gh-148680: Replace internal names with type_reprs of objects in string representations of ForwardRef

[DavidCEllis]

This adds a new ForwardRef.__resolved_forward_str__ attribute which takes the __forward_arg__ and replaces any internal __annotationlib_name_x__ names with the type_repr of the object they represent.

Before:

ForwardRef('ref | __annotationlib_name_1__', is_class=True, owner=<class '__main__.Example'>)
ref | __annotationlib_name_1__

After:

ForwardRef('ref | str', is_class=True, owner=<class '__main__.Example'>)
ref | str

This approach replaces the extra_names with their type_repr when the forwardref is evaluated to a string. I'm fairly sure that trying to get the original names as they are in the source would be both slower and significantly more complicated.

This logic is largely based on something I already have for my reannotate library.

• Issue: annotationlib - evaluating forward references in STRING format can 'leak' internal names #148680

[JelleZijlstra]

Can you make the tests rely less on direct assignment to __extra_names__? I don't care too much about the behavior if you manually construct ForwardRefs and set attributes on them, what matters is the buggy behavior with things you get from get_annotations.

[DavidCEllis]

Yes, I can do that here. This was partly done to avoid the owner=... part of the repr.

The other example of this in test_evaluate_string_format_extra_names exists largely to exercise the logic for the single identifier case. I'm actually not sure you can get the single identifier case with standard get_annotations?

I need this in reannotate for splitting up unions within forward references but unless you're doing similar manipulations I'm not sure this is a case you can get?

Perhaps the isidentifier special case should be removed? The other logic should work for it anyway.

[JelleZijlstra]

We might need to cache this, it's probably pretty slow. What do you think?

[DavidCEllis]

This is in fact, not very fast. Definitely worth caching if it's going to be accessed frequently.

[DavidCEllis]

>>> a_anno
ForwardRef('unknown | str | int | list[str] | tuple[int, ...]', is_class=True, owner=<class '__main__.Example'>)
>>> b_anno
ForwardRef('unknown', is_class=True, owner=<class '__main__.Example'>)

>>> a = timeit(lambda: a_anno.__resolved_forward_str__, number=10_000)
>>> b = timeit(lambda: b_anno.__resolved_forward_str__, number=10_000)
>>> a
0.18359258100008446
>>> b
0.0018204959997092374
>>> a / b
100.8475607907994