Fix bounded self types in override incompatibility checking (#15045)

Fixes #15041

Related to #14882 and #14017 (the older one is where I added the xfail
test)

Author: hauntsaninja

mypy/checker.py

@@ -1954,11 +1954,15 @@ def bind_and_map_method(
                 # If we have an overload, filter to overloads that match the self type.
                 # This avoids false positives for concrete subclasses of generic classes,
                 # see testSelfTypeOverrideCompatibility for an example.
-                filtered_items = [
-                    item
-                    for item in mapped_typ.items
-                    if not item.arg_types or is_subtype(active_self_type, item.arg_types[0])
-                ]
+                filtered_items = []
+                for item in mapped_typ.items:
+                    if not item.arg_types:
+                        filtered_items.append(item)
+                    item_arg = item.arg_types[0]
+                    if isinstance(item_arg, TypeVarType):
+                        item_arg = item_arg.upper_bound
+                    if is_subtype(active_self_type, item_arg):
+                        filtered_items.append(item)
                 # If we don't have any filtered_items, maybe it's always a valid override
                 # of the superclass? However if you get to that point you're in murky type
                 # territory anyway, so we just preserve the type and have the behaviour match

test-data/unit/check-selftype.test

@@ -232,7 +232,7 @@ class C(A[None]):
                                      # N:          def f(self, s: int) -> int
 [builtins fixtures/tuple.pyi]
 
-[case testSelfTypeOverrideCompatibilityTypeVar-xfail]
+[case testSelfTypeOverrideCompatibilityTypeVar]
 from typing import overload, TypeVar, Union
 
 AT = TypeVar("AT", bound="A")
@@ -266,6 +266,26 @@ class B(A):
     def f(*a, **kw): ...
 [builtins fixtures/dict.pyi]
 
+[case testSelfTypeOverrideCompatibilitySelfTypeVar]
+from typing import Any, Generic, Self, TypeVar, overload
+
+T_co = TypeVar('T_co', covariant=True)
+
+class Config(Generic[T_co]):
+	@overload
+	def get(self, instance: None) -> Self: ...
+	@overload
+	def get(self, instance: Any) -> T_co: ...
+	def get(self, *a, **kw): ...
+
+class MultiConfig(Config[T_co]):
+	@overload
+	def get(self, instance: None) -> Self: ...
+	@overload
+	def get(self, instance: Any) -> T_co: ...
+	def get(self, *a, **kw): ...
+[builtins fixtures/dict.pyi]
+
 [case testSelfTypeSuper]
 from typing import TypeVar, cast