Merge pull request #9204 from Microsoft/promiseAndAsyncUpdates

Update Promise and PromiseLike, fix async functions issues with never.

Author: rbuckton

src/compiler/checker.ts

@@ -2794,6 +2794,10 @@ namespace ts {
             return type && (type.flags & TypeFlags.Any) !== 0;
         }
 
+        function isTypeNever(type: Type) {
+            return type && (type.flags & TypeFlags.Never) !== 0;
+        }
+
         // Return the type of a binding element parent. We check SymbolLinks first to see if a type has been
         // assigned by contextual typing.
         function getTypeForBindingElementParent(node: VariableLikeDeclaration) {
@@ -11779,6 +11783,16 @@ namespace ts {
             return emptyObjectType;
         }
 
+        function createPromiseReturnType(func: FunctionLikeDeclaration, promisedType: Type) {
+            const promiseType = createPromiseType(promisedType);
+            if (promiseType === emptyObjectType) {
+                error(func, Diagnostics.An_async_function_or_method_must_have_a_valid_awaitable_return_type);
+                return unknownType;
+            }
+
+            return promiseType;
+        }
+
         function getReturnTypeFromBody(func: FunctionLikeDeclaration, contextualMapper?: TypeMapper): Type {
             const contextualSignature = getContextualSignatureForFunctionLikeDeclaration(func);
             if (!func.body) {
@@ -11814,19 +11828,12 @@ namespace ts {
                 else {
                     types = checkAndAggregateReturnExpressionTypes(func, contextualMapper);
                     if (!types) {
-                        return neverType;
+                        // For an async function, the return type will not be never, but rather a Promise for never.
+                        return isAsync ? createPromiseReturnType(func, neverType) : neverType;
                     }
                     if (types.length === 0) {
-                        if (isAsync) {
-                            // For an async function, the return type will not be void, but rather a Promise for void.
-                            const promiseType = createPromiseType(voidType);
-                            if (promiseType === emptyObjectType) {
-                                error(func, Diagnostics.An_async_function_or_method_must_have_a_valid_awaitable_return_type);
-                                return unknownType;
-                            }
-                            return promiseType;
-                        }
-                        return voidType;
+                        // For an async function, the return type will not be void, but rather a Promise for void.
+                        return isAsync ? createPromiseReturnType(func, voidType) : voidType;
                     }
                 }
                 // When yield/return statements are contextually typed we allow the return type to be a union type.
@@ -11840,7 +11847,7 @@ namespace ts {
                     else {
                         error(func, Diagnostics.No_best_common_type_exists_among_return_expressions);
                         // Defer to unioning the return types so we get a) downstream errors earlier and b) better Salsa experience
-                        return getUnionType(types);
+                        return isAsync ? createPromiseReturnType(func, getUnionType(types)) : getUnionType(types);
                     }
                 }
 
@@ -11853,21 +11860,10 @@ namespace ts {
             }
 
             const widenedType = getWidenedType(type);
-            if (isAsync) {
-                // From within an async function you can return either a non-promise value or a promise. Any
-                // Promise/A+ compatible implementation will always assimilate any foreign promise, so the
-                // return type of the body is awaited type of the body, wrapped in a native Promise<T> type.
-                const promiseType = createPromiseType(widenedType);
-                if (promiseType === emptyObjectType) {
-                    error(func, Diagnostics.An_async_function_or_method_must_have_a_valid_awaitable_return_type);
-                    return unknownType;
-                }
-
-                return promiseType;
-            }
-            else {
-                return widenedType;
-            }
+            // From within an async function you can return either a non-promise value or a promise. Any
+            // Promise/A+ compatible implementation will always assimilate any foreign promise, so the
+            // return type of the body is awaited type of the body, wrapped in a native Promise<T> type.
+            return isAsync ? createPromiseReturnType(func, widenedType) : widenedType;
         }
 
         function checkAndAggregateYieldOperandTypes(func: FunctionLikeDeclaration, contextualMapper: TypeMapper): Type[] {
@@ -13896,7 +13892,7 @@ namespace ts {
 
         function checkNonThenableType(type: Type, location?: Node, message?: DiagnosticMessage) {
             type = getWidenedType(type);
-            if (!isTypeAny(type) && isTypeAssignableTo(type, getGlobalThenableType())) {
+            if (!isTypeAny(type) && !isTypeNever(type) && isTypeAssignableTo(type, getGlobalThenableType())) {
                 if (location) {
                     if (!message) {
                         message = Diagnostics.Operand_for_await_does_not_have_a_valid_callable_then_member;
@@ -13927,12 +13923,15 @@ namespace ts {
             //  }
             //
 
-            if (promise.flags & TypeFlags.Any) {
+            if (isTypeAny(promise)) {
                 return undefined;
             }
 
-            if ((promise.flags & TypeFlags.Reference) && (<GenericType>promise).target === tryGetGlobalPromiseType()) {
-                return (<GenericType>promise).typeArguments[0];
+            if (promise.flags & TypeFlags.Reference) {
+                if ((<GenericType>promise).target === tryGetGlobalPromiseType()
+                    || (<GenericType>promise).target === getGlobalPromiseLikeType()) {
+                    return (<GenericType>promise).typeArguments[0];
+                }
             }
 
             const globalPromiseLikeType = getInstantiatedGlobalPromiseLikeType();
@@ -13941,17 +13940,17 @@ namespace ts {
             }
 
             const thenFunction = getTypeOfPropertyOfType(promise, "then");
-            if (thenFunction && (thenFunction.flags & TypeFlags.Any)) {
+            if (!thenFunction || isTypeAny(thenFunction)) {
                 return undefined;
             }
 
-            const thenSignatures = thenFunction ? getSignaturesOfType(thenFunction, SignatureKind.Call) : emptyArray;
+            const thenSignatures = getSignaturesOfType(thenFunction, SignatureKind.Call);
             if (thenSignatures.length === 0) {
                 return undefined;
             }
 
             const onfulfilledParameterType = getTypeWithFacts(getUnionType(map(thenSignatures, getTypeOfFirstParameterOfSignature)), TypeFacts.NEUndefined);
-            if (onfulfilledParameterType.flags & TypeFlags.Any) {
+            if (isTypeAny(onfulfilledParameterType)) {
                 return undefined;
             }
 
@@ -13960,12 +13959,11 @@ namespace ts {
                 return undefined;
             }
 
-            const valueParameterType = getUnionType(map(onfulfilledParameterSignatures, getTypeOfFirstParameterOfSignature));
-            return valueParameterType;
+            return getUnionType(map(onfulfilledParameterSignatures, getTypeOfFirstParameterOfSignature));
         }
 
         function getTypeOfFirstParameterOfSignature(signature: Signature) {
-            return getTypeAtPosition(signature, 0);
+            return signature.parameters.length > 0 ? getTypeAtPosition(signature, 0) : neverType;
         }
 
         /**

src/lib/es2015.promise.d.ts

@@ -3,59 +3,149 @@
  */
 interface Promise<T> {
     /**
-    * Attaches callbacks for the resolution and/or rejection of the Promise.
-    * @param onfulfilled The callback to execute when the Promise is resolved.
-    * @param onrejected The callback to execute when the Promise is rejected.
-    * @returns A Promise for the completion of which ever callback is executed.
-    */
-    then<TResult>(onfulfilled?: (value: T) => TResult | PromiseLike<TResult>, onrejected?: (reason: any) => TResult | PromiseLike<TResult>): Promise<TResult>;
-    then<TResult>(onfulfilled?: (value: T) => TResult | PromiseLike<TResult>, onrejected?: (reason: any) => void): Promise<TResult>;
+     * Attaches callbacks for the resolution and/or rejection of the Promise.
+     * @param onfulfilled The callback to execute when the Promise is resolved.
+     * @param onrejected The callback to execute when the Promise is rejected.
+     * @returns A Promise for the completion of which ever callback is executed.
+     */
+    then<TResult1, TResult2>(onfulfilled: (value: T) => TResult1 | PromiseLike<TResult1>, onrejected: (reason: any) => TResult2 | PromiseLike<TResult2>): Promise<TResult1 | TResult2>;
+
+    /**
+     * Attaches callbacks for the resolution and/or rejection of the Promise.
+     * @param onfulfilled The callback to execute when the Promise is resolved.
+     * @param onrejected The callback to execute when the Promise is rejected.
+     * @returns A Promise for the completion of which ever callback is executed.
+     */
+    then<TResult>(onfulfilled: (value: T) => TResult | PromiseLike<TResult>, onrejected: (reason: any) => TResult | PromiseLike<TResult>): Promise<TResult>;
+
+    /**
+     * Attaches callbacks for the resolution and/or rejection of the Promise.
+     * @param onfulfilled The callback to execute when the Promise is resolved.
+     * @returns A Promise for the completion of which ever callback is executed.
+     */
+    then<TResult>(onfulfilled: (value: T) => TResult | PromiseLike<TResult>): Promise<TResult>;
+
+    /**
+     * Creates a new Promise with the same internal state of this Promise.
+     * @returns A Promise.
+     */
+    then(): Promise<T>;
 
     /**
      * Attaches a callback for only the rejection of the Promise.
      * @param onrejected The callback to execute when the Promise is rejected.
      * @returns A Promise for the completion of the callback.
      */
-    catch(onrejected?: (reason: any) => T | PromiseLike<T>): Promise<T>;
-    catch(onrejected?: (reason: any) => void): Promise<T>;
+    catch<TResult>(onrejected: (reason: any) => TResult | PromiseLike<TResult>): Promise<T | TResult>;
+
+    /**
+     * Attaches a callback for only the rejection of the Promise.
+     * @param onrejected The callback to execute when the Promise is rejected.
+     * @returns A Promise for the completion of the callback.
+     */
+    catch(onrejected: (reason: any) => T | PromiseLike<T>): Promise<T>;
 }
 
 interface PromiseConstructor {
-    /** 
-      * A reference to the prototype. 
+    /**
+      * A reference to the prototype.
       */
     readonly prototype: Promise<any>;
 
     /**
      * Creates a new Promise.
-     * @param executor A callback used to initialize the promise. This callback is passed two arguments: 
-     * a resolve callback used resolve the promise with a value or the result of another promise, 
+     * @param executor A callback used to initialize the promise. This callback is passed two arguments:
+     * a resolve callback used resolve the promise with a value or the result of another promise,
      * and a reject callback used to reject the promise with a provided reason or error.
      */
     new <T>(executor: (resolve: (value?: T | PromiseLike<T>) => void, reject: (reason?: any) => void) => void): Promise<T>;
 
     /**
-     * Creates a Promise that is resolved with an array of results when all of the provided Promises 
+     * Creates a Promise that is resolved with an array of results when all of the provided Promises
      * resolve, or rejected when any Promise is rejected.
      * @param values An array of Promises.
      * @returns A new Promise.
      */
     all<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10>(values: [T1 | PromiseLike<T1>, T2 | PromiseLike<T2>, T3 | PromiseLike<T3>, T4 | PromiseLike <T4>, T5 | PromiseLike<T5>, T6 | PromiseLike<T6>, T7 | PromiseLike<T7>, T8 | PromiseLike<T8>, T9 | PromiseLike<T9>, T10 | PromiseLike<T10>]): Promise<[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10]>;
+
+    /**
+     * Creates a Promise that is resolved with an array of results when all of the provided Promises
+     * resolve, or rejected when any Promise is rejected.
+     * @param values An array of Promises.
+     * @returns A new Promise.
+     */
     all<T1, T2, T3, T4, T5, T6, T7, T8, T9>(values: [T1 | PromiseLike<T1>, T2 | PromiseLike<T2>, T3 | PromiseLike<T3>, T4 | PromiseLike <T4>, T5 | PromiseLike<T5>, T6 | PromiseLike<T6>, T7 | PromiseLike<T7>, T8 | PromiseLike<T8>, T9 | PromiseLike<T9>]): Promise<[T1, T2, T3, T4, T5, T6, T7, T8, T9]>;
+
+    /**
+     * Creates a Promise that is resolved with an array of results when all of the provided Promises
+     * resolve, or rejected when any Promise is rejected.
+     * @param values An array of Promises.
+     * @returns A new Promise.
+     */
     all<T1, T2, T3, T4, T5, T6, T7, T8>(values: [T1 | PromiseLike<T1>, T2 | PromiseLike<T2>, T3 | PromiseLike<T3>, T4 | PromiseLike <T4>, T5 | PromiseLike<T5>, T6 | PromiseLike<T6>, T7 | PromiseLike<T7>, T8 | PromiseLike<T8>]): Promise<[T1, T2, T3, T4, T5, T6, T7, T8]>;
+
+    /**
+     * Creates a Promise that is resolved with an array of results when all of the provided Promises
+     * resolve, or rejected when any Promise is rejected.
+     * @param values An array of Promises.
+     * @returns A new Promise.
+     */
     all<T1, T2, T3, T4, T5, T6, T7>(values: [T1 | PromiseLike<T1>, T2 | PromiseLike<T2>, T3 | PromiseLike<T3>, T4 | PromiseLike <T4>, T5 | PromiseLike<T5>, T6 | PromiseLike<T6>, T7 | PromiseLike<T7>]): Promise<[T1, T2, T3, T4, T5, T6, T7]>;
+
+    /**
+     * Creates a Promise that is resolved with an array of results when all of the provided Promises
+     * resolve, or rejected when any Promise is rejected.
+     * @param values An array of Promises.
+     * @returns A new Promise.
+     */
     all<T1, T2, T3, T4, T5, T6>(values: [T1 | PromiseLike<T1>, T2 | PromiseLike<T2>, T3 | PromiseLike<T3>, T4 | PromiseLike <T4>, T5 | PromiseLike<T5>, T6 | PromiseLike<T6>]): Promise<[T1, T2, T3, T4, T5, T6]>;
+
+    /**
+     * Creates a Promise that is resolved with an array of results when all of the provided Promises
+     * resolve, or rejected when any Promise is rejected.
+     * @param values An array of Promises.
+     * @returns A new Promise.
+     */
     all<T1, T2, T3, T4, T5>(values: [T1 | PromiseLike<T1>, T2 | PromiseLike<T2>, T3 | PromiseLike<T3>, T4 | PromiseLike <T4>, T5 | PromiseLike<T5>]): Promise<[T1, T2, T3, T4, T5]>;
+
+    /**
+     * Creates a Promise that is resolved with an array of results when all of the provided Promises
+     * resolve, or rejected when any Promise is rejected.
+     * @param values An array of Promises.
+     * @returns A new Promise.
+     */
     all<T1, T2, T3, T4>(values: [T1 | PromiseLike<T1>, T2 | PromiseLike<T2>, T3 | PromiseLike<T3>, T4 | PromiseLike <T4>]): Promise<[T1, T2, T3, T4]>;
+
+    /**
+     * Creates a Promise that is resolved with an array of results when all of the provided Promises
+     * resolve, or rejected when any Promise is rejected.
+     * @param values An array of Promises.
+     * @returns A new Promise.
+     */
     all<T1, T2, T3>(values: [T1 | PromiseLike<T1>, T2 | PromiseLike<T2>, T3 | PromiseLike<T3>]): Promise<[T1, T2, T3]>;
+
+    /**
+     * Creates a Promise that is resolved with an array of results when all of the provided Promises
+     * resolve, or rejected when any Promise is rejected.
+     * @param values An array of Promises.
+     * @returns A new Promise.
+     */
     all<T1, T2>(values: [T1 | PromiseLike<T1>, T2 | PromiseLike<T2>]): Promise<[T1, T2]>;
 
+    /**
+     * Creates a Promise that is resolved with an array of results when all of the provided Promises
+     * resolve, or rejected when any Promise is rejected.
+     * @param values An array of Promises.
+     * @returns A new Promise.
+     */
+    all<T>(values: (T | PromiseLike<T>)[]): Promise<T[]>;
+
     /**
      * Creates a new rejected promise for the provided reason.
      * @param reason The reason the promise was rejected.
      * @returns A new rejected Promise.
      */
-    reject(reason: any): Promise<void>;
+    reject(reason: any): Promise<never>;
 
     /**
      * Creates a new rejected promise for the provided reason.