Package Language Servers Into Neovim Using Nix

The introduction of the language server protocol has made it easier to use a variety of different text editors for programming with hints and autocompletion instead of requiring more complex IDEs.

Unfortunately, it also means that most text editors don’t come bundled with their own language server and instead expect it to be installed separately on your machine. While there are some tools that intend to make it easier to install language servers from inside Neovim, such as mason.nvim or lazy-lsp.nvim, I prefer the guarantee that the Neovim package contains everything that I need to use the LSP at install time.

nix2vim

The flake nix2vim is a framework for building a Neovim package and Lua configuration with Nix. It comes with a function called neovimBuilder that can be paired with imported modules to add plugins, setup and use statements, vim options settings all in the Nix language for translation into Lua. You can also add lua sections if you need to bail out to normal Lua code.

One of the benefits of this is that you can use Nix expressions inside of the Neovim configuration, which means that nixpkgs can be included directly and rendered into Nix store paths when the final output is transpiled to Lua.

LSP Configuration

It’s easy enough to configure the LSP and include its package at the same time. In my config, I include the language server program alongside its settings:

use.lspconfig.lua_ls.setup = dsl.callWith {
  settings = {
    Lua = {
      diagnostics = {
        globals = [
          "vim"
          "hs"
        ];
      };
    };
  };
  capabilities = dsl.rawLua "require('cmp_nvim_lsp').default_capabilities()";
  cmd = [ "${pkgs.lua-language-server}/bin/lua-language-server" ];
};

In this case, I’m using dsl functions to mimic certain Lua calls and to bail out for more complex code. For the actual language server command, I’m identifying the store path to the nixpkgs object and including the program directly.

When the Neovim package is built, the language server becomes a dependency, so therefore you have a guarantee that the LSP is ready when you launch Neovim. You can also imagine calling the Neovim package as a function and passing the specific version of the language server based on the needs of the project, and/or including only the language servers you need for those projects with a project-specific Neovim.