home-manager: import modules relative to the location

[kalbasit]

I pin the home-manager in my configuration and there's no home-manager channel available, this PR removes the dependency on the channel.

[rycee]

Hmm, won't this be problematic for people pulling Home Manager directly from the online tarball? I.e., having something like

programs.home-manager.path = https://github.com/rycee/home-manager/archive/master.tar.gz

in their configuration. Seems to me that the import ../modules would then refer to the modules of the running Home Manager, not the most recently downloaded one.

[kalbasit]

That's interesting. I've always thought the first home-manager you install goes away in favor of the one in programs.home-manager.path per the implementation: https://github.com/rycee/home-manager/blob/ef29f321e071cc4ebea35560ef93aec66a1032f2/modules/programs/home-manager.nix#L36-L41

I think the right step is to unify them in one and your work on #475 is a step forward in the right direction.

What should we do with this PR though? It caught me off guard that it referenced a channel when you expect a source to be self-contained.

[rycee]

Sorry, I had a closer look and I believe this change is safe. The ../modules should still refer to the newly downloaded modules even though it doesn't go the detour through <home-manager>.

[rycee]

Rebased to master in 30f3baa. Thanks!