formatter-development

Purpose

Use this skill when implementing or modifying Biome's formatters. It covers the trait-based formatting system, IR generation, comment handling, and testing with Prettier comparison.

Prerequisites

1. Install required tools: just install-tools (includes wasm-bindgen-cli and wasm-opt)
2. Language-specific crates must exist: biome_{lang}_syntax, biome_{lang}_formatter
3. For Prettier comparison: Install bun and run pnpm install in repo root

Code Standards

CRITICAL: No Emojis

Emojis are BANNED in all formatter code:

• NO emojis in code comments
• NO emojis in rustdoc documentation
• NO emojis in test files
• NO emojis in debug output or error messages