home-manager: set FLAKE_ARG with HOME_MANAGER_PATH

[usertam]

Description

I use a flake setup with home-manager. Currently setting programs.home-manager.path will still result in:

No configuration file found. Please create one at ~/.config/home-manager/home.nix

And so I have to either ln -s <dotfiles> ~/.config/home-manager or each time do home-manager switch --flake <dotfiles> which kinda defeats the purpose of having programs.home-manager.path.

I think it makes sense for home-manager to set FLAKE_ARG automatically when both programs.home-manager.path and $path/flake.nix exist.

Checklist

• Change is backwards compatible.

• Code formatted with ./format.

• Code tested through nix-shell --pure tests -A run.all or nix develop --ignore-environment .#all using Flakes.

• Test cases updated/added. See example.

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module

  • Added myself as module maintainer. See example.

Maintainer CC

[usertam]

I just picked the edit here, let me know if a squash is needed.

[usertam]

I think I might have misunderstood programs.home-manager.path. Originally I thought it was like environment.darwinConfig but then it was actually used for the home-manager package itself, and not the config. Both my usage and this PR are wrong.

In this case I think an extra option like programs.home-manager.config would be more proper.