Musi for Visual Studio Code

Musi language support for VS Code: syntax highlighting, language-server features, inlay hints, formatting, and package workflows for .ms projects.

Features

• Syntax highlighting for .ms files and Musi fenced code blocks in Markdown
• Diagnostics, hover, semantic highlighting, references, formatting, and inlay hints from musi_lsp for .ms files
• Rust Analyzer style inlay hints for literal argument names and inferred binding types
• A Musi command center for package, workspace, editor, and language-server actions
• CLI-backed formatting for Musi Markdown fences without starting the LSP
• Package and workspace commands for run, check, build, test, and format actions
• musi.json schema validation
• Check-on-save fallback when LSP diagnostics are unavailable
• Named run configurations from VS Code settings
• Status and progress feedback for package checks and language-server startup, restart, and stop flows

Requirements

Install the Musi tools and make them available on PATH:

• musi for package commands, fallback checks, and Markdown fence formatting
• musi_lsp for editor diagnostics, hover, semantic tokens, formatting, and inlay hints

If the binaries are not on PATH, configure:

{
  "musi.cliPath": "/path/to/musi",
  "musi.lspPath": "/path/to/musi_lsp"
}

When working inside the Musi repository, the extension also checks workspace build outputs before falling back to Cargo bin and PATH.

Package detection

The extension treats the closest ancestor musi.json as the owning package root. Package commands, run configurations, task execution, and check-on-save use that package root.

Files without an owning musi.json still get syntax highlighting. Package commands and package checks stay disabled until the file belongs to a package.

Commands

Open the command palette and run Musi: Open Command Center for the main workflow picker. It groups actions into:

• Project: run, test, build, and check the owning package
• Workspace: check, test, build, and format the workspace
• Editor: configure inlay hints and edit run configurations
• Language Server: show status, restart musi_lsp, and open LSP output

Direct commands are also available:

• Musi: Run Current Package
• Musi: Check Current Package
• Musi: Build Current Package
• Musi: Test Current Package
• Musi: Format Document
• Musi: Format Workspace
• Musi: Check Workspace
• Musi: Build Workspace
• Musi: Test Workspace
• Musi: Configure Inlay Hints
• Musi: Show Status
• Musi: Start Language Server
• Musi: Stop Language Server
• Musi: Restart Language Server
• Musi: Show Language Server Output

Inlay hints

Musi enables editor-friendly hints by default:

• Parameter name hints appear for literal arguments, such as numbers, strings, and templates.
• Inferred type hints appear for declarations without explicit annotations.
• Hints can be changed from Musi: Configure Inlay Hints without editing JSON.

Use "musi.inlayHints.parameterNames.enabled": "all" for every positional argument, or "none" to hide parameter names.

Formatting

For .ms files, Format Document uses musi_lsp when the language server is running. If LSP formatting is unavailable, the extension falls back to musi fmt.

For Markdown files, Musi fenced code blocks are formatted with musi fmt. Markdown formatting does not start or attach the Musi LSP.

Formatter behavior comes from the owning package's musi.json plus VS Code formatting options where supported.

Settings

Common settings:

{
  "musi.cliPath": "musi",
  "musi.lspPath": "musi_lsp",
  "musi.lsp.enabled": true,
  "musi.checkOnSave": true,
  "musi.hover.maximumLength": 500,
  "musi.inlayHints.enabled": true,
  "musi.inlayHints.parameterNames.enabled": "literals",
  "musi.inlayHints.parameterNames.suppressWhenArgumentMatchesName": true,
  "musi.inlayHints.variableTypes.enabled": true,
  "musi.inlayHints.variableTypes.suppressWhenTypeMatchesName": true
}

Runtime and terminal settings:

{
  "musi.runtime.args": [],
  "musi.runtime.env": {},
  "musi.runtime.envFile": "",
  "musi.runtime.cwd": "",
  "musi.terminal.clearBeforeRun": false,
  "musi.terminal.focusOnRun": true,
  "musi.terminal.reuseTerminal": true
}

Named run configuration example:

{
  "musi.runConfigurations": [
    {
      "name": "dev",
      "entry": "index.ms",
      "runtimeArgs": ["--watch"],
      "env": {
        "MUSI_ENV": "dev"
      },
      "preLaunchTask": "build"
    }
  ]
}

Markdown support

Musi code fences in Markdown use the musi or ms language tag:

```musi
let total : Int := 42;
```

The extension highlights these fences and formats them through musi fmt.

Troubleshooting

If diagnostics, hover, semantic highlighting, or formatting do not appear:

1. Run Musi: Show Status.
2. Run Musi: Show Language Server Output.
3. Confirm musi_lsp is installed or set musi.lspPath.
4. Confirm the file belongs to a package with an ancestor musi.json.
5. Run Musi: Restart Language Server after changing binary paths or inlay hint settings.

If package commands fail:

1. Confirm musi is installed or set musi.cliPath.
2. Check the package root detected from the nearest musi.json.
3. Verify runtime settings such as musi.runtime.cwd, musi.runtime.env, and musi.runtime.envFile.

License

MIT