Fix propagation of AttributeErrors raised by exposed descriptors

[gschaffner]

Closes #478.

This uses inspect.getattr_static to avoid triggering the descriptor lookup that hasattr usually triggers. The logic also needs a fallback to hasattr since getattr_static "may not be able to retrieve all attributes that getattr can fetch (like dynamically created attributes)".

Per the docs, getattr_static "may find attributes that getattr can’t (like descriptors that raise AttributeError)". I am not aware of any edge cases where hasattr will return False but where getattr_static will succeed without raising an AttributeError (although I did not not dive into CPython's getattr_static implementation to look for such cases), but perhaps there is some edge case that makes using getattr_static a bad choice here. If you know of a better way to fix #478 please let me know :)

I was a bit liberal with adding the tests for multiple configs since the runtime it adds is negligible and extra safety is good. I also slightly broke PEP 8 line length in the tests I added—please change my code style if RPyC uses a different style :)

[comrumino]

Sorry for the slow response time!

I think my only gripe would be potential performance implications of try-except blocks. Typically try-except has a higher overhead than if else statement. Do you think it would be possible to change to a if-else logic flow?

[gschaffner]

Hi, and sorry for the delay!

Considering try-catch overhead makes sense. The try-catch cost can be avoided in the common case if we try-catch on getattr_static() if and only if hasattr(obj, name) is False already—see the latest commit. In cases where hasattr(obj, name) is True (which implies that getattr_static(obj, name) isn't a __get__ descriptor raising AttributeError()), this avoids both (a) try-catch and (b) calling inspect.getattr_static. However, the try-catch + getattr_static overhead would still apply to cases where hasattr() is False. My assumption is that this should be a less common case, though.

As far as I can tell, the only way to rewrite hasattr_static without any try-catch on getattr_static would be to copy the logic of inspect.getattr_static but have it return bools rather than raising. It seems a bit messy to maintain a copy of https://github.com/python/cpython/blob/v3.10.5/Lib/inspect.py#L1731-L1774 though.

I've also rebased onto master to resolve the conflict.