Fix overloaded static methods on instances (#13482)

Author: ilevkivskyi

mypy/checkmember.py

@@ -302,7 +302,7 @@ def analyze_instance_member_access(
             mx.msg.cant_assign_to_method(mx.context)
         signature = function_type(method, mx.named_type("builtins.function"))
         signature = freshen_function_type_vars(signature)
-        if name == "__new__":
+        if name == "__new__" or method.is_static:
             # __new__ is special and behaves like a static method -- don't strip
             # the first argument.
             pass
@@ -315,6 +315,8 @@ def analyze_instance_member_access(
                     signature, dispatched_type, method.is_class, mx.context, name, mx.msg
                 )
             signature = bind_self(signature, mx.self_type, is_classmethod=method.is_class)
+        # TODO: should we skip these steps for static methods as well?
+        # Since generic static methods should not be allowed.
         typ = map_instance_to_supertype(typ, method.info)
         member_type = expand_type_by_instance(signature, typ)
         freeze_type_vars(member_type)

test-data/unit/check-overloading.test

@@ -6527,3 +6527,20 @@ class Test:
     def foo(self, arg: Sequence[A]) -> None: ...
     def foo(self, arg: Union[Sequence[E], Sequence[A]]) -> None:
         ...
+
+[case testOverloadedStaticMethodOnInstance]
+from typing import overload
+
+class Snafu(object):
+    @overload
+    @staticmethod
+    def snafu(value: bytes) -> bytes: ...
+    @overload
+    @staticmethod
+    def snafu(value: str) -> str: ...
+    @staticmethod
+    def snafu(value):
+        ...
+reveal_type(Snafu().snafu('123'))  # N: Revealed type is "builtins.str"
+reveal_type(Snafu.snafu('123'))  # N: Revealed type is "builtins.str"
+[builtins fixtures/staticmethod.pyi]