Better typings for Promise.all(), etc. like #31117

src/lib/es2015.iterable.d.ts

@@ -203,7 +203,7 @@ interface PromiseConstructor {
      * @param values An array of Promises.
      * @returns A new Promise.
      */
-    all<TAll>(values: Iterable<TAll | PromiseLike<TAll>>): Promise<TAll[]>;
+    all<TAll>(values: Iterable<TAll>): Promise<(TAll extends undefined ? TAll : TAll extends PromiseLike<infer UAll> ? UAll : TAll)[]>;
 }
 
 declare namespace Reflect {

src/lib/es2015.promise.d.ts

@@ -1,3 +1,9 @@
+// The undefined case is for strictNullChecks false, in which case
+// undefined extends PromiseLike<infer U> is true, which would otherwise
+// make Awaited<undefined> -> unknown. When strictNullChecks is false
+// and T is undefined, should infer U be undefined, instead of unknown?
+type Awaited<T> = T extends undefined ? T : T extends PromiseLike<infer U> ? U : T;
+
 interface PromiseConstructor {
     /**
      * A reference to the prototype.
@@ -18,95 +24,15 @@ interface PromiseConstructor {
      * @param values An array of Promises.
      * @returns A new Promise.
      */
-    all<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10>(values: readonly [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: readonly [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: readonly [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: readonly [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: readonly [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: readonly [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: readonly [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: readonly [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: readonly [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: readonly (T | PromiseLike<T>)[]): Promise<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: readonly T[]): Promise<T extends PromiseLike<infer U> ? U : T>;
+    all<T extends readonly any[]>(values: T): Promise<{ -readonly [P in keyof T]: Awaited<T[P]> }>;
 
     /**
      * Creates a Promise that is resolved or rejected when any of the provided Promises are resolved
      * or rejected.
      * @param values An iterable of Promises.
      * @returns A new Promise.
      */
-    race<T>(values: Iterable<T>): Promise<T extends PromiseLike<infer U> ? U : T>;
+    race<T>(values: Iterable<T>): Promise<Awaited<T>>;
 
     /**
      * Creates a new rejected promise for the provided reason.
@@ -120,10 +46,10 @@ interface PromiseConstructor {
      * @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 .
+     * Creates a new resolved promise.
      * @returns A resolved promise.
      */
     resolve(): Promise<void>;

src/lib/es2018.asyncgenerator.d.ts

@@ -2,9 +2,9 @@
 
 interface AsyncGenerator<T = unknown, TReturn = any, TNext = unknown> extends AsyncIterator<T, TReturn, TNext> {
     // NOTE: 'next' is defined using a tuple to ensure we report the correct assignability errors in all places.
-    next(...args: [] | [TNext]): Promise<IteratorResult<T, TReturn>>;
-    return(value: TReturn | PromiseLike<TReturn>): Promise<IteratorResult<T, TReturn>>;
-    throw(e: any): Promise<IteratorResult<T, TReturn>>;
+    next(...args: [] | [TNext]): Promise<IteratorResult<T, TReturn extends undefined ? TReturn : TReturn extends PromiseLike<infer UReturn> ? UReturn : TReturn>>;
+    return(value: TReturn): Promise<IteratorResult<T, TReturn extends undefined ? TReturn : TReturn extends PromiseLike<infer UReturn> ? UReturn : TReturn>>;
+    throw(e: any): Promise<IteratorResult<T, TReturn extends undefined ? TReturn : TReturn extends PromiseLike<infer UReturn> ? UReturn : TReturn>>;
     [Symbol.asyncIterator](): AsyncGenerator<T, TReturn, TNext>;
 }
 

src/lib/es2018.asynciterable.d.ts

@@ -11,9 +11,9 @@ interface SymbolConstructor {
 
 interface AsyncIterator<T, TReturn = any, TNext = undefined> {
     // NOTE: 'next' is defined using a tuple to ensure we report the correct assignability errors in all places.
-    next(...args: [] | [TNext]): Promise<IteratorResult<T, TReturn>>;
-    return?(value?: TReturn | PromiseLike<TReturn>): Promise<IteratorResult<T, TReturn>>;
-    throw?(e?: any): Promise<IteratorResult<T, TReturn>>;
+    next(...args: [] | [TNext]): Promise<IteratorResult<T, TReturn extends undefined ? TReturn : TReturn extends PromiseLike<infer UReturn> ? UReturn : TReturn>>;
+    return?(value?: TReturn): Promise<IteratorResult<T, TReturn extends undefined ? TReturn : TReturn extends PromiseLike<infer UReturn> ? UReturn : TReturn>>;
+    throw?(e?: any): Promise<IteratorResult<T, TReturn extends undefined ? TReturn : TReturn extends PromiseLike<infer UReturn> ? UReturn : TReturn>>;
 }
 
 interface AsyncIterable<T> {
@@ -22,4 +22,4 @@ interface AsyncIterable<T> {
 
 interface AsyncIterableIterator<T> extends AsyncIterator<T> {
     [Symbol.asyncIterator](): AsyncIterableIterator<T>;
-}
+}

src/lib/es5.d.ts

@@ -1387,7 +1387,7 @@ 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: T) => TResult1) | null, onrejected?: ((reason: any) => TResult2) | null): PromiseLike<(TResult1 extends undefined ? TResult1 : TResult1 extends PromiseLike<infer UResult1> ? UResult1 : TResult1) | (TResult2 extends undefined ? TResult2 : TResult2 extends PromiseLike<infer UResult2> ? UResult2 : TResult2)>;
 }
 
 /**
@@ -1400,14 +1400,14 @@ 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: T) => TResult1) | null, onrejected?: ((reason: any) => TResult2) | null): Promise<(TResult1 extends undefined ? TResult1 : TResult1 extends PromiseLike<infer UResult1> ? UResult1 : TResult1) | (TResult2 extends undefined ? TResult2 : TResult2 extends PromiseLike<infer UResult2> ? UResult2 : 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<T | (TResult extends undefined ? TResult : TResult extends PromiseLike<infer UResult> ? UResult : TResult)>;
 }
 
 interface ArrayLike<T> {

tests/baselines/reference/asyncArrowFunction11_es5.types

@@ -11,9 +11,9 @@ class A {
         await Promise.resolve();
 >await Promise.resolve() : void
 >Promise.resolve() : Promise<void>
->Promise.resolve : { <T>(value: T | PromiseLike<T>): Promise<T>; (): Promise<void>; }
+>Promise.resolve : { <T>(value: T): Promise<Awaited<T>>; (): Promise<void>; }
 >Promise : PromiseConstructor
->resolve : { <T>(value: T | PromiseLike<T>): Promise<T>; (): Promise<void>; }
+>resolve : { <T>(value: T): Promise<Awaited<T>>; (): Promise<void>; }
 
         const obj = { ["a"]: () => this }; // computed property name after `await` triggers case
 >obj : { ["a"]: () => this; }

tests/baselines/reference/asyncArrowFunction5_es2017.errors.txt

@@ -16,7 +16,7 @@ tests/cases/conformance/async/es2017/asyncArrowFunction/asyncArrowFunction5_es20
 !!! error TS1005: ',' expected.
                              ~~~~~~~
 !!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'Promise' must be of type 'PromiseConstructor', but here has type 'any'.
-!!! related TS6203 /.ts/lib.es2015.promise.d.ts:152:13: 'Promise' was also declared here.
+!!! related TS6203 /.ts/lib.es2015.promise.d.ts:78:13: 'Promise' was also declared here.
                                     ~
 !!! error TS1005: ',' expected.
                                            ~~

tests/baselines/reference/asyncArrowFunction5_es5.errors.txt

@@ -16,7 +16,7 @@ tests/cases/conformance/async/es5/asyncArrowFunction/asyncArrowFunction5_es5.ts(
 !!! error TS1005: ',' expected.
                              ~~~~~~~
 !!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'Promise' must be of type 'PromiseConstructor', but here has type 'any'.
-!!! related TS6203 /.ts/lib.es2015.promise.d.ts:152:13: 'Promise' was also declared here.
+!!! related TS6203 /.ts/lib.es2015.promise.d.ts:78:13: 'Promise' was also declared here.
                                     ~
 !!! error TS1005: ',' expected.
                                            ~~

tests/baselines/reference/asyncArrowFunction5_es6.errors.txt

@@ -16,7 +16,7 @@ tests/cases/conformance/async/es6/asyncArrowFunction/asyncArrowFunction5_es6.ts(
 !!! error TS1005: ',' expected.
                              ~~~~~~~
 !!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'Promise' must be of type 'PromiseConstructor', but here has type 'any'.
-!!! related TS6203 /.ts/lib.es2015.promise.d.ts:152:13: 'Promise' was also declared here.
+!!! related TS6203 /.ts/lib.es2015.promise.d.ts:78:13: 'Promise' was also declared here.
                                     ~
 !!! error TS1005: ',' expected.
                                            ~~

tests/baselines/reference/asyncArrowFunction9_es2017.errors.txt

@@ -16,7 +16,7 @@ tests/cases/conformance/async/es2017/asyncArrowFunction/asyncArrowFunction9_es20
 !!! error TS1005: ',' expected.
                                           ~~~~~~~
 !!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'Promise' must be of type 'PromiseConstructor', but here has type 'any'.
-!!! related TS6203 /.ts/lib.es2015.promise.d.ts:152:13: 'Promise' was also declared here.
+!!! related TS6203 /.ts/lib.es2015.promise.d.ts:78:13: 'Promise' was also declared here.
                                                  ~
 !!! error TS1005: ',' expected.
                                                         ~~

tests/baselines/reference/asyncArrowFunction9_es5.errors.txt

@@ -16,7 +16,7 @@ tests/cases/conformance/async/es5/asyncArrowFunction/asyncArrowFunction9_es5.ts(
 !!! error TS1005: ',' expected.
                                           ~~~~~~~
 !!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'Promise' must be of type 'PromiseConstructor', but here has type 'any'.
-!!! related TS6203 /.ts/lib.es2015.promise.d.ts:152:13: 'Promise' was also declared here.
+!!! related TS6203 /.ts/lib.es2015.promise.d.ts:78:13: 'Promise' was also declared here.
                                                  ~
 !!! error TS1005: ',' expected.
                                                         ~~

tests/baselines/reference/asyncArrowFunction9_es6.errors.txt

@@ -16,7 +16,7 @@ tests/cases/conformance/async/es6/asyncArrowFunction/asyncArrowFunction9_es6.ts(
 !!! error TS1005: ',' expected.
                                           ~~~~~~~
 !!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'Promise' must be of type 'PromiseConstructor', but here has type 'any'.
-!!! related TS6203 /.ts/lib.es2015.promise.d.ts:152:13: 'Promise' was also declared here.
+!!! related TS6203 /.ts/lib.es2015.promise.d.ts:78:13: 'Promise' was also declared here.
                                                  ~
 !!! error TS1005: ',' expected.
                                                         ~~

tests/baselines/reference/asyncFunctionDeclaration15_es5.errors.txt

@@ -7,7 +7,7 @@ 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.
   Construct signature return types 'Thenable' and 'PromiseLike<T>' are incompatible.
     The types returned by 'then(...)' are incompatible between these types.
-      Type 'void' is not assignable to type 'PromiseLike<TResult1 | TResult2>'.
+      Type 'void' is not assignable to type 'PromiseLike<(TResult1 extends undefined ? TResult1 : TResult1 extends PromiseLike<infer UResult1> ? UResult1 : TResult1) | (TResult2 extends undefined ? TResult2 : TResult2 extends PromiseLike<infer UResult2> ? UResult2 : 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.
 
@@ -39,7 +39,7 @@ 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:   Construct signature return types 'Thenable' and 'PromiseLike<T>' are incompatible.
 !!! error TS1055:     The types returned by 'then(...)' are incompatible between these types.
-!!! error TS1055:       Type 'void' is not assignable to type 'PromiseLike<TResult1 | TResult2>'.
+!!! error TS1055:       Type 'void' is not assignable to type 'PromiseLike<(TResult1 extends undefined ? TResult1 : TResult1 extends PromiseLike<infer UResult1> ? UResult1 : TResult1) | (TResult2 extends undefined ? TResult2 : TResult2 extends PromiseLike<infer UResult2> ? UResult2 : TResult2)>'.
     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/asyncFunctionReturnType.js

@@ -67,13 +67,14 @@ async function fGenericIndexedTypeForKProp<TObj extends Obj, K extends keyof TOb
     return obj[key];
 }
 
-async function fGenericIndexedTypeForPromiseOfKProp<TObj extends Obj, K extends keyof TObj>(obj: TObj, key: K): Promise<TObj[K]> {
+async function fGenericIndexedTypeForPromiseOfKProp<TObj extends Obj, K extends keyof TObj>(obj: TObj, key: K): Promise<TObj[K] extends undefined ? TObj[K] : TObj[K] extends PromiseLike<infer U> ? U : TObj[K]> {
     return Promise.resolve(obj[key]);
 }
 
-async function fGenericIndexedTypeForExplicitPromiseOfKProp<TObj extends Obj, K extends keyof TObj>(obj: TObj, key: K): Promise<TObj[K]> {
+async function fGenericIndexedTypeForExplicitPromiseOfKProp<TObj extends Obj, K extends keyof TObj>(obj: TObj, key: K): Promise<TObj[K] extends undefined ? TObj[K] : TObj[K] extends PromiseLike<infer U> ? U : TObj[K]> {
     return Promise.resolve<TObj[K]>(obj[key]);
-}
+}
+
 
 //// [asyncFunctionReturnType.js]
 var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {