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",