Better integration into package manager when loading third-party plugins

[zimbatm]

It would be great if direnv would have something like a .direnv.d or even environment variables to load third party plugins. I think it is time to package nix-direnv in nixpkgs itself.

Originally posted by @Mic92 in #3 (comment)

[zimbatm]

@Mic92 direnv looks in ~/.config/direnv/lib/*.sh for additional libs. (since v2.21)

Like you said it doesn't play nicely with package managers but I am open to suggestions. I don't know how bad it would be to load arbitrary code from the system yet.

[zimbatm]

Another experiment I have is a new source_url stdlib function over here: direnv/direnv#562
That might be better as it puts the .envrc write in control of the version that is being loaded.

[Mic92]

For nix we would need a search path for full integration to load plugins from all possible user and system profiles.

something like: DIRENV_PLUGIN_PATH=$HOME/.nix-profile/lib/direnv/:/run/current-system/sw/lib/direnv:/nix/var/nix/profiles/default/lib/direnv

If not set direnv could fallback to a compiled-in PREFIX, i.e

DIRENV_PLUGIN_PATH=/usr/local/lib/direnv/

if PREFIX == /usr/local/

For other package manager is is usually fine to only lookup in PREFIX.

[Mic92]

Now nix-direnv is loaded from the nix-profile: https://github.com/nix-community/nix-direnv#home-manager

[Mic92]

I think I am fine with the status quo of using home-manager to load this.