diff --git a/dev/tools/bin/conductor.dart b/dev/tools/bin/conductor.dart
index adafc58022f..97e530ba5da 100644
--- a/dev/tools/bin/conductor.dart
+++ b/dev/tools/bin/conductor.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 // See: https://github.com/flutter/flutter/wiki/Release-process
 
 import 'dart:io' as io;
diff --git a/dev/tools/dartdoc.dart b/dev/tools/dartdoc.dart
index ca50839269f..37729c213c1 100644
--- a/dev/tools/dartdoc.dart
+++ b/dev/tools/dartdoc.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:convert';
 import 'dart:io';
 
diff --git a/dev/tools/dartdoc_checker.dart b/dev/tools/dartdoc_checker.dart
index 57b488edd30..b3bac3c16a5 100644
--- a/dev/tools/dartdoc_checker.dart
+++ b/dev/tools/dartdoc_checker.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:io';
 
 import 'package:path/path.dart' as path;
diff --git a/dev/tools/find_engine_commit.dart b/dev/tools/find_engine_commit.dart
index 8b875539100..c8d67af0c1d 100644
--- a/dev/tools/find_engine_commit.dart
+++ b/dev/tools/find_engine_commit.dart
@@ -29,7 +29,7 @@ Future<void> main(List<String> args) async {
   _validate(args);
   await _fetchUpstream();
   await _fetchUpstream(engineRepo);
-  String flutterRevision;
+  String? flutterRevision;
   await for (final FlutterEngineRevision revision in _logEngineVersions()) {
     if (!await containsRevision(args[0], revision.engineRevision)) {
       if (flutterRevision == null) {
diff --git a/dev/tools/java_and_objc_doc.dart b/dev/tools/java_and_objc_doc.dart
index a2043dd4178..21fbd7faae4 100644
--- a/dev/tools/java_and_objc_doc.dart
+++ b/dev/tools/java_and_objc_doc.dart
@@ -25,8 +25,8 @@ Future<void> main(List<String> args) async {
 /// Fetches the zip archive at the specified url.
 ///
 /// Returns null if the archive fails to download after [maxTries] attempts.
-Future<Archive> fetchArchive(String url, int maxTries) async {
-  List<int> responseBytes;
+Future<Archive?> fetchArchive(String url, int maxTries) async {
+  List<int>? responseBytes;
   for (int i = 0; i < maxTries; i++) {
     final http.Response response = await http.get(Uri.parse(url));
     if (response.statusCode == 200) {
@@ -45,7 +45,7 @@ Future<Archive> fetchArchive(String url, int maxTries) async {
 
 Future<void> generateDocs(String url, String docName, String checkFile) async {
   const int maxTries = 5;
-  final Archive archive = await fetchArchive(url, maxTries);
+  final Archive? archive = await fetchArchive(url, maxTries);
   if (archive == null) {
     stderr.writeln('Failed to fetch zip archive from: $url after $maxTries attempts. Giving up.');
     exit(1);
diff --git a/dev/tools/lib/clean.dart b/dev/tools/lib/clean.dart
index 59e968e5f79..19075573b58 100644
--- a/dev/tools/lib/clean.dart
+++ b/dev/tools/lib/clean.dart
@@ -2,6 +2,8 @@
 // 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:args/command_runner.dart';
 import 'package:file/file.dart';
 import 'package:meta/meta.dart';
diff --git a/dev/tools/lib/codesign.dart b/dev/tools/lib/codesign.dart
index 27f9014e2f5..9b2e547ca0c 100644
--- a/dev/tools/lib/codesign.dart
+++ b/dev/tools/lib/codesign.dart
@@ -6,7 +6,7 @@ import 'dart:io' as io;
 
 import 'package:args/command_runner.dart';
 import 'package:file/file.dart';
-import 'package:meta/meta.dart';
+import 'package:meta/meta.dart' show visibleForTesting;
 import 'package:platform/platform.dart';
 import 'package:process/process.dart';
 
@@ -31,11 +31,10 @@ const String kUpstream = 'upstream';
 /// Command to codesign and verify the signatures of cached binaries.
 class CodesignCommand extends Command<void> {
   CodesignCommand({
-    @required this.checkouts,
-    @required this.flutterRoot,
-    FrameworkRepository framework,
-  })  : assert(flutterRoot != null),
-        fileSystem = checkouts.fileSystem,
+    required this.checkouts,
+    required this.flutterRoot,
+    FrameworkRepository? framework,
+  })  : fileSystem = checkouts.fileSystem,
         platform = checkouts.platform,
         stdio = checkouts.stdio,
         processManager = checkouts.processManager {
@@ -74,7 +73,7 @@ class CodesignCommand extends Command<void> {
   /// Root directory of the Flutter repository.
   final Directory flutterRoot;
 
-  FrameworkRepository _framework;
+  FrameworkRepository? _framework;
   FrameworkRepository get framework {
     return _framework ??= FrameworkRepository.localRepoAsUpstream(
       checkouts,
@@ -97,21 +96,21 @@ class CodesignCommand extends Command<void> {
           '"${platform.operatingSystem}"');
     }
 
-    if (argResults['verify'] as bool != true) {
+    if (argResults!['verify'] as bool != true) {
       throw ConductorException(
           'Sorry, but codesigning is not implemented yet. Please pass the '
           '--$kVerify flag to verify signatures.');
     }
 
     String revision;
-    if (argResults.wasParsed(kRevision)) {
+    if (argResults!.wasParsed(kRevision)) {
       stdio.printError(
           'Warning! When providing an arbitrary revision, the contents of the cache may not');
       stdio.printError(
           'match the expected binaries in the conductor tool. It is preferred to check out');
       stdio.printError(
           'the desired revision and run that version of the conductor.\n');
-      revision = argResults[kRevision] as String;
+      revision = argResults![kRevision] as String;
     } else {
       revision = (processManager.runSync(
         <String>['git', 'rev-parse', 'HEAD'],
@@ -127,7 +126,7 @@ class CodesignCommand extends Command<void> {
     framework.runFlutter(<String>['precache', '--android', '--ios', '--macos']);
 
     verifyExist();
-    if (argResults[kSignatures] as bool) {
+    if (argResults![kSignatures] as bool) {
       verifySignatures();
     }
   }
@@ -319,16 +318,16 @@ class CodesignCommand extends Command<void> {
     }
 
     stdio.printStatus(
-        'Verified that binaries for commit ${argResults[kRevision] as String} are codesigned and have '
+        'Verified that binaries for commit ${argResults![kRevision] as String} are codesigned and have '
         'expected entitlements.');
   }
 
-  List<String> _allBinaryPaths;
+  List<String>? _allBinaryPaths;
 
   /// Find every binary file in the given [rootDirectory].
   List<String> findBinaryPaths(String rootDirectory) {
     if (_allBinaryPaths != null) {
-      return _allBinaryPaths;
+      return _allBinaryPaths!;
     }
     final io.ProcessResult result = processManager.runSync(
       <String>[
@@ -343,7 +342,7 @@ class CodesignCommand extends Command<void> {
         .where((String s) => s.isNotEmpty)
         .toList();
     _allBinaryPaths = allFiles.where(isBinary).toList();
-    return _allBinaryPaths;
+    return _allBinaryPaths!;
   }
 
   /// Check mime-type of file at [filePath] to determine if it is binary.
diff --git a/dev/tools/lib/git.dart b/dev/tools/lib/git.dart
index caed631b927..41ed5fc9c0c 100644
--- a/dev/tools/lib/git.dart
+++ b/dev/tools/lib/git.dart
@@ -4,7 +4,6 @@
 
 import 'dart:io';
 
-import 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
 import './globals.dart';
@@ -18,7 +17,7 @@ class Git {
   String getOutput(
     List<String> args,
     String explanation, {
-    @required String workingDirectory,
+    required String workingDirectory,
     bool allowFailures = false,
   }) {
     final ProcessResult result = _run(args, workingDirectory);
@@ -26,14 +25,13 @@ class Git {
       return stdoutToString(result.stdout);
     }
     _reportFailureAndExit(args, workingDirectory, result, explanation);
-    return null; // for the analyzer's sake
   }
 
   int run(
     List<String> args,
     String explanation, {
     bool allowNonZeroExitCode = false,
-    @required String workingDirectory,
+    required String workingDirectory,
   }) {
     final ProcessResult result = _run(args, workingDirectory);
     if (result.exitCode != 0 && !allowNonZeroExitCode) {
@@ -50,7 +48,7 @@ class Git {
     );
   }
 
-  void _reportFailureAndExit(
+  Never _reportFailureAndExit(
     List<String> args,
     String workingDirectory,
     ProcessResult result,
diff --git a/dev/tools/lib/globals.dart b/dev/tools/lib/globals.dart
index 2234b79ca21..2ab44ca6ebd 100644
--- a/dev/tools/lib/globals.dart
+++ b/dev/tools/lib/globals.dart
@@ -39,10 +39,10 @@ class ConductorException implements Exception {
   String toString() => 'Exception: $message';
 }
 
-Directory _flutterRoot;
+Directory? _flutterRoot;
 Directory get localFlutterRoot {
   if (_flutterRoot != null) {
-    return _flutterRoot;
+    return _flutterRoot!;
   }
   String filePath;
   const FileSystem fileSystem = LocalFileSystem();
@@ -54,14 +54,14 @@ Directory get localFlutterRoot {
       r'(file:\/\/[^"]*[/\\]dev\/tools[/\\][^"]+\.dart)',
       multiLine: true,
     );
-    final Match match =
+    final Match? match =
         pattern.firstMatch(Uri.decodeFull(platform.script.path));
     if (match == null) {
       throw Exception(
         'Cannot determine path of script!\n${platform.script.path}',
       );
     }
-    filePath = Uri.parse(match.group(1)).path.replaceAll(r'%20', ' ');
+    filePath = Uri.parse(match.group(1)!).path.replaceAll(r'%20', ' ');
   } else {
     filePath = platform.script.toFilePath();
   }
@@ -74,7 +74,7 @@ Directory get localFlutterRoot {
     ),
   );
   _flutterRoot = fileSystem.directory(checkoutsDirname);
-  return _flutterRoot;
+  return _flutterRoot!;
 }
 
 bool assertsEnabled() {
@@ -102,9 +102,9 @@ String getValueFromEnvOrArgs(
 ) {
   final String envName = fromArgToEnvName(name);
   if (env[envName] != null ) {
-    return env[envName];
+    return env[envName]!;
   }
-  final String argValue = argResults[name] as String;
+  final String? argValue = argResults[name] as String?;
   if (argValue != null) {
     return argValue;
   }
@@ -130,7 +130,7 @@ List<String> getValuesFromEnvOrArgs(
 ) {
   final String envName = fromArgToEnvName(name);
   if (env[envName] != null && env[envName] != '') {
-    return env[envName].split(',');
+    return env[envName]!.split(',');
   }
   final List<String> argValues = argResults[name] as List<String>;
   if (argValues != null) {
diff --git a/dev/tools/lib/repository.dart b/dev/tools/lib/repository.dart
index 63ee5c68e0a..33632706a56 100644
--- a/dev/tools/lib/repository.dart
+++ b/dev/tools/lib/repository.dart
@@ -23,8 +23,8 @@ enum RemoteName {
 
 class Remote {
   const Remote({
-    @required RemoteName name,
-    @required this.url,
+    required RemoteName name,
+    required this.url,
   }) : _name = name;
 
   final RemoteName _name;
@@ -37,7 +37,6 @@ class Remote {
       case RemoteName.mirror:
         return 'mirror';
     }
-    throw ConductorException('Invalid value of _name: $_name'); // For analyzer
   }
 
   /// The URL of the remote.
@@ -47,13 +46,13 @@ class Remote {
 /// A source code repository.
 abstract class Repository {
   Repository({
-    @required this.name,
-    @required this.fetchRemote,
-    @required this.processManager,
-    @required this.stdio,
-    @required this.platform,
-    @required this.fileSystem,
-    @required this.parentDirectory,
+    required this.name,
+    required this.fetchRemote,
+    required this.processManager,
+    required this.stdio,
+    required this.platform,
+    required this.fileSystem,
+    required this.parentDirectory,
     this.initialRef,
     this.localUpstream = false,
     this.useExistingCheckout = false,
@@ -69,10 +68,10 @@ abstract class Repository {
   ///
   /// This value can be null, in which case attempting to publish will lead to
   /// a [ConductorException].
-  final Remote pushRemote;
+  final Remote? pushRemote;
 
   /// The initial ref (branch or commit name) to check out.
-  final String initialRef;
+  final String? initialRef;
   final Git git;
   final ProcessManager processManager;
   final Stdio stdio;
@@ -84,7 +83,7 @@ abstract class Repository {
   /// If the repository will be used as an upstream for a test repo.
   final bool localUpstream;
 
-  Directory _checkoutDirectory;
+  Directory? _checkoutDirectory;
 
   /// Directory for the repository checkout.
   ///
@@ -92,23 +91,23 @@ abstract class Repository {
   /// cloned on the filesystem until this getter is accessed.
   Directory get checkoutDirectory {
     if (_checkoutDirectory != null) {
-      return _checkoutDirectory;
+      return _checkoutDirectory!;
     }
     _checkoutDirectory = parentDirectory.childDirectory(name);
-    lazilyInitialize();
-    return _checkoutDirectory;
+    lazilyInitialize(_checkoutDirectory!);
+    return _checkoutDirectory!;
   }
 
   /// Ensure the repository is cloned to disk and initialized with proper state.
-  void lazilyInitialize() {
-    if (!useExistingCheckout && _checkoutDirectory.existsSync()) {
-      stdio.printTrace('Deleting $name from ${_checkoutDirectory.path}...');
-      _checkoutDirectory.deleteSync(recursive: true);
+  void lazilyInitialize(Directory checkoutDirectory) {
+    if (!useExistingCheckout && checkoutDirectory.existsSync()) {
+      stdio.printTrace('Deleting $name from ${checkoutDirectory.path}...');
+      checkoutDirectory.deleteSync(recursive: true);
     }
 
-    if (!_checkoutDirectory.existsSync()) {
+    if (!checkoutDirectory.existsSync()) {
       stdio.printTrace(
-        'Cloning $name from ${fetchRemote.url} to ${_checkoutDirectory.path}...',
+        'Cloning $name from ${fetchRemote.url} to ${checkoutDirectory.path}...',
       );
       git.run(
         <String>[
@@ -117,21 +116,21 @@ abstract class Repository {
           fetchRemote.name,
           '--',
           fetchRemote.url,
-          _checkoutDirectory.path
+          checkoutDirectory.path
         ],
         'Cloning $name repo',
         workingDirectory: parentDirectory.path,
       );
       if (pushRemote != null) {
         git.run(
-          <String>['remote', 'add', pushRemote.name, pushRemote.url],
-          'Adding remote ${pushRemote.url} as ${pushRemote.name}',
-          workingDirectory: _checkoutDirectory.path,
+          <String>['remote', 'add', pushRemote!.name, pushRemote!.url],
+          'Adding remote ${pushRemote!.url} as ${pushRemote!.name}',
+          workingDirectory: checkoutDirectory.path,
         );
         git.run(
-          <String>['fetch', pushRemote.name],
-          'Fetching git remote ${pushRemote.name}',
-          workingDirectory: _checkoutDirectory.path,
+          <String>['fetch', pushRemote!.name],
+          'Fetching git remote ${pushRemote!.name}',
+          workingDirectory: checkoutDirectory.path,
         );
       }
       if (localUpstream) {
@@ -141,7 +140,7 @@ abstract class Repository {
           git.run(
             <String>['checkout', channel, '--'],
             'check out branch $channel locally',
-            workingDirectory: _checkoutDirectory.path,
+            workingDirectory: checkoutDirectory.path,
           );
         }
       }
@@ -151,7 +150,7 @@ abstract class Repository {
       git.run(
         <String>['checkout', '${fetchRemote.name}/$initialRef'],
         'Checking out initialRef $initialRef',
-        workingDirectory: _checkoutDirectory.path,
+        workingDirectory: checkoutDirectory.path,
       );
     }
     final String revision = reverseParse('HEAD');
@@ -404,8 +403,8 @@ class FrameworkRepository extends Repository {
         name: RemoteName.upstream, url: FrameworkRepository.defaultUpstream),
     bool localUpstream = false,
     bool useExistingCheckout = false,
-    String initialRef,
-    Remote pushRemote,
+    String? initialRef,
+    Remote? pushRemote,
   }) : super(
           name: name,
           fetchRemote: fetchRemote,
@@ -428,7 +427,7 @@ class FrameworkRepository extends Repository {
     Checkouts checkouts, {
     String name = 'framework',
     bool useExistingCheckout = false,
-    @required String upstreamPath,
+    required String upstreamPath,
   }) {
     return FrameworkRepository(
       checkouts,
@@ -455,7 +454,7 @@ class FrameworkRepository extends Repository {
       );
 
   @override
-  Repository cloneRepository(String cloneName) {
+  Repository cloneRepository(String? cloneName) {
     assert(localUpstream);
     cloneName ??= 'clone-of-$name';
     return FrameworkRepository(
@@ -529,7 +528,7 @@ class EngineRepository extends Repository {
         name: RemoteName.upstream, url: EngineRepository.defaultUpstream),
     bool localUpstream = false,
     bool useExistingCheckout = false,
-    Remote pushRemote,
+    Remote? pushRemote,
   }) : super(
           name: name,
           fetchRemote: fetchRemote,
@@ -550,7 +549,7 @@ class EngineRepository extends Repository {
   static const String defaultBranch = 'master';
 
   @override
-  Repository cloneRepository(String cloneName) {
+  Repository cloneRepository(String? cloneName) {
     assert(localUpstream);
     cloneName ??= 'clone-of-$name';
     return EngineRepository(
@@ -571,14 +570,13 @@ enum RepositoryType {
 
 class Checkouts {
   Checkouts({
-    @required this.fileSystem,
-    @required this.platform,
-    @required this.processManager,
-    @required this.stdio,
-    @required Directory parentDirectory,
+    required this.fileSystem,
+    required this.platform,
+    required this.processManager,
+    required this.stdio,
+    required Directory parentDirectory,
     String directoryName = 'flutter_conductor_checkouts',
-  })  : assert(parentDirectory != null),
-        directory = parentDirectory.childDirectory(directoryName) {
+  })  : directory = parentDirectory.childDirectory(directoryName) {
     if (!directory.existsSync()) {
       directory.createSync(recursive: true);
     }
diff --git a/dev/tools/lib/roll_dev.dart b/dev/tools/lib/roll_dev.dart
index 29b5c582eb3..977d808748f 100644
--- a/dev/tools/lib/roll_dev.dart
+++ b/dev/tools/lib/roll_dev.dart
@@ -23,10 +23,10 @@ const String kSkipTagging = 'skip-tagging';
 /// Create a new dev release without cherry picks.
 class RollDevCommand extends Command<void> {
   RollDevCommand({
-    @required this.checkouts,
-    @required this.fileSystem,
-    @required this.platform,
-    @required this.stdio,
+    required this.checkouts,
+    required this.fileSystem,
+    required this.platform,
+    required this.stdio,
   }) {
     argParser.addOption(
       kIncrement,
@@ -92,7 +92,7 @@ class RollDevCommand extends Command<void> {
   @override
   void run() {
     rollDev(
-      argResults: argResults,
+      argResults: argResults!,
       repository: FrameworkRepository(checkouts),
       stdio: stdio,
       usage: argParser.usage,
@@ -105,10 +105,10 @@ class RollDevCommand extends Command<void> {
 /// Returns true if publishing was successful, else false.
 @visibleForTesting
 bool rollDev({
-  @required String usage,
-  @required ArgResults argResults,
-  @required Stdio stdio,
-  @required FrameworkRepository repository,
+  required String usage,
+  required ArgResults argResults,
+  required Stdio stdio,
+  required FrameworkRepository repository,
 }) {
   final String remoteName = argResults[kRemoteName] as String;
   final String level = argResults[kIncrement] as String;
diff --git a/dev/tools/lib/start.dart b/dev/tools/lib/start.dart
index cffa6a164ea..ff9e06654df 100644
--- a/dev/tools/lib/start.dart
+++ b/dev/tools/lib/start.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:convert' show jsonEncode;
 
 import 'package:args/command_runner.dart';
diff --git a/dev/tools/lib/state.dart b/dev/tools/lib/state.dart
index 76f52a43da9..37d87068614 100644
--- a/dev/tools/lib/state.dart
+++ b/dev/tools/lib/state.dart
@@ -2,6 +2,8 @@
 // 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:platform/platform.dart';
 
 import './globals.dart';
diff --git a/dev/tools/lib/status.dart b/dev/tools/lib/status.dart
index 2b6dc422777..3fd454f22e4 100644
--- a/dev/tools/lib/status.dart
+++ b/dev/tools/lib/status.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:convert' show jsonDecode;
 
 import 'package:args/command_runner.dart';
diff --git a/dev/tools/lib/stdio.dart b/dev/tools/lib/stdio.dart
index 83be05107de..a9099965996 100644
--- a/dev/tools/lib/stdio.dart
+++ b/dev/tools/lib/stdio.dart
@@ -40,10 +40,10 @@ abstract class Stdio {
 /// A logger that will print out trace messages.
 class VerboseStdio extends Stdio {
   VerboseStdio({
-    @required this.stdout,
-    @required this.stderr,
-    @required this.stdin,
-  }) : assert(stdout != null), assert(stderr != null), assert(stdin != null);
+    required this.stdout,
+    required this.stderr,
+    required this.stdin,
+  });
 
   factory VerboseStdio.local() => VerboseStdio(
     stdout: io.stdout,
@@ -81,6 +81,6 @@ class VerboseStdio extends Stdio {
 
   @override
   String readLineSync() {
-    return stdin.readLineSync();
+    return stdin.readLineSync()!;
   }
 }
diff --git a/dev/tools/lib/version.dart b/dev/tools/lib/version.dart
index cd4452480db..6a93beae44e 100644
--- a/dev/tools/lib/version.dart
+++ b/dev/tools/lib/version.dart
@@ -2,18 +2,18 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'package:meta/meta.dart';
-
 /// Possible string formats that `flutter --version` can return.
 enum VersionType {
   /// A stable flutter release.
   ///
   /// Example: '1.2.3'
   stable,
+
   /// A pre-stable flutter release.
   ///
   /// Example: '1.2.3-4.5.pre'
   development,
+
   /// A master channel flutter version.
   ///
   /// Example: '1.2.3-4.0.pre.10'
@@ -30,13 +30,13 @@ final Map<VersionType, RegExp> versionPatterns = <VersionType, RegExp>{
 
 class Version {
   Version({
-    @required this.x,
-    @required this.y,
-    @required this.z,
+    required this.x,
+    required this.y,
+    required this.z,
     this.m,
     this.n,
     this.commits,
-    @required this.type,
+    required this.type,
   }) {
     switch (type) {
       case VersionType.stable:
@@ -67,11 +67,13 @@ class Version {
 
     versionString = versionString.trim();
     // stable tag
-    Match match = versionPatterns[VersionType.stable].firstMatch(versionString);
+    Match? match = versionPatterns[VersionType.stable]!.firstMatch(versionString);
     if (match != null) {
       // parse stable
-      final List<int> parts =
-          match.groups(<int>[1, 2, 3]).map(int.parse).toList();
+      final List<int> parts = match
+          .groups(<int>[1, 2, 3])
+          .map((String? s) => int.parse(s!))
+          .toList();
       return Version(
         x: parts[0],
         y: parts[1],
@@ -80,11 +82,11 @@ class Version {
       );
     }
     // development tag
-    match = versionPatterns[VersionType.development].firstMatch(versionString);
+    match = versionPatterns[VersionType.development]!.firstMatch(versionString);
     if (match != null) {
       // parse development
       final List<int> parts =
-          match.groups(<int>[1, 2, 3, 4, 5]).map(int.parse).toList();
+          match.groups(<int>[1, 2, 3, 4, 5]).map((String? s) => int.parse(s!)).toList();
       return Version(
         x: parts[0],
         y: parts[1],
@@ -95,11 +97,14 @@ class Version {
       );
     }
     // latest tag
-    match = versionPatterns[VersionType.latest].firstMatch(versionString);
+    match = versionPatterns[VersionType.latest]!.firstMatch(versionString);
     if (match != null) {
       // parse latest
-      final List<int> parts =
-          match.groups(<int>[1, 2, 3, 4, 5, 6]).map(int.parse).toList();
+      final List<int> parts = match.groups(
+        <int>[1, 2, 3, 4, 5, 6],
+      ).map(
+        (String? s) => int.parse(s!),
+      ).toList();
       return Version(
         x: parts[0],
         y: parts[1],
@@ -118,13 +123,13 @@ class Version {
   factory Version.increment(
     Version previousVersion,
     String increment, {
-    VersionType nextVersionType,
+    VersionType? nextVersionType,
   }) {
     final int nextX = previousVersion.x;
     int nextY = previousVersion.y;
     int nextZ = previousVersion.z;
-    int nextM = previousVersion.m;
-    int nextN = previousVersion.n;
+    int? nextM = previousVersion.m;
+    int? nextN = previousVersion.n;
     if (nextVersionType == null) {
       if (previousVersion.type == VersionType.latest) {
         nextVersionType = VersionType.development;
@@ -137,7 +142,6 @@ class Version {
       case 'x':
         // This was probably a mistake.
         throw Exception('Incrementing x is not supported by this tool.');
-        break;
       case 'y':
         // Dev release following a beta release.
         nextY += 1;
@@ -155,13 +159,12 @@ class Version {
       case 'm':
         // Regular dev release.
         assert(previousVersion.type == VersionType.development);
-        assert(nextM != null);
-        nextM += 1;
+        nextM = nextM! + 1;
         nextN = 0;
         break;
       case 'n':
         // Hotfix to internal roll.
-        nextN += 1;
+        nextN = nextN! + 1;
         break;
       default:
         throw Exception('Unknown increment level $increment.');
@@ -186,13 +189,13 @@ class Version {
   final int z;
 
   /// Zero-indexed count of dev releases after a beta release.
-  final int m;
+  final int? m;
 
   /// Number of hotfixes required to make a dev release.
-  final int n;
+  final int? n;
 
   /// Number of commits past last tagged dev release.
-  final int commits;
+  final int? commits;
 
   final VersionType type;
 
@@ -206,6 +209,5 @@ class Version {
       case VersionType.latest:
         return '$x.$y.$z-$m.$n.pre.$commits';
     }
-    return null; // For analyzer
   }
 }
diff --git a/dev/tools/localization/bin/encode_kn_arb_files.dart b/dev/tools/localization/bin/encode_kn_arb_files.dart
index f974215c544..d2cb20f52b3 100644
--- a/dev/tools/localization/bin/encode_kn_arb_files.dart
+++ b/dev/tools/localization/bin/encode_kn_arb_files.dart
@@ -13,6 +13,8 @@
 // This utility is run by `gen_localizations.dart` if --overwrite is passed
 // in as an option.
 
+// @dart = 2.8
+
 import 'dart:convert';
 import 'dart:io';
 
diff --git a/dev/tools/localization/bin/gen_date_localizations.dart b/dev/tools/localization/bin/gen_date_localizations.dart
index 5da786a05e3..e361a4fa67a 100644
--- a/dev/tools/localization/bin/gen_date_localizations.dart
+++ b/dev/tools/localization/bin/gen_date_localizations.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 /// This program extracts localized date symbols and patterns from the intl
 /// package for the subset of locales supported by the flutter_localizations
 /// package.
diff --git a/dev/tools/localization/bin/gen_localizations.dart b/dev/tools/localization/bin/gen_localizations.dart
index 75a23d82f5c..975c2785173 100644
--- a/dev/tools/localization/bin/gen_localizations.dart
+++ b/dev/tools/localization/bin/gen_localizations.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 // This program generates a getMaterialTranslation() and a
 // getCupertinoTranslation() function that look up the translations provided by
 // the arb files. The returned value is a generated instance of a
diff --git a/dev/tools/localization/bin/gen_missing_localizations.dart b/dev/tools/localization/bin/gen_missing_localizations.dart
index d505e659f53..c4ca16252be 100644
--- a/dev/tools/localization/bin/gen_missing_localizations.dart
+++ b/dev/tools/localization/bin/gen_missing_localizations.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 // This program updates the language locale arb files with any missing resource
 // entries that are included in the English arb files. This is useful when
 // adding new resources for localization. You can just add the appropriate
diff --git a/dev/tools/localization/gen_cupertino_localizations.dart b/dev/tools/localization/gen_cupertino_localizations.dart
index f93b012354e..e1f4968ea47 100644
--- a/dev/tools/localization/gen_cupertino_localizations.dart
+++ b/dev/tools/localization/gen_cupertino_localizations.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'localizations_utils.dart';
 
 String generateCupertinoHeader(String regenerateInstructions) {
diff --git a/dev/tools/localization/gen_material_localizations.dart b/dev/tools/localization/gen_material_localizations.dart
index 31170cc1b23..528cd8c8ae5 100644
--- a/dev/tools/localization/gen_material_localizations.dart
+++ b/dev/tools/localization/gen_material_localizations.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'localizations_utils.dart';
 
 String generateMaterialHeader(String regenerateInstructions) {
diff --git a/dev/tools/localization/localizations_utils.dart b/dev/tools/localization/localizations_utils.dart
index 63ea14e804e..ae1e4451c9f 100644
--- a/dev/tools/localization/localizations_utils.dart
+++ b/dev/tools/localization/localizations_utils.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:convert';
 import 'dart:io';
 
diff --git a/dev/tools/localization/localizations_validator.dart b/dev/tools/localization/localizations_validator.dart
index ef0e78bfe59..640320c839a 100644
--- a/dev/tools/localization/localizations_validator.dart
+++ b/dev/tools/localization/localizations_validator.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:convert' show json;
 import 'dart:io';
 
diff --git a/dev/tools/mega_gallery.dart b/dev/tools/mega_gallery.dart
index 8a5d0a54e8f..ee7ddce25f9 100644
--- a/dev/tools/mega_gallery.dart
+++ b/dev/tools/mega_gallery.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 /// Make `n` copies of flutter_gallery.
 
 import 'dart:io';
diff --git a/dev/tools/pubspec.yaml b/dev/tools/pubspec.yaml
index 1b587b0f617..83a691bfa2e 100644
--- a/dev/tools/pubspec.yaml
+++ b/dev/tools/pubspec.yaml
@@ -2,7 +2,7 @@ name: dev_tools
 description: Various repository development tools for flutter.
 
 environment:
-  sdk: ">=2.6.0 <3.0.0"
+  sdk: ">=2.12.0 <3.0.0"
 
 dependencies:
   archive: 3.1.2
diff --git a/dev/tools/test/clean_test.dart b/dev/tools/test/clean_test.dart
index 2c84a5767ee..0f6d760078a 100644
--- a/dev/tools/test/clean_test.dart
+++ b/dev/tools/test/clean_test.dart
@@ -2,6 +2,8 @@
 // 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:args/command_runner.dart';
 import 'package:dev_tools/clean.dart';
 import 'package:dev_tools/repository.dart';
diff --git a/dev/tools/test/codesign_test.dart b/dev/tools/test/codesign_test.dart
index 25c436de1ef..76cbde21f5c 100644
--- a/dev/tools/test/codesign_test.dart
+++ b/dev/tools/test/codesign_test.dart
@@ -8,7 +8,6 @@ import 'package:dev_tools/globals.dart';
 import 'package:dev_tools/repository.dart';
 import 'package:file/file.dart';
 import 'package:file/memory.dart';
-import 'package:meta/meta.dart';
 import 'package:platform/platform.dart';
 
 import '../../../packages/flutter_tools/test/src/fake_process_manager.dart';
@@ -23,12 +22,12 @@ void main() {
     const String flutterBin =
         '${checkoutsParentDirectory}flutter_conductor_checkouts/framework/bin/flutter';
     const String revision = 'abcd1234';
-    CommandRunner<void> runner;
-    Checkouts checkouts;
-    MemoryFileSystem fileSystem;
-    FakePlatform platform;
-    TestStdio stdio;
-    FakeProcessManager processManager;
+    late CommandRunner<void> runner;
+    late Checkouts checkouts;
+    late MemoryFileSystem fileSystem;
+    late FakePlatform platform;
+    late TestStdio stdio;
+    late FakeProcessManager processManager;
     const List<String> binariesWithEntitlements = <String>[
       '$flutterCache/dart-sdk/bin/dart',
       '$flutterCache/dart-sdk/bin/dartaotruntime',
@@ -43,7 +42,7 @@ void main() {
 
     void createRunner({
       String operatingSystem = 'macos',
-      List<FakeCommand> commands,
+      List<FakeCommand>? commands,
     }) {
       stdio = TestStdio();
       fileSystem = MemoryFileSystem.test();
@@ -410,10 +409,10 @@ void main() {
 
 class FakeCodesignCommand extends CodesignCommand {
   FakeCodesignCommand({
-    @required Checkouts checkouts,
-    @required this.binariesWithEntitlements,
-    @required this.binariesWithoutEntitlements,
-    @required Directory flutterRoot,
+    required Checkouts checkouts,
+    required this.binariesWithEntitlements,
+    required this.binariesWithoutEntitlements,
+    required Directory flutterRoot,
   }) : super(checkouts: checkouts, flutterRoot: flutterRoot);
 
   @override
diff --git a/dev/tools/test/common.dart b/dev/tools/test/common.dart
index 306c33cedac..531a03f731c 100644
--- a/dev/tools/test/common.dart
+++ b/dev/tools/test/common.dart
@@ -38,10 +38,8 @@ Matcher throwsExceptionWith(String messageSubString) {
 class TestStdio extends Stdio {
   TestStdio({
     this.verbose = false,
-    List<String> stdin,
-  }) {
-    _stdin = stdin ?? <String>[];
-  }
+    List<String>? stdin,
+  }) : _stdin = stdin ?? <String>[];
 
   String get error => logs.where((String log) => log.startsWith(r'[error] ')).join('\n');
 
@@ -50,7 +48,7 @@ class TestStdio extends Stdio {
   }).join('\n');
 
   final bool verbose;
-  List<String> _stdin;
+  late final List<String> _stdin;
 
   @override
   String readLineSync() {
@@ -63,9 +61,9 @@ class TestStdio extends Stdio {
 
 class FakeArgResults implements ArgResults {
   FakeArgResults({
-    String level,
-    String commit,
-    String remote,
+    required String level,
+    required String commit,
+    String remote = 'upstream',
     bool justPrint = false,
     bool autoApprove = true, // so we don't have to mock stdin
     bool help = false,
@@ -83,22 +81,26 @@ class FakeArgResults implements ArgResults {
   };
 
   @override
-  String name;
+  String? name;
 
   @override
-  ArgResults command;
+  ArgResults? command;
 
   @override
   final List<String> rest = <String>[];
 
   @override
-  List<String> arguments;
+  List<String> get arguments {
+    assert(false, 'not yet implemented');
+    return <String>[];
+  }
 
   final Map<String, dynamic> _parsedArgs;
 
   @override
   Iterable<String> get options {
-    return null;
+    assert(false, 'not yet implemented');
+    return <String>[];
   }
 
   @override
@@ -108,6 +110,7 @@ class FakeArgResults implements ArgResults {
 
   @override
   bool wasParsed(String name) {
-    return null;
+    assert(false, 'not yet implemented');
+    return false;
   }
 }
diff --git a/dev/tools/test/roll_dev_integration_test.dart b/dev/tools/test/roll_dev_integration_test.dart
index a13b7f3cc19..f0a8243fec9 100644
--- a/dev/tools/test/roll_dev_integration_test.dart
+++ b/dev/tools/test/roll_dev_integration_test.dart
@@ -14,16 +14,16 @@ import './common.dart';
 
 void main() {
   group('roll-dev', () {
-    TestStdio stdio;
-    Platform platform;
-    ProcessManager processManager;
-    FileSystem fileSystem;
+    late TestStdio stdio;
+    late Platform platform;
+    late ProcessManager processManager;
+    late FileSystem fileSystem;
     const String usageString = 'Usage: flutter conductor.';
 
-    Checkouts checkouts;
-    FrameworkRepository frameworkUpstream;
-    FrameworkRepository framework;
-    Directory tempDir;
+    late Checkouts checkouts;
+    late FrameworkRepository frameworkUpstream;
+    late FrameworkRepository framework;
+    late Directory tempDir;
 
     setUp(() {
       platform = const LocalPlatform();
diff --git a/dev/tools/test/roll_dev_test.dart b/dev/tools/test/roll_dev_test.dart
index 2797212c89b..d6e32ac0105 100644
--- a/dev/tools/test/roll_dev_test.dart
+++ b/dev/tools/test/roll_dev_test.dart
@@ -2,6 +2,8 @@
 // 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:dev_tools/globals.dart';
 import 'package:dev_tools/repository.dart';
 import 'package:dev_tools/roll_dev.dart';
diff --git a/dev/tools/test/start_test.dart b/dev/tools/test/start_test.dart
index 683d9090cfe..6924502cc24 100644
--- a/dev/tools/test/start_test.dart
+++ b/dev/tools/test/start_test.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:convert' show jsonDecode;
 
 import 'package:args/command_runner.dart';
diff --git a/dev/tools/update_icons.dart b/dev/tools/update_icons.dart
index 9ab1f1655ff..d19b9374cc4 100644
--- a/dev/tools/update_icons.dart
+++ b/dev/tools/update_icons.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 // Regenerates the material icons file.
 // See https://github.com/flutter/flutter/wiki/Updating-Material-Design-Fonts-&-Icons