Capa Language, VSCode extension

Syntax highlighting for the Capa programming language, a capability-centric language with a pythonic surface, built around the idea that the authorities a function holds (network, filesystem, environment, ...) must be visible in its signature.

This extension provides TextMate-based highlighting. A capability-aware language server has shipped separately (python -m capa lsp); you can wire it up with any generic LSP client extension for VSCode (search the Marketplace for "Generic LSP" or similar) pointed at python -m capa lsp. A first-party VSCode extension that bundles the LSP client is on the roadmap.

What it highlights

• Keywords by category: declarations (fun, type, typestate, linear, trait, impl, capability, ...), control flow (if, then, elif, else, match, while, for, become, ...), storage modifiers (let, var, pub, consume), logical operators (and, or, not).
• Attributes and security labels (@security(...), @strict_ifc, @constant_time, and the information-flow labels @secret / @public), highlighted as attributes.
• Built-in primitive types (Int, Float, String, Bool, Char, Unit).
• Built-in capabilities (Stdio, Fs, Net, Env, Clock, Random, Proc, Db, Unsafe), highlighted distinctly from regular user types.
• Built-in generic types (List, Option, Result, Map, Set, Fun, JsonValue, IoError).
• Built-in variant constructors (Some, None, Ok, Err, and the JsonValue variants).
• Built-in functions (parse_int, parse_float, to_int, to_float, new_map, new_set, parse_json, to_json, py_import, py_invoke, declassify).
• Integer (decimal, hex, octal, binary), float, and string literals, with proper handling of ${...} interpolation (the interpolated expression is highlighted recursively).
• Range operators .. and ..=, the lambda body separator =>, the result-propagation operator ?, and the or-pattern separator |.
• Reserved-for-future-use keywords (async, await, yield, defer, where, mut) are flagged with the invalid.deprecated.reserved scope so themes can render them as a warning.

Install

From the VSCode Marketplace: search for "Capa Language" in the Extensions view, or run code --install-extension nelsonduarte.capa-language.

From source (development)

To work on the extension itself, install it locally:

Option A, symlink (preferred during development)

# macOS / Linux
ln -s "$(pwd)/vscode" ~/.vscode/extensions/capa-language

# Windows (PowerShell, as admin if your user dir is locked down)
New-Item -ItemType Junction -Path "$env:USERPROFILE\.vscode\extensions\capa-language" -Target "$pwd\vscode"

Restart VSCode. .capa files should now highlight.

Option B, copy

cp -r vscode ~/.vscode/extensions/capa-language

Or package as a .vsix:

npm install -g @vscode/vsce
cd vscode && vsce package
code --install-extension capa-language-0.8.0.vsix

What's not in this extension yet

• Bundled LSP client: the LSP server itself (python -m capa lsp) is shipped and delivers diagnostics, hover, go-to-definition, find-references, document symbols, and Quick Fixes. This extension does not yet auto-launch it; you currently wire it up through a generic LSP client extension or in a fork that adds the vscode-languageclient dependency. A first-party bundled client is queued.
• Snippets for fun main(stdio: Stdio) etc.: would be a small follow-up.
• Better indentation rules: Capa is indent-sensitive, but the auto-indent heuristics here are minimal. Use Tab and Shift-Tab explicitly.

Reporting issues

Open an issue at the main Capa repository: https://github.com/nelsonduarte/capa-language/issues. Mention "vscode" in the title.

License

MIT, same as the rest of the Capa project.