Mio — Programming Language Tools

Visual Studio Code support for the Mio programming language

Mio project · Language reference · Releases

Mio is a statically typed programming language with Japanese romaji keywords, a Mochi bytecode toolchain, and the modular Bunko standard library. This extension brings .mio files into VS Code with syntax highlighting, editor conventions, snippets, MioCore language server diagnostics, and Mio CLI commands.

The extension works without the Mio CLI for basic editing. CLI features are enabled automatically when mio (or mio.exe) is available on PATH, or when mio.executablePath points to a Mio executable.

Syntax preview

Dark theme:

Light theme:

These preview images are generated from the extension's TextMate scope palette. See docs/images/README.md for how to replace them with real editor screenshots.

Features

• TextMate syntax highlighting for the current Mio language version (V0.5, as used by Mio 1.0.0-beta.1):
  • keywords: kaku, waza, moshi, sore, aida, kaesu, nukeru, tsuzuku, yobu, kata, sentaku, awase, baai, koukai, teisu
  • hai, iie, and mu
  • built-in types: fixed-width integers, float32, float64, rune, bool, string, unit, resource, Map, and the numeric constraints Number, Integer, Signed, Float
  • function declarations and calls, closures, parameters, struct fields, enum variants, match arms, generic declarations and applications, imports, arrays, numbers, strings, runes, comments, and operators
  • keywords inside ordinary strings and comments are not highlighted
• Language configuration: auto-closing and surrounding pairs, bracket matching, // and /* ... */ comments, indentation rules, region markers, a Mio-aware word pattern, and brace/comment folding.
• Snippets for variables, constants, functions, closures, generics, conditionals, aida loops, nukeru/tsuzuku, returns, imports, structs, enums, exhaustive awase matches, arrays, Map, nullable values, and runes.
• Mio CLI commands:
  • Mio: Check Current File
  • Mio: Run Current File
  • Mio: Build Current File
  • Mio: Show Compiler Version
  • Mio: Open Output
• MioCore language server launched from the Mio CLI (mio lsp) through vscode-languageclient. It publishes compiler diagnostics for open buffers, including unsaved text, with document versioning, incremental edits, cancellation, and UTF-8 byte offset to VS Code UTF-16 position mapping.
• CLI fallback diagnostics from mio check --format=json when the language server is disabled, unavailable, or stopped. Only one diagnostic source is active at a time.
• Safe process execution: every CLI call uses an argument array with shell: false; paths containing spaces, Chinese, or Japanese are passed through unchanged.
• Bilingual README and a 128×128 Marketplace icon derived from the project's language logo.

Installation

From a VSIX (0.2.0)

code --install-extension mio-language-support-0.2.0.vsix

Then reload VS Code and open any .mio file.

From source

cd editors/vscode
npm ci
npm run compile
npx vsce package
code --install-extension mio-language-support-0.2.0.vsix

The extension is not published to the Visual Studio Marketplace yet. The publisher field is a placeholder derived from the project's GitHub organization; see PUBLISHING.md before publishing.

Supported platforms

• macOS (Apple Silicon and Intel)
• Windows (x64 and ARM64)
• Linux (x64 and ARM64)

The extension itself is platform-neutral. The Mio CLI must match your platform.

Mio CLI configuration

Build the CLI from the Mio repository:

go build -o mio ./cmd/mio
./mio version

Put mio on PATH (or mio.exe on Windows), or configure an absolute path. The extension does not scan the workspace for a Mio binary; it only uses the configured path or PATH.

mio.languageVersion is intentionally not exposed: the current Mio CLI has no language-version flag. The grammar and snippets target the V0.5 keyword set used by the current toolchain. See the version table below.

Bunko standard library

mio check and mio run need the Bunko root when a file imports kiso/.... The extension reuses the CLI's lookup rules:

1. MIO_BUNKO from the environment, if it points to a directory.
2. The nearest bunko/ directory above the source file.

If you keep Bunko outside the project, set MIO_BUNKO in the environment that launches VS Code.

Commands

Run and build save a dirty .mio buffer first. Manual Check Current File checks the in-memory text without forcing a save by copying the package's .mio files to a temporary directory. While the language server is running, diagnostics come from mio lsp, so the command reports that instead of starting a duplicate CLI check.

If the CLI is missing, the extension shows a guidance message with Open Settings and Installation Guide actions. Syntax highlighting and snippets continue to work.

Mio language versions

Keyword gates are copied from internal/token/token.go; the current Mio CLI loader uses token.V05 (internal/bunko/program.go).

The extension targets V0.5. It does not treat a V0.4-only keyword as valid in a V0.1 program because the plugin has no per-file version switch; such a switch would require a real CLI flag.

Current scope

• Syntax highlighting, language configuration, snippets, folding, the MioCore language server, and the five CLI commands described above.
• Diagnostics come from mio lsp. The server reuses Mio's Lexer, Parser, Resolver, and TypeChecker, analyzes unsaved buffers through an in-memory overlay, applies incremental edits, validates document versions, supports $/cancelRequest, and maps compiler byte offsets to UTF-16 positions.
• The compiler pipeline stops at the first error, so each analysis publishes at most one diagnostic. Package/import failures without a source position are shown at the start of the file with an explicit note instead of a guessed range.
• When the server is disabled, missing, or stops, the extension falls back to mio check --format=json and clears the other diagnostic collection, so the Problems panel never shows both sources at once.
• Semantic navigation (hover, go-to-definition, find references, document and workspace symbols, rename, signature help, semantic tokens) is not implemented yet; it is the next milestone. The extension does not register regex-based fake providers. See docs/LSP_PLAN.md.
• No debugger, test explorer, formatter, or Marketplace publication.

Known limitations

• Both the language server and the CLI fallback stop at the first compiler error; the Problems panel therefore shows at most one Mio diagnostic per analysis.
• Semantic navigation (hover, definition, references, document symbols) is not available yet.
• Import/package errors without a source position are shown at the start of the current file and include the reported file path in the message.
• Windows .cmd / .bat launchers are not executed. Configure the native mio.exe instead; this keeps process execution shell-free.
• mio.outputDirectory only affects mio build; mio run always runs the source file.
• The Marketplace publisher ID is not finalized. See PUBLISHING.md.

Development

npm ci
npm run compile
npm run lint
npm test
npx vsce package
npm run check:vsix

npm test first runs Node-based unit tests (manifest, grammar scopes, diagnostics mapping, CLI resolution, process runner, language server launch options), then launches a VS Code Extension Host through @vscode/test-electron for activation, language ID, command registration, snippets, folding, language-server diagnostics, CLI fallback, missing-CLI, and space/Chinese/Japanese path tests.

The pretest step builds cmd/mio into editors/vscode/.test-tmp/ when Go is available. If Go is not installed, real-CLI integration tests are skipped with an explicit marker; the extension itself has no Go dependency.

License and artwork

The plugin code is MIT-licensed; see LICENSE. The icon is a 128×128 RGBA conversion of the JetBrains Marketplace icon editors/jetbrains/src/main/resources/META-INF/pluginIcon.svg (using its embedded PNG artwork), not the icons/mio.svg file-type mark. Other Mio/Mochi character illustrations under assets/mascot/ are not bundled because their license is separate from the MIT-licensed code. See NOTICE.md.

Links

• Mio repository
• Mio language reference
• Bunko standard library
• JetBrains Mio — Programming Language Tools
• Issue tracker