tree-sitter grammar for roc

January 26, 2026 ยท View on GitHub

installing

Reference it from your editor somehow. //TODO

Helix

My full config for roc is below:

[language-server.roc-ls]
command = "roc_language_server"

[[language]]
name = "roc"
scope = "source.roc"
injection-regex = "roc"
file-types = ["roc"]
shebangs = ["roc"]
roots = []
comment-token = "#"
language-servers = ["roc-ls"]
indent = { tab-width = 2, unit = "  " }
auto-format = true
formatter = { command = "roc", args =[ "format", "--stdin", "--stdout"]}


[language.auto-pairs]
'(' = ')'
'{' = '}'
'[' = ']'
'"' = '"'
[[grammar]]

name = "roc"
source = { git = "https://github.com/faldor20/tree-sitter-roc.git", rev = "whateverTheLatestCommitIs" }
  1. After adding the above to your languages.toml, run hx --grammar fetch and then hx --grammar build
  2. Copy the queries into your helix config using:
mkdir -p '~/.config/helix/runtime/queries/roc/'
cp ./queries-generated/helix/queries/* '~/.config/helix/runtime/queries/roc/'
  1. Run hx --health roc in a new shell and verify that your changes have been picked up correctly. If things are green, you're good to go.

Neovim

Via nvim-treesitter plugin

Install the nvim-treesitter plugin using your favorite package manager. The Roc language is supported by nvim-treesitter. Install it with the command:

:TSInstall roc

Manually

Add the code in neovim/roc.lua to your config somewhere. Copy the folder queries-generated/neovim/queries to your neovim config at after/ or in a custom neovim plugin at its root directory ./ eg: after/queries/roc/highlights.luaor my_roc_plugin/queries/roc/highlights.lua

Emacs

A package providing a major mode for Roc is under development.

contributing

Setup

Nix

Currently i use nix for development so to start the dev environment in nix run

nix develop

I've had some odd issues with the system version of libc being incompatible with my version of treesitter. if tree-sitter is spitting out weird errors try running it in an isolated environments

nix develop -i

Not Nix

If you are outside of nix. You will need:

  1. The tree-sitter cli, which will be installed when you run npm install
  2. A c compiler like gcc or clang

Query templating

This repo keeps a single set of base queries in the queries folder and generates editor-specific query files via JSON mappings in query-maps. Each mapping contains per-file sections (highlights, indents, injections, locals, textobjects, tags) and must include every capture used in the base queries. Set a value to null or an empty string to drop a capture for a given editor.

To generate query outputs, run: npm run queries:generate This writes output to queries-generated//...

Running

Once you've made a change, to test it, run:

tree-sitter generate
tree-sitter test

if you add a new feature you should add a test to one of the test files in test/corpus/*.txt once you are happy with you changes run

tree-sitter test --update

and it will update the test files with your new parsed tree

Justfile

Common tasks are available via justfile:

  • just test-gen runs tree-sitter generate and tests.
  • just test-gen-filter TEST=... runs generate and filters tests.
  • just test runs tests only.
  • just test-update updates test corpus outputs.
  • just build-all builds WASM.
  • just generate-check ensures generated parser files are up-to-date.
  • just queries-generate generates editor query outputs.
  • just queries-check verifies generated queries are clean.
  • just ci runs generate-check, tests, and queries-check.

CI helpers

The following npm scripts are designed for CI:

  • npm run ts:generate-check ensures parser generation is clean.
  • npm run ts:test runs parser tests.
  • npm run queries:check validates query templating output.
  • npm run ci runs all checks.