Incremental Formatting

For editors, formatting must be FAST: ms-scale on save, ms-scale on every keystroke (with autoformat).

Strategies:

Reformat full file: simple but slow on big files. Black does this.

Reformat range: only the user's selection. clang-format supports.

Format on save: before write to disk. Most editors.

Format on type: after each ; or }. Some IDEs (JetBrains).

Incremental: detect what changed; reformat only affected nodes.

• Hard. Requires tracking edit ranges + AST node mapping.
• Tree-sitter is incremental: parse only what changed.
• Helps for large files in IDEs.

Performance optimizations:

• Cache parsed AST per file.
• Lazy: don't reparse on every keystroke; debounce ~150ms.
• Skip if unchanged.
• Multi-thread per file in batch mode.

CI usage:

• prettier --check returns non-zero if any file would be reformatted.
• gofmt -l lists unformatted files.
• Combined with pre-commit hook → only formatted code reaches the repo.

Pre-commit:

- repo: https://github.com/psf/black
  rev: 24.0.0
  hooks:
    - id: black

Editor integration:

• VSCode: format-on-save + per-language formatter.
• Vim: :Format command via plugin.
• Emacs: format-all package.
• IntelliJ: built-in formatters per language.

LSP textDocument/formatting + textDocument/rangeFormatting:

• Server returns text edits to apply.
• Editor displays diff or applies.

Async formatting: large files (~50k lines) may take seconds. Show progress; don't block UI.