Filter prerelease versions in package iterators by default

[wickman]

Pip has the --pre flag -- we should allow similar behavior.

[jsirois]

OK - modern pip does this via packaging which has only been around since 2014. We support setuptools>=2.2,<16 and 2.2 does not use packaging. I have not dug deeper, but I want to take a bit more care if I implement this, so I'm going to drop from the 1.1 release and move to a 1.2 milestone.

[daveFNbuck]

+1, pulling in prerelease versions is probably worse than not supporting old setuptools. The logic is pretty simple, perhaps we could just reimplement it if old setuptools support is a priority.

[jsirois]

OK - looking back into this, it looks like the only version of setuptools that depends on packaging is 7.0b1. The 7.0 version doesn't use packaging and the 8.0 version uses it, but it pulls from a vendored version. So one option is to exclude 7.0b1, ie add !=7.0b1 to our requirement string, and then add our own dependency on packaging (16.8) at a top level to pick up packaging.specifiers.SpecifierSet which has the logic we need with a prereleases flag we can toggle.

I'll take a spin at this presently.

[daveFNbuck]

Thanks @jsirois!

[jsirois]

This is in and will go out with the 1.2.0 release - likely to be published and consumed by pants in this Friday's 1.3.0.dev8 pants release.

[daveFNbuck]

Thanks again for the quick turnaround on this!