pkg_resources: Wrong exception raised on parse error

Due to https://github.com/pypa/setuptools/pull/2137 parse errors raise pkg_resources.extern.packaging.requirements.InvalidRequirement instead of packaging.requirements.InvalidRequirement.

I believe this is happening because pkg_resources imports the vendored packaging.requirements module.

Reproducer:

from pkg_resources import Requirement
from packaging.requirements import InvalidRequirement
from pkg_resources.extern.packaging.requirements import InvalidRequirement as ExternInvalidRequirement

try:
    Requirement.parse(".")
except InvalidRequirement as err:
    print(type(err))
except ExternInvalidRequirement  as err:
    print(type(err))

$ python test.py
<class 'pkg_resources.extern.packaging.requirements.InvalidRequirement'>

[lkollar]

What makes you think that’s the wrong exception?

Sorry, I should have worded this differently. I think it’s more correct to say, it is not immediately obvious that setuptools vendors packaging and thus the exception type is based on the internal vendoring layout. I think this can surprise users who are not familiar with the fact the all dependencies are vendored. It also exposes an implementation detail on the public API.

I agree that exposing RequirementParseError or some other custom exception would be nicer, but I’m sure I’m missing some history here as @jaraco had a reason not do this in #2137.

[Eric-Arellano]

The other option I see

The third option, imo, is to restore RequirementParseError. It looks like it was only about 9 lines of code. By restoring it, you may be able to avoid a more complex change to your vendoring setup. (I know vendoring can be tricky - we vendor pip with https://github.com/pantsbuild/pex.)