+        /* @internal */ isTypeAssignableTo(type1: Type, type2: Type): boolean;
         /**
          * For a union, will include a property if it's defined in *any* of the member types.
          * So for `{ a } | { b }`, this will include both `a` and `b`.

src/services/codefixes/returnValueSurmise.ts

@@ -0,0 +1,226 @@
+/* @internal */
+namespace ts.codefix {
+    const fixId = "returnValueSurmise";
+    const fixIdAddReturnStatement = "fixAddReturnStatement";
+    const fixIdRemoveBlockBodyBrace = "fixRemoveBlockBodyBrace";
+    const fixIdReplaceBraceWithParen = "fixReplaceBraceWithParen";
+    const fixIdWrapTheBlockWithParen = "fixWrapTheBlockWithParen";
+    const errorCodes = [
+        Diagnostics.A_function_whose_declared_type_is_neither_void_nor_any_must_return_a_value.code,
+        Diagnostics.Type_0_is_not_assignable_to_type_1.code,
+        Diagnostics.Argument_of_type_0_is_not_assignable_to_parameter_of_type_1.code
+    ];
+
+    enum FixKind {
+        MissingReturnStatement,
+        MissingParentheses
+    }
+
+    interface MissingReturnInfo {
+        kind: FixKind.MissingReturnStatement;
+        declaration: FunctionLikeDeclaration;
+        expression: Expression;
+    }
+
+    interface MissingParenInfo {
+        kind: FixKind.MissingParentheses;
+        declaration: ArrowFunction;
+        expression: Expression;
+    }
+
+    type Info = MissingReturnInfo | MissingParenInfo;
+
+    registerCodeFix({
+        errorCodes,
+        fixIds: [fixIdAddReturnStatement, fixIdRemoveBlockBodyBrace, fixIdReplaceBraceWithParen, fixIdWrapTheBlockWithParen],
+        getCodeActions: context => {
+            const { program, sourceFile, span: { start }, errorCode } = context;
+            const info = getInfo(program.getTypeChecker(), sourceFile, start, errorCode);
+            if (!info) return undefined;
+
+            if (info.kind === FixKind.MissingReturnStatement) {
+                return concatenate(
+                    [getActionForfixAddReturnStatement(context, info.declaration, info.expression)],
+                    isArrowFunction(info.declaration) ? [
+                        getActionForfixRemoveBlockBodyBrace(context, info.declaration, info.expression),
+                        getActionForfixReplaceBraceWithParen(context, info.declaration, info.expression)
+                    ] : undefined);
+            }
+            else {
+                return [getActionForfixWrapTheBlockWithParen(context, info.declaration, info.expression)];
+            }
+        },
+        getAllCodeActions: context => codeFixAll(context, errorCodes, (changes, diag) => {
+            const info = getInfo(context.program.getTypeChecker(), diag.file, diag.start, diag.code);
+            if (!info) return undefined;
+
+            switch (context.fixId) {
+                case fixIdAddReturnStatement:
+                    addReturnStatement(changes, diag.file, info.declaration, info.expression);
+                    break;
+                case fixIdRemoveBlockBodyBrace:
+                    if (!isArrowFunction(info.declaration)) return undefined;
+                    removeBlockBodyBrace(changes, diag.file, info.declaration, info.expression, /* withParen */ false);
+                    break;
+                case fixIdReplaceBraceWithParen:
+                    if (!isArrowFunction(info.declaration)) return undefined;
+                    removeBlockBodyBrace(changes, diag.file, info.declaration, info.expression, /* withParen */ true);
+                    break;
+                case fixIdWrapTheBlockWithParen:
+                    if (!isArrowFunction(info.declaration)) return undefined;
+                    wrapBlockWithParen(changes, diag.file, info.declaration, info.expression);
+                    break;
+                default:
+                    Debug.fail(JSON.stringify(context.fixId));
+            }
+        }),
+    });
+
+    function updateFunctionLikeBody(declaration: FunctionLikeDeclaration, body: Block): FunctionLikeDeclaration {
+        switch (declaration.kind) {
+            case SyntaxKind.FunctionDeclaration:
+                return createFunctionDeclaration(declaration.decorators, declaration.modifiers, declaration.asteriskToken, declaration.name, declaration.typeParameters, declaration.parameters, declaration.type, body);
+            case SyntaxKind.MethodDeclaration:
+                return createMethod(declaration.decorators, declaration.modifiers, declaration.asteriskToken, declaration.name, declaration.questionToken, declaration.typeParameters, declaration.parameters, declaration.type, body);
+            case SyntaxKind.GetAccessor:
+                return createGetAccessor(declaration.decorators, declaration.modifiers, declaration.name, declaration.parameters, declaration.type, body);
+            case SyntaxKind.SetAccessor:
+                return createSetAccessor(declaration.decorators, declaration.modifiers, declaration.name, declaration.parameters, body);
+            case SyntaxKind.Constructor:
+                return createConstructor(declaration.decorators, declaration.modifiers, declaration.parameters, body);
+            case SyntaxKind.FunctionExpression:
+                return createFunctionExpression(declaration.modifiers, declaration.asteriskToken, declaration.name, declaration.typeParameters, declaration.parameters, declaration.type, body);
+            case SyntaxKind.ArrowFunction:
+                return createArrowFunction(declaration.modifiers, declaration.typeParameters, declaration.parameters, declaration.type, declaration.equalsGreaterThanToken, body);
+        }
+    }
+
+    function getFixInfo(checker: TypeChecker, declaration: FunctionLikeDeclaration, expectType: Type, isFunctionType: boolean): Info | undefined {
+        if (!declaration.body || !isBlock(declaration.body) || length(declaration.body.statements) !== 1) return undefined;
+
+        const firstStatement = first(declaration.body.statements);
+        if (isExpressionStatement(firstStatement) && checkFixedAssignableTo(checker, declaration, firstStatement.expression, expectType, isFunctionType)) {
+            return {
+                declaration,
+                kind: FixKind.MissingReturnStatement,
+                expression: firstStatement.expression
+            };
+        }
+        else if (isLabeledStatement(firstStatement) && isExpressionStatement(firstStatement.statement)) {
+            const node = createObjectLiteral([createPropertyAssignment(firstStatement.label, firstStatement.statement.expression)]);
+            if (checkFixedAssignableTo(checker, declaration, node, expectType, isFunctionType)) {
+                return isArrowFunction(declaration) ? {
+                    declaration,
+                    kind: FixKind.MissingParentheses,
+                    expression: node
+                } : {
+                        declaration,
+                        kind: FixKind.MissingReturnStatement,
+                        expression: node
+                    };
+            }
+        }
+        else if (isBlock(firstStatement) && length(firstStatement.statements) === 1) {
+            const firstBlockStatement = first(firstStatement.statements);
+            if (isLabeledStatement(firstBlockStatement) && isExpressionStatement(firstBlockStatement.statement)) {
+                const node = createObjectLiteral([createPropertyAssignment(firstBlockStatement.label, firstBlockStatement.statement.expression)]);
+                if (checkFixedAssignableTo(checker, declaration, node, expectType, isFunctionType)) {
+                    return {
+                        declaration,
+                        kind: FixKind.MissingReturnStatement,
+                        expression: node
+                    };
+                }
+            }
+        }
+
+        return undefined;
+    }
+
+    function checkFixedAssignableTo(checker: TypeChecker, declaration: FunctionLikeDeclaration, expr: Expression, type: Type, isFunctionType: boolean) {
+        return checker.isTypeAssignableTo(checker.getTypeAtLocation(isFunctionType ? updateFunctionLikeBody(declaration, createBlock([createReturn(expr)])) : expr), type);
+    }
+
+    function getInfo(checker: TypeChecker, sourceFile: SourceFile, position: number, errorCode: number): Info | undefined {
+        const node = getTokenAtPosition(sourceFile, position);
+        if (!node.parent) return undefined;
+
+        const declaration = findAncestor(node.parent, isFunctionLikeDeclaration);
+        switch (errorCode) {
+            case Diagnostics.A_function_whose_declared_type_is_neither_void_nor_any_must_return_a_value.code:
+                if (!declaration || !declaration.body || !declaration.type || !rangeContainsRange(declaration.type, node)) return undefined;
+                return getFixInfo(checker, declaration, checker.getTypeFromTypeNode(declaration.type), /* isFunctionType */ false);
+            case Diagnostics.Argument_of_type_0_is_not_assignable_to_parameter_of_type_1.code:
+                if (!declaration || !isCallExpression(declaration.parent) || !declaration.body) return undefined;
+                const pos = declaration.parent.arguments.indexOf(<Expression>declaration);
+                const type = checker.getContextualTypeForArgumentAtIndex(declaration.parent, pos);
+                if (!type) return undefined;
+                return getFixInfo(checker, declaration, type, /* isFunctionType */ true);
+            case Diagnostics.Type_0_is_not_assignable_to_type_1.code:
+                if (!isDeclarationName(node) || !isVariableLike(node.parent) && !isJsxAttribute(node.parent)) return undefined;
+                const initializer = getVariableLikeInitializer(node.parent);
+                if (!initializer || !isFunctionLikeDeclaration(initializer) || !initializer.body) return undefined;
+                return getFixInfo(checker, initializer, checker.getTypeAtLocation(node.parent), /* isFunctionType */ true);
+        }
+
+        if (isDeclarationName(node) && (isVariableLike(node.parent) || isJsxAttribute(node.parent))) {
+            const initializer = getVariableLikeInitializer(node.parent);
+            if (!initializer || !isFunctionLikeDeclaration(initializer) || !initializer.body) return undefined;
+            return getFixInfo(checker, initializer, checker.getTypeAtLocation(node.parent), /* isFunctionType */ true);
+        }
+        return undefined;
+    }
+
+    function getVariableLikeInitializer(declaration: VariableLikeDeclaration): Expression | undefined {
+        switch (declaration.kind) {
+            case SyntaxKind.VariableDeclaration:
+            case SyntaxKind.Parameter:
+            case SyntaxKind.BindingElement:
+            case SyntaxKind.PropertyDeclaration:
+            case SyntaxKind.PropertyAssignment:
+                return declaration.initializer;
+            case SyntaxKind.JsxAttribute:
+                return declaration.initializer && (isJsxExpression(declaration.initializer) ? declaration.initializer.expression : undefined);
+            case SyntaxKind.ShorthandPropertyAssignment:
+            case SyntaxKind.PropertySignature:
+            case SyntaxKind.EnumMember:
+            case SyntaxKind.JSDocPropertyTag:
+            case SyntaxKind.JSDocParameterTag:
+                return undefined;
+            default:
+                Debug.fail("unexpected token");
+        }
+    }
+
+    function addReturnStatement(changes: textChanges.ChangeTracker, sourceFile: SourceFile, declaration: FunctionLikeDeclaration, expression: Expression) {
+        changes.replaceNode(sourceFile, declaration.body!, createBlock([createReturn(expression)]));
+    }
+
+    function removeBlockBodyBrace(changes: textChanges.ChangeTracker, sourceFile: SourceFile, declaration: ArrowFunction, expression: Expression, withParen: boolean) {
+        changes.replaceNode(sourceFile, declaration.body, (withParen || needsParentheses(expression)) ? createParen(expression) : expression);
+    }
+
+    function wrapBlockWithParen(changes: textChanges.ChangeTracker, sourceFile: SourceFile, declaration: ArrowFunction, expression: Expression) {
+        changes.replaceNode(sourceFile, declaration.body, createParen(expression));
+    }
+
+    function getActionForfixAddReturnStatement(context: CodeFixContext, declaration: FunctionLikeDeclaration, expression: Expression) {
+        const changes = textChanges.ChangeTracker.with(context, t => addReturnStatement(t, context.sourceFile, declaration, expression));
+        return createCodeFixAction(fixId, changes, Diagnostics.Add_a_return_statement, fixIdAddReturnStatement, Diagnostics.Surmise_all_return_value);
+    }
+
+    function getActionForfixRemoveBlockBodyBrace(context: CodeFixContext, declaration: ArrowFunction, expression: Expression) {
+        const changes = textChanges.ChangeTracker.with(context, t => removeBlockBodyBrace(t, context.sourceFile, declaration, expression, /* withParen */ false));
+        return createCodeFixAction(fixId, changes, Diagnostics.Remove_block_body_braces, fixIdRemoveBlockBodyBrace, Diagnostics.Surmise_all_return_value);
+    }
+
+    function getActionForfixReplaceBraceWithParen(context: CodeFixContext, declaration: ArrowFunction, expression: Expression) {
+        const changes = textChanges.ChangeTracker.with(context, t => removeBlockBodyBrace(t, context.sourceFile, declaration, expression, /* withParen */ true));
+        return createCodeFixAction(fixId, changes, Diagnostics.Replace_braces_with_parentheses, fixIdReplaceBraceWithParen, Diagnostics.Surmise_all_return_value);
+    }
+
+    function getActionForfixWrapTheBlockWithParen(context: CodeFixContext, declaration: ArrowFunction, expression: Expression) {
+        const changes = textChanges.ChangeTracker.with(context, t => wrapBlockWithParen(t, context.sourceFile, declaration, expression));
+        return createCodeFixAction(fixId, changes, Diagnostics.Wrap_this_block_with_parentheses, fixIdWrapTheBlockWithParen, Diagnostics.Surmise_all_return_value);
+    }
+}

src/services/refactors/addOrRemoveBracesToArrowFunction.ts

@@ -64,10 +64,6 @@ namespace ts.refactor.addOrRemoveBracesToArrowFunction {
         return { renameFilename: undefined, renameLocation: undefined, edits };
     }
 
-    function needsParentheses(expression: Expression) {
-        return isBinaryExpression(expression) && expression.operatorToken.kind === SyntaxKind.CommaToken || isObjectLiteralExpression(expression);
-    }
-
     function getConvertibleArrowFunctionAtPosition(file: SourceFile, startPosition: number): Info | undefined {
         const node = getTokenAtPosition(file, startPosition);
         const func = getContainingFunction(node);

src/services/tsconfig.json

@@ -55,6 +55,7 @@
         "codefixes/fixClassIncorrectlyImplementsInterface.ts",
         "codefixes/importFixes.ts",
         "codefixes/fixSpelling.ts",
+        "codefixes/returnValueSurmise.ts",
         "codefixes/fixAddMissingMember.ts",
         "codefixes/fixAddMissingNewOperator.ts",
         "codefixes/fixCannotFindModule.ts",

src/services/utilities.ts

@@ -1899,6 +1899,11 @@ namespace ts {
         return idx === -1 ? -1 : idx + 1;
     }
 
+    /* @internal */
+    export function needsParentheses(expression: Expression) {
+        return isBinaryExpression(expression) && expression.operatorToken.kind === SyntaxKind.CommaToken || isObjectLiteralExpression(expression);
+    }
+
     export function getContextualTypeFromParent(node: Expression, checker: TypeChecker): Type | undefined {
         const { parent } = node;
         switch (parent.kind) {

tests/cases/fourslash/codeFixSurmiseReturnValue1.ts

@@ -0,0 +1,9 @@
+/// <reference path='fourslash.ts' />
+
+//// function Foo (): number {
+////     1
+//// }
+
+verify.codeFixAvailable([
+    { description: 'Add a return statement' },
+]);

tests/cases/fourslash/codeFixSurmiseReturnValue10.ts

@@ -0,0 +1,9 @@
+/// <reference path='fourslash.ts' />
+
+//// const a: ((() => number) | (() => undefined)) = () => { 1 }
+
+verify.codeFixAvailable([
+    { description: 'Add a return statement' },
+    { description: 'Remove block body braces' },
+    { description: 'Replace braces with parentheses' },
+]);

tests/cases/fourslash/codeFixSurmiseReturnValue11.ts

@@ -0,0 +1,13 @@
+/// <reference path='fourslash.ts' />
+//// interface A {
+////     bar: string
+//// }
+//// 
+//// function Foo (): A {
+////     { bar: '123' }
+//// }
+
+verify.codeFixAvailable([
+    { description: 'Add a return statement' },
+    { description: 'Remove unused label' },
+]);

tests/cases/fourslash/codeFixSurmiseReturnValue12.ts

@@ -0,0 +1,16 @@
+/// <reference path='fourslash.ts' />
+//// interface A {
+////     bar: string
+//// }
+//// 
+//// function Foo (a: () => A) { a() }
+//// Foo(() => {  
+////     { bar: '123' }
+//// })
+
+verify.codeFixAvailable([
+    { description: 'Add a return statement' },
+    { description: 'Remove block body braces' },
+    { description: 'Replace braces with parentheses' },
+    { description: 'Remove unused label' },
+]);

tests/cases/fourslash/codeFixSurmiseReturnValue13.ts

@@ -0,0 +1,19 @@
+/// <reference path='fourslash.ts' />
+//// interface A {
+////     bar: string
+//// }
+//// 
+//// const a: () => A = () => {
+////     { bar: '1' }    
+//// }
+
+verify.codeFixAvailable([
+    { description: 'Add a return statement' },
+    { description: 'Remove block body braces' },
+    { description: 'Replace braces with parentheses' },
+    { description: 'Remove unused label' },
+]);
+
+interface A {
+    bar: string
+}

tests/cases/fourslash/codeFixSurmiseReturnValue14.ts

@@ -0,0 +1,13 @@
+/// <reference path='fourslash.ts' />
+//// interface A {
+////     bar: string
+//// }
+//// 
+//// const a: () => A = () => {
+////     bar: '1'   
+//// }
+
+verify.codeFixAvailable([
+    { description: 'Wrap this block with parentheses' },
+    { description: 'Remove unused label' },
+]);

tests/cases/fourslash/codeFixSurmiseReturnValue15.ts

@@ -0,0 +1,12 @@
+/// <reference path='fourslash.ts' />
+//// interface A {
+////     bar: string
+//// }
+//// 
+//// function Foo (a: () => A) { a() }
+//// Foo(() => { bar: '1' })
+
+verify.codeFixAvailable([
+    { description: 'Wrap this block with parentheses' },
+    { description: 'Remove unused label' },
+]);