dry4dart

A command-line tool that finds candidate duplicate Dart code across files and directories. Reports fuzzy structural matches by file and line range so developers can review similar declarations before refactoring.

Features

• Compares top-level functions, methods, constructors, getters, and setters
• Structural matching via normalized syntax nodes and Jaccard similarity
• Text and JSON output formats
• Excludes generated files (.g.dart, .freezed.dart, .mocks.dart, .config.dart, .gr.dart) by default
• Optional non-zero exit when any candidate is found, for continuous integration use

Overview

dry4dart compares top-level Dart declarations by first converting each declaration into normalized syntax nodes. The normalized form is then walked to collect a set of structural fingerprints, one for the whole declaration and one for each nested subexpression.

Similarity is Jaccard similarity over those fingerprint sets:

score = shared fingerprints / all fingerprints seen in either declaration

A score of 1.0 means the normalized structures have the same fingerprint set. Lower scores mean the declarations still share structure, but each declaration also has some structure the other does not. The default --threshold 0.82 reports candidates whose normalized structures are close enough to be worth review.

For example, these two functions score 1.0: their names, local names, predicates, and mapped functions differ, but those incidental symbols are removed by normalization and the retained structure is identical.

List<int> alpha(List<int> xs) {
  final ys = xs.where(isOdd);
  return ys.map((x) => x + 1).toList();
}

List<int> beta(List<int> items) {
  final kept = items.where(isEven);
  return kept.map((x) => x + 2).toList();
}

Scores below 1.0 reflect smaller divergences. Two functions that match except for one extra local binding typically score around 0.89, because the extra binding contributes a few unique fingerprints to the Jaccard union.

Installation

dry4dart is not published on pub.dev. Install it from the Git repository as a development dependency so each project pins the tool and resolves analyzer against the same constraints as the project itself.

dart pub add --dev dry4dart --git-url https://github.com/brackendev/dry4dart.git --git-ref v0.2.0
dart run dry4dart lib

dart pub add --dev writes the entry into the dev_dependencies section of pubspec.yaml. If editing pubspec.yaml by hand, the resulting entry is:

dev_dependencies:
  dry4dart:
    git:
      url: https://github.com/brackendev/dry4dart.git
      ref: v0.2.0

dry4dart requires Dart 3.11 or later. It depends on package:analyzer to parse Dart source. Because analyzer changes its public syntax tree across major versions, dry4dart supports a bounded analyzer range, currently 13.1.0 through 14.x. See pubspec.yaml in this repository for the current constraint if dependency resolution fails in a project that already pins analyzer indirectly.

For ad-hoc scans where a development dependency is impractical, install dry4dart globally. A globally installed analyzer may not match the project being scanned, which can cause newer language features to misparse.

dart pub global activate --source git https://github.com/brackendev/dry4dart.git --git-ref v0.2.0
dry4dart lib

Usage

dart run dry4dart [options] [file-or-directory ...]

A globally activated install exposes the same command as dry4dart without the dart run prefix.

Option	Description
--threshold N	Minimum structural similarity score. Default 0.82.
--min-lines N	Minimum source lines in a candidate declaration. Default 4.
--min-nodes N	Minimum normalized syntax nodes in a candidate declaration. Default 20.
--format F	Output format: text or json. Default text.
--json	Same as --format json.
--text	Same as --format text.
--include-generated	Include .g.dart, .freezed.dart, .mocks.dart, .config.dart, and .gr.dart files.
--fail-on-findings	Exit with status 1 when any candidate is reported.
--help	Show usage information.
--version	Show the dry4dart version.

By default, findings do not fail the command. Use --fail-on-findings for continuous integration checks.

Examples:

dart run dry4dart lib
dart run dry4dart lib/foo.dart lib/bar.dart
dart run dry4dart --json --threshold 0.9 lib

All paths in one invocation share the same search set. Directory arguments expand recursively to .dart files, so dart run dry4dart lib test/foo_test.dart compares test/foo_test.dart with every Dart file under lib and with any other files in the same invocation.

Default text output is intended for quick reading:

DUPLICATE score=0.89
  lib/billing/invoice.dart:12-32
  lib/billing/receipt.dart:40-60

JSON output is intended for tools:

{
  "candidates": [
    {
      "score": 0.8909090909090909,
      "left": {"file": "lib/billing/invoice.dart", "startLine": 12, "endLine": 32},
      "right": {"file": "lib/billing/receipt.dart", "startLine": 40, "endLine": 60},
      "leftNodes": 88,
      "rightNodes": 91
    }
  ]
}

Development

dart test

Issues

Report bugs or request features at github.com/brackendev/dry4dart/issues.

Related project

Inspired by dry4clj.