Roc lang support for Zed

An extension for Zed that adds Roc language support:

• syntax highlighting through treesitter and
• type tooltips, error marker, completion ... through the roc language server

Prerequisites

• Install Roc from the roc-lang website
• Ensure the roc binary is in your PATH
• Install Zed from the Zed website
• Install the Zed extension WebAssembly target for development:

  rustup target add wasm32-wasip2

• Website: roc-lang.org
• Tree Sitter: tree-sitter-roc
• Language Server: This extension uses the new experimental LSP integrated into the roc CLI via roc experimental-lsp.

Development

Installing the Dev Extension

1. Open Zed's command palette (Cmd+Shift+P / Ctrl+Shift+P)
2. Run "zed: install dev extension"
3. Select this repository folder
4. Click "Rebuild" if prompted

Note: The version shown in Zed's Extensions panel may display the marketplace version even when the dev extension is active. This is a Zed caching behavior when the extension ID matches a marketplace extension.

Verifying the Dev Extension is Running

Check Zed's logs (Command palette → "zed: open log file") and look for:

compiling Rust extension /path/to/your/zed-roc

If the path points to your local repository (not ~/Library/Application Support/Zed/extensions/installed/roc), the dev extension is active.

Key Files

• extension.toml - Extension manifest (id, version, grammar source, language config)
• languages/roc/config.toml - Language configuration (file extensions, comments, brackets)
• languages/roc/*.scm - Tree-sitter queries (highlights, indents, etc.)
• src/lib.rs - Rust extension entry point that launches roc experimental-lsp --stdio

Validating Changes

cargo fmt -- --check
cargo clippy --all-targets -- -D warnings
cargo test
cargo build --target wasm32-wasip2

Updating the Tree-sitter Grammar

Zed fetches the grammar from the repository and commit in extension.toml. The local grammars/roc/ directory is ignored and only used as a working checkout when syncing query files.

To update:

1. Update the commit hash in extension.toml under [grammars.roc]
2. Sync query files:

   just sync-queries

3. In Zed, click "Rebuild" on the extension

Troubleshooting

Extension not detecting .roc files:

• Check Zed logs for errors (Command palette → "zed: open log file")
• Ensure languages = ["languages/roc"] is in extension.toml

Conflict with marketplace version:

• Uninstall the marketplace Roc extension first
• If uninstall doesn't work, quit Zed and manually edit the extensions index.json to remove "roc" entries
• Zed stores extensions in:
  • macOS: ~/Library/Application Support/Zed/extensions/
  • Linux: ~/.local/share/zed/extensions/

Grammar compilation errors:

• Check that [grammars.roc] in extension.toml points to a valid repository and commit
• Remove any cached grammars/roc.wasm or extension.wasm, then rebuild the extension

Useful Commands

# Sync query files from grammar to languages
just sync-queries
# Clean build artifacts
just clean
# Check Zed logs (macOS)
tail -f ~/Library/Logs/Zed/Zed.log | grep -i roc

The just recipes are optional conveniences. The validation commands above only require Rust.