External Gemfile, how to configure formatter?

[Jeffrey04]

So I am new to Ruby, and I am currently in a project where I should not update the project Gemfile, hence I setup ruby-lsp to refer to an external Gemfile. It seems to work fine, but I am interested to know how do I trigger formatting (can I get it to format on save?) for the project, using the gems defined by the external Gemfile?

This is my formatter settings in settings.json (I get same outcome if I change formatter from auto to rubocop)

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

  "[ruby]": {
    "editor.defaultFormatter": "Shopify.ruby-lsp",
  },

And the external Gemfile is (rubocop matches the one defined in the project)

source "https://rubygems.org"

gem "ruby-lsp"
gem "rubocop", "1.26.1"
gem "rubocop-rails"
gem "rubocop-minitest"

When I ask vscode to format my ruby code (CMD+SHIFT+P -> Format Document), it is prompting me to install a formatter extension (There is no formatter for ruby files installed)

[vinistock]

Thanks for the question. I think there are multiple things involved here.

First, you don't have to add ruby-lsp to your project's Gemfile and neither do you need to use an external one. If everything is configured correctly with Ruby activation, the Ruby LSP itself will composed a special bundle under the .ruby-lsp directory that connects to your project's main bundle. The only purpose of rubyLsp.bundleGemfile is for users who are stuck in a Ruby version older than 3.0 or that intentionally never add their development gems to their project's bundle.

Remove the rubyLsp.bundleGemfile configuration and let the LSP set up the composed bundle by itself. It will hook up to RuboCop and related configurations automatically.

What could be causing trouble is the Nix environment activation. I'm not familiar with Nix, so I don't know if the custom activation script is correct. After removing bundleGemfile, try to start the editor and check the Ruby LSP channel in the Output tab. Are there any logs that show errors? Did it get stuck somewhere?

[Jeffrey04]

in the Output tab for ruby-lsp, all i ever see is just

2025-07-27 16:56:30.669 [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/ship_it using shell: /Users/jeffrey04/.nix-profile/bin/bash

I don't see any other line apart from that and this is what the GUI reports

so i suppose a proper way to do it is to allow (notice the removal of &&)

`nix develop /Users/jeffrey04/Projects/home-manager/devenvs/ruby-3.3 --command ruby -EUTF-8:UTF-8 '/Users/jeffrey04/.vscode-oss/extensions/shopify.ruby-lsp-0.9.31/activation.rb'

Let's see if I can figure out how to submit a new feature PR for nix develop flake?

[Jeffrey04]

thansk for the tip, and I somehow managed to get gemini-cli to generate a patch that somewhat works, will submit a PR to begin some work for nix-develop as a version manager

EDIT: submitted a PR #3691

[Jeffrey04]

@vinistock just out of curiosity, is there anything else i can do for the PR?