more ui-as-code (#35393)

* more ui-as-code

* address review comments

dev/bots/analyze-sample-code.dart

@@ -531,10 +531,12 @@ linter:
   File _writeSection(Section section) {
     final String sectionId = _createNameFromSource('sample', section.start.filename, section.start.line);
     final File outputFile = File(path.join(_tempDirectory.path, '$sectionId.dart'))..createSync(recursive: true);
-    final List<Line> mainContents = headers.toList();
-    mainContents.add(const Line(''));
-    mainContents.add(Line('// From: ${section.start.filename}:${section.start.line}'));
-    mainContents.addAll(section.code);
+    final List<Line> mainContents = <Line>[
+      ...headers,
+      const Line(''),
+      Line('// From: ${section.start.filename}:${section.start.line}'),
+      ...section.code,
+    ];
     outputFile.writeAsStringSync(mainContents.map<String>((Line line) => line.code).join('\n'));
     return outputFile;
   }
@@ -820,10 +822,9 @@ class Line {
 class Section {
   const Section(this.code);
   factory Section.combine(List<Section> sections) {
-    final List<Line> code = <Line>[];
-    for (Section section in sections) {
-      code.addAll(section.code);
-    }
+    final List<Line> code = sections
+      .expand((Section section) => section.code)
+      .toList();
     return Section(code);
   }
   factory Section.fromStrings(Line firstLine, List<String> code) {

dev/bots/analyze.dart

@@ -40,9 +40,10 @@ Future<void> main(List<String> args) async {
 
   {
     // Analyze all the Dart code in the repo.
-    final List<String> options = <String>['--flutter-repo'];
-    options.addAll(args);
-    await _runFlutterAnalyze(flutterRoot, options: options);
+    await _runFlutterAnalyze(flutterRoot, options: <String>[
+      '--flutter-repo',
+      ...args,
+    ]);
   }
 
   // Ensure that all package dependencies are in sync.
@@ -59,9 +60,12 @@ Future<void> main(List<String> args) async {
   // Try with the --watch analyzer, to make sure it returns success also.
   // The --benchmark argument exits after one run.
   {
-    final List<String> options = <String>['--flutter-repo', '--watch', '--benchmark'];
-    options.addAll(args);
-    await _runFlutterAnalyze(flutterRoot, options: options);
+    await _runFlutterAnalyze(flutterRoot, options: <String>[
+      '--flutter-repo',
+      '--watch',
+      '--benchmark',
+      ...args,
+    ]);
   }
 
   await _checkForTrailingSpaces();
@@ -79,9 +83,11 @@ Future<void> main(List<String> args) async {
       workingDirectory: flutterRoot,
     );
     {
-      final List<String> options = <String>['--watch', '--benchmark'];
-      options.addAll(args);
-      await _runFlutterAnalyze(outDir.path, options: options);
+      await _runFlutterAnalyze(outDir.path, options: <String>[
+        '--watch',
+        '--benchmark',
+        ...args,
+      ]);
     }
   } finally {
     outDir.deleteSync(recursive: true);

dev/bots/prepare_package.dart

@@ -601,14 +601,14 @@ class ArchivePublisher {
     if (dest.endsWith('.json')) {
       mimeType = 'application/json';
     }
-    final List<String> args = <String>[];
-    // Use our preferred MIME type for the files we care about
-    // and let gsutil figure it out for anything else.
-    if (mimeType != null) {
-      args.addAll(<String>['-h', 'Content-Type:$mimeType']);
-    }
-    args.addAll(<String>['cp', src, dest]);
-    return await _runGsUtil(args);
+    return await _runGsUtil(<String>[
+      // Use our preferred MIME type for the files we care about
+      // and let gsutil figure it out for anything else.
+      if (mimeType != null) ...<String>['-h', 'Content-Type:$mimeType'],
+      'cp',
+      src,
+      dest,
+    ]);
   }
 }
 

dev/bots/test.dart

@@ -754,11 +754,13 @@ Future<void> _runFlutterWebTest(String workingDirectory, {
   Duration timeout = _kLongTimeout,
   List<String> tests,
 }) async {
-  final List<String> args = <String>['test', '-v', '--platform=chrome'];
-  if (flutterTestArgs != null && flutterTestArgs.isNotEmpty)
-    args.addAll(flutterTestArgs);
-
-  args.addAll(tests);
+  final List<String> args = <String>[
+    'test',
+    '-v',
+    '--platform=chrome',
+    ...?flutterTestArgs,
+    ...tests,
+  ];
 
   // TODO(jonahwilliams): fix relative path issues to make this unecessary.
   final Directory oldCurrent = Directory.current;
@@ -791,9 +793,11 @@ Future<void> _runFlutterTest(String workingDirectory, {
   Map<String, String> environment,
   List<String> tests = const <String>[],
 }) async {
-  final List<String> args = <String>['test', ...options];
-  if (flutterTestArgs != null && flutterTestArgs.isNotEmpty)
-    args.addAll(flutterTestArgs);
+  final List<String> args = <String>[
+    'test',
+    ...options,
+    ...?flutterTestArgs,
+  ];
 
   final bool shouldProcessOutput = useFlutterTestFormatter && !expectFailure && !options.contains('--coverage');
   if (shouldProcessOutput) {

dev/bots/test/prepare_package_test.dart

@@ -106,16 +106,14 @@ void main() {
 
       test('sets PUB_CACHE properly', () async {
         final String createBase = path.join(tempDir.absolute.path, 'create_');
-        final Map<String, List<ProcessResult>> calls = <String, List<ProcessResult>>{
+        final String archiveName = path.join(tempDir.absolute.path,
+            'flutter_${platformName}_v1.2.3-dev${platform.isLinux ? '.tar.xz' : '.zip'}');
+        processManager.fakeResults = <String, List<ProcessResult>>{
           'git clone -b dev https://chromium.googlesource.com/external/github.com/flutter/flutter': null,
           'git reset --hard $testRef': null,
           'git remote set-url origin https://github.com/flutter/flutter.git': null,
           'git describe --tags --exact-match $testRef': <ProcessResult>[ProcessResult(0, 0, 'v1.2.3', '')],
-        };
-        if (platform.isWindows) {
-          calls['7za x ${path.join(tempDir.path, 'mingit.zip')}'] = null;
-        }
-        calls.addAll(<String, List<ProcessResult>>{
+          if (platform.isWindows) '7za x ${path.join(tempDir.path, 'mingit.zip')}': null,
           '$flutter doctor': null,
           '$flutter update-packages': null,
           '$flutter precache': null,
@@ -124,17 +122,10 @@ void main() {
           '$flutter create --template=package ${createBase}package': null,
           '$flutter create --template=plugin ${createBase}plugin': null,
           'git clean -f -X **/.packages': null,
-        });
-        final String archiveName = path.join(tempDir.absolute.path,
-            'flutter_${platformName}_v1.2.3-dev${platform.isLinux ? '.tar.xz' : '.zip'}');
-        if (platform.isWindows) {
-          calls['7za a -tzip -mx=9 $archiveName flutter'] = null;
-        } else if (platform.isMacOS) {
-          calls['zip -r -9 $archiveName flutter'] = null;
-        } else if (platform.isLinux) {
-          calls['tar cJf $archiveName flutter'] = null;
-        }
-        processManager.fakeResults = calls;
+          if (platform.isWindows) '7za a -tzip -mx=9 $archiveName flutter': null
+          else if (platform.isMacOS) 'zip -r -9 $archiveName flutter': null
+          else if (platform.isLinux) 'tar cJf $archiveName flutter': null,
+        };
         await creator.initializeRepo();
         await creator.createArchive();
         expect(
@@ -149,16 +140,14 @@ void main() {
 
       test('calls the right commands for archive output', () async {
         final String createBase = path.join(tempDir.absolute.path, 'create_');
+        final String archiveName = path.join(tempDir.absolute.path,
+            'flutter_${platformName}_v1.2.3-dev${platform.isLinux ? '.tar.xz' : '.zip'}');
         final Map<String, List<ProcessResult>> calls = <String, List<ProcessResult>>{
           'git clone -b dev https://chromium.googlesource.com/external/github.com/flutter/flutter': null,
           'git reset --hard $testRef': null,
           'git remote set-url origin https://github.com/flutter/flutter.git': null,
           'git describe --tags --exact-match $testRef': <ProcessResult>[ProcessResult(0, 0, 'v1.2.3', '')],
-        };
-        if (platform.isWindows) {
-          calls['7za x ${path.join(tempDir.path, 'mingit.zip')}'] = null;
-        }
-        calls.addAll(<String, List<ProcessResult>>{
+          if (platform.isWindows) '7za x ${path.join(tempDir.path, 'mingit.zip')}': null,
           '$flutter doctor': null,
           '$flutter update-packages': null,
           '$flutter precache': null,
@@ -167,16 +156,10 @@ void main() {
           '$flutter create --template=package ${createBase}package': null,
           '$flutter create --template=plugin ${createBase}plugin': null,
           'git clean -f -X **/.packages': null,
-        });
-        final String archiveName = path.join(tempDir.absolute.path,
-            'flutter_${platformName}_v1.2.3-dev${platform.isLinux ? '.tar.xz' : '.zip'}');
-        if (platform.isWindows) {
-          calls['7za a -tzip -mx=9 $archiveName flutter'] = null;
-        } else if (platform.isMacOS) {
-          calls['zip -r -9 $archiveName flutter'] = null;
-        } else if (platform.isLinux) {
-          calls['tar cJf $archiveName flutter'] = null;
-        }
+          if (platform.isWindows) '7za a -tzip -mx=9 $archiveName flutter': null
+          else if (platform.isMacOS) 'zip -r -9 $archiveName flutter': null
+          else if (platform.isLinux) 'tar cJf $archiveName flutter': null,
+        };
         processManager.fakeResults = calls;
         creator = ArchiveCreator(
           tempDir,
@@ -206,16 +189,14 @@ void main() {
 
       test('non-strict mode calls the right commands', () async {
         final String createBase = path.join(tempDir.absolute.path, 'create_');
+        final String archiveName = path.join(tempDir.absolute.path,
+            'flutter_${platformName}_v1.2.3-dev${platform.isLinux ? '.tar.xz' : '.zip'}');
         final Map<String, List<ProcessResult>> calls = <String, List<ProcessResult>>{
           'git clone -b dev https://chromium.googlesource.com/external/github.com/flutter/flutter': null,
           'git reset --hard $testRef': null,
           'git remote set-url origin https://github.com/flutter/flutter.git': null,
           'git describe --tags --abbrev=0 $testRef': <ProcessResult>[ProcessResult(0, 0, 'v1.2.3', '')],
-        };
-        if (platform.isWindows) {
-          calls['7za x ${path.join(tempDir.path, 'mingit.zip')}'] = null;
-        }
-        calls.addAll(<String, List<ProcessResult>>{
+          if (platform.isWindows) '7za x ${path.join(tempDir.path, 'mingit.zip')}': null,
           '$flutter doctor': null,
           '$flutter update-packages': null,
           '$flutter precache': null,
@@ -224,16 +205,10 @@ void main() {
           '$flutter create --template=package ${createBase}package': null,
           '$flutter create --template=plugin ${createBase}plugin': null,
           'git clean -f -X **/.packages': null,
-        });
-        final String archiveName = path.join(tempDir.absolute.path,
-            'flutter_${platformName}_v1.2.3-dev${platform.isLinux ? '.tar.xz' : '.zip'}');
-        if (platform.isWindows) {
-          calls['7za a -tzip -mx=9 $archiveName flutter'] = null;
-        } else if (platform.isMacOS) {
-          calls['zip -r -9 $archiveName flutter'] = null;
-        } else if (platform.isLinux) {
-          calls['tar cJf $archiveName flutter'] = null;
-        }
+          if (platform.isWindows) '7za a -tzip -mx=9 $archiveName flutter': null
+          else if (platform.isMacOS) 'zip -r -9 $archiveName flutter': null
+          else if (platform.isLinux) 'tar cJf $archiveName flutter': null,
+        };
         processManager.fakeResults = calls;
         creator = ArchiveCreator(
           tempDir,

dev/bots/unpublish_package.dart

@@ -377,13 +377,12 @@ class ArchiveUnpublisher {
     if (dest.endsWith('.json')) {
       mimeType = 'application/json';
     }
-    final List<String> args = <String>[];
-    // Use our preferred MIME type for the files we care about
-    // and let gsutil figure it out for anything else.
-    if (mimeType != null) {
-      args.addAll(<String>['-h', 'Content-Type:$mimeType']);
-    }
-    args.addAll(<String>['cp', src, dest]);
+    final List<String> args = <String>[
+      // Use our preferred MIME type for the files we care about
+      // and let gsutil figure it out for anything else.
+      if (mimeType != null) ...<String>['-h', 'Content-Type:$mimeType'],
+      ...<String>['cp', src, dest],
+    ];
     return await _runGsUtil(args, confirm: confirmed);
   }
 }

dev/devicelab/lib/framework/apk_utils.dart

@@ -252,10 +252,10 @@ Future<ProcessResult> _resultOfGradleTask({String workingDirectory, String task,
 
   print('\nUsing JAVA_HOME=$javaHome');
 
-  final List<String> args = <String>['app:$task'];
-  if (options != null) {
-    args.addAll(options);
-  }
+  final List<String> args = <String>[
+    'app:$task',
+    ...?options,
+  ];
   final String gradle = Platform.isWindows ? 'gradlew.bat' : './gradlew';
   print('Running Gradle: ${path.join(workingDirectory, gradle)} ${args.join(' ')}');
   print(File(path.join(workingDirectory, gradle)).readAsStringSync());

dev/devicelab/lib/tasks/analysis.dart

@@ -28,11 +28,12 @@ Future<TaskResult> analyzerBenchmarkTask() async {
     await dart(<String>['dev/tools/mega_gallery.dart', '--out=${_megaGalleryDirectory.path}']);
   });
 
-  final Map<String, dynamic> data = <String, dynamic>{};
-  data.addAll((await _run(_FlutterRepoBenchmark())).asMap('flutter_repo', 'batch'));
-  data.addAll((await _run(_FlutterRepoBenchmark(watch: true))).asMap('flutter_repo', 'watch'));
-  data.addAll((await _run(_MegaGalleryBenchmark())).asMap('mega_gallery', 'batch'));
-  data.addAll((await _run(_MegaGalleryBenchmark(watch: true))).asMap('mega_gallery', 'watch'));
+  final Map<String, dynamic> data = <String, dynamic>{
+    ...(await _run(_FlutterRepoBenchmark())).asMap('flutter_repo', 'batch'),
+    ...(await _run(_FlutterRepoBenchmark(watch: true))).asMap('flutter_repo', 'watch'),
+    ...(await _run(_MegaGalleryBenchmark())).asMap('mega_gallery', 'batch'),
+    ...(await _run(_MegaGalleryBenchmark(watch: true))).asMap('mega_gallery', 'watch'),
+  };
 
   return TaskResult.success(data, benchmarkScoreKeys: data.keys.toList());
 }

dev/devicelab/lib/tasks/gallery.dart

@@ -64,8 +64,8 @@ class GalleryTransitionTest {
     final Map<String, dynamic> data = <String, dynamic>{
       'transitions': transitions,
       'missed_transition_count': _countMissedTransitions(transitions),
+      ...summary,
     };
-    data.addAll(summary);
 
     return TaskResult.success(data, benchmarkScoreKeys: <String>[
       'missed_transition_count',

dev/devicelab/lib/tasks/integration_tests.dart

@@ -124,8 +124,8 @@ class DriverTest {
         testTarget,
         '-d',
         deviceId,
+        ...extraOptions,
       ];
-      options.addAll(extraOptions);
       await flutter('drive', options: options, environment: Map<String, String>.from(environment));
 
       return TaskResult.success(null);

dev/devicelab/lib/tasks/microbenchmarks.dart

@@ -48,13 +48,14 @@ TaskFunction createMicrobenchmarkTask() {
       return _run();
     }
 
-    final Map<String, double> allResults = <String, double>{};
-    allResults.addAll(await _runMicrobench('lib/stocks/layout_bench.dart'));
-    allResults.addAll(await _runMicrobench('lib/stocks/build_bench.dart'));
-    allResults.addAll(await _runMicrobench('lib/geometry/rrect_contains_bench.dart'));
-    allResults.addAll(await _runMicrobench('lib/gestures/velocity_tracker_bench.dart'));
-    allResults.addAll(await _runMicrobench('lib/gestures/gesture_detector_bench.dart'));
-    allResults.addAll(await _runMicrobench('lib/stocks/animation_bench.dart'));
+    final Map<String, double> allResults = <String, double>{
+      ...await _runMicrobench('lib/stocks/layout_bench.dart'),
+      ...await _runMicrobench('lib/stocks/build_bench.dart'),
+      ...await _runMicrobench('lib/geometry/rrect_contains_bench.dart'),
+      ...await _runMicrobench('lib/gestures/velocity_tracker_bench.dart'),
+      ...await _runMicrobench('lib/gestures/gesture_detector_bench.dart'),
+      ...await _runMicrobench('lib/stocks/animation_bench.dart'),
+    };
 
     return TaskResult.success(allResults, benchmarkScoreKeys: allResults.keys.toList());
   };

dev/devicelab/lib/tasks/perf_tests.dart

@@ -289,10 +289,11 @@ class CompileTest {
       await device.unlock();
       await flutter('packages', options: <String>['get']);
 
-      final Map<String, dynamic> metrics = <String, dynamic>{}
-        ..addAll(await _compileAot())
-        ..addAll(await _compileApp(reportPackageContentSizes: reportPackageContentSizes))
-        ..addAll(await _compileDebug());
+      final Map<String, dynamic> metrics = <String, dynamic>{
+        ...await _compileAot(),
+        ...await _compileApp(reportPackageContentSizes: reportPackageContentSizes),
+        ...await _compileDebug(),
+      };
 
       return TaskResult.success(metrics, benchmarkScoreKeys: metrics.keys.toList());
     });
@@ -533,10 +534,11 @@ class MemoryTest {
       final ListStatistics endMemoryStatistics = ListStatistics(_endMemory);
       final ListStatistics diffMemoryStatistics = ListStatistics(_diffMemory);
 
-      final Map<String, dynamic> memoryUsage = <String, dynamic>{};
-      memoryUsage.addAll(startMemoryStatistics.asMap('start'));
-      memoryUsage.addAll(endMemoryStatistics.asMap('end'));
-      memoryUsage.addAll(diffMemoryStatistics.asMap('diff'));
+      final Map<String, dynamic> memoryUsage = <String, dynamic>{
+        ...startMemoryStatistics.asMap('start'),
+        ...endMemoryStatistics.asMap('end'),
+        ...diffMemoryStatistics.asMap('diff'),
+      };
 
       _device = null;
       _startMemory.clear();

dev/devicelab/test/run_test.dart

@@ -15,14 +15,12 @@ void main() {
 
   group('run.dart script', () {
     Future<ProcessResult> runScript(List<String> testNames) async {
-      final List<String> options = <String>['bin/run.dart'];
-      for (String testName in testNames) {
-        options..addAll(<String>['-t', testName]);
-      }
       final String dart = path.absolute(path.join('..', '..', 'bin', 'cache', 'dart-sdk', 'bin', 'dart'));
-      final ProcessResult scriptProcess = processManager.runSync(
-        <String>[dart, ...options]
-      );
+      final ProcessResult scriptProcess = processManager.runSync(<String>[
+        dart,
+        'bin/run.dart',
+        for (String testName in testNames) ...<String>['-t', testName],
+      ]);
       return scriptProcess;
     }
 

dev/manual_tests/lib/text.dart

@@ -1401,8 +1401,7 @@ String zalgo(math.Random random, int targetLength, { bool includeSpacingCombinin
     }
   }
   base ??= String.fromCharCode(randomCharacter(random));
-  final List<int> characters = <int>[];
-  characters.addAll(these);
+  final List<int> characters = these.toList();
   return base + String.fromCharCodes(characters);
 }
 

dev/snippets/lib/snippets.dart

@@ -127,15 +127,16 @@ class SnippetGenerator {
       'description': description,
       'code': htmlEscape.convert(result.join('\n')),
       'language': language ?? 'dart',
-    }..addAll(type == SnippetType.application
-        ? <String, String>{
-            'serial': metadata['serial'].toString() ?? '0',
-            'id':
-                injections.firstWhere((_ComponentTuple tuple) => tuple.name == 'id').mergedContent,
-            'app':
-                htmlEscape.convert(injections.firstWhere((_ComponentTuple tuple) => tuple.name == 'app').mergedContent),
-          }
-        : <String, String>{'serial': '', 'id': '', 'app': ''});
+      'serial': '',
+      'id': '',
+      'app': '',
+    };
+    if (type == SnippetType.application) {
+      substitutions
+        ..['serial'] = metadata['serial'].toString() ?? '0'
+        ..['id'] = injections.firstWhere((_ComponentTuple tuple) => tuple.name == 'id').mergedContent
+        ..['app'] = htmlEscape.convert(injections.firstWhere((_ComponentTuple tuple) => tuple.name == 'app').mergedContent);
+    }
     return skeleton.replaceAllMapped(RegExp('{{(${substitutions.keys.join('|')})}}'), (Match match) {
       return substitutions[match[1]];
     });

examples/flutter_gallery/lib/demo/colors_demo.dart

@@ -99,26 +99,24 @@ class PaletteTabView extends StatelessWidget {
     final TextTheme textTheme = Theme.of(context).textTheme;
     final TextStyle whiteTextStyle = textTheme.body1.copyWith(color: Colors.white);
     final TextStyle blackTextStyle = textTheme.body1.copyWith(color: Colors.black);
-    final List<Widget> colorItems = primaryKeys.map<Widget>((int index) {
-      return DefaultTextStyle(
-        style: index > colors.threshold ? whiteTextStyle : blackTextStyle,
-        child: ColorItem(index: index, color: colors.primary[index]),
-      );
-    }).toList();
-
-    if (colors.accent != null) {
-      colorItems.addAll(accentKeys.map<Widget>((int index) {
-        return DefaultTextStyle(
-          style: index > colors.threshold ? whiteTextStyle : blackTextStyle,
-          child: ColorItem(index: index, color: colors.accent[index], prefix: 'A'),
-        );
-      }).toList());
-    }
-
     return Scrollbar(
       child: ListView(
         itemExtent: kColorItemHeight,
-        children: colorItems,
+        children: <Widget>[
+          ...primaryKeys.map<Widget>((int index) {
+            return DefaultTextStyle(
+              style: index > colors.threshold ? whiteTextStyle : blackTextStyle,
+              child: ColorItem(index: index, color: colors.primary[index]),
+            );
+          }),
+          if (colors.accent != null)
+            ...accentKeys.map<Widget>((int index) {
+              return DefaultTextStyle(
+                style: index > colors.threshold ? whiteTextStyle : blackTextStyle,
+                child: ColorItem(index: index, color: colors.accent[index], prefix: 'A'),
+              );
+            }),
+        ],
       )
     );
   }

examples/flutter_gallery/lib/demo/material/bottom_app_bar_demo.dart

@@ -349,52 +349,42 @@ class _DemoBottomAppBar extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final List<Widget> rowContents = <Widget> [
-      IconButton(
-        icon: const Icon(Icons.menu, semanticLabel: 'Show bottom sheet'),
-        onPressed: () {
-          showModalBottomSheet<void>(
-            context: context,
-            builder: (BuildContext context) => const _DemoDrawer(),
-          );
-        },
-      ),
-    ];
-
-    if (kCenterLocations.contains(fabLocation)) {
-      rowContents.add(
-        const Expanded(child: SizedBox()),
-      );
-    }
-
-    rowContents.addAll(<Widget> [
-      IconButton(
-        icon: const Icon(Icons.search, semanticLabel: 'show search action',),
-        onPressed: () {
-          Scaffold.of(context).showSnackBar(
-            const SnackBar(content: Text('This is a dummy search action.')),
-          );
-        },
-      ),
-      IconButton(
-        icon: Icon(
-          Theme.of(context).platform == TargetPlatform.iOS
-              ? Icons.more_horiz
-              : Icons.more_vert,
-          semanticLabel: 'Show menu actions',
-        ),
-        onPressed: () {
-          Scaffold.of(context).showSnackBar(
-            const SnackBar(content: Text('This is a dummy menu action.')),
-          );
-        },
-      ),
-    ]);
-
     return BottomAppBar(
       color: color,
-      child: Row(children: rowContents),
       shape: shape,
+      child: Row(children: <Widget>[
+        IconButton(
+          icon: const Icon(Icons.menu, semanticLabel: 'Show bottom sheet'),
+          onPressed: () {
+            showModalBottomSheet<void>(
+              context: context,
+              builder: (BuildContext context) => const _DemoDrawer(),
+            );
+          },
+        ),
+        if (kCenterLocations.contains(fabLocation)) const Expanded(child: SizedBox()),
+        IconButton(
+          icon: const Icon(Icons.search, semanticLabel: 'show search action',),
+          onPressed: () {
+            Scaffold.of(context).showSnackBar(
+              const SnackBar(content: Text('This is a dummy search action.')),
+            );
+          },
+        ),
+        IconButton(
+          icon: Icon(
+            Theme.of(context).platform == TargetPlatform.iOS
+                ? Icons.more_horiz
+                : Icons.more_vert,
+            semanticLabel: 'Show menu actions',
+          ),
+          onPressed: () {
+            Scaffold.of(context).showSnackBar(
+              const SnackBar(content: Text('This is a dummy menu action.')),
+            );
+          },
+        ),
+      ]),
     );
   }
 }

examples/flutter_gallery/lib/gallery/demo.dart

@@ -97,7 +97,8 @@ class TabbedComponentDemoScaffold extends StatelessWidget {
       child: Scaffold(
         appBar: AppBar(
           title: Text(title),
-          actions: (actions ?? <Widget>[])..add(
+          actions: <Widget>[
+            ...?actions,
             Builder(
               builder: (BuildContext context) {
                 return IconButton(
@@ -106,17 +107,17 @@ class TabbedComponentDemoScaffold extends StatelessWidget {
                 );
               },
             ),
-          )..addAll(showExampleCodeAction ? <Widget>[
-            Builder(
-              builder: (BuildContext context) {
-                return IconButton(
-                  icon: const Icon(Icons.code),
-                  tooltip: 'Show example code',
-                  onPressed: () => _showExampleCode(context),
-                );
-              },
-            ),
-          ] : <Widget>[]),
+            if (showExampleCodeAction)
+              Builder(
+                builder: (BuildContext context) {
+                  return IconButton(
+                    icon: const Icon(Icons.code),
+                    tooltip: 'Show example code',
+                    onPressed: () => _showExampleCode(context),
+                  );
+                },
+              ),
+          ],
           bottom: TabBar(
             isScrollable: isScrollable,
             tabs: demos.map<Widget>((ComponentDemoTabData data) => Tab(text: data.tabName)).toList(),

packages/flutter/lib/src/foundation/assertions.dart

@@ -477,12 +477,10 @@ class FlutterError extends Error with DiagnosticableTreeMixin implements Asserti
   /// using [ErrorHint]s or other [DiagnosticsNode]s.
   factory FlutterError(String message) {
     final List<String> lines = message.split('\n');
-    final List<DiagnosticsNode> parts = <DiagnosticsNode>[];
-    parts.add(ErrorSummary(lines.first));
-    if (lines.length > 1)  {
-      parts.addAll(lines.skip(1).map<DiagnosticsNode>((String line) => ErrorDescription(line)));
-    }
-    return FlutterError.fromParts(parts);
+    return FlutterError.fromParts(<DiagnosticsNode>[
+      ErrorSummary(lines.first),
+      ...lines.skip(1).map<DiagnosticsNode>((String line) => ErrorDescription(line)),
+    ]);
   }
 
   /// Create an error message from a list of [DiagnosticsNode]s.

packages/flutter/lib/src/foundation/diagnostics.dart

@@ -1541,61 +1541,46 @@ abstract class DiagnosticsNode {
     if (kReleaseMode) {
       return <String, Object>{};
     }
-    final Map<String, Object> data = <String, Object>{
+    final bool hasChildren = getChildren().isNotEmpty;
+    return <String, Object>{
       'description': toDescription(),
       'type': runtimeType.toString(),
+      if (name != null)
+        'name': name,
+      if (!showSeparator)
+        'showSeparator': showSeparator,
+      if (level != DiagnosticLevel.info)
+        'level': describeEnum(level),
+      if (showName == false)
+        'showName': showName,
+      if (emptyBodyDescription != null)
+        'emptyBodyDescription': emptyBodyDescription,
+      if (style != DiagnosticsTreeStyle.sparse)
+        'style': describeEnum(style),
+      if (allowTruncate)
+        'allowTruncate': allowTruncate,
+      if (hasChildren)
+        'hasChildren': hasChildren,
+      if (linePrefix?.isNotEmpty == true)
+        'linePrefix': linePrefix,
+      if (!allowWrap)
+        'allowWrap': allowWrap,
+      if (allowNameWrap)
+        'allowNameWrap': allowNameWrap,
+      ...delegate.additionalNodeProperties(this),
+      if (delegate.includeProperties)
+        'properties': toJsonList(
+          delegate.filterProperties(getProperties(), this),
+          this,
+          delegate,
+        ),
+      if (delegate.subtreeDepth > 0)
+        'children': toJsonList(
+          delegate.filterChildren(getChildren(), this),
+          this,
+          delegate,
+        ),
     };
-    if (name != null)
-      data['name'] = name;
-
-    if (!showSeparator)
-      data['showSeparator'] = showSeparator;
-    if (level != DiagnosticLevel.info)
-      data['level'] = describeEnum(level);
-    if (showName == false)
-      data['showName'] = showName;
-    if (emptyBodyDescription != null)
-      data['emptyBodyDescription'] = emptyBodyDescription;
-    if (style != DiagnosticsTreeStyle.sparse)
-      data['style'] = describeEnum(style);
-
-    if (allowTruncate)
-      data['allowTruncate'] = allowTruncate;
-
-    final bool hasChildren = getChildren().isNotEmpty;
-    if (hasChildren)
-      data['hasChildren'] = hasChildren;
-
-    if (linePrefix?.isNotEmpty == true)
-      data['linePrefix'] = linePrefix;
-
-    if (!allowWrap)
-      data['allowWrap'] = allowWrap;
-
-    if (allowNameWrap)
-      data['allowNameWrap'] = allowNameWrap;
-
-    data.addAll(delegate.additionalNodeProperties(this));
-
-    if (delegate.includeProperties) {
-      final List<DiagnosticsNode> properties = getProperties();
-      data['properties'] = toJsonList(
-        delegate.filterProperties(properties, this),
-        this,
-        delegate,
-      );
-    }
-
-    if (delegate.subtreeDepth > 0) {
-      final List<DiagnosticsNode> children = getChildren();
-      data['children'] = toJsonList(
-        delegate.filterChildren(children, this),
-        this,
-        delegate,
-      );
-    }
-
-    return data;
   }
 
   /// Serializes a [List] of [DiagnosticsNode]s to a JSON list according to

packages/flutter/lib/src/material/about.dart

@@ -268,34 +268,33 @@ class AboutDialog extends StatelessWidget {
     final String name = applicationName ?? _defaultApplicationName(context);
     final String version = applicationVersion ?? _defaultApplicationVersion(context);
     final Widget icon = applicationIcon ?? _defaultApplicationIcon(context);
-    List<Widget> body = <Widget>[];
-    if (icon != null)
-      body.add(IconTheme(data: const IconThemeData(size: 48.0), child: icon));
-    body.add(Expanded(
-      child: Padding(
-        padding: const EdgeInsets.symmetric(horizontal: 24.0),
+    return AlertDialog(
+      content: SingleChildScrollView(
         child: ListBody(
           children: <Widget>[
-            Text(name, style: Theme.of(context).textTheme.headline),
-            Text(version, style: Theme.of(context).textTheme.body1),
-            Container(height: 18.0),
-            Text(applicationLegalese ?? '', style: Theme.of(context).textTheme.caption),
+            Row(
+              crossAxisAlignment: CrossAxisAlignment.start,
+              children: <Widget>[
+                if (icon != null) IconTheme(data: const IconThemeData(size: 48.0), child: icon),
+                Expanded(
+                  child: Padding(
+                    padding: const EdgeInsets.symmetric(horizontal: 24.0),
+                    child: ListBody(
+                      children: <Widget>[
+                        Text(name, style: Theme.of(context).textTheme.headline),
+                        Text(version, style: Theme.of(context).textTheme.body1),
+                        Container(height: 18.0),
+                        Text(applicationLegalese ?? '', style: Theme.of(context).textTheme.caption),
+                      ],
+                    ),
+                  ),
+                ),
+              ],
+            ),
+            ...?children,
           ],
         ),
       ),
-    ));
-    body = <Widget>[
-      Row(
-        crossAxisAlignment: CrossAxisAlignment.start,
-        children: body,
-      ),
-    ];
-    if (children != null)
-      body.addAll(children);
-    return AlertDialog(
-      content: SingleChildScrollView(
-        child: ListBody(children: body),
-      ),
       actions: <Widget>[
         FlatButton(
           child: Text(MaterialLocalizations.of(context).viewLicensesButtonLabel),
@@ -457,24 +456,6 @@ class _LicensePageState extends State<LicensePage> {
     final String name = widget.applicationName ?? _defaultApplicationName(context);
     final String version = widget.applicationVersion ?? _defaultApplicationVersion(context);
     final MaterialLocalizations localizations = MaterialLocalizations.of(context);
-    final List<Widget> contents = <Widget>[
-      Text(name, style: Theme.of(context).textTheme.headline, textAlign: TextAlign.center),
-      Text(version, style: Theme.of(context).textTheme.body1, textAlign: TextAlign.center),
-      Container(height: 18.0),
-      Text(widget.applicationLegalese ?? '', style: Theme.of(context).textTheme.caption, textAlign: TextAlign.center),
-      Container(height: 18.0),
-      Text('Powered by Flutter', style: Theme.of(context).textTheme.body1, textAlign: TextAlign.center),
-      Container(height: 24.0),
-    ];
-    contents.addAll(_licenses);
-    if (!_loaded) {
-      contents.add(const Padding(
-        padding: EdgeInsets.symmetric(vertical: 24.0),
-        child: Center(
-          child: CircularProgressIndicator(),
-        ),
-      ));
-    }
     return Scaffold(
       appBar: AppBar(
         title: Text(localizations.licensesPageTitle),
@@ -491,7 +472,23 @@ class _LicensePageState extends State<LicensePage> {
             child: Scrollbar(
               child: ListView(
                 padding: const EdgeInsets.symmetric(horizontal: 8.0, vertical: 12.0),
-                children: contents,
+                children: <Widget>[
+                  Text(name, style: Theme.of(context).textTheme.headline, textAlign: TextAlign.center),
+                  Text(version, style: Theme.of(context).textTheme.body1, textAlign: TextAlign.center),
+                  Container(height: 18.0),
+                  Text(widget.applicationLegalese ?? '', style: Theme.of(context).textTheme.caption, textAlign: TextAlign.center),
+                  Container(height: 18.0),
+                  Text('Powered by Flutter', style: Theme.of(context).textTheme.body1, textAlign: TextAlign.center),
+                  Container(height: 24.0),
+                  ..._licenses,
+                  if (!_loaded)
+                    const Padding(
+                      padding: EdgeInsets.symmetric(vertical: 24.0),
+                      child: Center(
+                        child: CircularProgressIndicator(),
+                      ),
+                    )
+                ],
               ),
             ),
           ),

packages/flutter/lib/src/material/date_picker.dart

@@ -392,8 +392,9 @@ class DayPicker extends StatelessWidget {
     final int month = displayedMonth.month;
     final int daysInMonth = getDaysInMonth(year, month);
     final int firstDayOffset = _computeFirstDayOffset(year, month, localizations);
-    final List<Widget> labels = <Widget>[];
-    labels.addAll(_getDayHeaders(themeData.textTheme.caption, localizations));
+    final List<Widget> labels = <Widget>[
+      ..._getDayHeaders(themeData.textTheme.caption, localizations),
+    ];
     for (int i = 0; true; i += 1) {
       // 1-based day of month, e.g. 1-31 for January, and 1-29 for February on
       // a leap year.

packages/flutter/lib/src/material/scaffold.dart

@@ -2110,14 +2110,12 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
     }
 
     if (_currentBottomSheet != null || _dismissedBottomSheets.isNotEmpty) {
-      final List<Widget> bottomSheets = <Widget>[];
-      if (_dismissedBottomSheets.isNotEmpty)
-        bottomSheets.addAll(_dismissedBottomSheets);
-      if (_currentBottomSheet != null)
-        bottomSheets.add(_currentBottomSheet._widget);
       final Widget stack = Stack(
-        children: bottomSheets,
         alignment: Alignment.bottomCenter,
+        children: <Widget>[
+          ..._dismissedBottomSheets,
+          if (_currentBottomSheet != null) _currentBottomSheet._widget,
+        ],
       );
       _addIfNonNull(
         children,

packages/flutter/lib/src/painting/borders.dart

@@ -528,22 +528,18 @@ class _CompoundBorder extends ShapeBorder {
       final ShapeBorder merged = ours.add(other, reversed: reversed)
                              ?? other.add(ours, reversed: !reversed);
       if (merged != null) {
-        final List<ShapeBorder> result = <ShapeBorder>[];
-        result.addAll(borders);
+        final List<ShapeBorder> result = <ShapeBorder>[...borders];
         result[reversed ? result.length - 1 : 0] = merged;
         return _CompoundBorder(result);
       }
     }
     // We can't, so fall back to just adding the new border to the list.
-    final List<ShapeBorder> mergedBorders = <ShapeBorder>[];
-    if (reversed)
-      mergedBorders.addAll(borders);
-    if (other is _CompoundBorder)
-      mergedBorders.addAll(other.borders);
-    else
-      mergedBorders.add(other);
-    if (!reversed)
-      mergedBorders.addAll(borders);
+    final List<ShapeBorder> mergedBorders = <ShapeBorder>[
+      if (reversed) ...borders,
+      if (other is _CompoundBorder) ...other.borders
+      else other,
+      if (!reversed) ...borders,
+    ];
     return _CompoundBorder(mergedBorders);
   }
 

packages/flutter/lib/src/rendering/box.dart

@@ -498,13 +498,11 @@ class BoxConstraints extends Constraints {
   }) {
     assert(() {
       void throwError(DiagnosticsNode message) {
-        final List<DiagnosticsNode> information = <DiagnosticsNode>[message];
-        if (informationCollector != null) {
-          information.addAll(informationCollector());
-        }
-
-        information.add(DiagnosticsProperty<BoxConstraints>('The offending constraints were', this, style: DiagnosticsTreeStyle.errorProperty));
-        throw FlutterError.fromParts(information);
+        throw FlutterError.fromParts(<DiagnosticsNode>[
+          message,
+          if (informationCollector != null) ...informationCollector(),
+          DiagnosticsProperty<BoxConstraints>('The offending constraints were', this, style: DiagnosticsTreeStyle.errorProperty),
+        ]);
       }
       if (minWidth.isNaN || maxWidth.isNaN || minHeight.isNaN || maxHeight.isNaN) {
         final List<String> affectedFieldsList = <String>[];
@@ -1952,12 +1950,12 @@ abstract class RenderBox extends RenderObject {
 
           information.add(node.describeForError('The nearest ancestor providing an unbounded height constraint is'));
         }
-        final List<DiagnosticsNode> errorParts = <DiagnosticsNode>[];
-        errorParts.addAll(information);
-        errorParts.add(DiagnosticsProperty<BoxConstraints>('The constraints that applied to the $runtimeType were', constraints, style: DiagnosticsTreeStyle.errorProperty));
-        errorParts.add(DiagnosticsProperty<Size>('The exact size it was given was', _size, style: DiagnosticsTreeStyle.errorProperty));
-        errorParts.add(ErrorHint('See https://flutter.dev/docs/development/ui/layout/box-constraints for more information.'));
-        throw FlutterError.fromParts(errorParts);
+        throw FlutterError.fromParts(<DiagnosticsNode>[
+          ...information,
+          DiagnosticsProperty<BoxConstraints>('The constraints that applied to the $runtimeType were', constraints, style: DiagnosticsTreeStyle.errorProperty),
+          DiagnosticsProperty<Size>('The exact size it was given was', _size, style: DiagnosticsTreeStyle.errorProperty),
+          ErrorHint('See https://flutter.dev/docs/development/ui/layout/box-constraints for more information.'),
+        ]);
      }
       // verify that the size is within the constraints
       if (!constraints.isSatisfiedBy(_size)) {

packages/flutter/lib/src/rendering/custom_paint.dart

@@ -628,12 +628,11 @@ class RenderCustomPaint extends RenderProxyBox {
 
     final bool hasBackgroundSemantics = _backgroundSemanticsNodes != null && _backgroundSemanticsNodes.isNotEmpty;
     final bool hasForegroundSemantics = _foregroundSemanticsNodes != null && _foregroundSemanticsNodes.isNotEmpty;
-    final List<SemanticsNode> finalChildren = <SemanticsNode>[];
-    if (hasBackgroundSemantics)
-      finalChildren.addAll(_backgroundSemanticsNodes);
-    finalChildren.addAll(children);
-    if (hasForegroundSemantics)
-      finalChildren.addAll(_foregroundSemanticsNodes);
+    final List<SemanticsNode> finalChildren = <SemanticsNode>[
+      if (hasBackgroundSemantics) ..._backgroundSemanticsNodes,
+      ...children,
+      if (hasForegroundSemantics) ..._foregroundSemanticsNodes,
+    ];
     super.assembleSemanticsNode(node, config, finalChildren);
   }
 

packages/flutter/lib/src/rendering/object.dart

@@ -3326,15 +3326,16 @@ class _RootSemanticsFragment extends _InterestingSemanticsFragment {
 
     node.rect = owner.semanticBounds;
 
-    final List<SemanticsNode> children = <SemanticsNode>[];
-    for (_InterestingSemanticsFragment fragment in _children) {
-      assert(fragment.config == null);
-      children.addAll(fragment.compileChildren(
-        parentSemanticsClipRect: parentSemanticsClipRect,
-        parentPaintClipRect: parentPaintClipRect,
-        elevationAdjustment: 0.0,
-      ));
-    }
+    final List<SemanticsNode> children = _children
+      .expand((_InterestingSemanticsFragment fragment) {
+        assert(fragment.config == null);
+        return fragment.compileChildren(
+          parentSemanticsClipRect: parentSemanticsClipRect,
+          parentPaintClipRect: parentPaintClipRect,
+          elevationAdjustment: 0.0,
+        );
+      })
+      .toList();
     node.updateWith(config: null, childrenInInversePaintOrder: children);
 
     // The root node is the only semantics node allowed to be invisible. This
@@ -3447,14 +3448,13 @@ class _SwitchableSemanticsFragment extends _InterestingSemanticsFragment {
       }
     }
 
-    final List<SemanticsNode> children = <SemanticsNode>[];
-    for (_InterestingSemanticsFragment fragment in _children) {
-      children.addAll(fragment.compileChildren(
+    final List<SemanticsNode> children = _children
+      .expand((_InterestingSemanticsFragment fragment) => fragment.compileChildren(
         parentSemanticsClipRect: node.parentSemanticsClipRect,
         parentPaintClipRect: node.parentPaintClipRect,
         elevationAdjustment: 0.0,
-      ));
-    }
+      ))
+      .toList();
 
     if (_config.isSemanticBoundary) {
       owner.assembleSemanticsNode(node, _config, children);

packages/flutter/lib/src/rendering/sliver.dart

@@ -421,14 +421,12 @@ class SliverConstraints extends Constraints {
       void verify(bool check, String message) {
         if (check)
           return;
-        final List<DiagnosticsNode> information = <DiagnosticsNode>[];
-        information.add(ErrorSummary('$runtimeType is not valid: $message'));
-
-        if (informationCollector != null) {
-          information.addAll(informationCollector());
-        }
-        information.add(DiagnosticsProperty<SliverConstraints>('The offending constraints were', this, style: DiagnosticsTreeStyle.errorProperty));
-        throw FlutterError.fromParts(information);
+        throw FlutterError.fromParts(<DiagnosticsNode>[
+          ErrorSummary('$runtimeType is not valid: $message'),
+          if (informationCollector != null)
+            ...informationCollector(),
+          DiagnosticsProperty<SliverConstraints>('The offending constraints were', this, style: DiagnosticsTreeStyle.errorProperty)
+        ]);
       }
       verify(axis != null, 'The "axis" is null.');
       verify(growthDirection != null, 'The "growthDirection" is null.');
@@ -700,15 +698,12 @@ class SliverGeometry extends Diagnosticable {
       void verify(bool check, String summary, {List<DiagnosticsNode> details}) {
         if (check)
           return;
-        final List<DiagnosticsNode> information = <DiagnosticsNode>[];
-        information.add(ErrorSummary('$runtimeType is not valid: $summary'));
-        if (details != null) {
-          information.addAll(details);
-        }
-        if (informationCollector != null) {
-          information.addAll(informationCollector());
-        }
-        throw FlutterError.fromParts(information);
+        throw FlutterError.fromParts(<DiagnosticsNode>[
+          ErrorSummary('$runtimeType is not valid: $summary'),
+          ...?details,
+          if (informationCollector != null)
+            ...informationCollector(),
+        ]);
       }
 
       verify(scrollExtent != null, 'The "scrollExtent" is null.');

packages/flutter/lib/src/semantics/semantics.dart

@@ -2280,12 +2280,9 @@ class _SemanticsSortGroup extends Comparable<_SemanticsSortGroup> {
       horizontalGroups = horizontalGroups.reversed.toList();
     }
 
-    final List<SemanticsNode> result = <SemanticsNode>[];
-    for (_SemanticsSortGroup group in horizontalGroups) {
-      final List<SemanticsNode> sortedKnotNodes = group.sortedWithinKnot();
-      result.addAll(sortedKnotNodes);
-    }
-    return result;
+    return horizontalGroups
+      .expand((_SemanticsSortGroup group) => group.sortedWithinKnot())
+      .toList();
   }
 
   /// Sorts [nodes] where nodes intersect both vertically and horizontally.
@@ -2423,12 +2420,9 @@ List<SemanticsNode> _childrenInDefaultOrder(List<SemanticsNode> children, TextDi
   }
   verticalGroups.sort();
 
-  final List<SemanticsNode> result = <SemanticsNode>[];
-  for (_SemanticsSortGroup group in verticalGroups) {
-    final List<SemanticsNode> sortedGroupNodes = group.sortedWithinVerticalGroup();
-    result.addAll(sortedGroupNodes);
-  }
-  return result;
+  return verticalGroups
+    .expand((_SemanticsSortGroup group) => group.sortedWithinVerticalGroup())
+    .toList();
 }
 
 /// The implementation of [Comparable] that implements the ordering of

packages/flutter/lib/src/widgets/nested_scroll_view.dart

@@ -272,15 +272,15 @@ class NestedScrollView extends StatefulWidget {
   }
 
   List<Widget> _buildSlivers(BuildContext context, ScrollController innerController, bool bodyIsScrolled) {
-    final List<Widget> slivers = <Widget>[];
-    slivers.addAll(headerSliverBuilder(context, bodyIsScrolled));
-    slivers.add(SliverFillRemaining(
-      child: PrimaryScrollController(
-        controller: innerController,
-        child: body,
+    return <Widget>[
+      ...headerSliverBuilder(context, bodyIsScrolled),
+      SliverFillRemaining(
+        child: PrimaryScrollController(
+          controller: innerController,
+          child: body,
+        ),
       ),
-    ));
-    return slivers;
+    ];
   }
 
   @override

packages/flutter/lib/src/widgets/widget_inspector.dart

@@ -1534,14 +1534,13 @@ mixin WidgetInspectorService {
     List<DiagnosticsNode> nodes,
     _SerializationDelegate delegate,
   ) {
-    final List<DiagnosticsNode> children = <DiagnosticsNode>[];
-    for (DiagnosticsNode child in nodes) {
-      if (!delegate.summaryTree || _shouldShowInSummaryTree(child)) {
-        children.add(child);
-      } else {
-        children.addAll(_getChildrenFiltered(child, delegate));
-      }
-    }
+    final List<DiagnosticsNode> children = <DiagnosticsNode>[
+      for (DiagnosticsNode child in nodes)
+        if (!delegate.summaryTree || _shouldShowInSummaryTree(child))
+          child
+        else
+          ..._getChildrenFiltered(child, delegate),
+    ];
     return children;
   }
 
@@ -2154,8 +2153,10 @@ class _WidgetInspectorState extends State<WidgetInspector>
       return size == null ? double.maxFinite : size.width * size.height;
     }
     regularHits.sort((RenderObject a, RenderObject b) => _area(a).compareTo(_area(b)));
-    final Set<RenderObject> hits = <RenderObject>{};
-    hits..addAll(edgeHits)..addAll(regularHits);
+    final Set<RenderObject> hits = <RenderObject>{
+      ...edgeHits,
+      ...regularHits,
+    };
     return hits.toList();
   }
 

packages/flutter/test/foundation/diagnostics_json_test.dart

@@ -174,11 +174,7 @@ void main() {
       final Map<String, Object> result = testTree.toDiagnosticsNode().toJsonMap(TestDiagnosticsSerializationDelegate(
           subtreeDepth: 1,
           childFilter: (List<DiagnosticsNode> nodes, DiagnosticsNode owner) {
-            final List<DiagnosticsNode> result = <DiagnosticsNode>[];
-            for (DiagnosticsNode node in nodes) {
-              result.addAll(node.getChildren());
-            }
-            return result;
+            return nodes.expand((DiagnosticsNode node) => node.getChildren()).toList();
           }
       ));
       final List<Map<String, Object>> children = result['children'];

packages/flutter/test/rendering/paragraph_test.dart

@@ -260,13 +260,13 @@ void main() {
     expect(paragraph.size.height, 26.0);
 
     // Test the sizes of nested spans.
-    final List<ui.TextBox> boxes = <ui.TextBox>[];
     final String text = testSpan.toStringDeep();
-    for (int i = 0; i < text.length; ++i) {
-      boxes.addAll(paragraph.getBoxesForSelection(
+    final List<ui.TextBox> boxes = <ui.TextBox>[
+      for (int i = 0; i < text.length; ++i)
+        ...paragraph.getBoxesForSelection(
           TextSelection(baseOffset: i, extentOffset: i + 1)
-      ));
-    }
+        ),
+    ];
     expect(boxes.length, equals(4));
 
     // anyOf is needed here and below because Linux and Mac have different text

packages/flutter_test/lib/src/binding.dart

@@ -836,15 +836,11 @@ class AutomatedTestWidgetsFlutterBinding extends TestWidgetsFlutterBinding {
       _allowedAssetKeys = <String>{};
       return;
     }
-    final Map<String, dynamic> manifest = json.decode(
-        manifestFile.readAsStringSync());
+    final Map<String, dynamic> manifest = json.decode(manifestFile.readAsStringSync());
     _allowedAssetKeys = <String>{
       'AssetManifest.json',
+      ...manifest.values.cast<List<dynamic>>().expand<dynamic>((List<dynamic> e) => e).cast<String>(),
     };
-    for (List<dynamic> value in manifest.values) {
-      final List<String> strList = List<String>.from(value);
-      _allowedAssetKeys.addAll(strList);
-    }
   }
 
   @override

packages/flutter_test/pubspec.yaml

@@ -2,7 +2,7 @@ name: flutter_test
 
 environment:
   # The pub client defaults to an <2.0.0 sdk constraint which we need to explicitly overwrite.
-  sdk: ">=2.2.0 <3.0.0"
+  sdk: ">=2.2.2 <3.0.0"
 
 dependencies:
   # To update these, use "flutter update-packages --force-upgrade".

packages/flutter_tools/bin/fuchsia_attach.dart

@@ -72,6 +72,7 @@ Future<void> main(List<String> args) async {
     // Otherwise assume the package is flat.
     targetFile = entrypoint;
   }
+  final String deviceName = argResults['device'];
   final List<String> command = <String>[
     'attach',
     '--module',
@@ -86,14 +87,9 @@ Future<void> main(List<String> args) async {
     outputDill,
     '--packages',
     packages,
+    if (deviceName != null && deviceName.isNotEmpty) ...<String>['-d', deviceName],
+    if (verbose) '--verbose',
   ];
-  final String deviceName = argResults['device'];
-  if (deviceName != null && deviceName.isNotEmpty) {
-    command.addAll(<String>['-d', deviceName]);
-  }
-  if (verbose) {
-    command.add('--verbose');
-  }
   Cache.disableLocking(); // ignore: invalid_use_of_visible_for_testing_member
   await runner.run(
     command,

packages/flutter_tools/lib/src/android/android_device.dart

@@ -520,40 +520,40 @@ class AndroidDevice extends Device {
       '-f', '0x20000000', // FLAG_ACTIVITY_SINGLE_TOP
       '--ez', 'enable-background-compilation', 'true',
       '--ez', 'enable-dart-profiling', 'true',
+      if (traceStartup)
+        ...<String>['--ez', 'trace-startup', 'true'],
+      if (route != null)
+        ...<String>['--es', 'route', route],
+      if (debuggingOptions.enableSoftwareRendering)
+        ...<String>['--ez', 'enable-software-rendering', 'true'],
+      if (debuggingOptions.skiaDeterministicRendering)
+        ...<String>['--ez', 'skia-deterministic-rendering', 'true'],
+      if (debuggingOptions.traceSkia)
+        ...<String>['--ez', 'trace-skia', 'true'],
+      if (debuggingOptions.traceSystrace)
+        ...<String>['--ez', 'trace-systrace', 'true'],
+      if (debuggingOptions.dumpSkpOnShaderCompilation)
+        ...<String>['--ez', 'dump-skp-on-shader-compilation', 'true'],
+      if (debuggingOptions.debuggingEnabled)
+        ...<String>[
+          if (debuggingOptions.buildInfo.isDebug)
+            ...<String>[
+              ...<String>['--ez', 'enable-checked-mode', 'true'],
+              ...<String>['--ez', 'verify-entry-points', 'true'],
+            ],
+          if (debuggingOptions.startPaused)
+            ...<String>['--ez', 'start-paused', 'true'],
+          if (debuggingOptions.disableServiceAuthCodes)
+            ...<String>['--ez', 'disable-service-auth-codes', 'true'],
+          if (debuggingOptions.dartFlags.isNotEmpty)
+            ...<String>['--es', 'dart-flags', debuggingOptions.dartFlags],
+          if (debuggingOptions.useTestFonts)
+            ...<String>['--ez', 'use-test-fonts', 'true'],
+          if (debuggingOptions.verboseSystemLogs)
+            ...<String>['--ez', 'verbose-logging', 'true'],
+        ],
+      apk.launchActivity,
     ];
-
-    if (traceStartup)
-      cmd.addAll(<String>['--ez', 'trace-startup', 'true']);
-    if (route != null)
-      cmd.addAll(<String>['--es', 'route', route]);
-    if (debuggingOptions.enableSoftwareRendering)
-      cmd.addAll(<String>['--ez', 'enable-software-rendering', 'true']);
-    if (debuggingOptions.skiaDeterministicRendering)
-      cmd.addAll(<String>['--ez', 'skia-deterministic-rendering', 'true']);
-    if (debuggingOptions.traceSkia)
-      cmd.addAll(<String>['--ez', 'trace-skia', 'true']);
-    if (debuggingOptions.traceSystrace)
-      cmd.addAll(<String>['--ez', 'trace-systrace', 'true']);
-    if (debuggingOptions.dumpSkpOnShaderCompilation)
-      cmd.addAll(<String>['--ez', 'dump-skp-on-shader-compilation', 'true']);
-    if (debuggingOptions.debuggingEnabled) {
-      if (debuggingOptions.buildInfo.isDebug) {
-        cmd.addAll(<String>['--ez', 'enable-checked-mode', 'true']);
-        cmd.addAll(<String>['--ez', 'verify-entry-points', 'true']);
-      }
-      if (debuggingOptions.startPaused)
-        cmd.addAll(<String>['--ez', 'start-paused', 'true']);
-      if (debuggingOptions.disableServiceAuthCodes)
-        cmd.addAll(<String>['--ez', 'disable-service-auth-codes', 'true']);
-      if (debuggingOptions.dartFlags.isNotEmpty)
-        cmd.addAll(<String>['--es', 'dart-flags', debuggingOptions.dartFlags]);
-      if (debuggingOptions.useTestFonts)
-        cmd.addAll(<String>['--ez', 'use-test-fonts', 'true']);
-      if (debuggingOptions.verboseSystemLogs) {
-        cmd.addAll(<String>['--ez', 'verbose-logging', 'true']);
-      }
-    }
-    cmd.add(apk.launchActivity);
     final String result = (await runAdbCheckedAsync(cmd)).stdout;
     // This invocation returns 0 even when it fails.
     if (result.contains('Error: ')) {

packages/flutter_tools/lib/src/android/android_studio_validator.dart

@@ -17,15 +17,13 @@ class AndroidStudioValidator extends DoctorValidator {
   final AndroidStudio _studio;
 
   static List<DoctorValidator> get allValidators {
-    final List<DoctorValidator> validators = <DoctorValidator>[];
     final List<AndroidStudio> studios = AndroidStudio.allInstalled();
-    if (studios.isEmpty) {
-      validators.add(NoAndroidStudioValidator());
-    } else {
-      validators.addAll(studios
-          .map<DoctorValidator>((AndroidStudio studio) => AndroidStudioValidator(studio)));
-    }
-    return validators;
+    return <DoctorValidator>[
+      if (studios.isEmpty)
+        NoAndroidStudioValidator()
+      else
+        ...studios.map<DoctorValidator>((AndroidStudio studio) => AndroidStudioValidator(studio))
+    ];
   }
 
   @override

packages/flutter_tools/lib/src/asset.dart

@@ -216,10 +216,10 @@ class _ManifestAssetBundle implements AssetBundle {
       }
     }
 
-    final List<_Asset> materialAssets = <_Asset>[];
-    if (flutterManifest.usesMaterialDesign && includeDefaultFonts) {
-      materialAssets.addAll(_getMaterialAssets(_fontSetMaterial));
-    }
+    final List<_Asset> materialAssets = <_Asset>[
+      if (flutterManifest.usesMaterialDesign && includeDefaultFonts)
+        ..._getMaterialAssets(_fontSetMaterial),
+    ];
     for (_Asset asset in materialAssets) {
       assert(asset.assetFileExists);
       entries[asset.entryUri.path] ??= DevFSFileContent(asset.assetFile);
@@ -421,20 +421,18 @@ List<Map<String, dynamic>> _parseFonts(
   PackageMap packageMap, {
   String packageName,
 }) {
-  final List<Map<String, dynamic>> fonts = <Map<String, dynamic>>[];
-  if (manifest.usesMaterialDesign && includeDefaultFonts) {
-    fonts.addAll(_getMaterialFonts(_ManifestAssetBundle._fontSetMaterial));
-  }
-  if (packageName == null) {
-    fonts.addAll(manifest.fontsDescriptor);
-  } else {
-    fonts.addAll(_createFontsDescriptor(_parsePackageFonts(
-      manifest,
-      packageName,
-      packageMap,
-    )));
-  }
-  return fonts;
+  return <Map<String, dynamic>>[
+    if (manifest.usesMaterialDesign && includeDefaultFonts)
+      ..._getMaterialFonts(_ManifestAssetBundle._fontSetMaterial),
+    if (packageName == null)
+      ...manifest.fontsDescriptor
+    else
+      ..._createFontsDescriptor(_parsePackageFonts(
+        manifest,
+        packageName,
+        packageMap,
+      )),
+  ];
 }
 
 /// Prefixes family names and asset paths of fonts included from packages with

packages/flutter_tools/lib/src/base/build.dart

@@ -228,7 +228,7 @@ class AOTSnapshotter {
     final List<String> commonBuildOptions = <String>['-arch', targetArch, '-miphoneos-version-min=8.0'];
 
     final String assemblyO = fs.path.join(outputPath, 'snapshot_assembly.o');
-    final RunResult compileResult = await xcode.cc(commonBuildOptions.toList()..addAll(<String>['-c', assemblyPath, '-o', assemblyO]));
+    final RunResult compileResult = await xcode.cc(<String>[...commonBuildOptions, '-c', assemblyPath, '-o', assemblyO]);
     if (compileResult.exitCode != 0) {
       printError('Failed to compile AOT snapshot. Compiler terminated with exit code ${compileResult.exitCode}');
       return compileResult;
@@ -237,14 +237,15 @@ class AOTSnapshotter {
     final String frameworkDir = fs.path.join(outputPath, 'App.framework');
     fs.directory(frameworkDir).createSync(recursive: true);
     final String appLib = fs.path.join(frameworkDir, 'App');
-    final List<String> linkArgs = commonBuildOptions.toList()..addAll(<String>[
-        '-dynamiclib',
-        '-Xlinker', '-rpath', '-Xlinker', '@executable_path/Frameworks',
-        '-Xlinker', '-rpath', '-Xlinker', '@loader_path/Frameworks',
-        '-install_name', '@rpath/App.framework/App',
-        '-o', appLib,
-        assemblyO,
-    ]);
+    final List<String> linkArgs = <String>[
+      ...commonBuildOptions,
+      '-dynamiclib',
+      '-Xlinker', '-rpath', '-Xlinker', '@executable_path/Frameworks',
+      '-Xlinker', '-rpath', '-Xlinker', '@loader_path/Frameworks',
+      '-install_name', '@rpath/App.framework/App',
+      '-o', appLib,
+      assemblyO,
+    ];
     final RunResult linkResult = await xcode.clang(linkArgs);
     if (linkResult.exitCode != 0) {
       printError('Failed to link AOT snapshot. Linker terminated with exit code ${compileResult.exitCode}');
@@ -371,8 +372,10 @@ class JITSnapshotter {
       genSnapshotArgs.addAll(extraGenSnapshotOptions);
     }
 
-    final Set<String> outputPaths = <String>{};
-    outputPaths.addAll(<String>[isolateSnapshotData, isolateSnapshotInstructions]);
+    final Set<String> outputPaths = <String>{
+      isolateSnapshotData,
+      isolateSnapshotInstructions,
+    };
 
     // There are a couple special cases below where we create a snapshot
     // with only the data section, which only contains interpreted code.

packages/flutter_tools/lib/src/base/fingerprint.dart

@@ -94,9 +94,11 @@ class Fingerprinter {
   }
 
   Future<List<String>> _getPaths() async {
-    final Set<String> paths = _paths.toSet();
-    for (String depfilePath in _depfilePaths)
-      paths.addAll(await readDepfile(depfilePath));
+    final Set<String> paths = <String>{
+      ..._paths,
+      for (String depfilePath in _depfilePaths)
+        ...await readDepfile(depfilePath),
+    };
     final FingerprintPathFilter filter = _pathFilter ?? (String path) => true;
     return paths.where(filter).toList()..sort();
   }
@@ -118,7 +120,7 @@ class Fingerprint {
       final List<int> bytes = file.readAsBytesSync();
       _checksums[file.path] = md5.convert(bytes).toString();
     }
-    _properties = <String, String>{}..addAll(properties);
+    _properties = <String, String>{...properties};
   }
 
   /// Creates a Fingerprint from serialized JSON.

packages/flutter_tools/lib/src/cache.dart

@@ -637,30 +637,22 @@ class FlutterSdk extends EngineCachedArtifact {
 
   @override
   List<List<String>> getBinaryDirs() {
-    final List<List<String>> binaryDirs = <List<String>>[
+    return <List<String>>[
       <String>['common', 'flutter_patched_sdk.zip'],
       <String>['common', 'flutter_patched_sdk_product.zip'],
-    ];
-    if (cache.includeAllPlatforms) {
-      binaryDirs.addAll(<List<String>>[
-        <String>['windows-x64', 'windows-x64/artifacts.zip'],
-        <String>['linux-x64', 'linux-x64/artifacts.zip'],
-        <String>['darwin-x64', 'darwin-x64/artifacts.zip'],
-      ]);
-    } else if (platform.isWindows) {
-      binaryDirs.addAll(<List<String>>[
-        <String>['windows-x64', 'windows-x64/artifacts.zip'],
-      ]);
-    } else if (platform.isMacOS) {
-      binaryDirs.addAll(<List<String>>[
-        <String>['darwin-x64', 'darwin-x64/artifacts.zip'],
-      ]);
-    } else if (platform.isLinux) {
-      binaryDirs.addAll(<List<String>>[
+      if (cache.includeAllPlatforms)
+        ...<List<String>>[
+          <String>['windows-x64', 'windows-x64/artifacts.zip'],
+          <String>['linux-x64', 'linux-x64/artifacts.zip'],
+          <String>['darwin-x64', 'darwin-x64/artifacts.zip'],
+        ]
+      else if (platform.isWindows)
+        <String>['windows-x64', 'windows-x64/artifacts.zip']
+      else if (platform.isMacOS)
+        <String>['darwin-x64', 'darwin-x64/artifacts.zip']
+      else if (platform.isLinux)
         <String>['linux-x64', 'linux-x64/artifacts.zip'],
-      ]);
-    }
-    return binaryDirs;
+    ];
   }
 
   @override
@@ -745,28 +737,31 @@ class AndroidEngineArtifacts extends EngineCachedArtifact {
 
   @override
   List<List<String>> getBinaryDirs() {
-    final List<List<String>> binaryDirs = <List<String>>[];
-    if (cache.includeAllPlatforms) {
-      binaryDirs
-        ..addAll(_osxBinaryDirs)
-        ..addAll(_linuxBinaryDirs)
-        ..addAll(_windowsBinaryDirs)
-        ..addAll(_androidBinaryDirs)
-        ..addAll(_dartSdks);
-    } else if (platform.isWindows) {
-      binaryDirs
-        ..addAll(_windowsBinaryDirs)
-        ..addAll(_androidBinaryDirs);
-    } else if (platform.isMacOS) {
-      binaryDirs
-        ..addAll(_osxBinaryDirs)
-        ..addAll(_androidBinaryDirs);
-    } else if (platform.isLinux) {
-      binaryDirs
-        ..addAll(_linuxBinaryDirs)
-        ..addAll(_androidBinaryDirs);
-    }
-    return binaryDirs;
+    return <List<String>>[
+      if (cache.includeAllPlatforms)
+        ...<List<String>>[
+          ..._osxBinaryDirs,
+          ..._linuxBinaryDirs,
+          ..._windowsBinaryDirs,
+          ..._androidBinaryDirs,
+          ..._dartSdks,
+        ]
+      else if (platform.isWindows)
+        ...<List<String>>[
+          ..._windowsBinaryDirs,
+          ..._androidBinaryDirs,
+        ]
+      else if (platform.isMacOS)
+        ...<List<String>>[
+          ..._osxBinaryDirs,
+          ..._androidBinaryDirs,
+        ]
+      else if (platform.isLinux)
+        ...<List<String>>[
+          ..._linuxBinaryDirs,
+          ..._androidBinaryDirs,
+        ]
+    ];
   }
 
   @override
@@ -782,11 +777,10 @@ class IOSEngineArtifacts extends EngineCachedArtifact {
 
   @override
   List<List<String>> getBinaryDirs() {
-    final List<List<String>> binaryDirs = <List<String>>[];
-    if (platform.isMacOS || cache.includeAllPlatforms) {
-      binaryDirs.addAll(_iosBinaryDirs);
-    }
-    return binaryDirs;
+    return <List<String>>[
+      if (platform.isMacOS || cache.includeAllPlatforms)
+        ..._iosBinaryDirs,
+    ];
   }
 
   @override
@@ -914,10 +908,10 @@ final Map<int, List<int>> _flattenNameSubstitutions = <int, List<int>>{
 /// Given a name containing slashes, colons, and backslashes, expand it into
 /// something that doesn't.
 String _flattenNameNoSubdirs(String fileName) {
-  final List<int> replacedCodeUnits = <int>[];
-  for (int codeUnit in fileName.codeUnits) {
-    replacedCodeUnits.addAll(_flattenNameSubstitutions[codeUnit] ?? <int>[codeUnit]);
-  }
+  final List<int> replacedCodeUnits = <int>[
+    for (int codeUnit in fileName.codeUnits)
+      ..._flattenNameSubstitutions[codeUnit] ?? <int>[codeUnit],
+  ];
   return String.fromCharCodes(replacedCodeUnits);
 }
 

packages/flutter_tools/lib/src/commands/daemon.dart

@@ -618,10 +618,10 @@ class AppDomain extends Domain {
   }
 
   void _sendAppEvent(AppInstance app, String name, [ Map<String, dynamic> args ]) {
-    final Map<String, dynamic> eventArgs = <String, dynamic>{'appId': app.id};
-    if (args != null)
-      eventArgs.addAll(args);
-    sendEvent('app.$name', eventArgs);
+    sendEvent('app.$name', <String, dynamic>{
+      'appId': app.id,
+      ...?args,
+    });
   }
 }
 

packages/flutter_tools/lib/src/commands/format.dart

@@ -61,23 +61,14 @@ class FormatCommand extends FlutterCommand {
     }
 
     final String dartfmt = sdkBinaryName('dartfmt');
-    final List<String> command = <String>[dartfmt];
-
-    if (argResults['dry-run']) {
-      command.add('-n');
-    }
-    if (argResults['machine']) {
-      command.add('-m');
-    }
-    if (!argResults['dry-run'] && !argResults['machine']) {
-      command.add('-w');
-    }
-
-    if (argResults['set-exit-if-changed']) {
-      command.add('--set-exit-if-changed');
-    }
-
-    command..addAll(argResults.rest);
+    final List<String> command = <String>[
+      dartfmt,
+      if (argResults['dry-run']) '-n',
+      if (argResults['machine']) '-m',
+      if (!argResults['dry-run'] && !argResults['machine']) '-w',
+      if (argResults['set-exit-if-changed']) '--set-exit-if-changed',
+      ...argResults.rest,
+    ];
 
     final int result = await runCommandAndStreamOutput(command);
     if (result != 0)

packages/flutter_tools/lib/src/commands/test.dart

@@ -179,15 +179,13 @@ class TestCommand extends FastFlutterCommand {
         );
       }
     } else {
-      final List<String> fileCopy = <String>[];
-      for (String file in files) {
-        if (file.endsWith(platform.pathSeparator)) {
-          fileCopy.addAll(_findTests(fs.directory(file)));
-        } else {
-          fileCopy.add(file);
-        }
-      }
-      files = fileCopy;
+      files = <String>[
+        for (String file in files)
+          if (file.endsWith(platform.pathSeparator))
+            ..._findTests(fs.directory(file))
+          else
+            file
+      ];
     }
 
     CoverageCollector collector;

packages/flutter_tools/lib/src/commands/update_packages.dart

@@ -728,9 +728,11 @@ class PubspecYaml {
     // Merge the lists of dependencies we've seen in this file from dependencies, dev dependencies,
     // and the dependencies we know this file mentions that are already pinned
     // (and which didn't get special processing above).
-    final Set<String> implied = Set<String>.from(directDependencies)
-      ..addAll(specialDependencies)
-      ..addAll(devDependencies);
+    final Set<String> implied = <String>{
+      ...directDependencies,
+      ...specialDependencies,
+      ...devDependencies,
+    };
 
     // Create a new set to hold the list of packages we've already processed, so
     // that we don't redundantly process them multiple times.
@@ -751,12 +753,12 @@ class PubspecYaml {
       transitiveDevDependencyOutput.add('  $package: ${versions.versionFor(package)} $kTransitiveMagicString');
 
     // Build a sorted list of all dependencies for the checksum.
-    final Set<String> checksumDependencies = <String>{}
-      ..addAll(directDependencies)
-      ..addAll(devDependencies)
-      ..addAll(transitiveDependenciesAsList)
-      ..addAll(transitiveDevDependenciesAsList);
-    checksumDependencies.removeAll(specialDependencies);
+    final Set<String> checksumDependencies = <String>{
+      ...directDependencies,
+      ...devDependencies,
+      ...transitiveDependenciesAsList,
+      ...transitiveDevDependenciesAsList,
+    }..removeAll(specialDependencies);
 
     // Add a blank line before and after each section to keep the resulting output clean.
     transitiveDependencyOutput

packages/flutter_tools/lib/src/dart/pub.dart

@@ -96,12 +96,12 @@ Future<void> pubGet({
       'Running "flutter pub $command" in ${fs.path.basename(directory)}...',
       timeout: timeoutConfiguration.slowOperation,
     );
-    final List<String> args = <String>['--verbosity=warning'];
-    if (FlutterCommand.current != null && FlutterCommand.current.globalResults['verbose'])
-      args.add('--verbose');
-    args.addAll(<String>[command, '--no-precompile']);
-    if (offline)
-      args.add('--offline');
+    final List<String> args = <String>[
+      '--verbosity=warning',
+      if (FlutterCommand.current != null && FlutterCommand.current.globalResults['verbose']) '--verbose',
+      ...<String>[command, '--no-precompile'],
+      if (offline) '--offline',
+    ];
     try {
       await pub(
         args,
@@ -228,21 +228,13 @@ const String _pubCacheEnvironmentKey = 'PUB_CACHE';
 String _getPubEnvironmentValue(PubContext pubContext) {
   // DO NOT update this function without contacting kevmoo.
   // We have server-side tooling that assumes the values are consistent.
-  final List<String> values = <String>[];
-
   final String existing = platform.environment[_pubEnvironmentKey];
-
-  if ((existing != null) && existing.isNotEmpty) {
-    values.add(existing);
-  }
-
-  if (isRunningOnBot) {
-    values.add('flutter_bot');
-  }
-
-  values.add('flutter_cli');
-  values.addAll(pubContext._values);
-
+  final List<String> values = <String>[
+    if (existing != null && existing.isNotEmpty) existing,
+    if (isRunningOnBot) 'flutter_bot',
+    'flutter_cli',
+    ...pubContext._values,
+  ];
   return values.join(':');
 }
 

packages/flutter_tools/lib/src/device.dart

@@ -161,11 +161,10 @@ class DeviceManager {
 
   /// Get diagnostics about issues with any connected devices.
   Future<List<String>> getDeviceDiagnostics() async {
-    final List<String> diagnostics = <String>[];
-    for (DeviceDiscovery discoverer in _platformDiscoverers) {
-      diagnostics.addAll(await discoverer.getDiagnostics());
-    }
-    return diagnostics;
+    return <String>[
+      for (DeviceDiscovery discoverer in _platformDiscoverers)
+        ...await discoverer.getDiagnostics(),
+    ];
   }
 
   /// Find and return a list of devices based on the current project and environment.

packages/flutter_tools/lib/src/doctor.dart

@@ -60,45 +60,37 @@ class _DefaultDoctorValidatorsProvider implements DoctorValidatorsProvider {
   @override
   List<DoctorValidator> get validators {
     if (_validators == null) {
-      _validators = <DoctorValidator>[];
-      _validators.add(FlutterValidator());
-
-      if (androidWorkflow.appliesToHostPlatform)
-        _validators.add(GroupedValidator(<DoctorValidator>[androidValidator, androidLicenseValidator]));
-
-      if (iosWorkflow.appliesToHostPlatform || macOSWorkflow.appliesToHostPlatform)
-        _validators.add(GroupedValidator(<DoctorValidator>[xcodeValidator, cocoapodsValidator]));
-
-      if (iosWorkflow.appliesToHostPlatform)
-        _validators.add(iosValidator);
-
-      if (webWorkflow.appliesToHostPlatform)
-        _validators.add(const WebValidator());
-
-      // Add desktop doctors to workflow if the flag is enabled.
-      if (flutterDesktopEnabled) {
-        if (linuxWorkflow.appliesToHostPlatform) {
-          _validators.add(LinuxDoctorValidator());
-        }
-        if (windowsWorkflow.appliesToHostPlatform) {
-          _validators.add(visualStudioValidator);
-        }
-      }
-
-      final List<DoctorValidator> ideValidators = <DoctorValidator>[];
-      ideValidators.addAll(AndroidStudioValidator.allValidators);
-      ideValidators.addAll(IntelliJValidator.installedValidators);
-      ideValidators.addAll(VsCodeValidator.installedValidators);
-      if (ideValidators.isNotEmpty)
-        _validators.addAll(ideValidators);
-      else
-        _validators.add(NoIdeValidator());
-
-      if (ProxyValidator.shouldShow)
-        _validators.add(ProxyValidator());
-
-      if (deviceManager.canListAnything)
-        _validators.add(DeviceValidator());
+      final List<DoctorValidator> ideValidators = <DoctorValidator>[
+        ...AndroidStudioValidator.allValidators,
+        ...IntelliJValidator.installedValidators,
+        ...VsCodeValidator.installedValidators,
+      ];
+
+      _validators = <DoctorValidator>[
+        FlutterValidator(),
+        if (androidWorkflow.appliesToHostPlatform)
+          GroupedValidator(<DoctorValidator>[androidValidator, androidLicenseValidator]),
+        if (iosWorkflow.appliesToHostPlatform || macOSWorkflow.appliesToHostPlatform)
+          GroupedValidator(<DoctorValidator>[xcodeValidator, cocoapodsValidator]),
+        if (iosWorkflow.appliesToHostPlatform)
+          iosValidator,
+        if (webWorkflow.appliesToHostPlatform)
+          const WebValidator(),
+        // Add desktop doctors to workflow if the flag is enabled.
+        if (flutterDesktopEnabled)
+          ...<DoctorValidator>[
+            if (linuxWorkflow.appliesToHostPlatform) LinuxDoctorValidator(),
+            if (windowsWorkflow.appliesToHostPlatform) visualStudioValidator,
+          ],
+        if (ideValidators.isNotEmpty)
+          ...ideValidators
+        else
+          NoIdeValidator(),
+        if (ProxyValidator.shouldShow)
+          ProxyValidator(),
+        if (deviceManager.canListAnything)
+          DeviceValidator(),
+      ];
     }
     return _validators;
   }

packages/flutter_tools/lib/src/ios/simulators.dart

@@ -144,12 +144,16 @@ class SimControl {
   }
 
   Future<RunResult> launch(String deviceId, String appIdentifier, [ List<String> launchArgs ]) {
-    final List<String> args = <String>[_xcrunPath, 'simctl', 'launch', deviceId, appIdentifier];
-    if (launchArgs != null)
-      args.addAll(launchArgs);
     Future<RunResult> result;
     try {
-      result = runCheckedAsync(args);
+      result = runCheckedAsync(<String>[
+        _xcrunPath,
+        'simctl',
+        'launch',
+        deviceId,
+        appIdentifier,
+        ...?launchArgs,
+      ]);
     } on ProcessException catch (exception) {
       throwToolExit('Unable to launch $appIdentifier on $deviceId:\n$exception');
     }

packages/flutter_tools/lib/src/runner/flutter_command.dart

@@ -407,12 +407,10 @@ abstract class FlutterCommand extends Command<void> {
     }
 
     // Send screen.
-    final Map<String, String> additionalUsageValues = <String, String>{};
     final Map<String, String> currentUsageValues = await usageValues;
-
-    if (currentUsageValues != null) {
-      additionalUsageValues.addAll(currentUsageValues);
-    }
+    final Map<String, String> additionalUsageValues = <String, String>{
+      ...?currentUsageValues,
+    };
     if (commandResult != null) {
       switch (commandResult.exitStatus) {
         case ExitStatus.success:
@@ -429,11 +427,12 @@ abstract class FlutterCommand extends Command<void> {
     flutterUsage.sendCommand(commandPath, parameters: additionalUsageValues);
 
     // Send timing.
-    final List<String> labels = <String>[];
-    if (commandResult?.exitStatus != null)
-      labels.add(getEnumName(commandResult.exitStatus));
-    if (commandResult?.timingLabelParts?.isNotEmpty ?? false)
-      labels.addAll(commandResult.timingLabelParts);
+    final List<String> labels = <String>[
+      if (commandResult?.exitStatus != null)
+        getEnumName(commandResult.exitStatus),
+      if (commandResult?.timingLabelParts?.isNotEmpty ?? false)
+        ...commandResult.timingLabelParts,
+    ];
 
     final String label = labels
         .where((String label) => !isBlank(label))

packages/flutter_tools/lib/src/test/runner.dart

@@ -47,26 +47,19 @@ Future<int> runTests(
   bool web = false,
 }) async {
   // Compute the command-line arguments for package:test.
-  final List<String> testArgs = <String>[];
-  if (!terminal.supportsColor) {
-    testArgs.addAll(<String>['--no-color']);
-  }
-
-  if (machine) {
-    testArgs.addAll(<String>['-r', 'json']);
-  } else {
-    testArgs.addAll(<String>['-r', 'compact']);
-  }
-
-  testArgs.add('--concurrency=$concurrency');
-
-  for (String name in names) {
-    testArgs..add('--name')..add(name);
-  }
-
-  for (String plainName in plainNames) {
-    testArgs..add('--plain-name')..add(plainName);
-  }
+  final List<String> testArgs = <String>[
+    if (!terminal.supportsColor)
+      '--no-color',
+    if (machine)
+      ...<String>['-r', 'json']
+    else
+      ...<String>['-r', 'compact'],
+    '--concurrency=$concurrency',
+    for (String name in names)
+      ...<String>['--name', name],
+    for (String plainName in plainNames)
+      ...<String>['--plain-name', plainName],
+  ];
   if (web) {
     final String tempBuildDir = fs.systemTempDirectory
       .createTempSync('_flutter_test')
@@ -80,10 +73,11 @@ Future<int> runTests(
     if (!result) {
       throwToolExit('Failed to compile tests');
     }
-    testArgs.add('--platform=chrome');
-    testArgs.add('--precompiled=$tempBuildDir');
-    testArgs.add('--');
-    testArgs.addAll(testFiles);
+    testArgs
+      ..add('--platform=chrome')
+      ..add('--precompiled=$tempBuildDir')
+      ..add('--')
+      ..addAll(testFiles);
     hack.registerPlatformPlugin(
       <Runtime>[Runtime.chrome],
       () {
@@ -94,8 +88,9 @@ Future<int> runTests(
     return exitCode;
   }
 
-  testArgs.add('--');
-  testArgs.addAll(testFiles);
+  testArgs
+    ..add('--')
+    ..addAll(testFiles);
 
   // Configure package:test to use the Flutter engine for child processes.
   final String shellPath = artifacts.getArtifactPath(Artifact.flutterTester);

packages/flutter_tools/lib/src/version.dart

@@ -133,12 +133,15 @@ class FlutterVersion {
   String get frameworkCommitDate => _latestGitCommitDate();
 
   static String _latestGitCommitDate([ String branch ]) {
-    final List<String> args = <String>['git', 'log'];
-
-    if (branch != null)
-      args.add(branch);
-
-    args.addAll(<String>['-n', '1', '--pretty=format:%ad', '--date=iso']);
+    final List<String> args = <String>[
+      'git',
+      'log',
+      if (branch != null) branch,
+      '-n',
+      '1',
+      '--pretty=format:%ad',
+      '--date=iso',
+    ];
     return _runSync(args, lenient: false);
   }
 

packages/flutter_tools/test/base/fingerprint_test.dart

@@ -211,7 +211,8 @@ void main() {
       expect(await fingerprinter.doesFingerprintMatch(), isFalse);
     }, overrides: <Type, Generator>{
       Platform: () => mockPlatformDisabledCache,
-    }..addAll(contextOverrides));
+      ...contextOverrides,
+    });
 
     final Platform mockPlatformEnabledCache = MockPlatform();
     mockPlatformEnabledCache.environment['DISABLE_FLUTTER_BUILD_CACHE']  = 'false';
@@ -231,7 +232,8 @@ void main() {
       expect(await fingerprinter.doesFingerprintMatch(), isTrue);
     }, overrides: <Type, Generator>{
       Platform: () => mockPlatformEnabledCache,
-    }..addAll(contextOverrides));
+      ...contextOverrides,
+    });
 
     testUsingContext('fails to write fingerprint if inputs are missing', () async {
       final Fingerprinter fingerprinter = Fingerprinter(

packages/flutter_tools/test/commands/build_bundle_test.dart

@@ -53,13 +53,11 @@ void main() {
     Future<BuildBundleCommand> runCommandIn(String projectPath, { List<String> arguments }) async {
       final BuildBundleCommand command = BuildBundleCommand(bundleBuilder: mockBundleBuilder);
       final CommandRunner<void> runner = createTestCommandRunner(command);
-
-      final List<String> commandArgs = <String>['bundle'];
-      if (arguments != null)
-        commandArgs.addAll(arguments);
-      commandArgs.add('--target=$projectPath/lib/main.dart');
-
-      await runner.run(commandArgs);
+      await runner.run(<String>[
+        'bundle',
+        ...?arguments,
+        '--target=$projectPath/lib/main.dart',
+      ]);
       return command;
     }
 

packages/flutter_tools/test/commands/create_test.dart

@@ -1129,10 +1129,11 @@ Future<void> _createProject(
   Cache.flutterRoot = '../..';
   final CreateCommand command = CreateCommand();
   final CommandRunner<void> runner = createTestCommandRunner(command);
-  final List<String> args = <String>['create'];
-  args.addAll(createArgs);
-  args.add(dir.path);
-  await runner.run(args);
+  await runner.run(<String>[
+    'create',
+    ...createArgs,
+    dir.path,
+  ]);
 
   bool pathExists(String path) {
     final String fullPath = fs.path.join(dir.path, path);

packages/flutter_tools/test/commands/ide_config_test.dart

@@ -85,9 +85,11 @@ void main() {
       dir ??= tempDir;
       final IdeConfigCommand command = IdeConfigCommand();
       final CommandRunner<void> runner = createTestCommandRunner(command);
-      final List<String> finalArgs = <String>['--flutter-root=${tempDir.absolute.path}', 'ide-config'];
-      finalArgs.addAll(args);
-      await runner.run(finalArgs);
+      await runner.run(<String>[
+        '--flutter-root=${tempDir.absolute.path}',
+        'ide-config',
+        ...args,
+      ]);
 
       for (String path in expectedContents.keys) {
         final String absPath = fs.path.join(tempDir.absolute.path, path);
@@ -148,8 +150,10 @@ void main() {
         'template',
       );
       _populateDir(templateManifest);
-      final Map<String, String> expectedContents = templateManifest;
-      expectedContents.addAll(flutterManifest);
+      final Map<String, String> expectedContents = <String, String>{
+        ...templateManifest,
+        ...flutterManifest,
+      };
       return _updateIdeConfig(
         expectedContents: expectedContents,
       );
@@ -171,8 +175,10 @@ void main() {
         tempDir,
         'template',
       );
-      final Map<String, String> expectedContents = templateManifest;
-      expectedContents.addAll(overwrittenManifest);
+      final Map<String, String> expectedContents = <String, String>{
+        ...templateManifest,
+        ...overwrittenManifest,
+      };
       return _updateIdeConfig(
         args: <String>['--overwrite'],
         expectedContents: expectedContents,
@@ -200,8 +206,10 @@ void main() {
         'existing',
       );
       _populateDir(flutterManifest);
-      final Map<String, String> expectedContents = flutterManifest;
-      expectedContents.addAll(templateManifest);
+      final Map<String, String> expectedContents = <String, String>{
+        ...flutterManifest,
+        ...templateManifest,
+      };
       return _updateIdeConfig(
         args: <String>['--update-templates'],
         expectedContents: expectedContents,
@@ -225,8 +233,10 @@ void main() {
         'existing',
         isTemplate: true,
       );
-      final Map<String, String> expectedContents = flutterManifest;
-      expectedContents.addAll(updatedTemplates);
+      final Map<String, String> expectedContents = <String, String>{
+        ...flutterManifest,
+        ...updatedTemplates,
+      };
       return _updateIdeConfig(
         args: <String>['--update-templates', '--overwrite'],
         expectedContents: expectedContents,
@@ -259,8 +269,10 @@ void main() {
         'flutter.iml${Template.copyTemplateExtension}',
       );
       updatedTemplates.remove(flutterIml);
-      final Map<String, String> expectedContents = flutterManifest;
-      expectedContents.addAll(updatedTemplates);
+      final Map<String, String> expectedContents = <String, String>{
+        ...flutterManifest,
+        ...updatedTemplates,
+      };
       return _updateIdeConfig(
         args: <String>['--update-templates', '--overwrite'],
         expectedContents: expectedContents,
@@ -298,8 +310,10 @@ void main() {
       updatedTemplates.remove(deepIml);
       deepIml = fs.path.join(deepIml, 'deep.iml');
       updatedTemplates.remove(deepIml);
-      final Map<String, String> expectedContents = flutterManifest;
-      expectedContents.addAll(updatedTemplates);
+      final Map<String, String> expectedContents = <String, String>{
+        ...flutterManifest,
+        ...updatedTemplates,
+      };
       return _updateIdeConfig(
         args: <String>['--update-templates', '--overwrite'],
         expectedContents: expectedContents,

packages/flutter_tools/test/commands/packages_test.dart

@@ -61,13 +61,12 @@ void main() {
     Future<PackagesCommand> runCommandIn(String projectPath, String verb, { List<String> args }) async {
       final PackagesCommand command = PackagesCommand();
       final CommandRunner<void> runner = createTestCommandRunner(command);
-
-      final List<String> commandArgs = <String>['packages', verb];
-      if (args != null)
-        commandArgs.addAll(args);
-      commandArgs.add(projectPath);
-
-      await runner.run(commandArgs);
+      await runner.run(<String>[
+        'packages',
+        verb,
+        ...?args,
+        projectPath,
+      ]);
       return command;
     }
 

packages/flutter_tools/test/src/testbed.dart

@@ -77,15 +77,13 @@ class Testbed {
   /// `overrides` may be used to provide new context values for the single test
   /// case or override any context values from the setup.
   FutureOr<T> run<T>(FutureOr<T> Function() test, {Map<Type, Generator> overrides}) {
-    final Map<Type, Generator> testOverrides = Map<Type, Generator>.from(_testbedDefaults);
-    // Add the initial setUp overrides
-    if (_overrides != null) {
-      testOverrides.addAll(_overrides);
-    }
-    // Add the test-specific overrides
-    if (overrides != null) {
-      testOverrides.addAll(overrides);
-    }
+    final Map<Type, Generator> testOverrides = <Type, Generator>{
+      ..._testbedDefaults,
+      // Add the initial setUp overrides
+      ...?_overrides,
+      // Add the test-specific overrides
+      ...?overrides,
+    };
     // Cache the original flutter root to restore after the test case.
     final String originalFlutterRoot = Cache.flutterRoot;
     return runInContext<T>(() {

packages/fuchsia_remote_debug_protocol/lib/src/fuchsia_remote_connection.dart

@@ -606,24 +606,21 @@ class _SshPortForwarder implements PortForwarder {
     // IPv6 interface, it cannot be used to connect to a websocket.
     final String formattedForwardingUrl =
         '${localSocket.port}:$_ipv4Loopback:$remotePort';
-    final List<String> command = <String>['ssh'];
-    if (isIpV6) {
-      command.add('-6');
-    }
-    if (sshConfigPath != null) {
-      command.addAll(<String>['-F', sshConfigPath]);
-    }
     final String targetAddress =
         isIpV6 && interface.isNotEmpty ? '$address%$interface' : address;
     const String dummyRemoteCommand = 'true';
-    command.addAll(<String>[
+    final List<String> command = <String>[
+      'ssh',
+      if (isIpV6) '-6',
+      if (sshConfigPath != null)
+        ...<String>['-F', sshConfigPath],
       '-nNT',
       '-f',
       '-L',
       formattedForwardingUrl,
       targetAddress,
       dummyRemoteCommand,
-    ]);
+    ];
     _log.fine("_SshPortForwarder running '${command.join(' ')}'");
     // Must await for the port forwarding function to completer here, as
     // forwarding must be completed before surfacing VM events (as the user may
@@ -649,20 +646,19 @@ class _SshPortForwarder implements PortForwarder {
     // uses the IPv4 loopback.
     final String formattedForwardingUrl =
         '${_localSocket.port}:$_ipv4Loopback:$_remotePort';
-    final List<String> command = <String>['ssh'];
     final String targetAddress = _ipV6 && _interface.isNotEmpty
         ? '$_remoteAddress%$_interface'
         : _remoteAddress;
-    if (_sshConfigPath != null) {
-      command.addAll(<String>['-F', _sshConfigPath]);
-    }
-    command.addAll(<String>[
+    final List<String> command = <String>[
+      'ssh',
+      if (_sshConfigPath != null)
+        ...<String>['-F', _sshConfigPath],
       '-O',
       'cancel',
       '-L',
       formattedForwardingUrl,
       targetAddress,
-    ]);
+    ];
     _log.fine(
         'Shutting down SSH forwarding with command: ${command.join(' ')}');
     final ProcessResult result = await _processManager.run(command);

packages/fuchsia_remote_debug_protocol/lib/src/runners/ssh_command_runner.dart

@@ -82,18 +82,16 @@ class SshCommandRunner {
   /// If the subprocess creating the SSH tunnel returns a nonzero exit status,
   /// then an [SshCommandError] is raised.
   Future<List<String>> run(String command) async {
-    final List<String> args = <String>['ssh'];
-    if (sshConfigPath != null) {
-      args.addAll(<String>['-F', sshConfigPath]);
-    }
-    if (isIpV6Address(address)) {
-      final String fullAddress =
-          interface.isEmpty ? address : '$address%$interface';
-      args.addAll(<String>['-6', fullAddress]);
-    } else {
-      args.add(address);
-    }
-    args.add(command);
+    final List<String> args = <String>[
+      'ssh',
+      if (sshConfigPath != null)
+        ...<String>['-F', sshConfigPath],
+      if (isIpV6Address(address))
+        ...<String>['-6', interface.isEmpty ? address : '$address%$interface']
+      else
+        address,
+      command,
+    ];
     _log.fine('Running command through SSH: ${args.join(' ')}');
     final ProcessResult result = await _processManager.run(args);
     if (result.exitCode != 0) {

packages/fuchsia_remote_debug_protocol/pubspec.yaml

@@ -5,7 +5,7 @@ author: Flutter Authors <flutter-dev@googlegroups.com>
 
 environment:
   # The pub client defaults to an <2.0.0 sdk constraint which we need to explicitly overwrite.
-  sdk: ">=2.2.0 <3.0.0"
+  sdk: ">=2.2.2 <3.0.0"
 
 dependencies:
   json_rpc_2: 2.1.0