More compatibility with pep425tags

[di]

This PR adds logging around get_config_var as mentioned here: pypa/pip#6908 (comment)

It also fixes #171.

(cc @pradyunsg @cjerdonek)

[brettcannon]

Comments are all stylistic.

I will also say that I initially left the logging out as I wasn't sure how useful it would be since I didn't notice logging being used in 'packaging' itself.

[di]

I will also say that I initially left the logging out as I wasn't sure how useful it would be since I didn't notice logging being used in 'packaging' itself.

Hmm, maybe we should slightly change the API that pip is expecting here and make the default warn=False? That way anyone else using packaging doesn't get unexpected log messages.

[brettcannon]

@di yeah, if we are going to bother to include it I think it should be off since it's only helpful when debugging and with 'packaging' as a library I think it should be silent by default.

[brettcannon]

So with this being false, how will this ever be true such that logging actually occurs? Is the assumption people will manually change locally when they need to? Or is it in case logging comes in the future for the whole the project or through some API?

[di]

Right, great point. I think what would be best is that users can turn on logging via an argument to sys_tags and this is propagated through. I feel like this would be easiest to integrate into pip and would have the least effect on other packaging.tags users. I added a commit which does this.

[pradyunsg]

The code changes LGTM. 2 blocker concerns:

• docs: we'd want to document the new warn parameter (packaging.tags is pretty well documented so this is in line with that)
• tests: the tests seem to be failing on the CI for pypy

[pradyunsg]

Thanks @di! ^>^

@brettcannon I merged on the assumption that you're OK with post-your-approval changes, and if you're not, we can iterate on/discuss reverting specific commits if needed (though I doubt that's the case here). :)

[brettcannon]

@pradyunsg I'm fine with it. 😄