Mojo

Mojo language support for Zed

Zed extension that adds Mojo language support for files with the .mojo suffix.

What is included

• Zed extension metadata in extension.toml
• Mojo language config in languages/mojo/config.toml
• Syntax highlighting queries in languages/mojo/highlights.scm
• Editor queries for bracket matching, indentation, outline, and Vim text objects
• LSP integration for mojo-lsp-server
• Mojo snippets in snippets/mojo.json
• Runnable detection for def main / fn main in languages/mojo/runnables.scm
• Default runnable task binding in languages/mojo/tasks.json
• Tree-sitter grammar pinned to vadim-su/tree-sitter-mojo

Install locally in Zed

1. Open Zed.
2. Run zed: extensions from the command palette.
3. Click Install Dev Extension.
4. Select this repository directory: zed_mojo.
5. Open a .mojo file.

If the extension does not appear immediately, reload Zed with zed: reload window.

Mojo language server

This extension registers mojo-lsp-server as the default language server for Mojo files. Completion, diagnostics, go-to-definition, hover, and other semantic features come from that LSP server.

The server is launched through the PATH inherited by Zed; the extension does not pin a machine-specific executable path.

By default, the extension starts the server with --skip-docstring-checks. This avoids extra parsing and type-checking work inside docstring examples, which can otherwise leave the server busy or stale after edits in some Mojo LSP builds.

Before opening a .mojo file, make sure the executable is visible from the environment that launches Zed:

which mojo-lsp-server

On Nix systems, launch Zed from a shell where mojo-lsp-server resolves successfully, or otherwise expose it through the environment used by Zed.

Configuring the language server

You can override the language server command, arguments, and environment in Zed settings. This is useful when Mojo imports require extra search paths via -I:

{
  "lsp": {
    "mojo-lsp-server": {
      "binary": {
        "path": "mojo-lsp-server",
        "arguments": ["-I", "/path/to/mojo/packages"],
        "env": {}
      },
      "initialization_options": {},
      "settings": {}
    }
  }
}

If autocomplete does not appear, first verify that Zed can start the server, then check zed: open log for LSP startup errors. Repeated mojo-lsp-server failed: server shut down messages mean the server process exited and Zed is still draining stale requests; reload the window to restart it.

Snippets

The extension includes snippets for common Mojo forms such as fn main, def main, struct, trait, alias, var, loops, conditionals, and tests. They are stored in snippets/mojo.json and appear alongside normal completion items.

Running Mojo files from Zed

Zed runs code through Tasks. This extension marks def main / fn main as a runnable with the tag mojo-main and ships a default language task in languages/mojo/tasks.json:

[
  {
    "label": "mojo run current file",
    "command": "mojo",
    "args": ["run", "$ZED_FILE"],
    "cwd": "$ZED_WORKTREE_ROOT",
    "save": "current",
    "use_new_terminal": false,
    "allow_concurrent_runs": false,
    "reveal": "always",
    "hide": "never",
    "tags": ["mojo-main"]
  }
]

After installing or updating the dev extension, reload Zed with zed: reload window and reopen a .mojo file. The inline runnable indicator should appear next to def main / fn main when gutter.runnables is enabled.

You can override the default action in a Mojo project's .zed/tasks.json, or globally via zed: open tasks, by defining your own task with "tags": ["mojo-main"].

This assumes the mojo executable is available in the shell environment that Zed uses. If Zed cannot find it, launch Zed from a terminal where mojo --version works, or add Mojo to your shell PATH.

Development

Run the native Rust checks:

cargo fmt --check
cargo check

Zed compiles Rust extensions to WebAssembly. To check that target locally, install it once and run the target check:

rustup target add wasm32-wasip1
cargo check --target wasm32-wasip1

Run the extension query and snippet checks:

bash scripts/check-snippets.sh
bash scripts/check-indents.sh
bash scripts/check-highlight-order.sh
bash scripts/check-runnables.sh

extension.wasm is a generated build artifact and is intentionally ignored by git.