Fix untyped decorator check for class instances (#5509)

Running `mypy --disallow-untyped-decorators` when the decorator is a typed callable instance produces an error even though `reveal_type` shows the correct type.

Related to #4191

mypy/checker.py

@@ -4220,9 +4220,19 @@ def is_typed_callable(c: Optional[Type]) -> bool:
 
 
 def is_untyped_decorator(typ: Optional[Type]) -> bool:
-    if not typ or not isinstance(typ, CallableType):
+    if not typ:
         return True
-    return typ.implicit
+    elif isinstance(typ, CallableType):
+        return not is_typed_callable(typ)
+    elif isinstance(typ, Instance):
+        method = typ.type.get_method('__call__')
+        if method:
+            return not is_typed_callable(method.type)
+        else:
+            return False
+    elif isinstance(typ, Overloaded):
+        return any(is_untyped_decorator(item) for item in typ.items())
+    return True
 
 
 def is_static(func: Union[FuncBase, Decorator]) -> bool:

test-data/unit/check-flags.test

@@ -132,6 +132,45 @@ def d3(p) -> Any:
 @d1  # E: Untyped decorator makes function "f" untyped
 def f() -> None: pass
 
+[case testDisallowUntypedDecoratorsCallableInstance]
+# flags: --disallow-untyped-decorators
+from typing import Callable
+
+class TypedDecorator:
+    def __call__(self, c: Callable) -> Callable:
+        return function
+
+class UntypedDecorator:
+    def __call__(self, c):
+        return function
+
+@TypedDecorator()
+def f() -> None: pass
+
+@UntypedDecorator()  # E: Untyped decorator makes function "g" untyped
+def g() -> None: pass
+
+@TypedDecorator()
+@UntypedDecorator()  # E: Untyped decorator makes function "h" untyped
+def h() -> None: pass
+
+@UntypedDecorator()  # E: Untyped decorator makes function "i" untyped
+@TypedDecorator()
+def i() -> None: pass
+
+reveal_type(f)  # E: Revealed type is 'def (*Any, **Any) -> Any'
+reveal_type(g)  # E: Revealed type is 'Any'
+reveal_type(h)  # E: Revealed type is 'def (*Any, **Any) -> Any'
+reveal_type(i)  # E: Revealed type is 'Any'
+
+[case testDisallowUntypedDecoratorsNonCallableInstance]
+# flags: --disallow-untyped-decorators
+class Decorator:
+    pass
+
+@Decorator()  # E: "Decorator" not callable
+def f() -> None: pass
+
 [case testSubclassingAny]
 # flags: --disallow-subclassing-any
 from typing import Any

test-data/unit/check-overloading.test

@@ -4849,3 +4849,27 @@ reveal_type(b)                   # E: Revealed type is 'builtins.int'
 c = single_plausible([Other()])  # E: List item 0 has incompatible type "Other"; expected "str"
 reveal_type(c)                   # E: Revealed type is 'builtins.str'
 [builtins fixtures/list.pyi]
+
+[case testDisallowUntypedDecoratorsOverload]
+# flags: --disallow-untyped-decorators
+from typing import Any, Callable, overload, TypeVar
+
+F = TypeVar('F', bound=Callable[..., Any])
+
+@overload
+def dec(x: F) -> F: ...
+@overload
+def dec(x: str) -> Callable[[F], F]: ...
+def dec(x) -> Any:
+    pass
+
+@dec
+def f(name: str) -> int:
+    return 0
+
+@dec('abc')
+def g(name: str) -> int:
+    return 0
+
+reveal_type(f)  # E: Revealed type is 'def (name: builtins.str) -> builtins.int'
+reveal_type(g)  # E: Revealed type is 'def (name: builtins.str) -> builtins.int'