highlight_fork 0.8.0

Syntax highlighting for Dart with lots of languages and themes support.

highlight_fork

Telosnex's Dart port of highlight.js 11, based on upstream master 696d9a4. The default registry contains 38 grammars and preserves all 78 existing fence aliases. Dart 3.8 or later is required.

Highlight code

import 'package:highlight_fork/highlight.dart';

void main() {
  ensureInitialized();
  final result = hljs.highlight('print("hello");', language: 'dart');
  print(result.toHtml());
}

hljs.highlightAuto(code) detects a language. An unknown explicit language throws ArgumentError. The result contains a DataNode tree at result.emitter.root. Each child is a text string or another DataNode with an optional scope. Scopes can contain dots, for example title.function and title.class. Embedded language scopes use language:javascript.

For a custom registry, import highlight_core.dart and create a Highlight instance. Register a grammar with engine.registerLanguage('dart', dart) from languages/dart.dart. The default registry does not load the full generated grammar set, including the 1C grammar.

Resume a parse

final first = hljs.highlight('/* first line\n', language: 'cpp');
final second = hljs.highlight(
  'second line */ int n = 1;\n',
  language: 'cpp',
  continuation: first.continuation,
);

HighlightContinuation is an opaque, reusable checkpoint. It retains open modes, callback data, and named embedded-language states. A checkpoint belongs to its engine and registered language definition. Aliases for that definition work. Resuming a checkpoint does not mutate it. This supports repeated parses of a partial trailing line.

Continuation does not guarantee that arbitrary chunks match a full parse. A chunk boundary can divide a token, delimiter, escape, or grammar lookahead. Even newline boundaries can change colours: JavaScript recognises hello\n() as a function call only when both lines are available. Concatenated HTML also has different span boundaries when a scope spans chunks. Tests compare scope paths per character instead.

Validation

From this directory:

dart pub get
dart test
dart test -p chrome
dart test -p chrome -c dart2wasm

The native integration tests use the highlight.js 11 fixtures in vendor/highlight.js. Initialize that submodule from the repository root before the tests. Browser tests cover the limited registry, continuation, vendor grammar ports, and public streaming benchmarks.

Reproduce the evaluation

dart run tool/evaluate.dart --bundle /path/to/hleval --output /tmp/highlight-evaluation
dart run tool/benchmark.dart
# Generate local browser fixtures, without committing private inputs:
dart run tool/evaluate.dart --bundle /path/to/hleval --output build/evaluation --skip-stream --emit-browser-test --emit-browser-stream-test
dart test build/evaluation --platform chrome --compiler dart2js
dart test build/evaluation --platform chrome --compiler dart2wasm

The evaluator reads the original bundle locally and writes fresh token runs, detection results, quality comparisons, and streaming timings. The public benchmark generates its own 20 KB inputs and can compile with dart2js or dart2wasm. Timing results include worst-chunk duration and scope differences from a full parse. Do not commit evaluation outputs: they can contain private source text.

Migration from 0.7.x

• Replace highlight.parse with hljs.highlight, or hljs.highlightAuto for detection.
• Call ensureInitialized() when using the default registry.
• Replace Result.nodes / Node with HighlightResult.emitter.root / DataNode.
• Replace parseWithContinuation and result.top with highlight(..., continuation: ...) and result.continuation.
• Theme keyword replaces legacy meta-keyword. Many built-in types now use type.
• Resolve dotted theme scopes explicitly or fall back to their parent scope.

License

MIT. Generated grammars retain the upstream highlight.js definitions.