Velt for Visual Studio Code

Language support for Velt (.vlt files; see the language reference):

• Syntax highlighting (keywords, types, strings, template literals with ${} substitutions, numbers with type suffixes such as 10u8 / 1.5f32, comments).
• Brackets, comment toggling, auto-closing pairs.
• Through the language server (velt lsp):
  • diagnostics from the parser, the module loader and the type checker, as you type (unsaved changes of other open files are taken into account);
  • formatting (Format Document, uses velt fmt);
  • outline / document symbols;
  • go to definition (locals, functions, types, members of this and of typed locals, enum variants, imported names — also into other files);
  • hover (declaration signatures; the inferred type of locals and expressions when the program type-checks);
  • completion (locals, module items, imports, prelude items, keywords; members after .);
  • find references, rename, document highlight (reads and writes of the name under the cursor);
  • workspace symbols (Ctrl+T: declarations in the open programs and the workspace folders);
  • quick fixes (light bulb) for compiler errors: remove mut, undefined → null, "a" + n → a template literal; and for a promise left floating as a statement: add await or wrap it in spawn(...);
  • inlay hints: inferred types of const / let / for ... of bindings and parameter names at call sites (toggle with editor.inlayHints.enabled);
  • signature help while typing call arguments (functions, methods, constructors, function-typed values);
  • semantic highlighting: types, functions, methods, parameters, properties, enum members; let bindings carry the mutable modifier (to underline them, add "editor.semanticTokenColorCustomizations": { "rules": { "*.mutable:velt": { "underline": true } } });
  • ▶ Run | Debug above main, and ▶ Run test | Debug test above each test.
• Debugging (F5): breakpoints in .vlt files, stepping and the call stack, with nothing to configure. See Debugging.

Requirements

The Velt toolchain. Install it with one line (Linux x86_64 and arm64, macOS, Windows x64):

curl -fsSL https://github.com/velt-lang/velt/releases/latest/download/get-velt.sh | sh   # Linux, macOS
irm https://github.com/velt-lang/velt/releases/latest/download/get-velt.ps1 | iex       # Windows (PowerShell)

The installer puts velt on your PATH; velt doctor checks the setup. If velt lives elsewhere, point the velt.serverPath setting at it. Other options: Platforms and installation.

Debugging

Install a debugger extension: CodeLLDB (recommended; it includes LLDB), LLDB DAP, or Microsoft's C/C++. Then press F5 in a package (a folder with package.vlt) or on an open .vlt file: the extension runs velt build --json, shows build errors in Problems, and starts the debugger on the program. No launch.json is needed; Velt: Generate launch.json (or velt init --editor vscode) writes one to customize (args, env, cwd, program, file, build, buildArgs, stopOnEntry):

{ "type": "velt", "request": "launch", "name": "Debug", "args": ["--port", "8080"] }

velt new already adds it. On Windows use CodeLLDB or LLDB DAP; the C/C++ extension's Visual Studio debugger needs "buildArgs": ["--backend", "llvm"] (needs clang), whose build has a PDB. templates/ has examples, including attaching to a program that velt dev --exe restarts on every change.

Settings

Commands: Velt: Restart Language Server (e.g. after rebuilding velt or changing a package's dependencies, which the server installs once per session), Velt: Run File, Velt: Debug File (also as buttons in the editor title) and Velt: Generate launch.json.

Development

The extension lives in editors/vscode of the Velt repository. With Node.js 18+:

cd editors/vscode
npm install
npx tsc -p .                        # compile src/ → out/
npx @vscode/vsce package            # → velt-<version>.vsix
code --install-extension velt-<version>.vsix

Or open editors/vscode in VS Code and press F5 to launch an Extension Development Host (run npx tsc -watch -p . alongside). npm test runs the unit tests of the debug configuration logic (src/test/).