Support @deprecated() on overloaded __get__ for generic descriptors

[Viicos]

Fixes #18323.
Follow up on #18090.

Notes:

• In analyze_descriptor_access, there is a distinction between typ and descriptor_type:
  

  mypy/mypy/checkmember.py

  Lines 687 to 688 in 9ff9946

  	typ = map_instance_to_supertype(descriptor_type, dunder_get.info)
  	dunder_get_type = expand_type_by_instance(bound_method, typ)

  it seems that in our case though, map_instance_to_supertype returns descriptor_type unchanged. The reason I'm mentioning this is that expand_type_by_instance uses typ and not descriptor_type. In warn_deprecated_overload_item, we have access to descriptor_type (passed as selftype):
  

  mypy/mypy/checkmember.py

  Lines 726 to 728 in 9ff9946

  	mx.chk.warn_deprecated_overload_item(
  	dunder_get, mx.context, target=inferred_dunder_get_type, selftype=descriptor_type
  	)

  and in this changeset I call expand_type_by_instance(candidate, selftype). Is this going to be an issue?
• To comply with the type checker, I had to change the type annotation of selftype to Instance. Is this going to be an issue?

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

[A5rocks]

I'm a bit surprised about this bind_self, actually. I cannot find where inferred_dunder_get_type gets passed to bind_self... I'm only looking at the code though. I'm certain it's used but... where?

[Viicos]

Hum, in analyze_descriptor_access, we pass inferred_dunder_get_type as target:

mypy/mypy/checkmember.py

Lines 726 to 728 in 9ff9946

	mx.chk.warn_deprecated_overload_item(
	dunder_get, mx.context, target=inferred_dunder_get_type, selftype=descriptor_type
	)

but not sure what you mean exactly

[A5rocks]

Like I'd expect some sort of symmetry: we repeat the actions we did to get target on each overload member. But I can't find where we bind_self.

---

To be specific, in analyze_descriptor_access (or in a function it calls) I expect a bind_self call as dunder_get turns into inferred_dunder_get_type... but I can't find one. Is it just not necessary?

[tyralla]

analyze_descriptor_access calls analyze_decorator_or_funcbase_access (eventually) calls bind_self. Is that what you are looking for?

[A5rocks]

Yep! Does that mean bind_self and expand_type_by_instance should be swapped (IE pass the result of bind_self to expand_type_by_instance) in this PR?

I'm not sure if there's a difference anyways but I think it's better to imitate what's elsewhere.

[tyralla]

Without spending much time, I can also only speculate if these different orders can make a difference. But I guess you are right. Synchronising both steps as well as possible should do no harm and might be beneficial in some cases. (At least, it frees the next one looking at the code from asking himself the same question.)

bind_self gets descriptor_type but expand_type_by_instance gets typ. Same question here?