Add Awaited<T> to core library

src/lib/es2015.iterable.d.ts

@@ -195,15 +195,15 @@ interface PromiseConstructor {
      * @param values An array of Promises.
      * @returns A new Promise.
      */
-    all<TAll>(values: Iterable<TAll | PromiseLike<TAll>>): Promise<TAll[]>;
+    all<T>(values: Iterable<T>): Promise<Awaited<T>[]>;
 
     /**
      * Creates a Promise that is resolved or rejected when any of the provided Promises are resolved
      * or rejected.
      * @param values An array of Promises.
      * @returns A new Promise.
      */
-    race<T>(values: Iterable<T | PromiseLike<T>>): Promise<T>;
+    race<T>(values: Iterable<T>): Promise<Awaited<T>>;
 }
 
 declare namespace Reflect {

src/lib/es2015.promise.d.ts

@@ -18,180 +18,173 @@ interface PromiseConstructor {
      * @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]>;
+    all<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10>(values: [T1, T2, T3, T4, T5, T6, T7, T8, T9, T10]): Promise<[Awaited<T1>, Awaited<T2>, Awaited<T3>, Awaited<T4>, Awaited<T5>, Awaited<T6>, Awaited<T7>, Awaited<T8>, Awaited<T9>, Awaited<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]>;
+    all<T1, T2, T3, T4, T5, T6, T7, T8, T9>(values: [T1, T2, T3, T4, T5, T6, T7, T8, T9]): Promise<[Awaited<T1>, Awaited<T2>, Awaited<T3>, Awaited<T4>, Awaited<T5>, Awaited<T6>, Awaited<T7>, Awaited<T8>, Awaited<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]>;
+    all<T1, T2, T3, T4, T5, T6, T7, T8>(values: [T1, T2, T3, T4, T5, T6, T7, T8]): Promise<[Awaited<T1>, Awaited<T2>, Awaited<T3>, Awaited<T4>, Awaited<T5>, Awaited<T6>, Awaited<T7>, Awaited<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]>;
+    all<T1, T2, T3, T4, T5, T6, T7>(values: [T1, T2, T3, T4, T5, T6, T7]): Promise<[Awaited<T1>, Awaited<T2>, Awaited<T3>, Awaited<T4>, Awaited<T5>, Awaited<T6>, Awaited<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]>;
+    all<T1, T2, T3, T4, T5, T6>(values: [T1, T2, T3, T4, T5, T6]): Promise<[Awaited<T1>, Awaited<T2>, Awaited<T3>, Awaited<T4>, Awaited<T5>, Awaited<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]>;
+    all<T1, T2, T3, T4, T5>(values: [T1, T2, T3, T4, T5]): Promise<[Awaited<T1>, Awaited<T2>, Awaited<T3>, Awaited<T4>, Awaited<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]>;
+    all<T1, T2, T3, T4>(values: [T1, T2, T3, T4]): Promise<[Awaited<T1>, Awaited<T2>, Awaited<T3>, Awaited<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]>;
+    all<T1, T2, T3>(values: [T1, T2, T3]): Promise<[Awaited<T1>, Awaited<T2>, Awaited<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]>;
+    all<T1, T2>(values: [T1, T2]): Promise<[Awaited<T1>, Awaited<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[]>;
+    all<T>(values: T[]): Promise<Awaited<T>[]>;
 
     /**
      * Creates a Promise that is resolved or rejected when any of the provided Promises are resolved
      * or rejected.
      * @param values An array of Promises.
      * @returns A new Promise.
      */
-    race<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>;
+    race<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10>(values: [T1, T2, T3, T4, T5, T6, T7, T8, T9, T10]): Promise<Awaited<T1 | T2 | T3 | T4 | T5 | T6 | T7 | T8 | T9 | T10>>;
 
     /**
      * Creates a Promise that is resolved or rejected when any of the provided Promises are resolved
      * or rejected.
      * @param values An array of Promises.
      * @returns A new Promise.
      */
-    race<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>;
+    race<T1, T2, T3, T4, T5, T6, T7, T8, T9>(values: [T1, T2, T3, T4, T5, T6, T7, T8, T9]): Promise<Awaited<T1 | T2 | T3 | T4 | T5 | T6 | T7 | T8 | T9>>;
 
     /**
      * Creates a Promise that is resolved or rejected when any of the provided Promises are resolved
      * or rejected.
      * @param values An array of Promises.
      * @returns A new Promise.
      */
-    race<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>;
+    race<T1, T2, T3, T4, T5, T6, T7, T8>(values: [T1, T2, T3, T4, T5, T6, T7, T8]): Promise<Awaited<T1 | T2 | T3 | T4 | T5 | T6 | T7 | T8>>;
 
     /**
      * Creates a Promise that is resolved or rejected when any of the provided Promises are resolved
      * or rejected.
      * @param values An array of Promises.
      * @returns A new Promise.
      */
-    race<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>;
+    race<T1, T2, T3, T4, T5, T6, T7>(values: [T1, T2, T3, T4, T5, T6, T7]): Promise<Awaited<T1 | T2 | T3 | T4 | T5 | T6 | T7>>;
 
     /**
      * Creates a Promise that is resolved or rejected when any of the provided Promises are resolved
      * or rejected.
      * @param values An array of Promises.
      * @returns A new Promise.
      */
-    race<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>;
+    race<T1, T2, T3, T4, T5, T6>(values: [T1, T2, T3, T4, T5, T6]): Promise<Awaited<T1 | T2 | T3 | T4 | T5 | T6>>;
 
     /**
      * Creates a Promise that is resolved or rejected when any of the provided Promises are resolved
      * or rejected.
      * @param values An array of Promises.
      * @returns A new Promise.
      */
-    race<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>;
+    race<T1, T2, T3, T4, T5>(values: [T1, T2, T3, T4, T5]): Promise<Awaited<T1 | T2 | T3 | T4 | T5>>;
 
     /**
      * Creates a Promise that is resolved or rejected when any of the provided Promises are resolved
      * or rejected.
      * @param values An array of Promises.
      * @returns A new Promise.
      */
-    race<T1, T2, T3, T4>(values: [T1 | PromiseLike<T1>, T2 | PromiseLike<T2>, T3 | PromiseLike<T3>, T4 | PromiseLike<T4>]): Promise<T1 | T2 | T3 | T4>;
+    race<T1, T2, T3, T4>(values: [T1, T2, T3, T4]): Promise<Awaited<T1 | T2 | T3 | T4>>;
 
     /**
      * Creates a Promise that is resolved or rejected when any of the provided Promises are resolved
      * or rejected.
      * @param values An array of Promises.
      * @returns A new Promise.
      */
-    race<T1, T2, T3>(values: [T1 | PromiseLike<T1>, T2 | PromiseLike<T2>, T3 | PromiseLike<T3>]): Promise<T1 | T2 | T3>;
+    race<T1, T2, T3>(values: [T1, T2, T3]): Promise<Awaited<T1 | T2 | T3>>;
 
     /**
      * Creates a Promise that is resolved or rejected when any of the provided Promises are resolved
      * or rejected.
      * @param values An array of Promises.
      * @returns A new Promise.
      */
-    race<T1, T2>(values: [T1 | PromiseLike<T1>, T2 | PromiseLike<T2>]): Promise<T1 | T2>;
+    race<T1, T2>(values: [T1, T2]): Promise<Awaited<T1 | T2>>;
 
     /**
      * Creates a Promise that is resolved or rejected when any of the provided Promises are resolved
      * or rejected.
      * @param values An array of Promises.
      * @returns A new Promise.
      */
-    race<T>(values: (T | PromiseLike<T>)[]): Promise<T>;
+    race<T>(values: T[]): Promise<Awaited<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<never>;
-
-    /**
-     * Creates a new rejected promise for the provided reason.
-     * @param reason The reason the promise was rejected.
-     * @returns A new rejected Promise.
-     */
-    reject<T>(reason: any): Promise<T>;
+    reject<T = never>(reason: any): Promise<Awaited<T>>;
 
     /**
      * Creates a new resolved promise for the provided value.
      * @param value A promise.
      * @returns A promise whose internal state matches the provided promise.
      */
-    resolve<T>(value: T | PromiseLike<T>): Promise<T>;
+    resolve<T>(value: T): Promise<Awaited<T>>;
 
     /**
      * Creates a new resolved promise .

src/lib/es5.d.ts

@@ -1273,6 +1273,12 @@ declare type PropertyDecorator = (target: Object, propertyKey: string | symbol)
 declare type MethodDecorator = <T>(target: Object, propertyKey: string | symbol, descriptor: TypedPropertyDescriptor<T>) => TypedPropertyDescriptor<T> | void;
 declare type ParameterDecorator = (target: Object, propertyKey: string | symbol, parameterIndex: number) => void;
 
+/** Gets the resulting type from awaiting `T`. This does **not** recursively unwrap nested promises. */
+declare type Awaited<T> =
+    T extends { then(onfulfilled: (value: infer U) => any): any; } ? U :
+    T extends { then(...args: any[]): any; } ? never :
+    T;
+
 declare type PromiseConstructorLike = new <T>(executor: (resolve: (value?: T | PromiseLike<T>) => void, reject: (reason?: any) => void) => void) => PromiseLike<T>;
 
 interface PromiseLike<T> {
@@ -1282,7 +1288,7 @@ interface PromiseLike<T> {
      * @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 = T, TResult2 = never>(onfulfilled?: ((value: T) => TResult1 | PromiseLike<TResult1>) | undefined | null, onrejected?: ((reason: any) => TResult2 | PromiseLike<TResult2>) | undefined | null): PromiseLike<TResult1 | TResult2>;
+    then<TResult1 = T, TResult2 = never>(onfulfilled?: ((value: Awaited<T>) => TResult1) | null, onrejected?: ((reason: any) => TResult2) | null): PromiseLike<Awaited<TResult1 | TResult2>>;
 }
 
 /**
@@ -1295,14 +1301,14 @@ interface Promise<T> {
      * @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 = T, TResult2 = never>(onfulfilled?: ((value: T) => TResult1 | PromiseLike<TResult1>) | undefined | null, onrejected?: ((reason: any) => TResult2 | PromiseLike<TResult2>) | undefined | null): Promise<TResult1 | TResult2>;
+    then<TResult1 = T, TResult2 = never>(onfulfilled?: ((value: Awaited<T>) => TResult1) | null, onrejected?: ((reason: any) => TResult2) | null): Promise<Awaited<TResult1 | TResult2>>;
 
     /**
      * 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<TResult = never>(onrejected?: ((reason: any) => TResult | PromiseLike<TResult>) | undefined | null): Promise<T | TResult>;
+    catch<TResult = never>(onrejected?: ((reason: any) => TResult) | null): Promise<Awaited<T | TResult>>;
 }
 
 interface ArrayLike<T> {

src/lib/esnext.promise.d.ts

@@ -8,5 +8,5 @@ interface Promise<T> {
      * @param onfinally The callback to execute when the Promise is settled (fulfilled or rejected).
      * @returns A Promise for the completion of the callback.
      */
-    finally(onfinally?: (() => void) | undefined | null): Promise<T>
+    finally(onfinally?: (() => void) | null): Promise<Awaited<T>>
 }

src/services/utilities.ts

@@ -3,8 +3,9 @@
 interface PromiseConstructor {
     new <T>(executor: (resolve: (value?: T | PromiseLike<T>) => void, reject: (reason?: any) => void) => void): Promise<T>;
     reject(reason: any): Promise<never>;
-    all<T>(values: (T | PromiseLike<T>)[]): Promise<T[]>;
+    all<T>(values: PromiseLike<T>[]): Promise<T[]>;
 }
+
 /* @internal */
 declare var Promise: PromiseConstructor;
 

tests/baselines/reference/asyncFunctionDeclaration15_es5.errors.txt

@@ -6,8 +6,8 @@ tests/cases/conformance/async/es5/functionDeclarations/asyncFunctionDeclaration1
 tests/cases/conformance/async/es5/functionDeclarations/asyncFunctionDeclaration15_es5.ts(10,23): error TS1055: Type 'typeof Thenable' is not a valid async function return type in ES5/ES3 because it does not refer to a Promise-compatible constructor value.
   Type 'Thenable' is not assignable to type 'PromiseLike<T>'.
     Types of property 'then' are incompatible.
-      Type '() => void' is not assignable to type '<TResult1 = T, TResult2 = never>(onfulfilled?: (value: T) => TResult1 | PromiseLike<TResult1>, onrejected?: (reason: any) => TResult2 | PromiseLike<TResult2>) => PromiseLike<TResult1 | TResult2>'.
-        Type 'void' is not assignable to type 'PromiseLike<TResult1 | TResult2>'.
+      Type '() => void' is not assignable to type '<TResult1 = T, TResult2 = never>(onfulfilled?: (value: Awaited<T>) => TResult1, onrejected?: (reason: any) => TResult2) => PromiseLike<Awaited<TResult1> | Awaited<TResult2>>'.
+        Type 'void' is not assignable to type 'PromiseLike<Awaited<TResult1> | Awaited<TResult2>>'.
 tests/cases/conformance/async/es5/functionDeclarations/asyncFunctionDeclaration15_es5.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/es5/functionDeclarations/asyncFunctionDeclaration15_es5.ts(23,25): error TS1320: Type of 'await' operand must either be a valid promise or must not contain a callable 'then' member.
 
@@ -37,8 +37,8 @@ tests/cases/conformance/async/es5/functionDeclarations/asyncFunctionDeclaration1
 !!! error TS1055: Type 'typeof Thenable' is not a valid async function return type in ES5/ES3 because it does not refer to a Promise-compatible constructor value.
 !!! error TS1055:   Type 'Thenable' is not assignable to type 'PromiseLike<T>'.
 !!! error TS1055:     Types of property 'then' are incompatible.
-!!! error TS1055:       Type '() => void' is not assignable to type '<TResult1 = T, TResult2 = never>(onfulfilled?: (value: T) => TResult1 | PromiseLike<TResult1>, onrejected?: (reason: any) => TResult2 | PromiseLike<TResult2>) => PromiseLike<TResult1 | TResult2>'.
-!!! error TS1055:         Type 'void' is not assignable to type 'PromiseLike<TResult1 | TResult2>'.
+!!! error TS1055:       Type '() => void' is not assignable to type '<TResult1 = T, TResult2 = never>(onfulfilled?: (value: Awaited<T>) => TResult1, onrejected?: (reason: any) => TResult2) => PromiseLike<Awaited<TResult1> | Awaited<TResult2>>'.
+!!! error TS1055:         Type 'void' is not assignable to type 'PromiseLike<Awaited<TResult1> | Awaited<TResult2>>'.
     async function fn7() { return; } // valid: Promise<void>
     async function fn8() { return 1; } // valid: Promise<number>
     async function fn9() { return null; } // valid: Promise<any>