read cache from env

[amtoine]

i was trying to help @stormasm with a strange bug of his and wanted to run something like the following to not use either my personal store nor my cache:

with-env {
    GIT_REPOS_HOME: /tmp/repos,
    GIT_REPOS_CACHE: /tmp/repos.cache
} {
    gm update-cache
}

description

this PR allows gm to read the cache location from $env.GIT_REPOS_CACHE before the XDG location and the default one.
this change happens in the get-repo-store-cache-path command and mirrors the behaviour from get-repo-store-path

Note
because the extension of the cache can now be anything, e.g. .cache in the snippet of this PR, gm can not assume that it's NUON directly

• open --raw $cache_file | from nuon is used to open the content of the cache
• to nuon | save --force $cache_file is used to dump the new cache to its file

user-facing changes

with-env {
    GIT_REPOS_HOME: /tmp/repos,
    GIT_REPOS_CACHE: /tmp/repos.cache
} {
    gm update-cache
}

can now be used to play with gm without messing with the real store of repos.

[stormasm]

@amtoine thanks for this ! I will continue to check it out and understand more how this works...

[melMass]

Agreed! we mentioned both in previous PRs