Contributing

The ruby-lsp repository contains three sub-projects:

the language server (ruby-lsp), which exists at the top level of the repository. Most features are implemented here since everything implemented in the server is available to all editors
the VS Code extension, which exists under the vscode directory. Any custom VS Code features are implemented here
the documentation website, which exists under the jekyll directory. All user facing documentation for both the Ruby LSP and the Rails add-on is contained here

This contributing guide is split by each component.

Initial setup

To start contributing to the Ruby LSP, ensure that all dependencies are installed as follows:

bundle install on the top level will install Ruby dependencies
bundle install in the jekyll directory will install documentation dependencies
yarn install in the vscode directory will install Node.js dependencies for the VS Code extension

Contributing to the server

This is the structure of the ruby-lsp gem:

lib/ruby_indexer: the code indexer to extract declarations from the workspace
lib/ruby_lsp/*.rb: foundational pieces of the language server, such as workers, queues, handling requests and so on
lib/ruby_lsp/requests: request implementation. These match one to one with the language server specification
lib/ruby_lsp/listeners: Prism dispatcher listeners. Most of the server’s infrastructure relies on a listener pattern to maximize performance while traversing ASTs. Note that a single request may depend on more than one listener

When adding or changing an existing feature, first identify which request is responsible for it in the specification. Then identify which file in the server implements that request and start thinking about the implementation.

When using VS Code, open the lsp.code-workspace file instead of just opening the regular folder. It contains configurations for working with the sub projects side by side effectively

Debugging

Live debugging the server

It is possible to live debug the development instance of the language server that is currently running when using VS Code:

CMD/CTRL + SHIFT + P to open the command palette
Search for Debug the Ruby LSP server. This command will restart the server in debug mode, allowing you to connect with a debugger. Note that the debug mode applies only until the editor is closed or Ruby LSP restarts
After the server has launched in debug mode, attach the debugger by going in Run and debug, selecting the Attach to existing server task and clicking run
You should now be able to put breakpoints in the UI and triggering requests will stop at those breakpoints

Caveat: since you are debugging the language server instance that is currently running in your own editor, features will not be available if the execution is currently suspended at a breakpoint.

Understanding Prism ASTs

The Ruby LSP uses Prism to parse and understand Ruby code. When working on a feature, it’s very common to need to inspect the structure of the Prism AST for a given code snippet, so that you can understand why a request is being triggered a certain way.

If you’re using VS Code, you can use the show syntax tree command to inspect the structure of an AST for an entire document or selection.

For other editors, using our IRB configurations is the easiest way of achieving the same:

bundle exec irb to launch IRB with our configurations. It will require all libraries for you
Then parse the Ruby code you’d like to understand better and start inspecting

source = <<~RUBY
  class Foo
    def bar
    end
  end
RUBY

ast = Prism.parse(source).value

Check the Prism documentation for more related information.

Tracing LSP requests and responses

In VS Code, you can verify what’s happening in the server by enabling tracing, which allows for different levels of logging.

{
  // Your JSON settings
  //
  // - `off`: no tracing
  // - `messages`: display requests and responses notifications
  // - `verbose`: display each request and response as JSON
  "ruby lsp.trace.server": "messages"
}

Manually testing a change

After you made a change or added a new feature, you can verify it in the editor by restarting the language server. In VS Code, this can be achieved by running the command Ruby LSP: restart, which will reboot the server and pick up your changes.

For other editors, you must manually restart the language server to pick up the latest changes.

Debugging tests

In VS Code, we recommend:

Setting breakpoints in the UI
Opening the test that will hit that breakpoint
Clicking the debug code lens button on top of examples

Alternatively (and for other editors), adding a binding.b statement in the code and executing the test in the terminal will also allow you to debug the code.

Writing tests

There are two types of tests in the Ruby LSP. The first type is likely familiar: standard Minitest files with a bunch of examples inside using the method declaration syntax.

The second type of test is our fixture/expectation framework. Adding a new fixture under test/fixtures will automatically make the framework run all requests against that fixture. By default, the framework only checks that the features don’t crash when running against the fixture. This is useful for ensuring that critical requests don’t break when using less common Ruby syntax.

To go beyond checking if the requests break for a fixture, you can add an expectation to test/expectations/NAME_OF_THE_REQUEST, which allows you to assert the expected response for a request and fixture combination.

For example, if we have a test/fixtures/foo.rb, then adding a test/expectations/semantic_highlighting/foo.exp.json will make the framework verify that when running semantic highlighting in the foo.rb fixture, the foo.exp.json response is expected.

Check existing fixture and expectation combinations for examples.

When to use each type of test

The fixture/expectation framework is intended to be used mostly by full document requests (language server features that are computed for the entire file every time).

Requests and features that are position specific or that operate under a different mechanism should just use regular Minitest tests.

Running the test suite

There are multiple ways to execute tests available.

# Run the entire test suite
bundle exec rake

# Run only indexing tests
bundle exec rake test:indexer

# Run only language server tests (excluding indexing)
bundle exec rake test

# Using the custom test framework to run a specific fixture example
# bin/test test/requests/the_request_you_want_to_run_test.rb name_of_fixture
bin/test test/requests/diagnostics_expectations_test.rb def_bad_formatting

Additionally, we use RuboCop for linting and Sorbet for type checking.

# Run linting
bundle exec rubocop

# Run type checking
bundle exec srb tc

Contributing to the VS Code extension

Before starting on this section, ensure that dependencies are installed.

In addition to what’s described here, the VS Code extension API documentation is a great place to gather more context about how extensions interact with the editor.

The VS Code extension currently has the following main parts:

Version manager integrations for Ruby environment activation
A ruby/debug client implementation
A test controller implementation
A Copilot chat participant
A dependencies tree implementation
The LSP client
A workspace abstraction to represent each active workspace in the editor

Testing changes

Open the lsp.code-workspace file instead of just opening the regular folder. It contains contains the configuration needed for using ‘Run and debug’ as described below.

We try to ensure thorough testing as much as possible. However, some tests are difficult to write, in particular those that interact with VS Code widgets.

For example, if running the test displays a dialog, the test has no easy way of clicking a button on it to continue execution. For these situations we use sinon to stub expected invocations and responses.

Note: client.test.ts is an integration style test that boots the development version of the ruby-lsp gem and runs requests against it.

Running tests

The easiest way to run tests is by selecting the Extension tests task in Run and debug and clicking run. That will run all tests and the results will appear in VS Code’s debug console.

Alternatively, you can also run the tests through the terminal, which will download a test VS Code version inside the repository and run tests against it. You can avoid the download by running the tests through the launch task.

Note: it is not possible to run a single test file or example.

Live debugging

It is possible to live debug the development version of the extension. Detailed information can be found in the VS Code extension documentation, but this section includes a short description.

Live debugging involves two VS Code windows. The first one is where you will be modifying the code and the second window will be where the development version of the extension is going to be running. You want to change the code in the first window, reload and verify the changes in the second window.

Start by launching the extension debugging with the Run extension task in the Run and debug panel. This will open the second VS Code window where the development version of the extension is running
Make the desired changes in the first original VS Code window
Click the reload button in the debug toolbar to load your recent changes into the second VS Code window
Perform the actions to verify your changes in the second window

If you wish to perform step by step debugging, all you have to do is add breakpoints through the UI in the first window where you are modifying the code - not in the second window where the development version of the extension is running.

Contributing to documentation

The Ruby LSP uses Jekyll to generate the documentation, whose source lives under the /jekyll folder. Before making any changes, ensure you performed initial setup.

After that, follow these steps to make and verify your changes:

Make the desired changes
Launch jekyll in development
```
bundle exec jekyll serve
```
Verify your changes locally by visiting http://localhost:4000/ruby-lsp

Contributing to the Ruby LSP Rails add-on

See https://github.com/Shopify/ruby-lsp-rails/blob/main/CONTRIBUTING.md