Add NIX_PATH action input

[Gerschtli]

Hey, this adds a new input named nixpkgs as default nixpkgs channel.

Resolves #17.
Resolves #6.

[domenkozar]

Wouldn't be setting NIX_PATH #6 be somewhat the same? I quite dislike channels, ideally, we'd disable Nix installation to set up a channel altogether.

[Gerschtli]

You mean like NIX_PATH=nixpkgs=channel:nixos-19.09? In this Environment it wouldn't make any differences I think.

[Gerschtli]

I added NIX_PATH as action input and went with the backwards compatible way. Of course I can set NIX_PATH arg to required to be more strict, but this decision is up to you :)

[Gerschtli]

Rebased PR to recent changes in master

[Mic92]

I tried this branch using:

    - uses: Gerschtli/install-nix-action@4a3097b877f501d409dc2c7e95dd6c3809ba1e43
      with:
        NIX_PATH: nixpkgs=channel:nixos-unstable

but it fails finding @actions/core: https://github.com/Mic92/nur-packages/runs/658701232

What I am doing wrong?

[Gerschtli]

Try the branch nix-path, in this branch I have pushed the node_modules folder which is necessary. It will be created in the release process of this action.

[Mic92]

Thanks! Works perfectly now: https://github.com/Mic92/nur-packages/blob/master/.github/workflows/build.yml

[domenkozar]

I guess this would allow us to tell installer to skip setting up a channel and save ~10s of installation time :) NixOS/nix#3588

[Gerschtli]

Oh awesome, did know of this option!

[domenkozar]

I think I'd prefer the following behavior:

• by default it would do as currently, let installation set the channel
• nixPath: false would disable channel and enforce empty NIX_PATH
• nixPath: ... would set NIX_PATH and disable the channel

[domenkozar]

I've implemented skip_adding_nixpkgs_channel in #33 and what's missing is just adding docs for NIX_PATH

[Mic92]

Cool. I switched back to the official install-nix-action and just the NIX_PATH manually: https://github.com/Mic92/nur-packages/blob/46606aa4ceb2f7e1c6c1824e35bde4339760f666/.github/workflows/build.yml

[Gerschtli]

PTAL

[domenkozar]

Thanks for the patience @Gerschtli :)