[bjeanes]

Motivation

Related to #1233.

An add-on can make the server handle a language besides Ruby and ERB. For example, my prototype add-on, ruby-lsp-slim-lang, does this for the Ruby inside Slim templates. That follows @vinistock wondering in #1233 whether templating engines may be a better fit for add-ons2.

However, the extension only sends Ruby and ERB files to the server. As such, an add-on like that can't be used from VS Code. In Neovim, where the client's ruby_lsp config decides which file types to send, adding slim to it is enough for the add-on to work.

Implementation

This adds a rubyLsp.addonLanguageIds setting, empty by default. The extension adds each language ID listed there alongside Ruby and ERB in:

• the client's document selector,
• the language status items, and
• the checks that activate a workspace when a document opens.

It's opt-in, because without a matching add-on the server would parse those files as Ruby.

Since any change under rubyLsp restarts the server, the client picks up the new list when it rebuilds its document selector. However, the language status items only read the list when the extension activates. They won't show a change to the setting until the window is reloaded, which I've left as is to keep this change small.

The extension's ERB delegation middleware checks for erb explicitly. Requests for other languages therefore go straight to the server.

Note

The add-on API has no way to register a document type, though @vinistock suggested in #1233 that one might be designed. So, ruby-lsp-slim-lang currently patches the server's document store to create its own. That is separate from this change, which only concerns which files the extension sends.

I made this change with Claude Code, which is why the commit has a Co-Authored-By trailer. I've reviewed it and tested it in VS Code myself, and I'm happy to drop the trailer if you'd prefer.

Automated Tests

I added unit tests for the list of supported language IDs, both by default and with the setting.

Manual Tests

1. In a Ruby project that uses Slim, add gem "ruby-lsp-slim-lang", require: false, github: "bjeanes/ruby-lsp-slim-lang" to the Gemfile and run bundle install.
2. Install a Slim syntax extension, so that .slim files get the slim language ID.
3. Add "rubyLsp.addonLanguageIds": ["slim"] to the workspace settings, then reload the window.
4. Open a .slim template and go to the definition of a helper or constant it uses. It should jump to the Ruby definition.
5. Remove the setting and reload the window. Go to definition in the template should no longer find anything.

[bjeanes]

I have signed the CLA!