Fixes corner case for comparing nested overloads

[sobolevn]

We have this really nasty bug in returns with our @curry plugin:

• Closes is_subtype function does not work correctly for two overloads #9147
• Closes Error to infer types from a curried function with more than two args #8978

So, this little fix solves the problem for us with very little effort.
In the ideal world, I would have to rewrite the whole thing to make the nested structures work.

Current problem is that we have a local state in matched_overloads and possible_invalid_overloads variables that is not syncronyzed with the nested calls.
I can also add a TODO note for later.

Refs dry-python/returns#410

[sobolevn]

Testing that this solves our issue:

from returns.curry import curry
from returns.io import IO

@curry
def test(a: int, b: int, c: int) -> int:
    ...

reveal_type(test)  # works
reveal_type(IO(1).apply(IO(test)))  # fails

Without this fix:

» mypy ex.py
ex.py:8: note: Revealed type is 'Overload(def (a: builtins.int) -> Overload(def (b: builtins.int, c: builtins.int) -> builtins.int, def (b: builtins.int) -> def (c: builtins.int) -> builtins.int), def (a: builtins.int, b: builtins.int) -> def (c: builtins.int) -> builtins.int, def (a: builtins.int, b: builtins.int, c: builtins.int) -> builtins.int)'
ex.py:9: note: Revealed type is 'returns.io.IO[Overload(def (b: builtins.int, c: builtins.int) -> builtins.int, def (b: builtins.int) -> def (c: builtins.int) -> builtins.int)]'
ex.py:9: error: Argument 1 to "IO" has incompatible type overloaded function; expected overloaded function

With this fix:

» python -m mypy /Users/sobolev/Documents/github/returns/ex.py --config-file=/Users/sobolev/Documents/github/returns/setup.cfg
/Users/sobolev/Documents/github/returns/ex.py:8: note: Revealed type is 'Overload(def (a: builtins.int) -> Overload(def (b: builtins.int, c: builtins.int) -> builtins.int, def (b: builtins.int) -> def (c: builtins.int) -> builtins.int), def (a: builtins.int, b: builtins.int) -> def (c: builtins.int) -> builtins.int, def (a: builtins.int, b: builtins.int, c: builtins.int) -> builtins.int)'
/Users/sobolev/Documents/github/returns/ex.py:9: note: Revealed type is 'returns.io.IO[Overload(def (b: builtins.int, c: builtins.int) -> builtins.int, def (b: builtins.int) -> def (c: builtins.int) -> builtins.int)]'

It works! 🎉

[sobolevn]

This failure does not seem related:

----------------------------- Captured stdout call -----------------------------

mypy: Failed to import, skipping

----------------------------- Captured stderr call -----------------------------

Inconsistency detected by ld.so: dl-open.c: 231: dl_open_worker: Assertion `_dl_debug_initialize (0, args->nsid)->r_state == RT_CONSISTENT' failed!

[gvanrossum]

Let me close and reopen the issue to see if re-running the tests fares better.

[gvanrossum]

There is no need to add a comment in the source referring to the bug (people can find that information using git blame).

[sobolevn]

👍

[gvanrossum]

LGTM. Would it be feasible to add a unit test?

[sobolevn]

@gvanrossum I don't know how to easily replicate this. Because creating a nested Overloaded is not possible without a plugin AFAIK.

I can write one if that's required. But, if you ask me I would probably leave this as-is.

[gvanrossum]

Okay, that's fine then.

[sobolevn]

@gvanrossum thanks a lot! 👍