pi-elixir

Pi package for Elixir projects: Mix post-edit hooks, Expert LSP bridge, commands, LLM tools, and Elixir/Phoenix/Ecto/OTP skills.

Features

• Auto-detection: Detects Elixir projects via mix.exs and shows 🔮 Expert connection status
• Post-edit hooks: Runs mix format, mix compile, and mix credo automatically after file edits
• Expert LSP bridge: Full language server integration for diagnostics, hover, definitions, references, symbols, completions, rename, and formatting
• LLM tools: elixir_mix and elixir_expert tools callable by the agent
• Slash commands: /elixir and /expert with argument completions
• Skills: Domain-specific thinking skills for Elixir, Phoenix, Ecto, and OTP
• Credo caching: Checks credo availability once per project instead of on every edit

Install

# Global (all projects)
pi install /path/to/pi-elixir

# Project-local (shareable via .pi/settings.json)
pi install -l /path/to/pi-elixir

# Try without installing
pi -e /path/to/pi-elixir

Prerequisites

• mix on PATH
• expert on PATH (for LSP features)

Structure

pi-elixir/
├── README.md
├── package.json
├── extensions/
│   ├── mix-format.ts        # Post-edit: mix format
│   ├── mix-compile.ts       # Post-edit: mix compile --warnings-as-errors
│   ├── mix-credo.ts         # Post-edit: mix credo (cached availability check)
│   ├── elixir-tools.ts      # elixir_mix tool + /elixir command
│   ├── elixir-expert.ts     # elixir_expert tool + /expert command + auto-start
│   ├── elixir-session.ts    # Project detection + system prompt guidance
│   └── lib/
│       ├── elixir-utils.ts      # Shared utilities (run commands, find mix root, etc.)
│       └── expert-lsp-client.ts # LSP client for Expert language server
└── skills/
    ├── elixir-thinking/     # General Elixir design patterns
    ├── phoenix-thinking/    # Phoenix and LiveView patterns
    ├── ecto-thinking/       # Ecto schemas, queries, migrations
    └── otp-thinking/        # OTP processes, supervisors, fault tolerance

Slash Commands

Mix helpers (/elixir)

/elixir doctor              # Check mix, expert, credo availability
/elixir format [file]       # Run mix format
/elixir compile             # Run mix compile --warnings-as-errors
/elixir credo               # Run mix credo
/elixir test [args...]      # Run mix test

Expert LSP (/expert)

/expert status              # Show session status
/expert start               # Start Expert LSP
/expert restart             # Restart Expert LSP
/expert shutdown            # Shut down Expert LSP
/expert diagnostics [file]  # Show diagnostics
/expert hover <file> <line> <char>
/expert definition <file> <line> <char>
/expert references <file> <line> <char>
/expert symbols <file>
/expert completion <file> <line> <char>
/expert rename <file> <line> <char> <newName> [--apply]
/expert format <file> [--apply]

Positions are 1-based for convenience. The extension converts to LSP's 0-based internally.

LLM Tools

elixir_mix

Action	Description
doctor	Check tool availability
format	Run mix format
compile	Run mix compile --warnings-as-errors
credo	Run mix credo (skips if not installed)
test	Run mix test

elixir_expert

Action	Description
status / start / restart / shutdown	Manage Expert sessions
diagnostics	Get published diagnostics
hover	Symbol information
definition	Go to definition
references	Find references
document_symbols	List file symbols
completion	Autocompletion candidates
rename	Preview/apply rename edits
formatting	Preview/apply formatting edits

Skills

Skill	Use when
/skill:elixir-thinking	Designing modules, processes, protocols, behaviours
/skill:phoenix-thinking	Working on Phoenix, LiveView, controllers, contexts
/skill:ecto-thinking	Changing schemas, changesets, queries, migrations
/skill:otp-thinking	Implementing GenServer, Supervisor, Task, Registry

How Expert LSP Works

The bridge in extensions/lib/expert-lsp-client.ts implements a JSON-RPC/LSP client:

1. Starts one Expert process per project root on session start
2. Sends initialize with workspace/text-document capabilities
3. Responds to server requests (client/registerCapability, workspace/configuration, etc.)
4. Syncs .ex, .exs, .heex, .leex files with didOpen/didChange/didSave
5. Caches textDocument/publishDiagnostics notifications
6. Exposes LSP features as tools and commands
7. Applies text-only workspace edits inside the project root

Configuration

Environment variables

PI_ELIXIR_EXPERT_COMMAND=/path/to/expert   # Override Expert binary
PI_ELIXIR_EXPERT_ARGS="--stdio"            # Override Expert args

Disable post-edit hooks

In .pi/settings.json:

{
  "packages": [
    {
      "source": "/path/to/pi-elixir",
      "extensions": [
        "extensions/mix-format.ts",
        "extensions/elixir-tools.ts",
        "extensions/elixir-expert.ts",
        "extensions/elixir-session.ts"
      ]
    }
  ]
}

This keeps formatting, commands, Expert LSP, and skills but disables automatic compile/credo.

Notes

• Expert starts automatically when opening an Elixir project
• Diagnostics depend on Expert publishing textDocument/publishDiagnostics; indexing may still be in progress after startup
• rename and formatting default to preview-only; pass apply=true or --apply to write edits
• Credo is only active when the dependency is installed in the project