return incorrectly considered to be yielded

[ghost]

TypeScript Version: 2.8.0-dev.20180302

Code

function* f() {
    yield 0;
    return "";
}

for (const x of f()) {
    const n: number = x;
}

Expected behavior:

No error.

Actual behavior:

src/a.ts(7,11): error TS2322: Type '"" | 0' is not assignable to type 'number'.
  Type '""' is not assignable to type 'number'.

[DanielRosenwasser]

See #22299 (comment)

The feature is working as intended. The returned type becomes the value of an IteratorResult when done is true.

[ghost]

Actually, then shouldn't we do the reverse?

function* f(): IterableIterator<number> {
    return "";
}

Currently this is not an error, but if you removed the type annotation, the return type would be inferred as IterableIterator<string>.

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.