Minimal screenshot tool.

pubspec.yaml

@@ -27,7 +27,10 @@ dev_dependencies:
   dart_style: ^3.0.0
   lints: ">=5.0.0 <7.0.0"
   matcher: ^0.12.15
+  puppeteer: ^3.18.0
   sass: ^1.87.0
+  shelf: ^1.4.2
+  shelf_static: ^1.1.3
   test: ^1.24.2
   test_descriptor: ^2.0.1
   test_process: ^2.0.3
@@ -36,3 +39,6 @@ dev_dependencies:
 
 executables:
   dartdoc: null
+
+dependency_overrides:
+  archive: ^4.0.0

test/end2end/dartdoc_test.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'dart:io';
+
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:dartdoc/src/dartdoc.dart' show Dartdoc, DartdocResults;
 import 'package:dartdoc/src/dartdoc_options.dart';
@@ -15,9 +17,13 @@ import 'package:dartdoc/src/package_config_provider.dart';
 import 'package:dartdoc/src/package_meta.dart';
 import 'package:dartdoc/src/warnings.dart';
 import 'package:path/path.dart' as path;
+import 'package:shelf/shelf_io.dart';
+import 'package:shelf_static/shelf_static.dart';
 import 'package:test/test.dart';
 
 import '../src/utils.dart';
+import 'screenshot_utils.dart';
+import 'test_browser.dart';
 
 final _resourceProvider = pubPackageMetaProvider.resourceProvider;
 final _pathContext = _resourceProvider.pathContext;
@@ -203,6 +209,41 @@ void main() {
       expect(level2.exists, isTrue);
       expect(level2.readAsStringSync(),
           contains('<link rel="canonical" href="$prefix/ex/Apple/m.html">'));
+
+      if (isScreenshotDirSet) {
+        final server = await _setupStaticHttpServer(tempDir.path);
+        final browser = TestBrowser(origin: 'http://localhost:${server.port}');
+        final allPaths = Directory(tempDir.path)
+            .listSync(recursive: true, followLinks: true)
+            .map((f) => path.relative(f.path, from: tempDir.path))
+            .where((p) => p.endsWith('.html'))
+            .toList();
+        final paths = [
+          'index.html',
+          'ex/index.html',
+          'ex/HtmlInjection-class.html',
+          'ex/IntSet/sum.html',
+        ];
+        assert(paths.every(allPaths.contains));
+        try {
+          await browser.startBrowser();
+          final session = await browser.createSession();
+          await session.withPage<void>(fn: (page) async {
+            for (final p in paths) {
+              await page.gotoOrigin('/$p');
+              final prefix = p.replaceAll('.html', '').replaceAll('.', '-');
+              await page.takeScreenshots(selector: 'body', prefix: prefix);
+            }
+          });
+        } finally {
+          await server.close();
+          await browser.close();
+        }
+      }
     });
   }, timeout: Timeout.factor(12));
 }
+
+Future<HttpServer> _setupStaticHttpServer(String path) async {
+  return await serve(createStaticHandler(path), 'localhost', 0);
+}

test/end2end/screenshot_utils.dart

@@ -0,0 +1,110 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+import 'package:path/path.dart' as p;
+import 'package:puppeteer/puppeteer.dart';
+
+// Default screen with 16:10 ratio.
+final desktopDeviceViewport = DeviceViewport(width: 1280, height: 800);
+
+final _screenshotDir = Platform.environment['SCREENSHOT_DIR'];
+final isScreenshotDirSet = _screenshotDir != null && _screenshotDir!.isNotEmpty;
+
+// Set this variable to enable screenshot files to be updated with new takes.
+// The default is to throw an exception to prevent accidental overrides from
+// separate tests.
+final _allowScreeshotUpdates = Platform.environment['SCREENSHOT_UPDATE'] == '1';
+
+// Note: The default values are the last, so we don't need reset
+//       the original values after taking the screenshots.
+final _themes = ['dark', 'light'];
+final _viewports = {
+  'mobile': DeviceViewport(width: 400, height: 800),
+  'tablet': DeviceViewport(width: 768, height: 1024),
+  'desktop': desktopDeviceViewport,
+};
+
+extension ScreenshotPageExt on Page {
+  Future<void> writeScreenshotToFile(String path) async {
+    await File(path).writeAsBytes(await screenshot());
+  }
+
+  /// Takes screenshots **if** `SCREENSHOT_DIR` environment variable is set.
+  ///
+  /// Iterates over viewports and themes, and generates screenshot files with the
+  /// following pattern:
+  /// - `SCREENSHOT_DIR/$prefix-desktop-dark.png`
+  /// - `SCREENSHOT_DIR/$prefix-desktop-light.png`
+  /// - `SCREENSHOT_DIR/$prefix-mobile-dark.png`
+  /// - `SCREENSHOT_DIR/$prefix-mobile-light.png`
+  /// - `SCREENSHOT_DIR/$prefix-tablet-dark.png`
+  /// - `SCREENSHOT_DIR/$prefix-tablet-light.png`
+  Future<void> takeScreenshots({
+    required String selector,
+    required String prefix,
+  }) async {
+    final handle = await $(selector);
+    await handle.takeScreenshots(prefix);
+  }
+}
+
+extension ScreenshotElementHandleExt on ElementHandle {
+  /// Takes screenshots **if** `SCREENSHOT_DIR` environment variable is set.
+  ///
+  /// Iterates over viewports and themes, and generates screenshot files with the
+  /// following pattern:
+  /// - `SCREENSHOT_DIR/$prefix-desktop-dark.png`
+  /// - `SCREENSHOT_DIR/$prefix-desktop-light.png`
+  /// - `SCREENSHOT_DIR/$prefix-mobile-dark.png`
+  /// - `SCREENSHOT_DIR/$prefix-mobile-light.png`
+  /// - `SCREENSHOT_DIR/$prefix-tablet-dark.png`
+  /// - `SCREENSHOT_DIR/$prefix-tablet-light.png`
+  Future<void> takeScreenshots(String prefix) async {
+    final body = await page.$('body');
+    final bodyClassAttr = (await body
+        .evaluate<String>('el => el.getAttribute("class")')) as String;
+    final bodyClasses = [
+      ...bodyClassAttr.split(' '),
+      '--ongoing-screenshot',
+    ];
+
+    for (final vp in _viewports.entries) {
+      await page.setViewport(vp.value);
+
+      for (final theme in _themes) {
+        final newClasses = [
+          ...bodyClasses.where((c) => !c.endsWith('-theme')),
+          '$theme-theme',
+        ];
+        await body.evaluate<String>('(el, v) => el.setAttribute("class", v)',
+            args: [newClasses.join(' ')]);
+
+        // The presence of the element is verified, continue only if screenshots are enabled.
+        if (!isScreenshotDirSet) continue;
+
+        // Arbitrary delay in the hope that potential ongoing updates complete.
+        await Future<void>.delayed(Duration(milliseconds: 500));
+
+        final path = p.join(_screenshotDir!, '$prefix-${vp.key}-$theme.png');
+        await _writeScreenshotToFile(path);
+      }
+    }
+
+    // restore the original body class attributes
+    await body.evaluate<String>('(el, v) => el.setAttribute("class", v)',
+        args: [bodyClassAttr]);
+  }
+
+  Future<void> _writeScreenshotToFile(String path) async {
+    final file = File(path);
+    final exists = file.existsSync();
+    if (exists && !_allowScreeshotUpdates) {
+      throw Exception('Screenshot update is detected in: $path');
+    }
+    await file.parent.create(recursive: true);
+    await File(path).writeAsBytes(await screenshot());
+  }
+}