Fix difference between callables and callback protocols

Fixes #15926 (comment)

Author: hauntsaninja

mypy/checkmember.py

@@ -779,12 +779,12 @@ def analyze_var(
 
         call_type: Optional[ProperType] = None
         if var.is_initialized_in_class and (not is_instance_var(var) or mx.is_operator):
-            if isinstance(typ, FunctionLike) and not typ.is_type_obj():
-                call_type = typ
-            elif var.is_property:
+            if var.is_property and (not isinstance(typ, FunctionLike) or typ.is_type_obj()):
                 call_type = get_proper_type(_analyze_member_access("__call__", typ, mx))
             else:
                 call_type = typ
+            if isinstance(call_type, Instance) and call_type.type.get_method("__call__"):
+                call_type = get_proper_type(_analyze_member_access("__call__", typ, mx))
 
         if isinstance(call_type, FunctionLike) and not call_type.is_type_obj():
             if mx.is_lvalue:

test-data/unit/check-protocols.test

@@ -4127,3 +4127,30 @@ class P(Protocol):
 
 class C(P): ...
 C(0)  # OK
+
+
+[case testCallbackProtocolMethod]
+from typing import Callable, Protocol
+
+class CallbackProtocol(Protocol):
+    def __call__(self, __x: int) -> int: ...
+
+def make_method_protocol() -> CallbackProtocol: ...
+def make_method_callable() -> Callable[[int], int]: ...
+
+class ClsProto:
+    meth = make_method_protocol()
+
+class ClsCall:
+    meth = make_method_callable()
+
+reveal_type(ClsProto.meth)  # N: Revealed type is "__main__.CallbackProtocol"
+reveal_type(ClsCall.meth)  # N: Revealed type is "def (builtins.int) -> builtins.int"
+
+def takes(p: ClsProto, c: ClsCall) -> None:
+    reveal_type(p.meth(0))  # E: Invalid self argument "ClsProto" to attribute function "meth" with type "Callable[[int], int]" \
+                            # E: Too many arguments for "__call__" of "CallbackProtocol" \
+                            # N: Revealed type is "builtins.int"
+    reveal_type(c.meth(0))  # E: Invalid self argument "ClsCall" to attribute function "meth" with type "Callable[[int], int]" \
+                            # E: Too many arguments \
+                            # N: Revealed type is "builtins.int"