Axon for VSCode

Language support for the Axon programming language: deterministic diagnostics, hover, go-to-definition, document symbols, context-aware completion, and an opt-in LLM advisor — all powered by axon-lsp, the language's official Language Server Protocol implementation.

What you get

• Diagnostics — lex, parse, and type errors surface as squiggles with axon-lex / axon-parse / axon-type source tags and precise ranges (a whole identifier for type errors, a single character for punctuation errors).
• Hover — built-in types (String, Integer, Channel<T>, Trusted<T>, …) and declaration keywords (type, flow, persona, channel, …) surface rich Markdown documentation; user-defined declarations show their kind and signature.
• Go-to-definition — jump from any reference to the matching top-level declaration.
• Document symbols — outline tree with sensible LSP SymbolKind per declaration kind.
• Completion — context-aware. Cursor inside a type annotation surfaces only types; cursor at top level surfaces declaration keyword snippets (flow, type, persona, …); cursor in a declaration's name slot stays out of your way.
• Optional LLM advisor — opt-in command (Axon: Ask Advisor) that consults an Anthropic-backed advisor grounded in the embedded language documentation. Requires a build of axon-lsp with --features llm and the appropriate environment variables; see the configuration section below.

Prerequisites

This extension talks to the axon-lsp binary over stdio. You need to have the binary on your machine before the extension can do anything. Three options, checked in order:

1. axon-lsp.serverPath setting (workspace or user) — absolute path to the binary. Wins if set.
2. AXON_LSP_PATH environment variable — same effect, slightly less discoverable in the editor's settings panel.
3. axon-lsp on PATH — falls back to a bare command name and relies on the OS to resolve. Works after cargo install or after downloading a release binary into a PATH directory.

If none of the three resolve, the extension surfaces a clear error message naming all options.

Configuration

{
  // Absolute path to the axon-lsp binary. Leave empty to fall back
  // to AXON_LSP_PATH or PATH.
  "axon-lsp.serverPath": "",

  // LSP traffic tracing. `verbose` runs the server with
  // `AXON_LSP_LOG=debug`.
  "axon-lsp.trace.server": "off"  // off | messages | verbose
}

For the LLM advisor (optional), the binary itself must be built with --features llm and the following env vars must be set when VSCode spawns the server:

• AXON_LSP_LLM_ENABLED=1 — runtime opt-in.
• ANTHROPIC_API_KEY=... — backing API key.
• AXON_LLM_MODEL=... — optional model override (default claude-haiku-4-5-20251001).

Set these in your shell profile or .envrc so VSCode inherits them. Without all three, Axon: Ask Advisor returns a structured MethodNotFound whose message names the missing pieces.

Commands

• Axon: Ask Advisor (axon-lsp.askAdvisor) — prompts for a question, optionally attaches the editor's current selection as code context, and shows the answer in the Axon Advisor output channel. Requires the LLM advisor to be enabled (see above).
• Axon: Restart Language Server (axon-lsp.restartServer) — stops and restarts the LSP client. Useful after upgrading the binary or changing environment variables.

Building locally

cd editors/vscode
npm install
npm run compile        # → out/extension.js

To produce a .vsix package: npm install -g @vscode/vsce then vsce package from this directory.

License

MIT — see the repository LICENSE.