TypeScript: TypeScript Language Server False Positive Error Reporting

Tracking as https://github.com/Effect-TS/effect is also hit by this

I working on a fix for this, I’ll put something up later this afternoon.

Unfortunately it seems like it doesn’t fix the issue, rather it does but it makes it appear in a different place, the return of the generator

It does appear to be the case only if there is no specified return, adding a return keyword makes the issue disappear

https://github.com/microsoft/TypeScript/issues/57903 doesn’t affect Effect as we don’t use async generators (provided I’ve understood the issue correctly)

Additional repro noted at https://github.com/microsoft/TypeScript/issues/57429#issuecomment-1981202521

I’m not sure how their rule works. If it depends on type information (looks like it does) then that error should go away after we fix this one.

Minimized repro

export interface Result<T, E> {
  mapErr<F>(fn: (error: E) => F): Result<T, F>;
  [Symbol.iterator](): Generator<E, T>;
}

declare const okIfObject: (value: unknown) => Result<Record<string, unknown>, 'ERR_NOT_AN_OBJECT'>;
declare const okIfInt: (value: unknown) => Result<number, 'ERR_NOT_AN_INT'>;
export declare function Do2<T, E>(job: () => Generator<E, T>): void;

declare let value: unknown;
Do2(function* () {
  const object = yield* okIfObject(value).mapErr(
    error => 0
  );

  const age = yield* okIfInt(object.age).mapErr(
    error => 0
  );

  return { age };
});