How to start ruby-lsp inside neovim in a direnv based setup?

[jessevdp]

I have a flake.nix based devShell that I activate using direnv.

The contents of my .envrc:

watch_file .ruby-version
use flake
layout ruby
PATH_add bin

The most notable part here is layout ruby which sets $GEM_HOME to a subdirectory inside the project directory.

Inside of neovim my $GEM_HOME seems to get overridden:

# On the CLI, outside of neovim
$ echo $GEM_HOME
/path/to/cwd/.direnv/ruby

# Inside of neovim
:!echo $GEM_HOME
/nix/store/k2jwbpszhzrsh0q4idxjw3gs2x5wbs7n-neovim-ruby-env/lib/ruby/gems/3.3.0

I'm assuming that since the ruby-lsp executable is run by neovim... that it is starting with the wrong $GEM_HOME.

require("lspconfig").ruby_lsp.setup({})

The contents of my LSP log:

[START][2025-02-18 11:04:06] LSP logging initiated
[ERROR][2025-02-18 11:04:06] .../vim/lsp/rpc.lua:770	"rpc"	"/path/to/cwd/.direnv/bin/ruby-lsp"	"stderr"	"Ignoring msgpack-1.7.5 because its extensions are not built. Try: gem pristine msgpack --version 1.7.5\n"
[ERROR][2025-02-18 11:04:06] .../vim/lsp/rpc.lua:770	"rpc"	"/path/to/cwd/.direnv/bin/ruby-lsp"	"stderr"	"Source locally installed gems is ignoring #<Bundler::StubSpecification name=msgpack version=1.7.5 platform=ruby> because it is missing extensions\n"
...

---

The contents of my `flake.nix` (not super important for this problem).

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-24.11";
    nixpkgs-ruby = {
      url = "github:bobvanderlinden/nixpkgs-ruby";
      inputs.nixpkgs.follows = "nixpkgs";
    };
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = {
    nixpkgs,
    nixpkgs-ruby,
    flake-utils,
    ...
  }:
    flake-utils.lib.eachDefaultSystem (system: let
      pkgs = nixpkgs.legacyPackages.${system};
      ruby = nixpkgs-ruby.lib.packageFromRubyVersionFile {
        file = ./.ruby-version;
        inherit system;
      };
    in {
      devShell = with pkgs;
        mkShell {
          buildInputs = [
            ruby
            postgresql_17
            libyaml # NOTE: for psych gem
            imagemagick # NOTE: for paperclip
          ];
        };
    });
}

[jessevdp]

I figured out that I can use direnv exec . <COMMAND> to get around my issue:

require("lspconfig").ruby_lsp.setup({
  cmd = { "direnv", "exec", ".", "ruby-lsp" },
})

I'm hoping this helps someone 😄