[RRFC] Respect standard file locations

Motivation ("The Why")

npm currently stores files/directories in the user's home directory, which is non-standard (at least on macOS) and messy. It also interferes with apps that expect standard folder locations to be used (for example Apple Time Machine which expects cache to be stored in ~/Library/Caches).

This is a continuation of #389, which was closed due to concerns with backwards-compatibility and not valuable enough for enough users.

I explain below why I don't see any backwards compatibility issues. These points were mentioned in the original RRFC, and I've asked for thoughts about reopening it, but received no response after 5 months which is why I'm opening a new one.

On the point of it not being valuable enough for enough users, the original RRFC is in fact the 7th most upvoted. There are certainly also lots of people who are annoyed by the current behavior, but don't care enough to look for an RRFC to upvote.

For example, for Rust's cargo it's the 5th most upvoted issue with 143 upvotes (and 1 downvote).

How

Current Behaviour

npm currently stores files/directories in the user's home directory.

Desired Behaviour

To follow standard locations, the following paths would be affected:

• The userconfig path - ~/.npm/
  I can't see why there would be any backwards compatibility issues with changing the cache location.

• The config path - ~/.npmrc
  This should be perfectly backwards compatible by looking for .npmrc in the following order (similar to git's approach):

  • $XDG_CONFIG_HOME
  • OS-standard directory
    • macOS: ~/Library/Application Support/npm/.npmrc
    • Linux: Not sure, maybe ~/.config/npm/.npmrc or the way it is now if that's truly standard
    • Windows: %AppData%\npm\.npmrc (I think)
  • ~/.npmrc

References

#389

Start by reading this RRFC alongside superseded issue #389 and its linked discussion. Establish an agreed cross-platform path policy for the listed userconfig and config locations, including backward-compatibility behavior; done means the proposal is resolved enough to guide implementation and validation.