Fix overload resolution for metaclass (#3511)

Fix #3452.

Author: elazarg

mypy/checkexpr.py

@@ -2691,8 +2691,12 @@ def overload_arg_similarity(actual: Type, formal: Type) -> int:
             else:
                 return 0
         elif isinstance(actual, TypeType):
+            item = actual.item
             if formal.type.fullname() in {"builtins.object", "builtins.type"}:
                 return 2
+            elif isinstance(item, Instance):
+                # FIX: this does not handle e.g. Union of instances
+                return overload_arg_similarity(item.type.metaclass_type, formal)
             else:
                 return 0
         else:

test-data/unit/check-classes.test

@@ -3289,6 +3289,38 @@ x3: M = cv
 
 [builtins fixtures/classmethod.pyi]
 
+[case testMetaclassOverloadResolution]
+from typing import Type, overload
+class A: pass
+
+class EM(type): pass
+class E(metaclass=EM): pass
+
+class EM1(type): pass
+class E1(metaclass=EM1): pass
+
+@overload
+def f(x: EM) -> int: ...
+@overload
+def f(x: EM1) -> A: ...
+@overload
+def f(x: str) -> str: ...
+def f(x: object) -> object: return ''
+
+e: EM
+reveal_type(f(e))  # E: Revealed type is 'builtins.int'
+
+et: Type[E]
+reveal_type(f(et))  # E: Revealed type is 'builtins.int'
+
+e1: EM1
+reveal_type(f(e1))  # E: Revealed type is '__main__.A'
+
+e1t: Type[E1]
+reveal_type(f(e1t))  # E: Revealed type is '__main__.A'
+
+reveal_type(f(''))  # E: Revealed type is 'builtins.str'
+
 -- Synthetic types crashes
 -- -----------------------