Further fix overload diagnostic for vararg and varkwarg

mypy/typeops.py

@@ -521,18 +521,16 @@ def callable_corresponding_argument(
 
         # def right(a: int = ...) -> None: ...
         # def left(__a: int = ..., *, a: int = ...) -> None: ...
-        from mypy.subtypes import is_subtype
+        from mypy.meet import meet_types
 
         if (
             not (by_name.required or by_pos.required)
             and by_pos.name is None
             and by_name.pos is None
         ):
-            # We actually want the intersection of by_name.typ and by_pos.typ
-            if is_subtype(by_name.typ, by_pos.typ):
-                return FormalArgument(by_name.name, by_pos.pos, by_name.typ, False)
-            if is_subtype(by_pos.typ, by_name.typ):
-                return FormalArgument(by_name.name, by_pos.pos, by_pos.typ, False)
+            return FormalArgument(
+                by_name.name, by_pos.pos, meet_types(by_name.typ, by_pos.typ), False
+            )
     return by_name if by_name is not None else by_pos
 
 

test-data/unit/check-overloading.test

@@ -246,6 +246,23 @@ def foo(*args: int | str, **kw: int) -> None:
     pass
 [builtins fixtures/tuple.pyi]
 
+[case testTypeCheckOverloadImplOverlapVarArgsAndKwargsUnion]
+from __future__ import annotations
+from typing import overload
+
+class Foo: ...
+
+@overload
+def foo(x: int) -> None: ...
+@overload
+def foo(*, x: Foo) -> None: ...
+@overload
+def foo(a: str, /) -> None: ...
+
+def foo(*args: int | str, **kw: int | Foo) -> None:
+    pass
+[builtins fixtures/tuple.pyi]
+
 [case testTypeCheckOverloadWithImplTooSpecificRetType]
 from typing import overload, Any