Fix "Cannot determine type of Any" issue in typeshed

[JukkaL]

[This was implemented by @sobolevn as part of #12134. Cherry-picking
it to a separate PR since the original PR is still incomplete and the
issue is causing trouble in typeshed.]

Sometimes mypy could generate Cannot determine type of "Any" in
_typeshed/__init__.pyi when running typeshed tests if there is an alias
to Any. This seems to happen only if files are passed in a specific order
to mypy, and seems related to import cycles. Fix the issue by special
casing the inference of type of Any.

This hopefully fixes #12421.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

ibis (https://github.com/ibis-project/ibis)
- ibis/expr/operations/__init__.py:3: error: Incompatible import of "Any" (imported name has type "object", local name has type "Type[ibis.expr.operations.analytic.Any]")

aiohttp (https://github.com/aio-libs/aiohttp)
+ aiohttp/web.py:283: error: Unused "type: ignore[assignment]" comment

[srittau]

Looking at the primer output:

• The ibis output is a bit weird. ibis/expr/operations/__init__.py star imports from all its sub-modules. Line 1 contains from .analytic import *, which imports a class named Any from that module, which is unrelated to typing.Any. Line 3 contains from .core import *. core.pyi has from typing import Any, ..., but no re-export. So I'm not sure why the star import also imports the conflicting Any.
• The aiohttp output looks positive:

try:
    from ssl import SSLContext
except ImportError:  # pragma: no cover
    SSLContext = Any  # type: ignore[misc,assignment]

The assignment override isn't necessary anymore.

[JukkaL]

Actually, it looks like #12431 may also fix the same issue. I'm going to postpone this until we've validated #12431.

[JelleZijlstra]

core.pyi has from typing import Any, ..., but no re-export. So I'm not sure why the star import also imports the conflicting Any.

I haven't looked at the ibis code myself, but this is what I'd expect if there's no __all__ since it matches the runtime behavior. In stubs we can restrict import * to only explicitly exported names, but at runtime it imports everything that doesn't start with an underscore, so that's what mypy should do too.

[srittau]

Good point. (I wish there was a way to disable that re-export by default behavior in Python, though.)

[AlexWaygood]

I can confirm that #12431 has fixed all the known instances of this problem over at typeshed 🎉:

• Revert "Use import instead of type alias in email/message.pyi" typeshed#7548
• Add _typeshed.Incomplete typeshed#7535

[JukkaL]

Closing this since the issue has now been fixed.