Better typings for AsyncIterator/Generator, like #31117

Author: jablko

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 PromiseLike<infer UReturn> ? UReturn : TReturn>>;
+    return(value: TReturn): Promise<IteratorResult<T, TReturn extends PromiseLike<infer UReturn> ? UReturn : TReturn>>;
+    throw(e: any): Promise<IteratorResult<T, 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 PromiseLike<infer UReturn> ? UReturn : TReturn>>;
+    return?(value?: TReturn): Promise<IteratorResult<T, TReturn extends PromiseLike<infer UReturn> ? UReturn : TReturn>>;
+    throw?(e?: any): Promise<IteratorResult<T, 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>;
-}
+}

tests/baselines/reference/user/TypeScript-Vue-Starter.log

@@ -0,0 +1,9 @@
+Exit Code: 1
+Standard output:
+src/components/Hello.spec.ts(4,1): error TS2593: Cannot find name 'describe'. Do you need to install type definitions for a test runner? Try `npm i @types/jest` or `npm i @types/mocha` and then add `jest` or `mocha` to the types field in your tsconfig.
+src/components/Hello.spec.ts(5,3): error TS2593: Cannot find name 'it'. Do you need to install type definitions for a test runner? Try `npm i @types/jest` or `npm i @types/mocha` and then add `jest` or `mocha` to the types field in your tsconfig.
+src/components/Hello.spec.ts(14,5): error TS2304: Cannot find name 'expect'.
+
+
+
+Standard error:

tests/baselines/reference/user/TypeScript-WeChat-Starter.log

@@ -1,12 +1,16 @@
 Exit Code: 1
 Standard output:
-../../../../../node_modules/@types/mocha/index.d.ts(2680,13): error TS2403: Subsequent variable declarations must have the same type.  Variable 'beforeEach' must be of type 'Lifecycle', but here has type 'HookFunction'.
-../../../../../node_modules/@types/mocha/index.d.ts(2698,13): error TS2403: Subsequent variable declarations must have the same type.  Variable 'afterEach' must be of type 'Lifecycle', but here has type 'HookFunction'.
-../../../../../node_modules/@types/mocha/index.d.ts(2714,13): error TS2403: Subsequent variable declarations must have the same type.  Variable 'describe' must be of type 'Describe', but here has type 'SuiteFunction'.
-../../../../../node_modules/@types/mocha/index.d.ts(2735,13): error TS2403: Subsequent variable declarations must have the same type.  Variable 'xdescribe' must be of type 'Describe', but here has type 'PendingSuiteFunction'.
-../../../../../node_modules/@types/mocha/index.d.ts(2749,13): error TS2403: Subsequent variable declarations must have the same type.  Variable 'it' must be of type 'It', but here has type 'TestFunction'.
-../../../../../node_modules/@types/mocha/index.d.ts(2763,13): error TS2403: Subsequent variable declarations must have the same type.  Variable 'test' must be of type 'It', but here has type 'TestFunction'.
-../../../../../node_modules/@types/mocha/index.d.ts(2770,13): error TS2403: Subsequent variable declarations must have the same type.  Variable 'xit' must be of type 'It', but here has type 'PendingTestFunction'.
+src/App.test.tsx(5,1): error TS2593: Cannot find name 'it'. Do you need to install type definitions for a test runner? Try `npm i @types/jest` or `npm i @types/mocha` and then add `jest` or `mocha` to the types field in your tsconfig.
+src/components/Hello.test.tsx(5,1): error TS2593: Cannot find name 'it'. Do you need to install type definitions for a test runner? Try `npm i @types/jest` or `npm i @types/mocha` and then add `jest` or `mocha` to the types field in your tsconfig.
+src/components/Hello.test.tsx(7,3): error TS2304: Cannot find name 'expect'.
+src/components/Hello.test.tsx(10,1): error TS2593: Cannot find name 'it'. Do you need to install type definitions for a test runner? Try `npm i @types/jest` or `npm i @types/mocha` and then add `jest` or `mocha` to the types field in your tsconfig.
+src/components/Hello.test.tsx(12,3): error TS2304: Cannot find name 'expect'.
+src/components/Hello.test.tsx(15,1): error TS2593: Cannot find name 'it'. Do you need to install type definitions for a test runner? Try `npm i @types/jest` or `npm i @types/mocha` and then add `jest` or `mocha` to the types field in your tsconfig.
+src/components/Hello.test.tsx(17,3): error TS2304: Cannot find name 'expect'.
+src/components/Hello.test.tsx(20,1): error TS2593: Cannot find name 'it'. Do you need to install type definitions for a test runner? Try `npm i @types/jest` or `npm i @types/mocha` and then add `jest` or `mocha` to the types field in your tsconfig.
+src/components/Hello.test.tsx(21,3): error TS2304: Cannot find name 'expect'.
+src/components/Hello.test.tsx(26,1): error TS2593: Cannot find name 'it'. Do you need to install type definitions for a test runner? Try `npm i @types/jest` or `npm i @types/mocha` and then add `jest` or `mocha` to the types field in your tsconfig.
+src/components/Hello.test.tsx(27,3): error TS2304: Cannot find name 'expect'.