Mark abort as having type NoReturn

[bjgill]

In #1995, typing was added to large parts of this project. This will be really useful to me.

One of the problems I have with the latest release is abort. PyCharm doesn't know that abort aborts. So it will complain about possibly uninitialised variables if I write code like this:

if foo:
    bar = 1
else:
    abort(404)

print(bar)

This is because abort is declared to return type None: def abort(status: t.Union[int, "Response"], *args, **kwargs) -> None:. This is not the case - I think abort always raises an exception.

Instead, what we want to do is change the return type to t.NoReturn. This expresses the correct meaning, which is that the abort function never returns. In turn, this will help PyCharm and other analysers understand code that uses abort better.

Checklist:

(a docs change, so I've skipped some steps)

- [ ] Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.

• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue. - this PR builds on redo type annotations #1995, which doesn't have an entry. Should I add an entry to cover both, or leave it alone?
  - [ ] Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.

[davidism]

See the test failure for why I didn't do this.

[bjgill]

Good point - I missed this in the tox output. I think I've found the problem - mypy's type inference doesn't seem to understand _aborter. It looks as if being explicit about the type of _aborter fixes the problem, though.

I'm not entirely sure why this is, which is a bit unsatisfactory.

[davidism]

Thanks for figuring it out!