Fix inference for overloaded __call__ with generic self

[hauntsaninja]

Fixes #8283

Co-authored-by: ilevkivskyi

[hauntsaninja]

Bit of a lazy hack to keep testTypeTupleCall and testTypeNamedTupleCall green

[ilevkivskyi]

This looks suspicious. ParamSpecType doesn't really make sense here (and it is unlikely it can get there without previously emitting an error), but TupleType is relatively common self-type for various user defined tuple types. Is it needed because type erasure touches some unhandled/incorectly handled corner case in is_subtype()? If yes, then that should be fixed instead.

[hauntsaninja]

Yeah, needs a change in is_subtype: #16073

[hauntsaninja]

Converting to draft since this needs #16073 and a regression test

[hauntsaninja]

@ilevkivskyi lol, looks like this PR gives me the test case I wanted in #16108 (comment). We create these kind of types in mypy.typevars.fill_typevars (at least).

I changed subtyping logic again to fix the case I care about by checking if all args are subtype of Any (for non-generic classes there are no args). But this isn't enough, since it doesn't work for callable generic tuple subclasses. So I added new clause, which works slightly more, but is a little sketchy

[ilevkivskyi]

This additional branch looks like a hack. We shouldn't need this. I think the real bug is that we are passing incomplete information when accessing __call__ on a tuple type. This diff I think is a (much) more cleaner fix:

--- a/mypy/checkexpr.py
+++ b/mypy/checkexpr.py
@@ -1476,6 +1476,7 @@ class ExpressionChecker(ExpressionVisitor[Type]):
         callable_node: Expression | None = None,
         callable_name: str | None = None,
         object_type: Type | None = None,
+        original_type: Type | None = None,
     ) -> tuple[Type, Type]:
         """Type check a call.
 
@@ -1538,7 +1539,7 @@ class ExpressionChecker(ExpressionVisitor[Type]):
                 is_super=False,
                 is_operator=True,
                 msg=self.msg,
-                original_type=callee,
+                original_type=original_type or callee,
                 chk=self.chk,
                 in_literal_context=self.is_literal_context(),
             )
@@ -1579,6 +1580,7 @@ class ExpressionChecker(ExpressionVisitor[Type]):
                 callable_node,
                 callable_name,
                 object_type,
+                original_type=callee,
             )
         else:
             return self.msg.not_callable(callee, context), AnyType(TypeOfAny.from_error)

[ilevkivskyi]

I think this should actually be combined with the if just above. I just realised that the if I added is incomplete, in fact if all type argument are either Any or *tuple[Any, ...] we are still good. But currently we are only considering only plain *tuple[Any, ...] or e.g. Any, Any, Any, while missing Any, *tuple[Any, ...], Any, which should be equally fine (note you don't need to check number of unpacks, it is already validated during semantic analyzis).

Note this also equally applies to the equivalent special case for plain instances I added around line 538. You may fix that as well if you want while you are at it.

[ilevkivskyi]

@hauntsaninja Looks better, but I think there is even cleaner solution. I left couple comments.

[hauntsaninja]

Thanks for the review!

[ilevkivskyi]

Thanks, LG! I have one last style comment.

[ilevkivskyi]

return False (here an in few places below) is now correct, but may be error prone if we will add another if after this case in the (distant) future. I like how you use if not self.proper_subtype + breaks + else: return True. I think it would be better to do the same here (and maybe move the comment below to between if left.type.has_base() and if not self.proper_subtype).

[github-actions]

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

prefect (https://github.com/PrefectHQ/prefect)
- src/prefect/server/utilities/database.py:631: error: Invalid self argument "URL" to attribute function "get_dialect" with type "Callable[[URL, bool], type[Dialect]]"  [misc]

[hauntsaninja]

Thanks for all the reviews!