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Compare screenshots, generate report of differences. (#8579)
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‎pkg/pub_integration/pubspec.yaml‎

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dev_dependencies:
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coverage: any # test already depends on it
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markdown: ^7.3.0
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shelf: ^1.4.0
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test: ^1.16.5

‎pkg/pub_integration/tool/compare_screenshots.dart‎

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// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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import 'dart:io';
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import 'package:markdown/markdown.dart';
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import 'package:path/path.dart' as p;
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/// Compares the screenshots from the previous and current test runs.
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/// Uses imagemagick for image processing.
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///
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/// `dart <script.dart> <before-dir> <after-dir> <report-dir>`
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Future<void> main(List<String> args) async {
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final beforeFiles = await _list(args[0]);
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final afterFiles = await _list(args[1]);
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final reportDir = Directory(args[2]);
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await reportDir.create(recursive: true);
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await _CompareTool(beforeFiles, afterFiles, reportDir)._compare();
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}
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class _CompareTool {
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final Directory _reportDir;
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final Map<String, File> _beforeFiles;
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final Map<String, File> _afterFiles;
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final _report = StringBuffer();
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_CompareTool(
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this._beforeFiles,
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this._afterFiles,
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this._reportDir,
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);
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Future<void> _compare() async {
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_report.writeln(
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'Screenshot comparison report generated at ${DateTime.now().toIso8601String()}.');
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final newFiles = _afterFiles.keys
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.where((key) => !_beforeFiles.containsKey(key))
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.toList();
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if (newFiles.isNotEmpty) {
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_report.writeln([
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'',
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'# New files',
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newFiles.map((e) => '- `$e`').join('\n'),
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].join('\n\n'));
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}
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final missingFiles = _beforeFiles.keys
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.where((key) => !_afterFiles.containsKey(key))
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.toList();
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if (missingFiles.isNotEmpty) {
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_report.writeln([
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'',
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'# Missing files',
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missingFiles.map((e) => '- `$e`').join('\n'),
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].join('\n\n'));
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}
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for (final path in _afterFiles.keys) {
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final after = _afterFiles[path]!;
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if (!_beforeFiles.containsKey(path)) continue;
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final before = _beforeFiles[path]!;
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// quick byte-content check
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final afterBytes = await after.readAsBytes();
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final beforeBytes = await before.readAsBytes();
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if (afterBytes.length == beforeBytes.length &&
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afterBytes.indexed.every((e) => beforeBytes[e.$1] == e.$2)) {
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continue;
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}
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final relativeDir = p.dirname(path);
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final basename = p.basenameWithoutExtension(path);
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final diffPath =
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p.join(_reportDir.path, relativeDir, '$basename-diff.png');
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await File(diffPath).parent.create(recursive: true);
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final pr = await Process.run('compare', [
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before.path,
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after.path,
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diffPath,
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]);
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if (pr.exitCode == 0) continue;
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final beforeFile =
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File(p.join(_reportDir.path, relativeDir, '$basename-before.png'));
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await beforeFile.writeAsBytes(beforeBytes);
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final afterFile =
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File(p.join(_reportDir.path, relativeDir, '$basename-after.png'));
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await afterFile.writeAsBytes(afterBytes);
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_report.writeln('`$path`\n');
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_report.writeln(
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'![before](${p.join(relativeDir, '$basename-before.png')})\n');
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_report
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.writeln('![after](${p.join(relativeDir, '$basename-after.png')})\n');
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_report
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.writeln('![diff](${p.join(relativeDir, '$basename-diff.png')})\n');
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_report.writeln();
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}
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await _writeIndexHtml();
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}
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Future<void> _writeIndexHtml() async {
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await File(p.join(_reportDir.path, 'index.html')).writeAsString([
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'<html><body>',
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markdownToHtml(_report.toString()),
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'</body></html>',
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].join('\n'));
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}
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}
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Future<Map<String, File>> _list(String path) async {
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final map = <String, File>{};
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await for (final file in Directory(path).list(recursive: true)) {
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if (file is! File) continue;
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final rp = p.relative(file.path, from: path);
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map[rp] = file;
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}
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return Map.fromEntries(
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map.entries.toList()..sort((a, b) => a.key.compareTo(b.key)));
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}

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