feat(36266): add a quick fix for incorrect return types in async functions

src/compiler/checker.ts

@@ -406,6 +406,7 @@ namespace ts {
             },
             getParameterType: getTypeAtPosition,
             getPromisedTypeOfPromise,
+            getAwaitedType: type => getAwaitedType(type),
             getReturnTypeOfSignature,
             isNullableType,
             getNullableType,
@@ -30795,7 +30796,7 @@ namespace ts {
                 if (globalPromiseType !== emptyGenericType && !isReferenceToType(returnType, globalPromiseType)) {
                     // The promise type was not a valid type reference to the global promise type, so we
                     // report an error and return the unknown type.
-                    error(returnTypeNode, Diagnostics.The_return_type_of_an_async_function_or_method_must_be_the_global_Promise_T_type);
+                    error(returnTypeNode, Diagnostics.The_return_type_of_an_async_function_or_method_must_be_the_global_Promise_T_type_Did_you_mean_to_write_Promise_0, typeToString(getAwaitedType(returnType) || voidType));
                     return;
                 }
             }

src/compiler/diagnosticMessages.json

@@ -215,7 +215,7 @@
         "category": "Error",
         "code": 1063
     },
-    "The return type of an async function or method must be the global Promise<T> type.": {
+    "The return type of an async function or method must be the global Promise<T> type. Did you mean to write 'Promise<{0}>'?": {
         "category": "Error",
         "code": 1064
     },
@@ -5197,6 +5197,14 @@
         "category": "Message",
         "code": 90035
     },
+    "Replace '{0}' with 'Promise<{1}>'": {
+        "category": "Message",
+        "code": 90036
+    },
+    "Fix all incorrect return type of an async functions": {
+        "category": "Message",
+        "code": 90037
+    },
     "Declare a private field named '{0}'.": {
         "category": "Message",
         "code": 90053

src/compiler/types.ts

@@ -3421,6 +3421,7 @@ namespace ts {
         getWidenedType(type: Type): Type;
         /* @internal */
         getPromisedTypeOfPromise(promise: Type, errorNode?: Node): Type | undefined;
+        getAwaitedType(type: Type): Type | undefined;
         getReturnTypeOfSignature(signature: Signature): Type;
         /**
          * Gets the type of a parameter at a given position in a signature.

src/services/codefixes/fixReturnTypeInAsyncFunction.ts

@@ -0,0 +1,66 @@
+/* @internal */
+namespace ts.codefix {
+    const fixId = "fixReturnTypeInAsyncFunction";
+    const errorCodes = [
+        Diagnostics.The_return_type_of_an_async_function_or_method_must_be_the_global_Promise_T_type_Did_you_mean_to_write_Promise_0.code,
+    ];
+
+    interface Info {
+        readonly returnTypeNode: TypeNode;
+        readonly returnType: Type;
+        readonly promisedTypeNode: TypeNode;
+        readonly promisedType: Type;
+    }
+
+    registerCodeFix({
+        errorCodes,
+        fixIds: [fixId],
+        getCodeActions: context => {
+            const { sourceFile, program, span } = context;
+            const checker = program.getTypeChecker();
+            const info = getInfo(sourceFile, program.getTypeChecker(), span.start);
+            if (!info) {
+                return undefined;
+            }
+            const { returnTypeNode, returnType, promisedTypeNode, promisedType } = info;
+            const changes = textChanges.ChangeTracker.with(context, t => doChange(t, sourceFile, returnTypeNode, promisedTypeNode));
+            return [createCodeFixAction(fixId, changes, [Diagnostics.Replace_0_with_Promise_1, checker.typeToString(returnType), checker.typeToString(promisedType)], fixId, Diagnostics.Fix_all_incorrect_return_type_of_an_async_functions)];
+        },
+        getAllCodeActions: context => codeFixAll(context, errorCodes, (changes, diag) => {
+            const info = getInfo(diag.file, context.program.getTypeChecker(), diag.start);
+            if (info) {
+                doChange(changes, diag.file, info.returnTypeNode, info.promisedTypeNode);
+            }
+        })
+    });
+
+    function getInfo(sourceFile: SourceFile, checker: TypeChecker, pos: number): Info | undefined {
+        const returnTypeNode = getReturnTypeNode(sourceFile, pos);
+        if (!returnTypeNode) {
+            return undefined;
+        }
+
+        const returnType = checker.getTypeFromTypeNode(returnTypeNode);
+        const promisedType = checker.getAwaitedType(returnType) || checker.getVoidType();
+        const promisedTypeNode = checker.typeToTypeNode(promisedType);
+        if (promisedTypeNode) {
+            return { returnTypeNode, returnType, promisedTypeNode, promisedType };
+        }
+    }
+
+    function doChange(changes: textChanges.ChangeTracker, sourceFile: SourceFile, returnTypeNode: TypeNode, promisedTypeNode: TypeNode): void {
+        changes.replaceNode(sourceFile, returnTypeNode, createTypeReferenceNode("Promise", [promisedTypeNode]));
+    }
+
+    function getReturnTypeNode(sourceFile: SourceFile, pos: number): TypeNode | undefined {
+        if (isInJSFile(sourceFile)) {
+            return undefined;
+        }
+
+        const token = getTokenAtPosition(sourceFile, pos);
+        const parent = findAncestor(token, isFunctionLikeDeclaration);
+        if (parent?.type) {
+            return parent.type;
+        }
+    }
+}

src/services/tsconfig.json

@@ -85,6 +85,7 @@
         "codefixes/fixMissingCallParentheses.ts",
         "codefixes/fixAwaitInSyncFunction.ts",
         "codefixes/inferFromUsage.ts",
+        "codefixes/fixReturnTypeInAsyncFunction.ts",
         "codefixes/disableJsDiagnostics.ts",
         "codefixes/helpers.ts",
         "codefixes/fixInvalidImportSyntax.ts",

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -2035,6 +2035,7 @@ declare namespace ts {
         getBaseTypes(type: InterfaceType): BaseType[];
         getBaseTypeOfLiteralType(type: Type): Type;
         getWidenedType(type: Type): Type;
+        getAwaitedType(type: Type): Type | undefined;
         getReturnTypeOfSignature(signature: Signature): Type;
         getNullableType(type: Type, flags: TypeFlags): Type;
         getNonNullableType(type: Type): Type;

tests/baselines/reference/api/typescript.d.ts

@@ -2035,6 +2035,7 @@ declare namespace ts {
         getBaseTypes(type: InterfaceType): BaseType[];
         getBaseTypeOfLiteralType(type: Type): Type;
         getWidenedType(type: Type): Type;
+        getAwaitedType(type: Type): Type | undefined;
         getReturnTypeOfSignature(signature: Signature): Type;
         getNullableType(type: Type, flags: TypeFlags): Type;
         getNonNullableType(type: Type): Type;

tests/baselines/reference/asyncFunctionDeclaration15_es6.errors.txt

@@ -1,10 +1,10 @@
-tests/cases/conformance/async/es6/functionDeclarations/asyncFunctionDeclaration15_es6.ts(6,23): error TS1064: The return type of an async function or method must be the global Promise<T> type.
+tests/cases/conformance/async/es6/functionDeclarations/asyncFunctionDeclaration15_es6.ts(6,23): error TS1064: The return type of an async function or method must be the global Promise<T> type. Did you mean to write 'Promise<{}>'?
 tests/cases/conformance/async/es6/functionDeclarations/asyncFunctionDeclaration15_es6.ts(6,23): error TS2355: A function whose declared type is neither 'void' nor 'any' must return a value.
-tests/cases/conformance/async/es6/functionDeclarations/asyncFunctionDeclaration15_es6.ts(7,23): error TS1064: The return type of an async function or method must be the global Promise<T> type.
-tests/cases/conformance/async/es6/functionDeclarations/asyncFunctionDeclaration15_es6.ts(8,23): error TS1064: The return type of an async function or method must be the global Promise<T> type.
+tests/cases/conformance/async/es6/functionDeclarations/asyncFunctionDeclaration15_es6.ts(7,23): error TS1064: The return type of an async function or method must be the global Promise<T> type. Did you mean to write 'Promise<any>'?
+tests/cases/conformance/async/es6/functionDeclarations/asyncFunctionDeclaration15_es6.ts(8,23): error TS1064: The return type of an async function or method must be the global Promise<T> type. Did you mean to write 'Promise<number>'?
 tests/cases/conformance/async/es6/functionDeclarations/asyncFunctionDeclaration15_es6.ts(8,23): error TS2355: A function whose declared type is neither 'void' nor 'any' must return a value.
-tests/cases/conformance/async/es6/functionDeclarations/asyncFunctionDeclaration15_es6.ts(9,23): error TS1064: The return type of an async function or method must be the global Promise<T> type.
-tests/cases/conformance/async/es6/functionDeclarations/asyncFunctionDeclaration15_es6.ts(10,23): error TS1064: The return type of an async function or method must be the global Promise<T> type.
+tests/cases/conformance/async/es6/functionDeclarations/asyncFunctionDeclaration15_es6.ts(9,23): error TS1064: The return type of an async function or method must be the global Promise<T> type. Did you mean to write 'Promise<void>'?
+tests/cases/conformance/async/es6/functionDeclarations/asyncFunctionDeclaration15_es6.ts(10,23): error TS1064: The return type of an async function or method must be the global Promise<T> type. Did you mean to write 'Promise<void>'?
 tests/cases/conformance/async/es6/functionDeclarations/asyncFunctionDeclaration15_es6.ts(17,16): error TS1058: The return type of an async function must either be a valid promise or must not contain a callable 'then' member.
 tests/cases/conformance/async/es6/functionDeclarations/asyncFunctionDeclaration15_es6.ts(23,25): error TS1320: Type of 'await' operand must either be a valid promise or must not contain a callable 'then' member.
 
@@ -17,23 +17,23 @@ tests/cases/conformance/async/es6/functionDeclarations/asyncFunctionDeclaration1
     async function fn1() { } // valid: Promise<void>
     async function fn2(): { } { } // error
                           ~~~
-!!! error TS1064: The return type of an async function or method must be the global Promise<T> type.
+!!! error TS1064: The return type of an async function or method must be the global Promise<T> type. Did you mean to write 'Promise<{}>'?
                           ~~~
 !!! error TS2355: A function whose declared type is neither 'void' nor 'any' must return a value.
     async function fn3(): any { } // error
                           ~~~
-!!! error TS1064: The return type of an async function or method must be the global Promise<T> type.
+!!! error TS1064: The return type of an async function or method must be the global Promise<T> type. Did you mean to write 'Promise<any>'?
     async function fn4(): number { } // error
                           ~~~~~~
-!!! error TS1064: The return type of an async function or method must be the global Promise<T> type.
+!!! error TS1064: The return type of an async function or method must be the global Promise<T> type. Did you mean to write 'Promise<number>'?
                           ~~~~~~
 !!! error TS2355: A function whose declared type is neither 'void' nor 'any' must return a value.
     async function fn5(): PromiseLike<void> { } // error
                           ~~~~~~~~~~~~~~~~~
-!!! error TS1064: The return type of an async function or method must be the global Promise<T> type.
+!!! error TS1064: The return type of an async function or method must be the global Promise<T> type. Did you mean to write 'Promise<void>'?
     async function fn6(): Thenable { } // error
                           ~~~~~~~~
-!!! error TS1064: The return type of an async function or method must be the global Promise<T> type.
+!!! error TS1064: The return type of an async function or method must be the global Promise<T> type. Did you mean to write 'Promise<void>'?
     async function fn7() { return; } // valid: Promise<void>
     async function fn8() { return 1; } // valid: Promise<number>
     async function fn9() { return null; } // valid: Promise<any>

tests/baselines/reference/asyncImportedPromise_es6.errors.txt

@@ -1,4 +1,4 @@
-tests/cases/conformance/async/es6/test.ts(3,25): error TS1064: The return type of an async function or method must be the global Promise<T> type.
+tests/cases/conformance/async/es6/test.ts(3,25): error TS1064: The return type of an async function or method must be the global Promise<T> type. Did you mean to write 'Promise<T>'?
 
 
 ==== tests/cases/conformance/async/es6/task.ts (0 errors) ====
@@ -9,5 +9,5 @@ tests/cases/conformance/async/es6/test.ts(3,25): error TS1064: The return type o
     class Test {
         async example<T>(): Task<T> { return; }
                             ~~~~~~~
-!!! error TS1064: The return type of an async function or method must be the global Promise<T> type.
+!!! error TS1064: The return type of an async function or method must be the global Promise<T> type. Did you mean to write 'Promise<T>'?
     }

tests/baselines/reference/asyncQualifiedReturnType_es6.errors.txt

@@ -1,4 +1,4 @@
-tests/cases/conformance/async/es6/asyncQualifiedReturnType_es6.ts(6,21): error TS1064: The return type of an async function or method must be the global Promise<T> type.
+tests/cases/conformance/async/es6/asyncQualifiedReturnType_es6.ts(6,21): error TS1064: The return type of an async function or method must be the global Promise<T> type. Did you mean to write 'Promise<void>'?
 
 
 ==== tests/cases/conformance/async/es6/asyncQualifiedReturnType_es6.ts (1 errors) ====
@@ -9,5 +9,5 @@ tests/cases/conformance/async/es6/asyncQualifiedReturnType_es6.ts(6,21): error T
     
     async function f(): X.MyPromise<void> {
                         ~~~~~~~~~~~~~~~~~
-!!! error TS1064: The return type of an async function or method must be the global Promise<T> type.
+!!! error TS1064: The return type of an async function or method must be the global Promise<T> type. Did you mean to write 'Promise<void>'?
     }

tests/cases/fourslash/codeFixReturnTypeInAsyncFunction1.ts

@@ -0,0 +1,10 @@
+/// <reference path='fourslash.ts' />
+
+// @target: es2015
+////async function fn(): number {}
+
+verify.codeFix({
+    index: 0,
+    description: [ts.Diagnostics.Replace_0_with_Promise_1.message, "number", "number"],
+    newFileContent: `async function fn(): Promise<number> {}`
+});

tests/cases/fourslash/codeFixReturnTypeInAsyncFunction10.ts

@@ -0,0 +1,13 @@
+/// <reference path='fourslash.ts' />
+
+// @target: es2015
+////type Foo = "a" | "b";
+////async function fn(): Foo {}
+
+verify.codeFix({
+    index: 0,
+    description: [ts.Diagnostics.Replace_0_with_Promise_1.message, "Foo", "Foo"],
+    newFileContent:
+`type Foo = "a" | "b";
+async function fn(): Promise<Foo> {}`
+});

tests/cases/fourslash/codeFixReturnTypeInAsyncFunction11.ts

@@ -0,0 +1,10 @@
+/// <reference path='fourslash.ts' />
+
+// @target: es2015
+////async function fn(): PromiseLike<string> {}
+
+verify.codeFix({
+    index: 0,
+    description: [ts.Diagnostics.Replace_0_with_Promise_1.message, "PromiseLike<string>", "string"],
+    newFileContent: `async function fn(): Promise<string> {}`
+});

tests/cases/fourslash/codeFixReturnTypeInAsyncFunction12.ts

@@ -0,0 +1,10 @@
+/// <reference path='fourslash.ts' />
+
+// @target: es2015
+////async function fn(): PromiseLike<void> {}
+
+verify.codeFix({
+    index: 0,
+    description: [ts.Diagnostics.Replace_0_with_Promise_1.message, "PromiseLike<void>", "void"],
+    newFileContent: `async function fn(): Promise<void> {}`
+});

tests/cases/fourslash/codeFixReturnTypeInAsyncFunction13.ts

@@ -0,0 +1,13 @@
+/// <reference path='fourslash.ts' />
+
+// @target: es2015
+////declare class Thenable { then(): void; }
+////async function fn(): Thenable {}
+
+verify.codeFix({
+    index: 0,
+    description: [ts.Diagnostics.Replace_0_with_Promise_1.message, "Thenable", "void"],
+    newFileContent:
+`declare class Thenable { then(): void; }
+async function fn(): Promise<void> {}`
+});

tests/cases/fourslash/codeFixReturnTypeInAsyncFunction14.ts

@@ -0,0 +1,10 @@
+/// <reference path='fourslash.ts' />
+
+// @target: es2015
+////async function fn(): string | symbol {}
+
+verify.codeFix({
+    index: 0,
+    description: [ts.Diagnostics.Replace_0_with_Promise_1.message, "string | symbol", "string | symbol"],
+    newFileContent: `async function fn(): Promise<string | symbol> {}`
+});

tests/cases/fourslash/codeFixReturnTypeInAsyncFunction15.ts

@@ -0,0 +1,10 @@
+/// <reference path='fourslash.ts' />
+
+// @target: es2015
+////const foo = async function (): number {}
+
+verify.codeFix({
+    index: 0,
+    description: [ts.Diagnostics.Replace_0_with_Promise_1.message, "number", "number"],
+    newFileContent: `const foo = async function (): Promise<number> {}`
+});

tests/cases/fourslash/codeFixReturnTypeInAsyncFunction16.ts

@@ -0,0 +1,15 @@
+/// <reference path='fourslash.ts' />
+
+// @target: es2015
+////class A {
+////    async foo(): number {}
+////}
+
+verify.codeFix({
+    index: 0,
+    description: [ts.Diagnostics.Replace_0_with_Promise_1.message, "number", "number"],
+    newFileContent:
+`class A {
+    async foo(): Promise<number> {}
+}`
+});

tests/cases/fourslash/codeFixReturnTypeInAsyncFunction17.ts

@@ -0,0 +1,10 @@
+/// <reference path='fourslash.ts' />
+
+// @target: es2015
+////const foo = async (): number => {}
+
+verify.codeFix({
+    index: 0,
+    description: [ts.Diagnostics.Replace_0_with_Promise_1.message, "number", "number"],
+    newFileContent: `const foo = async (): Promise<number> => {}`
+});

tests/cases/fourslash/codeFixReturnTypeInAsyncFunction2.ts

@@ -0,0 +1,10 @@
+/// <reference path='fourslash.ts' />
+
+// @target: es2015
+////async function fn(): boolean {}
+
+verify.codeFix({
+    index: 0,
+    description: [ts.Diagnostics.Replace_0_with_Promise_1.message, "boolean", "boolean"],
+    newFileContent: `async function fn(): Promise<boolean> {}`
+});

tests/cases/fourslash/codeFixReturnTypeInAsyncFunction3.ts

@@ -0,0 +1,10 @@
+/// <reference path='fourslash.ts' />
+
+// @target: es2015
+////async function fn(): string {}
+
+verify.codeFix({
+    index: 0,
+    description: [ts.Diagnostics.Replace_0_with_Promise_1.message, "string", "string"],
+    newFileContent: `async function fn(): Promise<string> {}`
+});

tests/cases/fourslash/codeFixReturnTypeInAsyncFunction4.ts

@@ -0,0 +1,10 @@
+/// <reference path='fourslash.ts' />
+
+// @target: es2015
+////async function fn(): void {}
+
+verify.codeFix({
+    index: 0,
+    description: [ts.Diagnostics.Replace_0_with_Promise_1.message, "void", "void"],
+    newFileContent: `async function fn(): Promise<void> {}`
+});

tests/cases/fourslash/codeFixReturnTypeInAsyncFunction5.ts

@@ -0,0 +1,10 @@
+/// <reference path='fourslash.ts' />
+
+// @target: es2015
+////async function fn(): null {}
+
+verify.codeFix({
+    index: 0,
+    description: [ts.Diagnostics.Replace_0_with_Promise_1.message, "null", "null"],
+    newFileContent: `async function fn(): Promise<null> {}`
+});

tests/cases/fourslash/codeFixReturnTypeInAsyncFunction6.ts

@@ -0,0 +1,10 @@
+/// <reference path='fourslash.ts' />
+
+// @target: es2015
+////async function fn(): undefined {}
+
+verify.codeFix({
+    index: 0,
+    description: [ts.Diagnostics.Replace_0_with_Promise_1.message, "undefined", "undefined"],
+    newFileContent: `async function fn(): Promise<undefined> {}`
+});

tests/cases/fourslash/codeFixReturnTypeInAsyncFunction7.ts

@@ -0,0 +1,10 @@
+/// <reference path='fourslash.ts' />
+
+// @target: es2015
+////async function fn(): any {}
+
+verify.codeFix({
+    index: 0,
+    description: [ts.Diagnostics.Replace_0_with_Promise_1.message, "any", "any"],
+    newFileContent: `async function fn(): Promise<any> {}`
+});

tests/cases/fourslash/codeFixReturnTypeInAsyncFunction8.ts

@@ -0,0 +1,10 @@
+/// <reference path='fourslash.ts' />
+
+// @target: es2015
+////async function fn(): symbol {}
+
+verify.codeFix({
+    index: 0,
+    description: [ts.Diagnostics.Replace_0_with_Promise_1.message, "symbol", "symbol"],
+    newFileContent: `async function fn(): Promise<symbol> {}`
+});

tests/cases/fourslash/codeFixReturnTypeInAsyncFunction9.ts

@@ -0,0 +1,13 @@
+/// <reference path='fourslash.ts' />
+
+// @target: es2015
+////interface Foo<T> {}
+////async function fn(): Foo<number> {}
+
+verify.codeFix({
+    index: 0,
+    description: [ts.Diagnostics.Replace_0_with_Promise_1.message, "Foo<number>", "Foo<number>"],
+    newFileContent:
+`interface Foo<T> {}
+async function fn(): Promise<Foo<number>> {}`
+});

tests/cases/fourslash/codeFixReturnTypeInAsyncFunction_fixAll.ts

@@ -0,0 +1,50 @@
+/// <reference path='fourslash.ts' />
+
+// @target: es2015
+////declare class Thenable { then(): void; }
+////interface Foo<T> {}
+////type Bar = "a" | "b";
+////
+////async function f1(): number {}
+////async function f2(): boolean {}
+////async function f3(): string {}
+////async function f4(): void {}
+////async function f5(): null {}
+////async function f6(): undefined {}
+////async function f7(): any {}
+////async function f8(): symbol {}
+////
+////async function f9(): Foo<number> {}
+////async function f10(): Bar {}
+////async function f11(): PromiseLike<string> {}
+////async function f12(): PromiseLike<void> {}
+////async function f13(): Thenable {}
+////
+////async function f14(): string | symbol {}
+
+
+verify.codeFixAll({
+    fixId: "fixReturnTypeInAsyncFunction",
+    fixAllDescription: ts.Diagnostics.Fix_all_incorrect_return_type_of_an_async_functions.message,
+    newFileContent:
+`declare class Thenable { then(): void; }
+interface Foo<T> {}
+type Bar = "a" | "b";
+
+async function f1(): Promise<number> {}
+async function f2(): Promise<boolean> {}
+async function f3(): Promise<string> {}
+async function f4(): Promise<void> {}
+async function f5(): Promise<null> {}
+async function f6(): Promise<undefined> {}
+async function f7(): Promise<any> {}
+async function f8(): Promise<symbol> {}
+
+async function f9(): Promise<Foo<number>> {}
+async function f10(): Promise<Bar> {}
+async function f11(): Promise<string> {}
+async function f12(): Promise<void> {}
+async function f13(): Promise<void> {}
+
+async function f14(): Promise<string | symbol> {}`
+});