How to use nixpkgs directly from lua?

[starptr]

I'm trying to use a binary, e.g. pkgs.hello, from lua. Although vim.system can use a binary that's added in extraPackages in the neovim-overlay.nix, I believe it is simply looking up the binary from path, which is a bit impure. Is it possible to explicitly call a package from nixpkgs?

[mrcjkb]

Calling a package from nixpkgs would be impure, too.
I'm guessing you mean you want Neovim to only see packages that are included in extraPackages?

You could build a wrapper that unsets PATH first. I don't think you'd really want to do that though. The point of Nix is not to isolate the environment of a package at runtime, it's to have input-reproducibility when building.

I prefer to use devShells to manage external dependencies. For example, some language servers can slow you down if you only want to quickly look at something. By having them in devShells, I can easily disable them without having to change my Neovim config.

[starptr]

Not exactly. As an example of a wrapped nix package (i.e. not neovim), you can write bash scripts inline in nix like e.g. ${pkgs.ripgrep}/bin/rg foo. So, you can package bash scripts in nix which have runtime dependencies on binaries both inside and outside of the nix store. Whichever is more appropriate definitely depends on a case-by-case basis. I think the lua init scripts in kickstart-nix.nvim are similar; sometimes you want them to have runtime dependencies that are not in the nix store like in your example so that the caller of the neovim binary can swap language servers at runtime. But there are scenarios where the lua init script depends on something that shouldn't need to change (i.e. the caller of the neovim binary should not be able to accidentally change/remove the runtime dependency), and for those situations, being able to refer directly to the nix store is nice.

As a concrete example, I'm invoking an executable that tells neovim what the system theme is. The caller of my neovim distribution should not be able to "dependency inject" this executable. If I can directly refer to the binary in the nix store from my lua script, then it is more durable than if I'm just referring to the binary by name. In other words, how can I do the ${pkgs.ripgrep}/bin/rg trick (like in a bash script), but in a lua init script instead?

[mrcjkb]

You can do that via plugin configs.
Plugins don't have to be a derivation, they can also be an attrset.

[starptr]

Thanks. For posterity: you can write vimscript in the plugin attrset's config property. This property ends up here, which is inlined here, which ends up here as an IFD file containing vimscript, which init.lua will call at the end.

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Not sure if this is related to the original question, but what does the runtime property do? I couldn't find mention of it in nixpkgs.

[mrcjkb]

You don't have to use Vimscript, you can also use Lua.

wrapNeovimUnstable is (as the name suggests) unstable and changes quite often (The reason I see it as safe to use is because I can pin it in my flake).

I'm not sure what the runtime attr is/was for. It may be an old attribute that has been removed by now.

[starptr]

Oh yes that's a good point. I'm a little more hesitant to use p.plugin.passthru.initLua atm because p.config is mentioned in the util function to normalize the plugin attrset, whereas the initLua attribute isn't mentioned anywhere else in nixpkgs (although I did see the effort to address this in NixOS/nixpkgs#172538). Also, I didn't realize wrapNeovimUnstable meant that the function itself has an unstable interface 😅, so that's good to keep in mind if I update the flake inputs.