Fix async function block return expr error in js (microsoft#37845)

Author: rbuckton

src/compiler/checker.ts

@@ -27244,7 +27244,7 @@ namespace ts {
             }
 
             const functionFlags = getFunctionFlags(func);
-            const type = returnType && getReturnOrPromisedType(returnType, functionFlags);
+            const type = returnType && unwrapReturnType(returnType, functionFlags);
 
             // Functions with with an explicitly specified 'void' or 'any' return type don't need any return expressions.
             if (type && maybeTypeOfKind(type, TypeFlags.Any | TypeFlags.Void)) {
@@ -27364,14 +27364,6 @@ namespace ts {
             }
         }
 
-        function getReturnOrPromisedType(type: Type | undefined, functionFlags: FunctionFlags) {
-            const isGenerator = !!(functionFlags & FunctionFlags.Generator);
-            const isAsync = !!(functionFlags & FunctionFlags.Async);
-            return type && isGenerator ? getIterationTypeOfGeneratorFunctionReturnType(IterationTypeKind.Return, type, isAsync) || errorType :
-                type && isAsync ? getAwaitedType(type) || errorType :
-                type;
-        }
-
         function checkFunctionExpressionOrObjectLiteralMethodDeferred(node: ArrowFunction | FunctionExpression | MethodDeclaration) {
             Debug.assert(node.kind !== SyntaxKind.MethodDeclaration || isObjectLiteralMethod(node));
 
@@ -27399,7 +27391,7 @@ namespace ts {
                     // check assignability of the awaited type of the expression body against the promised type of
                     // its return type annotation.
                     const exprType = checkExpression(node.body);
-                    const returnOrPromisedType = getReturnOrPromisedType(returnType, functionFlags);
+                    const returnOrPromisedType = returnType && unwrapReturnType(returnType, functionFlags);
                     if (returnOrPromisedType) {
                         if ((functionFlags & FunctionFlags.AsyncGenerator) === FunctionFlags.Async) { // Async function
                             const awaitedType = checkAwaitedType(exprType, node.body, Diagnostics.The_return_type_of_an_async_function_must_either_be_a_valid_promise_or_must_not_contain_a_callable_then_member);
@@ -32687,8 +32679,8 @@ namespace ts {
         function unwrapReturnType(returnType: Type, functionFlags: FunctionFlags) {
             const isGenerator = !!(functionFlags & FunctionFlags.Generator);
             const isAsync = !!(functionFlags & FunctionFlags.Async);
-            return isGenerator ? getIterationTypeOfGeneratorFunctionReturnType(IterationTypeKind.Return, returnType, isAsync) || errorType :
-                isAsync ? getPromisedTypeOfPromise(returnType) || errorType :
+            return isGenerator ? getIterationTypeOfGeneratorFunctionReturnType(IterationTypeKind.Return, returnType, isAsync) ?? errorType :
+                isAsync ? getAwaitedType(returnType) ?? errorType :
                 returnType;
         }
 
@@ -32725,7 +32717,7 @@ namespace ts {
                     }
                 }
                 else if (getReturnTypeFromAnnotation(func)) {
-                    const unwrappedReturnType = unwrapReturnType(returnType, functionFlags);
+                    const unwrappedReturnType = unwrapReturnType(returnType, functionFlags) ?? returnType;
                     const unwrappedExprType = functionFlags & FunctionFlags.Async
                         ? checkAwaitedType(exprType, node, Diagnostics.The_return_type_of_an_async_function_must_either_be_a_valid_promise_or_must_not_contain_a_callable_then_member)
                         : exprType;

tests/baselines/reference/asyncArrowFunction_allowJs.errors.txt

@@ -0,0 +1,38 @@
+tests/cases/conformance/async/es2017/asyncArrowFunction/file.js(3,17): error TS2322: Type '0' is not assignable to type 'string'.
+tests/cases/conformance/async/es2017/asyncArrowFunction/file.js(7,23): error TS2322: Type '0' is not assignable to type 'string'.
+tests/cases/conformance/async/es2017/asyncArrowFunction/file.js(12,2): error TS2322: Type '0' is not assignable to type 'string'.
+tests/cases/conformance/async/es2017/asyncArrowFunction/file.js(19,3): error TS2345: Argument of type '() => Promise<number>' is not assignable to parameter of type '() => string'.
+  Type 'Promise<number>' is not assignable to type 'string'.
+
+
+==== tests/cases/conformance/async/es2017/asyncArrowFunction/file.js (4 errors) ====
+    // Error (good)
+    /** @type {function(): string} */
+    const a = () => 0
+                    ~
+!!! error TS2322: Type '0' is not assignable to type 'string'.
+    
+    // Error (good)
+    /** @type {function(): string} */
+    const b = async () => 0
+                          ~
+!!! error TS2322: Type '0' is not assignable to type 'string'.
+    
+    // No error (bad)
+    /** @type {function(): string} */
+    const c = async () => {
+    	return 0
+    	~~~~~~~~
+!!! error TS2322: Type '0' is not assignable to type 'string'.
+    }
+    
+    /** @type {function(function(): string): void} */
+    const f = (p) => {}
+    
+    // Error (good)
+    f(async () => {
+      ~~~~~~~~~~~~~
+!!! error TS2345: Argument of type '() => Promise<number>' is not assignable to parameter of type '() => string'.
+!!! error TS2345:   Type 'Promise<number>' is not assignable to type 'string'.
+    	return 0
+    })

tests/baselines/reference/asyncArrowFunction_allowJs.symbols

@@ -0,0 +1,30 @@
+=== tests/cases/conformance/async/es2017/asyncArrowFunction/file.js ===
+// Error (good)
+/** @type {function(): string} */
+const a = () => 0
+>a : Symbol(a, Decl(file.js, 2, 5))
+
+// Error (good)
+/** @type {function(): string} */
+const b = async () => 0
+>b : Symbol(b, Decl(file.js, 6, 5))
+
+// No error (bad)
+/** @type {function(): string} */
+const c = async () => {
+>c : Symbol(c, Decl(file.js, 10, 5))
+
+	return 0
+}
+
+/** @type {function(function(): string): void} */
+const f = (p) => {}
+>f : Symbol(f, Decl(file.js, 15, 5))
+>p : Symbol(p, Decl(file.js, 15, 11))
+
+// Error (good)
+f(async () => {
+>f : Symbol(f, Decl(file.js, 15, 5))
+
+	return 0
+})

tests/baselines/reference/asyncArrowFunction_allowJs.types

@@ -0,0 +1,41 @@
+=== tests/cases/conformance/async/es2017/asyncArrowFunction/file.js ===
+// Error (good)
+/** @type {function(): string} */
+const a = () => 0
+>a : () => string
+>() => 0 : () => string
+>0 : 0
+
+// Error (good)
+/** @type {function(): string} */
+const b = async () => 0
+>b : () => string
+>async () => 0 : () => string
+>0 : 0
+
+// No error (bad)
+/** @type {function(): string} */
+const c = async () => {
+>c : () => string
+>async () => {	return 0} : () => string
+
+	return 0
+>0 : 0
+}
+
+/** @type {function(function(): string): void} */
+const f = (p) => {}
+>f : (arg0: () => string) => void
+>(p) => {} : (p: () => string) => void
+>p : () => string
+
+// Error (good)
+f(async () => {
+>f(async () => {	return 0}) : void
+>f : (arg0: () => string) => void
+>async () => {	return 0} : () => Promise<number>
+
+	return 0
+>0 : 0
+
+})

tests/cases/conformance/async/es2017/asyncArrowFunction/asyncArrowFunction_allowJs.ts

@@ -0,0 +1,27 @@
+// @allowJs: true
+// @checkJs: true
+// @noEmit: true
+// @target: es2017
+// @filename: file.js
+
+// Error (good)
+/** @type {function(): string} */
+const a = () => 0
+
+// Error (good)
+/** @type {function(): string} */
+const b = async () => 0
+
+// No error (bad)
+/** @type {function(): string} */
+const c = async () => {
+	return 0
+}
+
+/** @type {function(function(): string): void} */
+const f = (p) => {}
+
+// Error (good)
+f(async () => {
+	return 0
+})