How To: Use vscode-ruby-lsp with flake.nix based dev enviroment

[StoryparkNick]

Description

Hello! Thanks for this awesome set of libraries.

This is not a bug report, rather a quick info dump for anyone who uses nix flakes and vscode-ruby-lsp and wants to use the custom Ruby activation to make use of the Ruby from their flake.nix.

In essence, add a command to your flake.nix outputs, hardcoded here to use aarch64-dawin.

      # used to help vscode-ruby-lsp find the appropriate ruby and gems
      packages.aarch64-darwin.activate-ruby = pkgs.writeScriptBin "activate-ruby-nix" ''
        echo "export GEM_HOME=\"$GEM_HOME\""
        echo "export GEM_PATH=\"$GEM_PATH\""
        echo "export PATH=\"$(command -v ruby | xargs dirname):$GEM_HOME/bin:\$PATH\""
      '';

Add the follow lines to your VSCode config:

  "rubyLsp.rubyVersionManager": "custom",
  "rubyLsp.customRubyCommand": "eval \"$(nix run .#activate-ruby)\"",

Restart code, this will ensure the GEM_HOME, GEM_PATH and PATH env variables are set correctly, and vscode-ruby-lsp should now be able to find the appropriate Ruby exposed by your flake.

[StoryparkNick]

Closing this issue as it requires no action from the maintainers (although if there's a more appropriate label I'd appreciate it!).

Apologies if this feels like clutter but I often search issue trackers as a first point of call so hopefully this info is helpful to someone!

[vinistock]

Thank you for the kind words! Would you like to put a PR up to add these instructions to our version managers documentation? We can include a section for Nix with the commands and configuration you mentioned.

[omnibs]

Thank you for posting this! Your solution helped me make the extension work on a ruby-nix-enabled repo!

ruby-nix gives us a ruby with a read-only GEM_HOME, so I had to:

• Give the extension access to an "unlocked" ruby
• Give the extension a writable GEM_PATH and GEM_HOME

I made an overlay based on your script:

self: super: {
  activate-ruby-lsp = (super.writeShellScriptBin "activate-ruby-lsp" ''
    echo "export GEM_PATH=${builtins.toString ./path/to/lsp-gems}"
    echo "export GEM_HOME=${builtins.toString ./path/to/lsp-gems}"
    echo "export PATH=\"${super.ruby}/bin:\$GEM_HOME/bin:\$PATH\""
  '');
}

And my extension settings were slightly different too:

  "rubyLsp.rubyVersionManager": {
    "identifier": "custom"
  },
  "rubyLsp.customRubyCommand": "eval \"$(activate-ruby-lsp)\""

[Jeffrey04]

Just out of curiosity, why wouldn't this setup work?

"rubyLsp.rubyVersionManager": {
    "identifier": "custom"
},
"rubyLsp.customRubyCommand": "nix develop /Users/jeffrey04/Projects/home-manager/devenvs/ruby-3.3",
"rubyLsp.bundleGemfile": "/Users/jeffrey04/Projects/ruby-tools/ship_it/Gemfile"

I can't put ruby-lsp to the project Gemfile, hence I am using the bundleGemfile feature. On the other hand I use nix develop to setup a ruby dev environment, so i suppose calling nix develop is good enough, but it doesn't seem to work, even adapting the setup doesn't work either.

2025-07-25 15:26:16.780 [info] (ship_it) Running command: `nix develop /Users/jeffrey04/Projects/home-manager/devenvs/ruby-3.3 && ruby -EUTF-8:UTF-8 '/Users/jeffrey04/.vscode-oss/extensions/shopify.ruby-lsp-0.9.31/activation.rb'` in /Users/jeffrey04/Projects/ruby-tools/ship_it using shell: /Users/jeffrey04/.nix-profile/bin/bash

this is all i get from the output tag for ruby-lsp

and this is the screenshot of the ruby file type in status bar

EDIT: submitted a patch #3691