Formatter Development

Use crates/biome_formatter/CONTRIBUTING.md and the language formatter's guide as the canonical architecture references. Inspect neighboring node implementations before selecting IR primitives.

Workflow

1. Reproduce the behavior with a focused internal formatter spec or quick_test.
2. Inspect the node fields, comments, and nearby formatting rules.
3. Implement the smallest layout change using formatter IR.
4. Run focused formatter tests and inspect snapshots.
5. Compare with Prettier when compatibility is relevant.
6. Run formatter codegen for the language, then format and lint.

Node Rules

Generated node rules implement FormatNodeRule. In fmt_fields: