Migrate build commands to null safety (#95649)

packages/flutter_tools/lib/src/bundle_builder.dart

@@ -70,7 +70,7 @@ class BundleBuilder {
     final Target target = buildInfo.mode == BuildMode.debug
         ? const CopyFlutterBundle()
         : const ReleaseCopyFlutterBundle();
-    final BuildResult result = await buildSystem!.build(target, environment);
+    final BuildResult result = await buildSystem.build(target, environment);
 
     if (!result.success) {
       for (final ExceptionMeasurement measurement in result.exceptions.values) {

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

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:meta/meta.dart';
 
 import '../build_info.dart';
@@ -61,11 +59,11 @@ class BuildCommand extends FlutterCommand {
   String get category => FlutterCommandCategory.project;
 
   @override
-  Future<FlutterCommandResult> runCommand() async => null;
+  Future<FlutterCommandResult> runCommand() async => FlutterCommandResult.fail();
 }
 
 abstract class BuildSubCommand extends FlutterCommand {
-  BuildSubCommand({@required bool verboseHelp}) {
+  BuildSubCommand({required bool verboseHelp}) {
     requiresPubspecYaml();
     usesFatalWarningsOption(verboseHelp: verboseHelp);
   }

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

@@ -2,9 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-import 'package:meta/meta.dart';
-
 import '../android/android_builder.dart';
 import '../android/gradle_utils.dart';
 import '../base/common.dart';
@@ -20,7 +17,7 @@ import '../runner/flutter_command.dart' show FlutterCommandResult;
 import 'build.dart';
 
 class BuildAarCommand extends BuildSubCommand {
-  BuildAarCommand({ @required bool verboseHelp }) : super(verboseHelp: verboseHelp) {
+  BuildAarCommand({ required bool verboseHelp }) : super(verboseHelp: verboseHelp) {
     argParser
       ..addFlag(
         'debug',
@@ -52,7 +49,6 @@ class BuildAarCommand extends BuildSubCommand {
     argParser
       ..addMultiOption(
         'target-platform',
-        splitCommas: true,
         defaultsTo: <String>['android-arm', 'android-arm64', 'android-x64'],
         allowed: <String>['android-arm', 'android-arm64', 'android-x86', 'android-x64'],
         help: 'The target platform for which the project is compiled.',
@@ -116,10 +112,11 @@ class BuildAarCommand extends BuildSubCommand {
     final Iterable<AndroidArch> targetArchitectures =
         stringsArg('target-platform').map<AndroidArch>(getAndroidArchForName);
 
+    final String? buildNumberArg = stringArg('build-number');
     final String buildNumber = argParser.options.containsKey('build-number')
-      && stringArg('build-number') != null
-      && stringArg('build-number').isNotEmpty
-      ? stringArg('build-number')
+      && buildNumberArg != null
+      && buildNumberArg.isNotEmpty
+      ? buildNumberArg
       : '1.0';
 
     final File targetFile = globals.fs.file(globals.fs.path.join('lib', 'main.dart'));
@@ -141,7 +138,7 @@ class BuildAarCommand extends BuildSubCommand {
     }
 
     displayNullSafetyMode(androidBuildInfo.first.buildInfo);
-    await androidBuilder.buildAar(
+    await androidBuilder?.buildAar(
       project: _getProject(),
       target: targetFile.path,
       androidBuildInfo: androidBuildInfo,
@@ -154,9 +151,10 @@ class BuildAarCommand extends BuildSubCommand {
   /// Returns the [FlutterProject] which is determined from the remaining command-line
   /// argument if any or the current working directory.
   FlutterProject _getProject() {
-    if (argResults.rest.isEmpty) {
+    final List<String> remainingArguments = argResults!.rest;
+    if (remainingArguments.isEmpty) {
       return FlutterProject.current();
     }
-    return FlutterProject.fromDirectory(globals.fs.directory(findProjectRoot(globals.fs, argResults.rest.first)));
+    return FlutterProject.fromDirectory(globals.fs.directory(findProjectRoot(globals.fs, remainingArguments.first)));
   }
 }

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

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import '../android/android_builder.dart';
 import '../android/build_validation.dart';
 import '../android/gradle_utils.dart';
@@ -44,7 +42,6 @@ class BuildApkCommand extends BuildSubCommand {
               'To learn more, see: https://developer.android.com/studio/build/configure-apk-splits#configure-abi-split',
       )
       ..addMultiOption('target-platform',
-        splitCommas: true,
         defaultsTo: <String>['android-arm', 'android-arm64', 'android-x64'],
         allowed: <String>['android-arm', 'android-arm64', 'android-x86', 'android-x64'],
         help: 'The target platform for which the app is compiled.',
@@ -109,7 +106,7 @@ class BuildApkCommand extends BuildSubCommand {
     validateBuild(androidBuildInfo);
     displayNullSafetyMode(androidBuildInfo.buildInfo);
     globals.terminal.usesTerminalUi = true;
-    await androidBuilder.buildApk(
+    await androidBuilder?.buildApk(
       project: FlutterProject.current(),
       target: targetFile,
       androidBuildInfo: androidBuildInfo,

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

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import '../android/android_builder.dart';
 import '../android/build_validation.dart';
 import '../android/deferred_components_prebuild_validator.dart';
@@ -44,13 +42,11 @@ class BuildAppBundleCommand extends BuildSubCommand {
     addMultidexOption();
     addIgnoreDeprecationOption();
     argParser.addMultiOption('target-platform',
-      splitCommas: true,
       defaultsTo: <String>['android-arm', 'android-arm64', 'android-x64'],
       allowed: <String>['android-arm', 'android-arm64', 'android-x64'],
       help: 'The target platform for which the app is compiled.',
     );
     argParser.addFlag('deferred-components',
-      negatable: true,
       defaultsTo: true,
       help: 'Setting to false disables building with deferred components. All deferred code '
             'will be compiled into the base app, and assets act as if they were defined under'
@@ -58,7 +54,6 @@ class BuildAppBundleCommand extends BuildSubCommand {
             'non-deferred components apps.',
     );
     argParser.addFlag('validate-deferred-components',
-      negatable: true,
       defaultsTo: true,
       help: 'When enabled, deferred component apps will fail to build if setup problems are '
             'detected that would prevent deferred components from functioning properly. The '
@@ -121,7 +116,8 @@ class BuildAppBundleCommand extends BuildSubCommand {
     );
     // Do all setup verification that doesn't involve loading units. Checks that
     // require generated loading units are done after gen_snapshot in assemble.
-    if (FlutterProject.current().manifest.deferredComponents != null && boolArg('deferred-components') && boolArg('validate-deferred-components') && !boolArg('debug')) {
+    final List<DeferredComponent>? deferredComponents = FlutterProject.current().manifest.deferredComponents;
+    if (deferredComponents != null && boolArg('deferred-components') && boolArg('validate-deferred-components') && !boolArg('debug')) {
       final DeferredComponentsPrebuildValidator validator = DeferredComponentsPrebuildValidator(
         FlutterProject.current().directory,
         globals.logger,
@@ -129,14 +125,14 @@ class BuildAppBundleCommand extends BuildSubCommand {
         title: 'Deferred components prebuild validation',
       );
       validator.clearOutputDir();
-      await validator.checkAndroidDynamicFeature(FlutterProject.current().manifest.deferredComponents);
-      validator.checkAndroidResourcesStrings(FlutterProject.current().manifest.deferredComponents);
+      await validator.checkAndroidDynamicFeature(deferredComponents);
+      validator.checkAndroidResourcesStrings(deferredComponents);
 
       validator.handleResults();
 
       // Delete intermediates libs dir for components to resolve mismatching
       // abis supported by base and dynamic feature modules.
-      for (final DeferredComponent component in FlutterProject.current().manifest.deferredComponents) {
+      for (final DeferredComponent component in deferredComponents) {
         final Directory deferredLibsIntermediate = FlutterProject.current().directory
           .childDirectory('build')
           .childDirectory(component.name)
@@ -153,7 +149,7 @@ class BuildAppBundleCommand extends BuildSubCommand {
     validateBuild(androidBuildInfo);
     displayNullSafetyMode(androidBuildInfo.buildInfo);
     globals.terminal.usesTerminalUi = true;
-    await androidBuilder.buildAab(
+    await androidBuilder?.buildAab(
       project: FlutterProject.current(),
       target: targetFile,
       androidBuildInfo: androidBuildInfo,

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

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import '../base/common.dart';
 import '../build_info.dart';
 import '../bundle.dart';
@@ -18,8 +16,8 @@ import 'build.dart';
 class BuildBundleCommand extends BuildSubCommand {
   BuildBundleCommand({
     bool verboseHelp = false,
-    this.bundleBuilder,
-  }) : super(verboseHelp: verboseHelp) {
+    BundleBuilder? bundleBuilder,
+  }) :  _bundleBuilder = bundleBuilder ?? BundleBuilder(), super(verboseHelp: verboseHelp) {
     usesTargetOption();
     usesFilesystemOptions(hide: !verboseHelp);
     usesBuildNumberOption();
@@ -54,18 +52,14 @@ class BuildBundleCommand extends BuildSubCommand {
       )
       ..addFlag(
         'tree-shake-icons',
-        negatable: true,
-        defaultsTo: false,
         hide: !verboseHelp,
         help: '(deprecated) Icon font tree shaking is not supported by this command.',
       );
     usesPubOption();
     usesTrackWidgetCreation(verboseHelp: verboseHelp);
-
-    bundleBuilder ??= BundleBuilder();
   }
 
-  BundleBuilder bundleBuilder;
+  final BundleBuilder _bundleBuilder;
 
   @override
   final String name = 'bundle';
@@ -93,7 +87,7 @@ class BuildBundleCommand extends BuildSubCommand {
 
   @override
   Future<void> validateCommand() async {
-    if (argResults['tree-shake-icons'] as bool) {
+    if (boolArg('tree-shake-icons')) {
       throwToolExit('The "--tree-shake-icons" flag is deprecated for "build bundle" and will be removed in a future version of Flutter.');
     }
     return super.validateCommand();
@@ -101,7 +95,7 @@ class BuildBundleCommand extends BuildSubCommand {
 
   @override
   Future<FlutterCommandResult> runCommand() async {
-    final String targetPlatform = stringArg('target-platform');
+    final String targetPlatform = stringArg('target-platform')!;
     final TargetPlatform platform = getTargetPlatformForName(targetPlatform);
     if (platform == null) {
       throwToolExit('Unknown platform: $targetPlatform');
@@ -141,7 +135,7 @@ class BuildBundleCommand extends BuildSubCommand {
     final BuildInfo buildInfo = await getBuildInfo();
     displayNullSafetyMode(buildInfo);
 
-    await bundleBuilder.build(
+    await _bundleBuilder.build(
       platform: platform,
       buildInfo: buildInfo,
       mainPath: targetFile,

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

@@ -2,10 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
-import 'package:meta/meta.dart';
-
 import '../base/common.dart';
 import '../build_info.dart';
 import '../cache.dart';
@@ -20,7 +16,7 @@ import 'build.dart';
 /// A command to build a Fuchsia target.
 class BuildFuchsiaCommand extends BuildSubCommand {
   BuildFuchsiaCommand({
-    @required bool verboseHelp,
+    required bool verboseHelp,
   }) : super(verboseHelp: verboseHelp) {
     addTreeShakeIconsFlag();
     usesTargetOption();
@@ -83,9 +79,9 @@ class BuildFuchsiaCommand extends BuildSubCommand {
     await buildFuchsia(
       fuchsiaProject: flutterProject.fuchsia,
       target: targetFile,
-      targetPlatform: getTargetPlatformForName(stringArg('target-platform')),
+      targetPlatform: getTargetPlatformForName(stringArg('target-platform')!),
       buildInfo: buildInfo,
-      runnerPackageSource: stringArg('runner-source'),
+      runnerPackageSource: stringArg('runner-source')!,
     );
     return FlutterCommandResult.success();
   }

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

@@ -2,10 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:file/file.dart';
-import 'package:meta/meta.dart';
 
 import '../base/analyze_size.dart';
 import '../base/common.dart';
@@ -23,7 +20,7 @@ import 'build.dart';
 /// Builds an .app for an iOS app to be used for local testing on an iOS device
 /// or simulator. Can only be run on a macOS host.
 class BuildIOSCommand extends _BuildIOSSubCommand {
-  BuildIOSCommand({ @required bool verboseHelp }) : super(verboseHelp: verboseHelp) {
+  BuildIOSCommand({ required bool verboseHelp }) : super(verboseHelp: verboseHelp) {
     argParser
       ..addFlag('config-only',
         help: 'Update the project configuration without performing a build. '
@@ -67,7 +64,7 @@ class BuildIOSCommand extends _BuildIOSSubCommand {
 ///
 /// Can only be run on a macOS host.
 class BuildIOSArchiveCommand extends _BuildIOSSubCommand {
-  BuildIOSArchiveCommand({@required bool verboseHelp})
+  BuildIOSArchiveCommand({required bool verboseHelp})
       : super(verboseHelp: verboseHelp) {
     argParser.addOption(
       'export-options-plist',
@@ -99,7 +96,7 @@ class BuildIOSArchiveCommand extends _BuildIOSSubCommand {
   @override
   final bool shouldCodesign = true;
 
-  String get exportOptionsPlist => stringArg('export-options-plist');
+  String? get exportOptionsPlist => stringArg('export-options-plist');
 
   @override
   Directory _outputAppDirectory(String xcodeResultOutput) => globals.fs
@@ -109,21 +106,22 @@ class BuildIOSArchiveCommand extends _BuildIOSSubCommand {
 
   @override
   Future<FlutterCommandResult> runCommand() async {
-    if (exportOptionsPlist != null) {
-      final FileSystemEntityType type = globals.fs.typeSync(exportOptionsPlist);
+    final String? exportOptions = exportOptionsPlist;
+    if (exportOptions != null) {
+      final FileSystemEntityType type = globals.fs.typeSync(exportOptions);
       if (type == FileSystemEntityType.notFound) {
         throwToolExit(
-            '"$exportOptionsPlist" property list does not exist.');
+            '"$exportOptions" property list does not exist.');
       } else if (type != FileSystemEntityType.file) {
         throwToolExit(
-            '"$exportOptionsPlist" is not a file. See "xcodebuild -h" for available keys.');
+            '"$exportOptions" is not a file. See "xcodebuild -h" for available keys.');
       }
     }
     final FlutterCommandResult xcarchiveResult = await super.runCommand();
     final BuildInfo buildInfo = await getBuildInfo();
     displayNullSafetyMode(buildInfo);
 
-    if (exportOptionsPlist == null) {
+    if (exportOptions == null) {
       return xcarchiveResult;
     }
 
@@ -134,16 +132,16 @@ class BuildIOSArchiveCommand extends _BuildIOSSubCommand {
     }
 
     // Build IPA from generated xcarchive.
-    final BuildableIOSApp app = await buildableIOSApp(buildInfo);
-    Status status;
-    RunResult result;
+    final BuildableIOSApp app = await buildableIOSApp;
+    Status? status;
+    RunResult? result;
     final String outputPath = globals.fs.path.absolute(app.ipaOutputPath);
     try {
       status = globals.logger.startProgress('Building IPA...');
 
       result = await globals.processUtils.run(
         <String>[
-          ...globals.xcode.xcrunCommand(),
+          ...globals.xcode!.xcrunCommand(),
           'xcodebuild',
           '-exportArchive',
           if (shouldCodesign) ...<String>[
@@ -155,11 +153,11 @@ class BuildIOSArchiveCommand extends _BuildIOSSubCommand {
           '-exportPath',
           outputPath,
           '-exportOptionsPlist',
-          globals.fs.path.absolute(exportOptionsPlist),
+          globals.fs.path.absolute(exportOptions),
         ],
       );
     } finally {
-      status.stop();
+      status?.stop();
     }
 
     if (result.exitCode != 0) {
@@ -184,7 +182,7 @@ class BuildIOSArchiveCommand extends _BuildIOSSubCommand {
 
 abstract class _BuildIOSSubCommand extends BuildSubCommand {
   _BuildIOSSubCommand({
-    @required bool verboseHelp
+    required bool verboseHelp
   }) : super(verboseHelp: verboseHelp) {
     addTreeShakeIconsFlag();
     addSplitDebugInfoOption();
@@ -214,15 +212,19 @@ abstract class _BuildIOSSubCommand extends BuildSubCommand {
   bool get configOnly;
   bool get shouldCodesign;
 
-  Future<BuildableIOSApp> buildableIOSApp(BuildInfo buildInfo) async {
-    _buildableIOSApp ??= await applicationPackages.getPackageForPlatform(
+  late final Future<BuildInfo> cachedBuildInfo = getBuildInfo();
+
+  late final Future<BuildableIOSApp> buildableIOSApp = () async {
+    final BuildableIOSApp? app = await applicationPackages?.getPackageForPlatform(
       TargetPlatform.ios,
-      buildInfo: buildInfo,
-    ) as BuildableIOSApp;
-    return _buildableIOSApp;
-  }
+      buildInfo: await cachedBuildInfo,
+    ) as BuildableIOSApp?;
 
-  BuildableIOSApp _buildableIOSApp;
+    if (app == null) {
+      throwToolExit('Application not configured for iOS');
+    }
+    return app;
+  }();
 
   Directory _outputAppDirectory(String xcodeResultOutput);
 
@@ -232,7 +234,7 @@ abstract class _BuildIOSSubCommand extends BuildSubCommand {
   @override
   Future<FlutterCommandResult> runCommand() async {
     defaultBuildMode = environmentType == EnvironmentType.simulator ? BuildMode.debug : BuildMode.release;
-    final BuildInfo buildInfo = await getBuildInfo();
+    final BuildInfo buildInfo = await cachedBuildInfo;
 
     if (!supported) {
       throwToolExit('Building for iOS is only supported on macOS.');
@@ -250,14 +252,10 @@ abstract class _BuildIOSSubCommand extends BuildSubCommand {
       );
     }
 
-    final BuildableIOSApp app = await buildableIOSApp(buildInfo);
-
-    if (app == null) {
-      throwToolExit('Application not configured for iOS');
-    }
+    final BuildableIOSApp app = await buildableIOSApp;
 
     final String logTarget = environmentType == EnvironmentType.simulator ? 'simulator' : 'device';
-    final String typeName = globals.artifacts.getEngineType(TargetPlatform.ios, buildInfo.mode);
+    final String typeName = globals.artifacts!.getEngineType(TargetPlatform.ios, buildInfo.mode);
     if (xcodeBuildAction == XcodeBuildAction.build) {
       globals.printStatus('Building $app for $logTarget ($typeName)...');
     } else {
@@ -293,20 +291,24 @@ abstract class _BuildIOSSubCommand extends BuildSubCommand {
       final File precompilerTrace = globals.fs.directory(buildInfo.codeSizeDirectory)
         .childFile('trace.$arch.json');
 
-      final Directory outputAppDirectoryCandidate = _outputAppDirectory(result.output);
+      final String? resultOutput = result.output;
+      if (resultOutput == null) {
+        throwToolExit('Could not find app to analyze code size');
+      }
+      final Directory outputAppDirectoryCandidate = _outputAppDirectory(resultOutput);
 
-      Directory appDirectory;
+      Directory? appDirectory;
       if (outputAppDirectoryCandidate.existsSync()) {
         appDirectory = outputAppDirectoryCandidate.listSync()
             .whereType<Directory>()
-            .firstWhere((Directory directory) {
+            .where((Directory directory) {
           return globals.fs.path.extension(directory.path) == '.app';
-        }, orElse: () => null);
+        }).first;
       }
       if (appDirectory == null) {
         throwToolExit('Could not find app to analyze code size in ${outputAppDirectoryCandidate.path}');
       }
-      final Map<String, Object> output = await sizeAnalyzer.analyzeAotSnapshot(
+      final Map<String, Object?> output = await sizeAnalyzer.analyzeAotSnapshot(
         aotSnapshot: aotSnapshot,
         precompilerTrace: precompilerTrace,
         outputDirectory: appDirectory,

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

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:meta/meta.dart';
 
 import '../artifacts.dart';
@@ -31,12 +29,13 @@ import 'build.dart';
 /// managers.
 class BuildIOSFrameworkCommand extends BuildSubCommand {
   BuildIOSFrameworkCommand({
-    FlutterVersion flutterVersion, // Instantiating FlutterVersion kicks off networking, so delay until it's needed, but allow test injection.
-    @required BuildSystem buildSystem,
-    @required bool verboseHelp,
-    Cache cache,
-    Platform platform
-  }) : _flutterVersion = flutterVersion,
+    // Instantiating FlutterVersion kicks off networking, so delay until it's needed, but allow test injection.
+    @visibleForTesting FlutterVersion? flutterVersion,
+    required BuildSystem buildSystem,
+    required bool verboseHelp,
+    Cache? cache,
+    Platform? platform
+  }) : _injectedFlutterVersion = flutterVersion,
        _buildSystem = buildSystem,
        _injectedCache = cache,
        _injectedPlatform = platform,
@@ -54,26 +53,22 @@ class BuildIOSFrameworkCommand extends BuildSubCommand {
 
     argParser
       ..addFlag('debug',
-        negatable: true,
         defaultsTo: true,
         help: 'Whether to produce a framework for the debug build configuration. '
               'By default, all build configurations are built.'
       )
       ..addFlag('profile',
-        negatable: true,
         defaultsTo: true,
         help: 'Whether to produce a framework for the profile build configuration. '
               'By default, all build configurations are built.'
       )
       ..addFlag('release',
-        negatable: true,
         defaultsTo: true,
         help: 'Whether to produce a framework for the release build configuration. '
               'By default, all build configurations are built.'
       )
       ..addFlag('universal',
         help: '(deprecated) Produce universal frameworks that include all valid architectures.',
-        negatable: true,
         hide: !verboseHelp,
       )
       ..addFlag('xcframework',
@@ -97,16 +92,18 @@ class BuildIOSFrameworkCommand extends BuildSubCommand {
       );
   }
 
-  final BuildSystem _buildSystem;
+  final BuildSystem? _buildSystem;
   BuildSystem get buildSystem => _buildSystem ?? globals.buildSystem;
 
   Cache get _cache => _injectedCache ?? globals.cache;
-  final Cache _injectedCache;
+  final Cache? _injectedCache;
 
   Platform get _platform => _injectedPlatform ?? globals.platform;
-  final Platform _injectedPlatform;
+  final Platform? _injectedPlatform;
 
-  FlutterVersion _flutterVersion;
+  // FlutterVersion.instance kicks off git processing which can sometimes fail, so don't try it until needed.
+  FlutterVersion get _flutterVersion => _injectedFlutterVersion ?? globals.flutterVersion;
+  final FlutterVersion? _injectedFlutterVersion;
 
   @override
   bool get reportNullSafety => false;
@@ -124,7 +121,7 @@ class BuildIOSFrameworkCommand extends BuildSubCommand {
     DevelopmentArtifact.iOS,
   };
 
-  FlutterProject _project;
+  late final FlutterProject _project = FlutterProject.current();
 
   Future<List<BuildInfo>> getBuildInfos() async {
     final List<BuildInfo> buildInfos = <BuildInfo>[];
@@ -148,7 +145,6 @@ class BuildIOSFrameworkCommand extends BuildSubCommand {
   @override
   Future<void> validateCommand() async {
     await super.validateCommand();
-    _project = FlutterProject.current();
     if (!supported) {
       throwToolExit('Building frameworks for iOS is only supported on the Mac.');
     }
@@ -178,7 +174,7 @@ class BuildIOSFrameworkCommand extends BuildSubCommand {
     final List<BuildInfo> buildInfos = await getBuildInfos();
     displayNullSafetyMode(buildInfos.first);
     for (final BuildInfo buildInfo in buildInfos) {
-      final String productBundleIdentifier = await _project.ios.productBundleIdentifier(buildInfo);
+      final String? productBundleIdentifier = await _project.ios.productBundleIdentifier(buildInfo);
       globals.printStatus('Building frameworks for $productBundleIdentifier in ${getNameForBuildMode(buildInfo.mode)} mode...');
       final String xcodeBuildConfiguration = sentenceCase(getNameForBuildMode(buildInfo.mode));
       final Directory modeDirectory = outputDirectory.childDirectory(xcodeBuildConfiguration);
@@ -188,8 +184,6 @@ class BuildIOSFrameworkCommand extends BuildSubCommand {
       }
 
       if (boolArg('cocoapods')) {
-        // FlutterVersion.instance kicks off git processing which can sometimes fail, so don't try it until needed.
-        _flutterVersion ??= globals.flutterVersion;
         produceFlutterPodspec(buildInfo.mode, modeDirectory, force: boolArg('force'));
       } else {
         // Copy Flutter.xcframework.
@@ -263,7 +257,7 @@ class BuildIOSFrameworkCommand extends BuildSubCommand {
       // Fake out a semantic version with major.minor.(patch * 100) + hotfix.
       // A real increasing version is required to prompt CocoaPods to fetch
       // new artifacts when the source URL changes.
-      final int minorHotfixVersion = gitTagVersion.z * 100 + (gitTagVersion.hotfix ?? 0);
+      final int minorHotfixVersion = (gitTagVersion.z ?? 0) * 100 + (gitTagVersion.hotfix ?? 0);
 
       final File license = _cache.getLicenseFile();
       if (!license.existsSync()) {
@@ -309,7 +303,7 @@ end
     final Status status = globals.logger.startProgress(
       ' ├─Copying Flutter.xcframework...',
     );
-    final String engineCacheFlutterFrameworkDirectory = globals.artifacts.getArtifactPath(
+    final String engineCacheFlutterFrameworkDirectory = globals.artifacts!.getArtifactPath(
       Artifact.flutterXcframework,
       platform: TargetPlatform.ios,
       mode: buildInfo.mode,
@@ -369,15 +363,15 @@ end
             kIosArchs: defaultIOSArchsForEnvironment(sdkType)
                 .map(getNameForDarwinArch)
                 .join(' '),
-            kSdkRoot: await globals.xcode.sdkLocation(sdkType),
+            kSdkRoot: await globals.xcode!.sdkLocation(sdkType),
             ...buildInfo.toBuildSystemEnvironment(),
           },
-          artifacts: globals.artifacts,
+          artifacts: globals.artifacts!,
           fileSystem: globals.fs,
           logger: globals.logger,
           processManager: globals.processManager,
           platform: globals.platform,
-          engineVersion: globals.artifacts.isLocalEngine
+          engineVersion: globals.artifacts!.isLocalEngine
               ? null
               : globals.flutterVersion.engineRevision,
           generateDartPluginRegistry: true,
@@ -423,7 +417,7 @@ end
           'bitcode' : 'marker'; // In release, force bitcode embedding without archiving.
 
       List<String> pluginsBuildCommand = <String>[
-        ...globals.xcode.xcrunCommand(),
+        ...globals.xcode!.xcrunCommand(),
         'xcodebuild',
         '-alltargets',
         '-sdk',
@@ -439,7 +433,6 @@ end
       RunResult buildPluginsResult = await globals.processUtils.run(
         pluginsBuildCommand,
         workingDirectory: _project.ios.hostAppRoot.childDirectory('Pods').path,
-        allowReentrantFlutter: false,
       );
 
       if (buildPluginsResult.exitCode != 0) {
@@ -449,7 +442,7 @@ end
       // Always build debug for simulator.
       final String simulatorConfiguration = sentenceCase(getNameForBuildMode(BuildMode.debug));
       pluginsBuildCommand = <String>[
-        ...globals.xcode.xcrunCommand(),
+        ...globals.xcode!.xcrunCommand(),
         'xcodebuild',
         '-alltargets',
         '-sdk',
@@ -467,7 +460,6 @@ end
         workingDirectory: _project.ios.hostAppRoot
           .childDirectory('Pods')
           .path,
-        allowReentrantFlutter: false,
       );
 
       if (buildPluginsResult.exitCode != 0) {
@@ -515,7 +507,7 @@ end
       return;
     }
     final List<String> xcframeworkCommand = <String>[
-      ...globals.xcode.xcrunCommand(),
+      ...globals.xcode!.xcrunCommand(),
       'xcodebuild',
       '-create-xcframework',
       for (Directory framework in frameworks) ...<String>[
@@ -536,7 +528,6 @@ end
 
     final RunResult xcframeworkResult = await globals.processUtils.run(
       xcframeworkCommand,
-      allowReentrantFlutter: false,
     );
 
     if (xcframeworkResult.exitCode != 0) {

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

@@ -2,10 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
-import 'package:meta/meta.dart';
-
 import '../base/analyze_size.dart';
 import '../base/common.dart';
 import '../base/os.dart';
@@ -21,7 +17,7 @@ import 'build.dart';
 /// A command to build a linux desktop target through a build shell script.
 class BuildLinuxCommand extends BuildSubCommand {
   BuildLinuxCommand({
-    @required OperatingSystemUtils operatingSystemUtils,
+    required OperatingSystemUtils operatingSystemUtils,
     bool verboseHelp = false,
   }) : _operatingSystemUtils = operatingSystemUtils,
        super(verboseHelp: verboseHelp) {
@@ -63,7 +59,7 @@ class BuildLinuxCommand extends BuildSubCommand {
     final BuildInfo buildInfo = await getBuildInfo();
     final FlutterProject flutterProject = FlutterProject.current();
     final TargetPlatform targetPlatform =
-        getTargetPlatformForName(stringArg('target-platform'));
+        getTargetPlatformForName(stringArg('target-platform')!);
     final bool needCrossBuild =
         getNameForHostPlatformArch(_operatingSystemUtils.hostPlatform)
             != getNameForTargetPlatformArch(targetPlatform);
@@ -97,7 +93,7 @@ class BuildLinuxCommand extends BuildSubCommand {
       ),
       needCrossBuild: needCrossBuild,
       targetPlatform: targetPlatform,
-      targetSysroot: stringArg('target-sysroot'),
+      targetSysroot: stringArg('target-sysroot')!,
     );
     return FlutterCommandResult.success();
   }

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

@@ -2,10 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
-import 'package:meta/meta.dart';
-
 import '../base/analyze_size.dart';
 import '../base/common.dart';
 import '../build_info.dart';
@@ -20,7 +16,7 @@ import 'build.dart';
 /// A command to build a macOS desktop target through a build shell script.
 class BuildMacosCommand extends BuildSubCommand {
   BuildMacosCommand({
-    @required bool verboseHelp,
+    required bool verboseHelp,
   }) : super(verboseHelp: verboseHelp) {
     addCommonDesktopBuildOptions(verboseHelp: verboseHelp);
     usesBuildNumberOption();

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

@@ -2,10 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
-import 'package:meta/meta.dart';
-
 import '../base/common.dart';
 import '../build_info.dart';
 import '../build_system/targets/web.dart';
@@ -19,7 +15,7 @@ import 'build.dart';
 
 class BuildWebCommand extends BuildSubCommand {
   BuildWebCommand({
-    @required bool verboseHelp,
+    required bool verboseHelp,
   }) : super(verboseHelp: verboseHelp) {
     addTreeShakeIconsFlag(enabledByDefault: false);
     usesTargetOption();
@@ -31,14 +27,12 @@ class BuildWebCommand extends BuildSubCommand {
     addNullSafetyModeOptions(hide: !verboseHelp);
     addNativeNullAssertions();
     argParser.addFlag('csp',
-      defaultsTo: false,
       negatable: false,
       help: 'Disable dynamic generation of code in the generated output. '
             'This is necessary to satisfy CSP restrictions (see http://www.w3.org/TR/CSP/).'
     );
     argParser.addFlag(
       'source-maps',
-      defaultsTo: false,
       help: 'Generate a sourcemap file. These can be used by browsers '
             'to view and debug the original source code of a compiled and minified Dart '
             'application.'
@@ -91,12 +85,13 @@ class BuildWebCommand extends BuildSubCommand {
       throwToolExit('"build web" is not currently supported. To enable, run "flutter config --enable-web".');
     }
     final FlutterProject flutterProject = FlutterProject.current();
-    final String target = stringArg('target');
+    final String target = stringArg('target')!;
     final BuildInfo buildInfo = await getBuildInfo();
     if (buildInfo.isDebug) {
       throwToolExit('debug builds cannot be built directly for the web. Try using "flutter run"');
     }
-    if (stringArg('base-href') != null && !(stringArg('base-href').startsWith('/') && stringArg('base-href').endsWith('/'))) {
+    final String? baseHref = stringArg('base-href');
+    if (baseHref != null && !(baseHref.startsWith('/') && baseHref.endsWith('/'))) {
       throwToolExit('base-href should start and end with /');
     }
     if (!flutterProject.web.existsSync()) {
@@ -107,7 +102,7 @@ class BuildWebCommand extends BuildSubCommand {
         .childFile('index.html')
         .readAsStringSync()
         .contains(kBaseHrefPlaceholder) &&
-        stringArg('base-href') != null) {
+        baseHref != null) {
       throwToolExit(
         "Couldn't find the placeholder for base href. "
         r'Please add `<base href="$FLUTTER_BASE_HREF">` to web/index.html'
@@ -119,10 +114,10 @@ class BuildWebCommand extends BuildSubCommand {
       target,
       buildInfo,
       boolArg('csp'),
-      stringArg('pwa-strategy'),
+      stringArg('pwa-strategy')!,
       boolArg('source-maps'),
       boolArg('native-null-assertions'),
-      stringArg('base-href'),
+      baseHref,
     );
     return FlutterCommandResult.success();
   }

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

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:meta/meta.dart';
 
 import '../base/analyze_size.dart';
@@ -41,7 +39,7 @@ class BuildWindowsCommand extends BuildSubCommand {
   String get description => 'Build a Windows desktop application.';
 
   @visibleForTesting
-  VisualStudio visualStudioOverride;
+  VisualStudio? visualStudioOverride;
 
   @override
   Future<FlutterCommandResult> runCommand() async {

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

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:meta/meta.dart';
 
 import '../base/common.dart';
@@ -40,7 +38,7 @@ class BuildWindowsUwpCommand extends BuildSubCommand {
   String get description => 'Build a Windows UWP desktop application.';
 
   @visibleForTesting
-  VisualStudio visualStudioOverride;
+  VisualStudio? visualStudioOverride;
 
   @override
   Future<FlutterCommandResult> runCommand() async {

packages/flutter_tools/lib/src/globals.dart

@@ -50,7 +50,7 @@ import 'version.dart';
 String get flutterGit => platform.environment['FLUTTER_GIT_URL'] ?? 'https://github.com/flutter/flutter.git';
 
 Artifacts? get artifacts => context.get<Artifacts>();
-BuildSystem? get buildSystem => context.get<BuildSystem>();
+BuildSystem get buildSystem => context.get<BuildSystem>()!;
 Cache get cache => context.get<Cache>()!;
 CocoaPodsValidator? get cocoapodsValidator => context.get<CocoaPodsValidator>();
 Config get config => context.get<Config>()!;

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

@@ -1295,7 +1295,7 @@ abstract class FlutterCommand extends Command<void> {
 
       await generateLocalizationsSyntheticPackage(
         environment: environment,
-        buildSystem: globals.buildSystem!,
+        buildSystem: globals.buildSystem,
       );
 
       await pub.get(

packages/flutter_tools/lib/src/web/compile.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import '../artifacts.dart';
 import '../base/common.dart';
 import '../base/file_system.dart';
@@ -26,7 +24,7 @@ Future<void> buildWeb(
   String serviceWorkerStrategy,
   bool sourceMaps,
   bool nativeNullAssertions,
-  String baseHref,
+  String? baseHref,
 ) async {
   final bool hasWebPlugins = (await findPlugins(flutterProject))
     .any((Plugin p) => p.platforms.containsKey(WebPlugin.kConfigKey));
@@ -47,6 +45,7 @@ Future<void> buildWeb(
         kTargetFile: target,
         kHasWebPlugins: hasWebPlugins.toString(),
         kCspMode: csp.toString(),
+        if (baseHref != null)
           kBaseHref : baseHref,
         kSourceMapsEnabled: sourceMaps.toString(),
         kNativeNullAssertions: nativeNullAssertions.toString(),
@@ -54,13 +53,13 @@ Future<void> buildWeb(
          kServiceWorkerStrategy: serviceWorkerStrategy,
         ...buildInfo.toBuildSystemEnvironment(),
       },
-      artifacts: globals.artifacts,
+      artifacts: globals.artifacts!,
       fileSystem: globals.fs,
       logger: globals.logger,
       processManager: globals.processManager,
       platform: globals.platform,
       cacheDir: globals.cache.getRoot(),
-      engineVersion: globals.artifacts.isLocalEngine
+      engineVersion: globals.artifacts!.isLocalEngine
         ? null
         : globals.flutterVersion.engineRevision,
       flutterRootDir: globals.fs.directory(Cache.flutterRoot),

packages/flutter_tools/test/commands.shard/hermetic/build_web_test.dart

@@ -111,7 +111,6 @@ void main() {
         'DartObfuscation': 'false',
         'TrackWidgetCreation': 'false',
         'TreeShakeIcons': 'false',
-        'baseHref': null,
       });
     }),
   });

packages/flutter_tools/test/commands.shard/permeable/build_bundle_test.dart

@@ -89,8 +89,7 @@ void main() {
     globals.fs.file('lib/main.dart').createSync(recursive: true);
     globals.fs.file('pubspec.yaml').createSync(recursive: true);
     globals.fs.file('.packages').createSync(recursive: true);
-    final CommandRunner<void> runner = createTestCommandRunner(BuildBundleCommand()
-        ..bundleBuilder = FakeBundleBuilder());
+    final CommandRunner<void> runner = createTestCommandRunner(BuildBundleCommand(bundleBuilder: FakeBundleBuilder()));
 
     expect(() => runner.run(<String>[
       'bundle',
@@ -107,8 +106,7 @@ void main() {
     globals.fs.file('lib/main.dart').createSync(recursive: true);
     globals.fs.file('pubspec.yaml').createSync();
     globals.fs.file('.packages').createSync();
-    final CommandRunner<void> runner = createTestCommandRunner(BuildBundleCommand()
-        ..bundleBuilder = FakeBundleBuilder());
+    final CommandRunner<void> runner = createTestCommandRunner(BuildBundleCommand(bundleBuilder: FakeBundleBuilder()));
 
     expect(() => runner.run(<String>[
       'bundle',
@@ -125,8 +123,7 @@ void main() {
     globals.fs.file('lib/main.dart').createSync(recursive: true);
     globals.fs.file('pubspec.yaml').createSync();
     globals.fs.file('.packages').createSync();
-    final CommandRunner<void> runner = createTestCommandRunner(BuildBundleCommand()
-        ..bundleBuilder = FakeBundleBuilder());
+    final CommandRunner<void> runner = createTestCommandRunner(BuildBundleCommand(bundleBuilder: FakeBundleBuilder()));
 
     expect(() => runner.run(<String>[
       'bundle',
@@ -143,8 +140,7 @@ void main() {
     globals.fs.file('lib/main.dart').createSync(recursive: true);
     globals.fs.file('pubspec.yaml').createSync();
     globals.fs.file('.packages').createSync();
-    final CommandRunner<void> runner = createTestCommandRunner(BuildBundleCommand()
-      ..bundleBuilder = FakeBundleBuilder());
+    final CommandRunner<void> runner = createTestCommandRunner(BuildBundleCommand(bundleBuilder: FakeBundleBuilder()));
 
     expect(() => runner.run(<String>[
       'bundle',
@@ -161,8 +157,7 @@ void main() {
     globals.fs.file('lib/main.dart').createSync(recursive: true);
     globals.fs.file('pubspec.yaml').createSync();
     globals.fs.file('.packages').createSync();
-    final CommandRunner<void> runner = createTestCommandRunner(BuildBundleCommand()
-        ..bundleBuilder = FakeBundleBuilder());
+    final CommandRunner<void> runner = createTestCommandRunner(BuildBundleCommand(bundleBuilder: FakeBundleBuilder()));
 
     await runner.run(<String>[
       'bundle',
@@ -179,8 +174,7 @@ void main() {
     globals.fs.file('lib/main.dart').createSync(recursive: true);
     globals.fs.file('pubspec.yaml').createSync();
     globals.fs.file('.packages').createSync();
-    final CommandRunner<void> runner = createTestCommandRunner(BuildBundleCommand()
-        ..bundleBuilder = FakeBundleBuilder());
+    final CommandRunner<void> runner = createTestCommandRunner(BuildBundleCommand(bundleBuilder: FakeBundleBuilder()));
 
     await runner.run(<String>[
       'bundle',
@@ -197,8 +191,7 @@ void main() {
     globals.fs.file('lib/main.dart').createSync(recursive: true);
     globals.fs.file('pubspec.yaml').createSync();
     globals.fs.file('.packages').createSync();
-    final CommandRunner<void> runner = createTestCommandRunner(BuildBundleCommand()
-        ..bundleBuilder = FakeBundleBuilder());
+    final CommandRunner<void> runner = createTestCommandRunner(BuildBundleCommand(bundleBuilder: FakeBundleBuilder()));
 
     await runner.run(<String>[
       'bundle',