Missing generator's type parameter in functions and constructors

[falsandtru]

@rbuckton

TypeScript Version: master

Search Terms:

Code

export class Coroutine<T = unknown, R = unknown, S = unknown> {
  constructor(gen: (this: Coroutine<T, R, S>) => Generator<R, T, S> | AsyncGenerator<R, T, S>) {
  }
}
new Coroutine<0, 0, 1>(async function* g() {
  const a = yield 0;
  return 0;
});

Expected behavior:

Type g is AsyncGenerator<0, 0, 1>.
Type a is 1.

Actual behavior:

Type g is AsyncGenerator<0, 0, unknown>.
Type a is any.

Playground Link:

Related Issues:

[rbuckton]

This is an issue with contextual typing. The contextual type from the constructor isn't flowing to the async generator.

[falsandtru]

Since the constructor has been given all type parameters the type of the parameter gen must be AsyncGenerator<0, 0, 1>. All type parameters are clearly decided. And the return type of yield must be unknown with the current behavior, as is defined by the context type.

[falsandtru]

Note that the type declaration for this doesn't affect this bug. This is one of the verbose elements for effectivity of regression tests.

[falsandtru]

Same also with functions.

export function f<T = unknown, R = unknown, S = unknown>(gen: () => Generator<R, T, S> | AsyncGenerator<R, T, S>) {
}
f<0, 0, 1>(async function* g() {
  const a = yield 0;
  return 0;
});

[falsandtru]

@rbuckton Why you still haven't fixed this bug?

[falsandtru]

Thanks @rbuckton !

[falsandtru]

@RyanCavanaugh Label this.