Stubtest: check that the stub is abstract if the runtime is, even when the stub is an overloaded method (#14955)

#13323 means that stubtest will currently emit an error if the runtime
is decorated with `@abstractmethod` but the stub is not, but _only_ if
the stub is not an overloaded function, as overloaded functions have a
different internal representation in mypy. This PR fixes that
discrepancy.

Author: AlexWaygood

mypy/stubtest.py

@@ -1052,6 +1052,17 @@ def verify_overloadedfuncdef(
         if not callable(runtime):
             return
 
+    # mypy doesn't allow overloads where one overload is abstract but another isn't,
+    # so it should be okay to just check whether the first overload is abstract or not.
+    #
+    # TODO: Mypy *does* allow properties where e.g. the getter is abstract but the setter is not;
+    # and any property with a setter is represented as an OverloadedFuncDef internally;
+    # not sure exactly what (if anything) we should do about that.
+    first_part = stub.items[0]
+    if isinstance(first_part, nodes.Decorator) and first_part.is_overload:
+        for msg in _verify_abstract_status(first_part.func, runtime):
+            yield Error(object_path, msg, stub, runtime)
+
     for message in _verify_static_class_methods(stub, runtime, object_path):
         yield Error(object_path, "is inconsistent, " + message, stub, runtime)
 

mypy/test/teststubtest.py

@@ -1475,7 +1475,10 @@ def test_metaclass_abcmeta(self) -> Iterator[Case]:
     @collect_cases
     def test_abstract_methods(self) -> Iterator[Case]:
         yield Case(
-            stub="from abc import abstractmethod",
+            stub="""
+            from abc import abstractmethod
+            from typing import overload
+            """,
             runtime="from abc import abstractmethod",
             error=None,
         )
@@ -1504,15 +1507,64 @@ def some(self) -> None: ...
             """,
             error=None,
         )
-        # Runtime can miss `@abstractmethod`:
         yield Case(
             stub="""
             class A3:
+                @overload
+                def some(self, other: int) -> str: ...
+                @overload
+                def some(self, other: str) -> int: ...
+            """,
+            runtime="""
+            class A3:
+                @abstractmethod
+                def some(self, other) -> None: ...
+            """,
+            error="A3.some",
+        )
+        yield Case(
+            stub="""
+            class A4:
+                @overload
+                @abstractmethod
+                def some(self, other: int) -> str: ...
+                @overload
+                @abstractmethod
+                def some(self, other: str) -> int: ...
+            """,
+            runtime="""
+            class A4:
+                @abstractmethod
+                def some(self, other) -> None: ...
+            """,
+            error=None,
+        )
+        yield Case(
+            stub="""
+            class A5:
+                @abstractmethod
+                @overload
+                def some(self, other: int) -> str: ...
+                @abstractmethod
+                @overload
+                def some(self, other: str) -> int: ...
+            """,
+            runtime="""
+            class A5:
+                @abstractmethod
+                def some(self, other) -> None: ...
+            """,
+            error=None,
+        )
+        # Runtime can miss `@abstractmethod`:
+        yield Case(
+            stub="""
+            class A6:
                 @abstractmethod
                 def some(self) -> None: ...
             """,
             runtime="""
-            class A3:
+            class A6:
                 def some(self) -> None: ...
             """,
             error=None,