deprecate support for old setuptools, plan for drop in 4.0

[RonnyPfannschmidt]

modern setuptools with environment markers within requirements is released since quite a while now (setuptools 30 series, we are now at setuptools 40)

we should plan to remove the hacks in setup.py and move most of it to setup.cfg

[asottile]

For the most part, as long as pytest provides wheels this probably won't impact many (if any) as the wheel marker support works all the way back to the pip 6.x era

[nicoddemus]

I guess we could apply the deprecation right away, correct?

[nicoddemus]

By "right away" I mean in features for pytest 3.8.

[RonnyPfannschmidt]

@nicoddemus i just wanted to track this as a issue first, and see some impact and then sort it out after the regressions are fixed

if nobody complains until the regressions are gone i consider it fair game

[nicoddemus]

see some impact and then sort it out after the regressions are fixed

Which regressions? The ones that might come up when we deprecate the setuptools support, or the current regressions of the pytest 3.7.0 release?

[RonnyPfannschmidt]

@nicoddemus current ones

[nicoddemus]

@RonnyPfannschmidt hmmm missed this one.

[RonnyPfannschmidt]

actually we did it in #4149

[nicoddemus]

Oh right 🤦‍♂️