Remove reliance on LegacyVersion

[jaraco]

• Remove use of packaging.version.LegacyVersion. Fixes Remove support for LegacyVersion #2497.
• Add changelog. Ref Remove support for LegacyVersion #2497.
• egg_info: avoid non-PEP440 versions from tag_date
• package_index: don't create dists with non-PEP440 versions
• Suppress the now invalid pbr version.
• Update test_egg_fragment to include a name with a dash in it. Expand on interpret_distro_name to be a tiny bit smarter about inferring the pivot separating name and version.

Summary of changes

Closes #2497.

Pull Request Checklist

• Changes have tests
• News fragment added in changelog.d/.
  (See documentation for details)

[pradyunsg]

suggestion: When you do release this, do a major version bump.

I expect that a lot of users who will complain that this is a breaking change (because their internal $corp systems depended on non-PEP 440 versions). The answer for them can then be (a) Python has been spewing out a deprecation warning about this for months, (b) it's a major version bump; deal with it, and (c) was there anything related to this change that would have made you reach out/react to it sooner?

I'd strongly suggest asking the users what setuptools could have done to make the change less disruptive, rather than arguing whether the change is important -- the users will usually care mostly due to the immediate disruption it's caused them, and taking that moment to ask them "hey, how do you monitor for upcoming changes" is a useful exercise for both parties. :)

[pradyunsg]

Wait, there was never a release which spewed out deprecation warnings?

Hmm... I think doing a major version series that does that is a worthwhile thing -- otherwise, this is basically a major change being made without any heads up to any of the downstream users; who sometimes can't control the exact version of setuptools they're using (eg: in pip's isolated build environments).

Anyway, that's my two cents. I'mma step away and let y'all decide how you wanna manage changes around this project. :)

[jaraco]

Good idea. In #2840, I introduce such a warning. I'd expected that introducing that warning would have happened from the packaging package, but because it's vendored and pinned, that warning has been suppressed.

[pradyunsg]

Hiya @jaraco! Anything I can do to help move this forward?

/cc @abravalheri as well. :)

[jaraco]

The deprecation has been in place for 15 months. Let's remove support.

[pradyunsg]

Not a setuptools maintainer, but LGTM!