Reprocess decorators instead of the function they decorate

mypy/checker.py

@@ -610,9 +610,11 @@ def _visit_func_def(self, defn: FuncDef) -> None:
         """Type check a function definition."""
         self.check_func_item(defn, name=defn.name())
         if defn.info:
-            if not defn.is_dynamic() and not defn.is_overload:
-                # If the definition is the implementation for an overload, the legality
-                # of the override has already been typechecked.
+            if not defn.is_dynamic() and not defn.is_overload and not defn.is_decorated:
+                # If the definition is the implementation for an
+                # overload, the legality of the override has already
+                # been typechecked, and decorated methods will be
+                # checked when the decorator is.
                 self.check_method_override(defn)
             self.check_inplace_operator_method(defn)
         if defn.original_def:

test-data/unit/fine-grained.test

@@ -1439,6 +1439,36 @@ a.py:3: note: (Perhaps setting MYPYPATH or using the "--ignore-missing-imports"
 ==
 ==
 
+[case testDecoratorMethodCompat]
+from typing import Callable, List, TypeVar
+import x
+
+class Base: pass
+_Base = TypeVar('_Base', bound=Base)
+
+def dec(f: Callable[[_Base], int]) -> Callable[[_Base], List[int]]: pass
+
+class B(Base):
+    def foo(self) -> List[int]: pass
+
+class A(B):
+    @dec
+    def foo(self) -> int:
+        x.lol()
+        return 12
+
+[file x.py]
+def lol() -> str: pass
+[file x.py.2]
+def lol() -> int: pass
+[file x.py.3]
+def lol() -> str: pass
+
+[builtins fixtures/list.pyi]
+[out]
+==
+==
+
 [case testPreviousErrorInDecoratedFunction]
 import a
 [file a.py]