diff_view

A fast side-by-side diff view for Flutter, modelled on the JetBrains IDEs' diff viewer.

• Two synced panes with curved ribbons linking each change across the divider.
• Word-level highlights inside changed lines, plus your own syntax colors.
• Nested folding of unchanged regions ("… N unchanged lines").
• Line selection in the gutter (drag, Shift-click, Shift+arrows) with copy.
• Inlays: put any widget between lines (review comments, notes) without the view jumping.
• Self-painted rows with cached paragraphs, built for large files: on a 20,000-line diff, scrolling costs about 3 ms per frame (p95) on an M3 Pro.
• Rows can be paged in from a backend, or kept in memory.

It depends only on Flutter. Desktop is the main target; it works wherever Flutter runs.

Usage

import 'package:diff_view/diff_view.dart';

final diff = TextDiff.compute(oldText, newText, path: 'main.dart');

final theme = DiffThemeData.dark();
final controller = DiffViewController(
  document: diff.document,
  lines: diff.lines,
  theme: theme,
  devicePixelRatio: MediaQuery.devicePixelRatioOf(context),
);

SideBySideDiff(
  controller: controller,
  theme: theme,
  inlayBuilder: (context, spec) => const SizedBox.shrink(),
);

Dispose the controller when the view closes. See example/ for a complete app.

Syntax highlighting

Pass syntax: to TextDiff.compute. It returns (start, length, captureId) triples for each line, where captureId indexes the captureNames you give the controller (for example ['', 'keyword', 'string']). DiffThemeData.syntax maps capture names to colors, and a dotted name such as keyword.control falls back to keyword. Any tokenizer works; the example uses a small regex.

Your own diff or backend

TextDiff is a plain line diff (Myers) with a word diff inside changed lines. To use a different algorithm, or to page rows in from a server, build a DiffDocument (blocks and unchanged gaps) yourself and implement DiffLineSource; MemoryLineSource is the in-memory one.

Fonts

The default theme asks for JetBrains Mono and falls back to Menlo and the platform's monospace font. The package doesn't bundle a font; add one to your app, as the example does, or set fontFamily on the theme.

Limits

• Side by side only; there's no unified (single-column) mode yet.
• No screen-reader semantics for rows yet.
• TextDiff keeps memory proportional to the number of differences times the file length, so a large file that's completely rewritten is slow to diff.

License

MIT. The example bundles JetBrains Mono under the SIL Open Font License.