Separate global cache/registry and bin/package management directories and files

[Destroy666x]

Problem

Mixing these together is definitely not a great idea. It makes automated setups harder as they have to go for specific files/subdirs instead of just one directory, if you don't want to copy random package cache between machines. It also makes cleanup etc. harder and more confusing as can be seen by e.g. the advice here: #3289 (comment) (and the whole issue has been hanging on "needs input" status for few years now).

Proposed Solution

Separate these directories and allow separate environment variables for them, e.g. CARGO_HOME and CARGO_CACHE.

Some examples from other package managers:

• npm/yarn: https://docs.npmjs.com/cli/v8/using-npm/config#cache
• PHP's Composer: https://getcomposer.org/doc/03-cli.md#composer-cache-dir
• C#'s NuGet: https://learn.microsoft.com/en-us/nuget/consume-packages/managing-the-global-packages-and-cache-folders

Notes

No response

[epage]

If I'm understanding correctly, this appears to be a duplicate of #1734

[Destroy666x]

Not quite, it's a similar request which I also support, but it's related. That is more about following XDG standard (which also separates cache if you follow it very well), this is more focused on just tidying up directory structure and separating cache and the rest of global files, on all systems.

[epage]

Solving this kind of problem needs to be done in the context of #1734, so I'm closing in favor of that. We wouldn't want to design part way on this and realize there is a problem. Granted, if we decide support for these variables is important, it'll likely be stable in one of the earliest stages of the effort.