Extend Iterator and AsyncIterator with Symbol.dispose.

[jsonnull]

Fixes #59263

[jsonnull]

@microsoft-github-policy-service agree

[Josh-Cena]

Iterator and AsyncIterator aren't what they mean in JS yet. #58222

[jsonnull]

Iterator and AsyncIterator aren't what they mean in JS yet. #58222

I think I know what you mean, I suppose I assumed that using ESNext lib opts you into the assumption of a compliant runtime.

Edited to add:

I'm not sure how this would be any different from some other ESNext feature requiring runtime support. Either the runtime has it or one polyfills it, but that shouldn't change the signatures of the types. The way I'm seeing it, the line of logic suggesting that Iterator doesn't get the Symbol.dispose definition would also preclude a DisposableStack definition from existing in esnext.disposable lib, yet it does.

[Josh-Cena]

No; the problem is more awkward than any other ESNext lib type. Perhaps #54481 summarizes it better?

In essence, Iterator in the lib def actually means the iterator protocol, and the built-in Iterator prototype is actually IterableIterator by convention, but there's simply nothing that corresponds to what would be the Iterator value-space object. You can take a look at https://github.com/microsoft/TypeScript/pull/58222/files#diff-34a90d6d878aa68ba4a76cff928f6697d65b8faae714fcbf56a9d8606e94119e for what the (possible) solution to the situation would be like.

[jsonnull]

I'll take a look at revisiting this when some of the iterator changes required have moved forward.