class members are not listed when class is an ABC

[jairideout]

If a class derives from an ABC using the abc module, its members are not included in the generated autosummary RST (regardless of whether the derived class is abstract or concrete at runtime).

This happens because the abc module always sets empty __slots__ on abstract classes, and __slots__ take precedence over the class __dict__ when automodsumm searches for class members (see these lines). Thus, any class with an ABC in its inheritance chain will have an empty __slots__ attribute (unless other classes have added attributes to __slots__ along the way).

I'll have a PR in shortly with a minimal unit test case that reproduces the issue, and will include a potential fix.

The issue was originally discovered here: sunpy/sunpy#2348

[jairideout]

I have a PR in with an example and potential fix: #53

[jairideout]

Note: while implementing the fix, I found that this is only an issue in Python 3 when :inherited-members: is not in effect.