Check for abstract base class definitions with no abstractmethods

[Zac-HD]

from abc import ABC, ABCMeta, abstractmethod

class Base(ABC):  # I'd like a lint error here if there are no @abstract* decorated methods

    # @abstractmethod
    def method(self):
        ...

class MyABC(metaclass=ABCMeta):  # and here too for the same reason
    pass

Suggested message: {classname} is an abstract base class, but it has no abstract methods. Remember to use @abstractmethod, @abstractclassmethod, and/or @abstractproperty decorators.

We might also want to emit a warning for a probably-missing-decorator on any method of an ABC where the whole method body is ..., even if there are some abstract-decorated methods on the class.

[cooperlees]

I can't see how this could draw false positives ... so can do nothing but help. I feel this fits things bugbear looks for ... PR will be accepted.

[jakkdl]

I'm starting on a PR now!

We might also want to emit a warning for a probably-missing-decorator on any method of an ABC where the whole method body is ..., even if there are some abstract-decorated methods on the class.

How about extending this to the body being anything but pass, ... or string constants - to also catch

# @abstractmethod
def method(self):
  """my abstract method"""
  pass

Similar to pyright's check for @overload with an implementation https://github.com/microsoft/pyright/blob/6fa755c025cb5b18838d8bfdd85761184afa45f1/packages/pyright-internal/src/analyzer/parseTreeUtils.ts#L1999

[Zac-HD]

Closed by #274.

[jakkdl]

If you also want

We might also want to emit a warning for a probably-missing-decorator on any method of an ABC where the whole method body is ..., even if there are some abstract-decorated methods on the class.

you can open a separate issue for it, should be an easy one as well :)

[cooperlees]

I'm easy - I was going to release a new version today - Should we wait for this?

[Zac-HD]

Nah, let's release what we've got now and let future features take care of themselves.

(though Cooper, you might want to copy the auto release set up from flake8-async to make releases really easy in future?)

[cooperlees]

I'm not a fan of that tbh as we don't have good enough change log enforcement etc. with this project so the 1 commit + release via GitHub is there enough for me imo.