[WIP] Implement working scheme

[pradyunsg]

Closes #4575

This PR also:

• Builds upon fallback logic from [WIP] Implement --global and try to default to --user when it makes sense #2418 that tries to use user-scheme whenever possible, which closes Default to --user  #1668
  • "ask for forgiveness, not permission"
    • try to write a file instead of using os.access
    • (good idea with computers, not people)
• Adds a --global flag, which closes Add an explicit --global installation option #4865

I'm open to the idea of breaking this PR up but I think these changes are intertwined enough that we should consider them all in one bundle.

Since this is a topic that probably needs some discussion, I feel it'd be best to only discuss implementation related stuff here and have all the higher level discussion over at #4575.

I still need to make this refuse to install stuff in different schemes, write tests and documentation and probably more stuff. I'd appreciate some more eyeballs passing through this code though now.

TODO + self-notes

• Code
  • First Pass
    • Implement stuff in the dumbest manner.
  • Second Pass
    • Start refusing different scheme installations. (would resolve pip uninstall refuses to uninstall packags from ~/.local/lib/ #5176)
  • What about pip uninstall?
    • Think then bring up.
  • Changes based on feedback/reviews
  • Final Pass
• Tests
  • Ensure no existing tests need changing
  • Lots of tests? Just enough tests? Somewhere in the middle?
  • Think then bring up.
• Documentation
  • Options:
    • Rewrite the section "user installs"
    • Write a new "installation scheme"
  • Think then bring up.
• News
• pip config uses --global, --user, --venv; maybe they should be changed too?
  • Think then bring up.

[BrownTruck]

Hello!

I am an automated bot and I have noticed that this pull request is not currently able to be merged. If you are able to either merge the master branch into this pull request or rebase this pull request against master then it will eligible for code review and hopefully merging!

[tuukkamustonen]

@pradyunsg Do you have new plans with this, no recent discussion in #4575 at least?

[pradyunsg]

This got closed since I cleaned up the stale branches on my fork and this was one of them.

No new plans for this. Mostly just a matter of me getting/making time to do this. If I hit something unexpected, I'll make a comment over on that issue.

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.