pi-lsp-lite

Your agent can't see compiler errors. Now it can.

pi extension that runs language servers in the background and feeds diagnostics back inline after every edit. Errors appear on the same turn — no context switch, no separate command.

Go · Rust · TypeScript · Python · C/C++

Install

pi install npm:pi-lsp-lite

That's it. If you have gopls, rust-analyzer, typescript-language-server, pylsp, or clangd on PATH, diagnostics start flowing automatically.

What you see

  edit ─ src/main.go
  ✓ Edited src/main.go (replaced 2 lines)

  ⚠ LSP diagnostics for src/main.go (2 errors):
    error 12:5 [compiler] undefined: foo
    error 18:2 [compiler] too many arguments in call to bar
    + 1 diagnostic in 1 other file

The agent sees these too — they're appended to the tool result, so it can self-correct on the same turn.

Commands

| Command | What it does | |---------|-------------| | /lsp-status | Show running servers, PIDs, workspace roots, uptime | | /lsp-diag | Show all current diagnostics (or /lsp-diag path/to/file for one file) | | /lsp-add | Interactively add a new language server | | /lsp-remove | Disable a configured server | | /lsp-toggle | Flip a server on/off without removing config | | /lsp-install | Install a missing server binary |

Supported servers

| Server | Language | Install | |--------|----------|---------| | gopls | Go | go install golang.org/x/tools/gopls@latest | | rust-analyzer | Rust | rustup component add rust-analyzer | | typescript-language-server | TypeScript/JS | npm install -g typescript-language-server typescript | | pylsp | Python | pip install python-lsp-server | | clangd | C/C++ | Xcode CLI tools / apt install clangd |

Missing a server? /lsp-add lets you configure any LSP server that speaks stdio. Or add it to .pi-lsp-lite.json:

{
  "servers": {
    "haskell": {
      "extensions": [".hs"],
      "command": "haskell-language-server-wrapper",
      "args": ["--lsp"],
      "rootPatterns": ["cabal.project", "stack.yaml"]
    }
  }
}

Configuration

Works without config. For customisation, create .pi-lsp-lite.json (project) or ~/.pi-lsp-lite.json (global):

| Field | Description | Default | |-------|-------------|---------| | servers.<id>.diagnosticTimeout | Per-attempt timeout (ms) | per-language | | servers.<id>.maxRetries | Retry attempts on timeout (0-10) | 3 | | servers.<id>.disabled | Disable this server | false | | diagnosticTimeout | Global default timeout (ms) | 5000 | | documentIdleTimeout | Close idle documents after (ms) | 120000 |

Project config merges over global. Partial overrides work — only specify what you want to change.

How it works

1. Agent writes/edits a file
2. Extension detects the language, finds the workspace root
3. Spawns (or reuses) an LSP server for that language + root
4. Sends didChange, waits for publishDiagnostics
5. If timeout: retries with exponential backoff + jitter (up to maxRetries times)
6. Filters to errors + warnings, formats, appends to tool result + shows in TUI

Cross-file impact is detected via snapshot-diff: if editing lib.ts breaks caller.ts, you see "+ N diagnostics in M other files".

Servers are lazy (spawn on first edit), idle-shutdown after 240s, and clean up on session end.

Development

git clone https://github.com/mcphailtom/pi-lsp-lite
cd pi-lsp-lite && npm install
npm run check              # typecheck
npm test                   # unit tests (106, no servers needed)
npm run test:integration   # real server tests (needs servers on PATH)

See docs/ARCHITECTURE.md and docs/CONTRIBUTING.md.

License

MIT