BUG: Fix an issubclass failure for protocols with overloaded methods (#9904)

Co-authored-by: Shantanu <[email protected]>

Author: BvB93

mypy/subtypes.py

@@ -763,7 +763,7 @@ def non_method_protocol_members(tp: TypeInfo) -> List[str]:
 
     for member in tp.protocol_members:
         typ = get_proper_type(find_member(member, instance, instance))
-        if not isinstance(typ, CallableType):
+        if not isinstance(typ, (Overloaded, CallableType)):
             result.append(member)
     return result
 

test-data/unit/check-protocols.test

@@ -2382,7 +2382,7 @@ y: PBad = None  # E: Incompatible types in assignment (expression has type "None
 [out]
 
 [case testOnlyMethodProtocolUsableWithIsSubclass]
-from typing import Protocol, runtime_checkable, Union, Type
+from typing import Protocol, runtime_checkable, Union, Type, Sequence, overload
 @runtime_checkable
 class P(Protocol):
     def meth(self) -> int:
@@ -2404,6 +2404,17 @@ if issubclass(cls, P):
     reveal_type(cls)  # N: Revealed type is "Type[__main__.C]"
 else:
     reveal_type(cls)  # N: Revealed type is "Type[__main__.E]"
+
+@runtime_checkable
+class POverload(Protocol):
+    @overload
+    def meth(self, a: int) -> float: ...
+    @overload
+    def meth(self, a: str) -> Sequence[float]: ...
+    def meth(self, a):
+        pass
+
+reveal_type(issubclass(int, POverload))  # N: Revealed type is "builtins.bool"
 [builtins fixtures/isinstance.pyi]
 [typing fixtures/typing-full.pyi]
 [out]