Async and await can't be used as identifiers in 3.6

[bgw]

It looks like parso's tokenizer unconditionally treats async and await as keywords under 3.6. However, while that's valid on 3.7+, on 3.6 it's conditionally treated as a keyword or identifier depending on if you're inside an async function.

Black has some logic to support this behavior when parsing as <3.7: https://github.com/psf/black/blob/40e8b3a231bade22d838858435a33d60a8325306/blib2to3/pgen2/tokenize.py#L359

This was reported by @zhammer on Instagram/LibCST#32

It might not be worth supporting because it's an older version of Python, and the hacks required to support it are pretty ugly, but I figured I'd upstream this issue.

[davidhalter]

I think I had some discussions about this before. Not sure if it was in this issue tracker, but we ended up with the current solution for these reasons:

1. Using async/await as an identifier will be a syntax error in the future, so people should fix it now
2. The complexity was just not worth the benefit.
3. It's quite a bit of work. Especially because parso supports error recovery and finding all the edge cases where the tokenizer might fail is annoying.

So if you don't mind, I would close this. In a bit more than two years 3.6 will be end of life and there's a good chance that we'll drop support anyway.

I personally won't do the work, there are more important things to do. But if you want to do this, I would consider accepting a patch. It's definitely possible.