Allow stubtest to raise errors on abstract state mismatch (#13323)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>

mypy/stubtest.py

@@ -840,6 +840,18 @@ def verify_funcitem(
  if not callable(runtime):
  return
 
+ if isinstance(stub, nodes.FuncDef):
+ stub_abstract = stub.abstract_status == nodes.IS_ABSTRACT
+ runtime_abstract = getattr(runtime, "__isabstractmethod__", False)
+ # The opposite can exist: some implementations omit `@abstractmethod` decorators
+ if runtime_abstract and not stub_abstract:
+ yield Error(
+ object_path,
+ "is inconsistent, runtime method is abstract but stub is not",
+ 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

@@ -1268,6 +1268,104 @@ def test_type_var(self) -> Iterator[Case]:
  )
  yield Case(stub="C = ParamSpec('C')", runtime="C = ParamSpec('C')", error=None)
 
+ @collect_cases
+ def test_abstract_methods(self) -> Iterator[Case]:
+ yield Case(
+ stub="from abc import abstractmethod",
+ runtime="from abc import abstractmethod",
+ error=None,
+ )
+ yield Case(
+ stub="""
+ class A1:
+ def some(self) -> None: ...
+ """,
+ runtime="""
+ class A1:
+ @abstractmethod
+ def some(self) -> None: ...
+ """,
+ error="A1.some",
+ )
+ yield Case(
+ stub="""
+ class A2:
+ @abstractmethod
+ def some(self) -> None: ...
+ """,
+ runtime="""
+ class A2:
+ @abstractmethod
+ def some(self) -> None: ...
+ """,
+ error=None,
+ )
+ # Runtime can miss `@abstractmethod`:
+ yield Case(
+ stub="""
+ class A3:
+ @abstractmethod
+ def some(self) -> None: ...
+ """,
+ runtime="""
+ class A3:
+ def some(self) -> None: ...
+ """,
+ error=None,
+ )
+
+ @collect_cases
+ def test_abstract_properties(self) -> Iterator[Case]:
+ yield Case(
+ stub="from abc import abstractmethod",
+ runtime="from abc import abstractmethod",
+ error=None,
+ )
+ # Ensure that `@property` also can be abstract:
+ yield Case(
+ stub="""
+ class AP1:
+ def some(self) -> int: ...
+ """,
+ runtime="""
+ class AP1:
+ @property
+ @abstractmethod
+ def some(self) -> int: ...
+ """,
+ error="AP1.some",
+ )
+ yield Case(
+ stub="""
+ class AP2:
+ @property
+ @abstractmethod
+ def some(self) -> int: ...
+ """,
+ runtime="""
+ class AP2:
+ @property
+ @abstractmethod
+ def some(self) -> int: ...
+ """,
+ error=None,
+ )
+ # Runtime can miss `@abstractmethod`:
+ yield Case(
+ stub="""
+ class AP3:
+ @property
+ @abstractmethod
+ def some(self) -> int: ...
+ """,
+ runtime="""
+ class AP3:
+ @property
+ def some(self) -> int: ...
+ """,
+ error=None,
+ )
+
 
 def remove_color_code(s: str) -> str:
  return re.sub("\\x1b.*?m", "", s) # this works!