feat: errors.py

[henryiii]

This moves the ExceptionGroup backport into errors.py, and adds an ErrorCollector, based on the one in pyproject-metadata, see here. Pulled out of #847 in support of #1065.

No docs for this module (yet?), and ErrorCollector doesn't have an underscore, but maybe it should, since it's designed for our use. Edit: made it private.

This ErrorCollector doesn't have a toggle to turn off error collection, since it wasn't needed here (and probably not needed for any new API that always raises ExceptionGroups), though maybe it's still handy for debugging?

• feat: add errors module for ExceptionGroups (move only)
• feat: add ErrorCollector (All ErrorCollector changes in this commit)

[sirosen]

FWIW, this version of ErrorCollector provides the things I was wanting when I tried it: on_exit() and error() (the inner append() helper).

[sirosen]

I have a question about __all__, the class names, and the module name:

Is packaging.errors meant to be a public interface? Users presumably may want it to get packaging.errors.ExceptionGroup.

But should ErrorCollector be public? Does it make sense to name it _ErrorCollector to mark it internal to packaging?

[henryiii]

No docs for this module (yet?), and ErrorCollector doesn't have an underscore, but maybe it should, since it's designed for our use.

(above)

Yes on the packaging.errors.ExceptionGroup, users need it to handle ExceptionGroup before 3.11.