diff --git a/pkg/kernel/test/regression_37753_test.dart b/pkg/front_end/testcases/general/issue37753.dart
similarity index 100%
rename from pkg/kernel/test/regression_37753_test.dart
rename to pkg/front_end/testcases/general/issue37753.dart
diff --git a/pkg/front_end/testcases/general/issue37753.dart.textual_outline.expect b/pkg/front_end/testcases/general/issue37753.dart.textual_outline.expect
new file mode 100644
index 0000000..771fd22
--- /dev/null
+++ b/pkg/front_end/testcases/general/issue37753.dart.textual_outline.expect
@@ -0,0 +1,3 @@
+// @dart = 2.9
+Iterable<int> getElements() sync* {}
+main() => print(getElements());
diff --git a/pkg/front_end/testcases/general/issue37753.dart.textual_outline_modelled.expect b/pkg/front_end/testcases/general/issue37753.dart.textual_outline_modelled.expect
new file mode 100644
index 0000000..771fd22
--- /dev/null
+++ b/pkg/front_end/testcases/general/issue37753.dart.textual_outline_modelled.expect
@@ -0,0 +1,3 @@
+// @dart = 2.9
+Iterable<int> getElements() sync* {}
+main() => print(getElements());
diff --git a/pkg/front_end/testcases/general/issue37753.dart.weak.expect b/pkg/front_end/testcases/general/issue37753.dart.weak.expect
new file mode 100644
index 0000000..8ce1e9b
--- /dev/null
+++ b/pkg/front_end/testcases/general/issue37753.dart.weak.expect
@@ -0,0 +1,13 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+static method getElements() → core::Iterable<core::int*>* sync* {
+  core::Iterable<core::int*>* elements;
+  elements = (() → core::Iterable<core::int*>* sync* {
+    yield 7;
+  })(){() →* core::Iterable<core::int*>*};
+  yield* elements;
+}
+static method main() → dynamic
+  return core::print(self::getElements());
diff --git a/pkg/front_end/testcases/general/issue37753.dart.weak.outline.expect b/pkg/front_end/testcases/general/issue37753.dart.weak.outline.expect
new file mode 100644
index 0000000..2032eab
--- /dev/null
+++ b/pkg/front_end/testcases/general/issue37753.dart.weak.outline.expect
@@ -0,0 +1,8 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+static method getElements() → core::Iterable<core::int*>* sync* 
+  ;
+static method main() → dynamic
+  ;
diff --git a/pkg/front_end/testcases/general/issue37753.dart.weak.transformed.expect b/pkg/front_end/testcases/general/issue37753.dart.weak.transformed.expect
new file mode 100644
index 0000000..7321092
--- /dev/null
+++ b/pkg/front_end/testcases/general/issue37753.dart.weak.transformed.expect
@@ -0,0 +1,41 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+static method getElements() → core::Iterable<core::int*>* /* originally sync* */ {
+  function :sync_op_gen() → (core::_SyncIterator<dynamic>*, dynamic, dynamic) →* core::bool* {
+    core::int* :await_jump_var = 0;
+    dynamic :await_ctx_var;
+    function :sync_op(core::_SyncIterator<dynamic>* :iterator, dynamic :exception, dynamic :stack_trace) → core::bool* yielding {
+      {
+        core::Iterable<core::int*>* elements;
+        elements = (() → core::Iterable<core::int*>* /* originally sync* */ {
+          function :sync_op_gen() → (core::_SyncIterator<dynamic>*, dynamic, dynamic) →* core::bool* {
+            core::int* :await_jump_var = 0;
+            dynamic :await_ctx_var;
+            function :sync_op(core::_SyncIterator<dynamic>* :iterator, dynamic :exception, dynamic :stack_trace) → core::bool* yielding {
+              {
+                {
+                  :iterator.{core::_SyncIterator::_current} = 7;
+                  [yield] true;
+                }
+              }
+              return false;
+            }
+            return :sync_op;
+          }
+          return new core::_SyncIterable::•<core::int*>(:sync_op_gen);
+        })(){() →* core::Iterable<core::int*>*};
+        {
+          :iterator.{core::_SyncIterator::_yieldEachIterable} = elements;
+          [yield] true;
+        }
+      }
+      return false;
+    }
+    return :sync_op;
+  }
+  return new core::_SyncIterable::•<core::int*>(:sync_op_gen);
+}
+static method main() → dynamic
+  return core::print(self::getElements());
diff --git a/pkg/front_end/testcases/general/issue40662.dart b/pkg/front_end/testcases/general/issue40662.dart
index 611fc81..fba166b 100644
--- a/pkg/front_end/testcases/general/issue40662.dart
+++ b/pkg/front_end/testcases/general/issue40662.dart
@@ -3,7 +3,9 @@
 // BSD-style license that can be found in the LICENSE file.
 //
 // Regression test for https://github.com/dart-lang/sdk/issues/40662.
+
 // @dart=2.9
+
 bar(int a, List<int> b) {
   expect(-1, a);
   expect(-1, (b[0] - 2));
diff --git a/pkg/front_end/testcases/general/issue40662.dart.weak.transformed.expect b/pkg/front_end/testcases/general/issue40662.dart.weak.transformed.expect
index 79b6c00..90be483 100644
--- a/pkg/front_end/testcases/general/issue40662.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/general/issue40662.dart.weak.transformed.expect
@@ -86,6 +86,6 @@
 
 
 Extra constant evaluation status:
-Evaluated: InstanceInvocation @ org-dartlang-testcase:///issue40662.dart:8:10 -> IntConstant(-1)
-Evaluated: InstanceInvocation @ org-dartlang-testcase:///issue40662.dart:9:10 -> IntConstant(-1)
+Evaluated: InstanceInvocation @ org-dartlang-testcase:///issue40662.dart:10:10 -> IntConstant(-1)
+Evaluated: InstanceInvocation @ org-dartlang-testcase:///issue40662.dart:11:10 -> IntConstant(-1)
 Extra constant evaluation: evaluated: 94, effectively constant: 2
diff --git a/pkg/front_end/tool/_fasta/abcompile.dart b/pkg/front_end/tool/_fasta/abcompile.dart
index 26f815a..a9e3125 100644
--- a/pkg/front_end/tool/_fasta/abcompile.dart
+++ b/pkg/front_end/tool/_fasta/abcompile.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.9
-
 import 'dart:async';
 import 'dart:convert';
 import 'dart:math';
@@ -11,7 +9,7 @@
 
 import 'standard_deviation.dart';
 
-const String bRootPath =
+const String? bRootPath =
     bool.hasEnvironment("bRoot") ? String.fromEnvironment("bRoot") : null;
 const int abIterations = int.fromEnvironment("abIterations", defaultValue: 15);
 const int iterations = int.fromEnvironment("iterations", defaultValue: 15);
@@ -31,7 +29,7 @@
   Uri aRoot = Platform.script.resolve('../../../..');
 
   // The root of the other Dart SDK repo "B"
-  Uri bRoot = new Uri.directory(bRootPath);
+  Uri bRoot = new Uri.directory(bRootPath!);
 
   // Sanity check
   String relPath = 'pkg/front_end/tool/_fasta/compile.dart';
@@ -183,15 +181,15 @@
       workingDirectory: workingDirPath);
   // ignore: unawaited_futures
   stderr.addStream(process.stderr);
-  StreamSubscription<String> stdOutSubscription;
+  StreamSubscription<String>? stdOutSubscription;
   stdOutSubscription = process.stdout
       .transform(utf8.decoder)
       .transform(new LineSplitter())
       .listen(processLine, onDone: () {
-    stdOutSubscription.cancel();
+    stdOutSubscription!.cancel();
   }, onError: (e) {
     print('Error: $e');
-    stdOutSubscription.cancel();
+    stdOutSubscription!.cancel();
   });
   int code = await process.exitCode;
   if (code != 0) {
diff --git a/pkg/front_end/tool/_fasta/bench_maker.dart b/pkg/front_end/tool/_fasta/bench_maker.dart
index 22732a7..4e95837 100644
--- a/pkg/front_end/tool/_fasta/bench_maker.dart
+++ b/pkg/front_end/tool/_fasta/bench_maker.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.9
-
 library fasta.tool.entry_points;
 
 import "dart:convert" show JsonEncoder;
@@ -49,8 +47,10 @@
   final List<TypeParameter> usedTypeParameters = <TypeParameter>[];
 
   String serializeTypeChecks(List<Object> typeChecks) {
-    for (List<Object> list in typeChecks) {
-      writeTypeCheck(list[0], list[1], list[2]);
+    for (Object list in typeChecks) {
+      List<Object> typeCheck = list as List<Object>;
+      writeTypeCheck(typeCheck[0] as DartType, typeCheck[1] as DartType,
+          typeCheck[2] as bool);
     }
     writeClasses();
     return jsonEncode(this);
@@ -133,11 +133,11 @@
     }
   }
 
-  void writeClass(Class cls, Set<Class> writtenClasses) {
+  void writeClass(Class? cls, Set<Class> writtenClasses) {
     if (cls == null || !writtenClasses.add(cls)) return;
-    Supertype supertype = cls.supertype;
+    Supertype? supertype = cls.supertype;
     writeClass(supertype?.classNode, writtenClasses);
-    Supertype mixedInType = cls.mixedInType;
+    Supertype? mixedInType = cls.mixedInType;
     writeClass(mixedInType?.classNode, writtenClasses);
     for (Supertype implementedType in cls.implementedTypes) {
       writeClass(implementedType.classNode, writtenClasses);
@@ -164,7 +164,7 @@
       implementedType.asInterfaceType.accept1(this, sb);
       first = false;
     }
-    Procedure callOperator;
+    Procedure? callOperator;
     for (Procedure procedure in cls.procedures) {
       if (procedure.name.text == "call") {
         callOperator = procedure;
@@ -183,11 +183,11 @@
   }
 
   String computeName(TreeNode node) {
-    String name = nodeNames[node];
+    String? name = nodeNames[node];
     if (name != null) return name;
     if (node is Class) {
       Library library = node.enclosingLibrary;
-      String uriString = "${library?.importUri}";
+      String uriString = "${library.importUri}";
       if (uriString == "dart:core" || uriString == "dart:async") {
         if (!usedNames.add(node.name)) {
           throw "Class name conflict for $node";
@@ -336,7 +336,7 @@
     sb.write(name);
     if (node.promotedBound != null) {
       sb.write(" & ");
-      node.promotedBound.accept1(this, sb);
+      node.promotedBound!.accept1(this, sb);
     }
   }
 
diff --git a/pkg/front_end/tool/_fasta/command_line.dart b/pkg/front_end/tool/_fasta/command_line.dart
index d4b5b05..6ab0e47 100644
--- a/pkg/front_end/tool/_fasta/command_line.dart
+++ b/pkg/front_end/tool/_fasta/command_line.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.9
-
 library fasta.tool.command_line;
 
 import 'dart:io' show exit;
@@ -110,7 +108,7 @@
   /// All other options require an option value, either on the form `--option
   /// value` or `--option=value`.
   static ParsedArguments parse(
-      List<String> arguments, Map<String, ValueSpecification> specification) {
+      List<String> arguments, Map<String, ValueSpecification>? specification) {
     specification ??= const <String, ValueSpecification>{};
     ParsedArguments result = new ParsedArguments();
     int index = arguments.indexOf("--");
@@ -123,7 +121,7 @@
     while (iterator.moveNext()) {
       String argument = iterator.current;
       if (argument.startsWith("-") || argument == "/?" || argument == "/h") {
-        String value;
+        String? value;
         if (argument.startsWith("-D")) {
           value = argument.substring("-D".length);
           argument = "-D";
@@ -134,14 +132,14 @@
             argument = argument.substring(0, index);
           }
         }
-        ValueSpecification valueSpecification = specification[argument];
+        ValueSpecification? valueSpecification = specification[argument];
         if (valueSpecification == null) {
           throw new CommandLineProblem.deprecated(
               "Unknown option '$argument'.");
         }
         String canonicalArgument = argument;
         if (valueSpecification.alias != null) {
-          canonicalArgument = valueSpecification.alias;
+          canonicalArgument = valueSpecification.alias as String;
           valueSpecification = specification[valueSpecification.alias];
         }
         if (valueSpecification == null) {
@@ -268,7 +266,7 @@
       enableNullSafety: isExperimentEnabled(ExperimentalFlag.nonNullable,
           explicitExperimentalFlags: explicitExperimentalFlags));
 
-  final Target target = getTarget(targetName, flags);
+  final Target? target = getTarget(targetName, flags);
   if (target == null) {
     return throw new CommandLineProblem.deprecated(
         "Target '${targetName}' not recognized. "
@@ -302,7 +300,7 @@
 
   final bool compileSdk = options.containsKey(Flags.compileSdk);
 
-  final String singleRootScheme = options[Flags.singleRootScheme];
+  final String? singleRootScheme = options[Flags.singleRootScheme];
   final Uri singleRootBase = options[Flags.singleRootBase];
 
   final bool nnbdStrongMode = options[Flags.nnbdStrongMode];
@@ -418,7 +416,7 @@
             throwCommandLineProblem(
                 "Target '${target.name}' requires an explicit "
                 "'${Flags.platform}' option.");
-          })));
+          })!));
   compilerOptions
     ..sdkRoot = sdk
     ..sdkSummary = platform
@@ -439,9 +437,9 @@
     List<String> arguments,
     bool areRestArgumentsInputs,
     Future<T> f(CompilerContext context, List<String> restArguments)) {
-  ParsedArguments parsedArguments;
+  ParsedArguments? parsedArguments;
   ProcessedOptions options;
-  CommandLineProblem problem;
+  CommandLineProblem? problem;
   try {
     parsedArguments = ParsedArguments.parse(arguments, optionSpecification);
     options = analyzeCommandLine(
@@ -466,13 +464,13 @@
       exit(1);
     }
 
-    return f(c, parsedArguments.arguments);
+    return f(c, parsedArguments!.arguments);
   }, errorOnMissingInput: problem == null);
 }
 
 Message computeUsage(String programName, bool verbose) {
   String basicUsage = "Usage: $programName [options] dartfile\n";
-  String summary;
+  String? summary;
   String options =
       (verbose ? messageFastaUsageLong.message : messageFastaUsageShort.message)
           .trim();
@@ -508,7 +506,7 @@
 }
 
 Future<T> runProtectedFromAbort<T>(Future<T> Function() action,
-    [T failingValue]) async {
+    [T? failingValue]) async {
   if (CompilerContext.isActive) {
     throw "runProtectedFromAbort should be called from 'main',"
         " that is, outside a compiler context.";
@@ -527,14 +525,14 @@
 abstract class ValueSpecification {
   const ValueSpecification();
 
-  String get alias => null;
+  String? get alias => null;
 
   dynamic get defaultValue => null;
 
   bool get requiresValue => true;
 
   void processValue(ParsedArguments result, String canonicalArgument,
-      String argument, String value);
+      String argument, String? value);
 }
 
 class AliasValue extends ValueSpecification {
@@ -546,7 +544,7 @@
       throw new UnsupportedError("AliasValue.requiresValue");
 
   void processValue(ParsedArguments result, String canonicalArgument,
-      String argument, String value) {
+      String argument, String? value) {
     throw new UnsupportedError("AliasValue.processValue");
   }
 }
@@ -555,7 +553,7 @@
   const UriValue();
 
   void processValue(ParsedArguments result, String canonicalArgument,
-      String argument, String value) {
+      String argument, String? value) {
     if (result.options.containsKey(canonicalArgument)) {
       throw new CommandLineProblem.deprecated(
           "Multiple values for '$argument': "
@@ -563,7 +561,7 @@
     }
     // TODO(ahe): resolve Uris lazily, so that schemes provided by
     // other flags can be used for parsed command-line arguments too.
-    result.options[canonicalArgument] = resolveInputUri(value);
+    result.options[canonicalArgument] = resolveInputUri(value!);
   }
 }
 
@@ -571,13 +569,13 @@
   const StringValue();
 
   void processValue(ParsedArguments result, String canonicalArgument,
-      String argument, String value) {
+      String argument, String? value) {
     if (result.options.containsKey(canonicalArgument)) {
       throw new CommandLineProblem.deprecated(
           "Multiple values for '$argument': "
           "'${result.options[canonicalArgument]}' and '$value'.");
     }
-    result.options[canonicalArgument] = value;
+    result.options[canonicalArgument] = value!;
   }
 }
 
@@ -589,7 +587,7 @@
   bool get requiresValue => false;
 
   void processValue(ParsedArguments result, String canonicalArgument,
-      String argument, String value) {
+      String argument, String? value) {
     if (result.options.containsKey(canonicalArgument)) {
       throw new CommandLineProblem.deprecated(
           "Multiple values for '$argument': "
@@ -613,13 +611,13 @@
   const IntValue();
 
   void processValue(ParsedArguments result, String canonicalArgument,
-      String argument, String value) {
+      String argument, String? value) {
     if (result.options.containsKey(canonicalArgument)) {
       throw new CommandLineProblem.deprecated(
           "Multiple values for '$argument': "
           "'${result.options[canonicalArgument]}' and '$value'.");
     }
-    int parsedValue = int.tryParse(value);
+    int? parsedValue = int.tryParse(value!);
     if (parsedValue == null) {
       throw new CommandLineProblem.deprecated(
           "Value for '$argument', '$value', isn't an int.");
@@ -632,8 +630,8 @@
   const DefineValue();
 
   void processValue(ParsedArguments result, String canonicalArgument,
-      String argument, String value) {
-    int index = value.indexOf('=');
+      String argument, String? value) {
+    int index = value!.indexOf('=');
     String name;
     String expression;
     if (index != -1) {
@@ -651,10 +649,10 @@
   const StringListValue();
 
   void processValue(ParsedArguments result, String canonicalArgument,
-      String argument, String value) {
+      String argument, String? value) {
     result.options
         .putIfAbsent(canonicalArgument, () => <String>[])
-        .addAll(value.split(","));
+        .addAll(value!.split(","));
   }
 }
 
@@ -662,9 +660,9 @@
   const UriListValue();
 
   void processValue(ParsedArguments result, String canonicalArgument,
-      String argument, String value) {
+      String argument, String? value) {
     result.options
         .putIfAbsent(canonicalArgument, () => <Uri>[])
-        .addAll(value.split(",").map(resolveInputUri));
+        .addAll(value!.split(",").map(resolveInputUri));
   }
 }
diff --git a/pkg/front_end/tool/_fasta/compile_platform_legacy_test.dart b/pkg/front_end/tool/_fasta/compile_platform_legacy_test.dart
index 1f624d3..985026c 100644
--- a/pkg/front_end/tool/_fasta/compile_platform_legacy_test.dart
+++ b/pkg/front_end/tool/_fasta/compile_platform_legacy_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
-// @dart=2.9
-
 library fasta.test.compile_platform_test;
 
 import 'dart:io';
diff --git a/pkg/front_end/tool/_fasta/compile_platform_test.dart b/pkg/front_end/tool/_fasta/compile_platform_test.dart
index 1f624d3..985026c 100644
--- a/pkg/front_end/tool/_fasta/compile_platform_test.dart
+++ b/pkg/front_end/tool/_fasta/compile_platform_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
-// @dart=2.9
-
 library fasta.test.compile_platform_test;
 
 import 'dart:io';
diff --git a/pkg/front_end/tool/_fasta/generate_experimental_flags.dart b/pkg/front_end/tool/_fasta/generate_experimental_flags.dart
index f52aee6..a452b9f 100644
--- a/pkg/front_end/tool/_fasta/generate_experimental_flags.dart
+++ b/pkg/front_end/tool/_fasta/generate_experimental_flags.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.9
-
 import 'dart:io' show File;
 
 import 'package:_fe_analyzer_shared/src/scanner/characters.dart'
@@ -50,7 +48,7 @@
   int currentVersionMajor;
   int currentVersionMinor;
   {
-    String currentVersion = getAsVersionNumberString(yaml['current-version']);
+    String currentVersion = getAsVersionNumberString(yaml['current-version'])!;
     List<String> split = currentVersion.split(".");
     currentVersionMajor = int.parse(split[0]);
     currentVersionMinor = int.parse(split[1]);
@@ -84,7 +82,7 @@
   int currentVersionMajor;
   int currentVersionMinor;
   {
-    String currentVersion = getAsVersionNumberString(yaml['current-version']);
+    String currentVersion = getAsVersionNumberString(yaml['current-version'])!;
     List<String> split = currentVersion.split(".");
     currentVersionMajor = int.parse(split[0]);
     currentVersionMinor = int.parse(split[1]);
@@ -135,7 +133,7 @@
   for (String key in keys) {
     int major;
     int minor;
-    String enabledIn =
+    String? enabledIn =
         getAsVersionNumberString((features[key] as YamlMap)['enabledIn']);
     if (enabledIn == null) {
       major = currentVersionMajor;
@@ -192,7 +190,7 @@
   for (String key in keys) {
     int major;
     int minor;
-    String enabledIn =
+    String? enabledIn =
         getAsVersionNumberString((features[key] as YamlMap)['enabledIn']);
     if (enabledIn != null) {
       List<String> split = enabledIn.split(".");
@@ -213,9 +211,9 @@
   for (String key in keys) {
     int major;
     int minor;
-    String enabledIn =
+    String? enabledIn =
         getAsVersionNumberString((features[key] as YamlMap)['enabledIn']);
-    String experimentalReleaseVersion = getAsVersionNumberString(
+    String? experimentalReleaseVersion = getAsVersionNumberString(
         (features[key] as YamlMap)['experimentalReleaseVersion']);
     if (experimentalReleaseVersion != null) {
       List<String> split = experimentalReleaseVersion.split(".");
@@ -296,7 +294,7 @@
   return identifier.toString();
 }
 
-String getAsVersionNumberString(dynamic value) {
+String? getAsVersionNumberString(dynamic value) {
   if (value == null) return null;
   if (value is String) return value;
   if (value is double) return "$value";
diff --git a/pkg/front_end/tool/_fasta/generate_messages.dart b/pkg/front_end/tool/_fasta/generate_messages.dart
index 8ddafe5..3a971c3 100644
--- a/pkg/front_end/tool/_fasta/generate_messages.dart
+++ b/pkg/front_end/tool/_fasta/generate_messages.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.9
-
 import 'dart:io' show File, exitCode;
 
 import "package:_fe_analyzer_shared/src/messages/severity.dart"
@@ -96,7 +94,7 @@
     while (description is String) {
       description = yaml[description];
     }
-    Map<dynamic, dynamic> map = description;
+    Map<dynamic, dynamic>? map = description;
     if (map == null) {
       throw "No 'template:' in key $name.";
     }
@@ -109,7 +107,7 @@
         index = -1;
         // Continue looking for other problems.
       } else {
-        String otherName = indexNameMap[index];
+        String? otherName = indexNameMap[index];
         if (otherName != null) {
           print('Error: The "index:" field must be unique, '
               'but is the same for $otherName and $name');
@@ -166,8 +164,8 @@
   Template(this.text, {this.isShared}) : assert(isShared != null);
 }
 
-Template compileTemplate(String name, int index, String template, String tip,
-    Object analyzerCode, String severity) {
+Template compileTemplate(String name, int? index, String? template, String? tip,
+    Object? analyzerCode, String? severity) {
   if (template == null) {
     print('Error: missing template for message: $name');
     exitCode = 1;
@@ -194,9 +192,9 @@
 
   for (Match match
       in placeholderPattern.allMatches("$template\n${tip ?? ''}")) {
-    String name = match[1];
-    String padding = match[2];
-    String fractionDigits = match[3];
+    String name = match[1]!;
+    String? padding = match[2];
+    String? fractionDigits = match[3];
 
     String format(String name) {
       String conversion;
@@ -205,7 +203,7 @@
       } else {
         conversion = "$name.toStringAsFixed($fractionDigits)";
       }
-      if (padding.isNotEmpty) {
+      if (padding!.isNotEmpty) {
         if (padding.startsWith("0")) {
           conversion += ".padLeft(${int.parse(padding)}, '0')";
         } else {
@@ -416,13 +414,13 @@
     if (analyzerCode is String) {
       analyzerCode = <String>[analyzerCode];
     }
-    List<Object> codes = analyzerCode;
+    List<Object> codes = analyzerCode as List<Object>;
     // If "index:" is defined, then "analyzerCode:" should not be generated
     // in the front end. See comment in messages.yaml
     codeArguments.add('analyzerCodes: <String>["${codes.join('", "')}"]');
   }
   if (severity != null) {
-    String severityEnumName = severityEnumNames[severity];
+    String? severityEnumName = severityEnumNames[severity];
     if (severityEnumName == null) {
       throw "Unknown severity '$severity'";
     }
@@ -430,6 +428,7 @@
   }
 
   if (parameters.isEmpty && conversions.isEmpty && arguments.isEmpty) {
+    // ignore: unnecessary_null_comparison
     if (template != null) {
       codeArguments.add('message: r"""$template"""');
     }
@@ -448,6 +447,7 @@
   }
 
   List<String> templateArguments = <String>[];
+  // ignore: unnecessary_null_comparison
   if (template != null) {
     templateArguments.add('messageTemplate: r"""$template"""');
   }
diff --git a/pkg/front_end/tool/_fasta/log_collector.dart b/pkg/front_end/tool/_fasta/log_collector.dart
index 95dc56f..01fac75 100644
--- a/pkg/front_end/tool/_fasta/log_collector.dart
+++ b/pkg/front_end/tool/_fasta/log_collector.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.9
-
 import 'dart:convert' show jsonDecode, utf8;
 
 import 'dart:isolate' show RawReceivePort;
@@ -55,7 +53,7 @@
   String month = "${time.month}".padLeft(2, "0");
   String day = "${time.day}".padLeft(2, "0");
   String us = "${time.microsecondsSinceEpoch}".padLeft(19, '0');
-  Uri uri = Uri.base
+  Uri? uri = Uri.base
       .resolve("crash_logs/${data['client']}/$year-$month-$day/$us.log");
   File file = new File.fromUri(uri);
   await file.parent.create(recursive: true);
@@ -63,12 +61,12 @@
   print("Wrote ${uri.toFilePath()}");
 
   String type = data["type"];
-  String text = data["uri"];
+  String? text = data["uri"];
   uri = text == null ? null : Uri.parse(text);
   int charOffset = data["offset"];
   var error = data["error"];
   text = data["trace"];
-  StackTrace trace = text == null ? null : new StackTrace.fromString(text);
+  StackTrace? trace = text == null ? null : new StackTrace.fromString(text);
   String client = data["client"];
   print("""
 date: ${time}
diff --git a/pkg/kernel/lib/class_hierarchy.dart b/pkg/kernel/lib/class_hierarchy.dart
index 7a61ee2..f66182a 100644
--- a/pkg/kernel/lib/class_hierarchy.dart
+++ b/pkg/kernel/lib/class_hierarchy.dart
@@ -1722,8 +1722,6 @@
 /// are removed first; in the case of ties, classes with lower topological sort
 /// index are removed first.
 class _LubHeap extends Heap<_ClassInfo> {
-  _LubHeap() : super(_dummyClassInfo);
-
   @override
   bool sortsBefore(_ClassInfo a, _ClassInfo b) => sortsBeforeStatic(a, b);
 
@@ -1733,5 +1731,3 @@
     return a.topologicalIndex < b.topologicalIndex;
   }
 }
-
-final _ClassInfo _dummyClassInfo = new _ClassInfo(dummyClass);
diff --git a/pkg/kernel/lib/src/heap.dart b/pkg/kernel/lib/src/heap.dart
index f70098b..5cbeeab 100644
--- a/pkg/kernel/lib/src/heap.dart
+++ b/pkg/kernel/lib/src/heap.dart
@@ -5,9 +5,6 @@
 /// Basic implementation of a heap, with O(log n) insertion and removal.
 abstract class Heap<T> {
   final _items = <T>[];
-  final T _dummyValue;
-
-  Heap(this._dummyValue);
 
   bool get isEmpty => _items.isEmpty;
 
@@ -15,7 +12,7 @@
 
   void add(T item) {
     int index = _items.length;
-    _items.add(_dummyValue);
+    _items.add(item);
     while (index > 0) {
       T parent = _items[_parentIndex(index)];
       if (sortsBefore(parent, item)) break;
diff --git a/pkg/kernel/lib/text/serializer_combinators.dart b/pkg/kernel/lib/text/serializer_combinators.dart
index 7af498e..aae9ea2 100644
--- a/pkg/kernel/lib/text/serializer_combinators.dart
+++ b/pkg/kernel/lib/text/serializer_combinators.dart
@@ -714,7 +714,7 @@
 /// Serializes an object and uses it as a binder for the name that is retrieved
 /// from the object using [nameGetter] and (temporarily) modified using
 /// [nameSetter].  The binder is added to the enclosing environment.
-class Binder<T extends Node> extends TextSerializer<Tuple2<String, T>> {
+class Binder<T extends Node> extends TextSerializer<Tuple2<String?, T>> {
   final Tuple2Serializer<String, T> namedContents;
 
   Binder(TextSerializer<T> contents)
@@ -733,13 +733,13 @@
     return new Tuple2(name, object);
   }
 
-  void writeTo(StringBuffer buffer, Tuple2<String, T> namedObject,
+  void writeTo(StringBuffer buffer, Tuple2<String?, T> namedObject,
       SerializationState? state) {
     if (state == null) {
       throw StateError(
           "No serialization state provided for ${runtimeType}.writeTo.");
     }
-    String nameClue = namedObject.first;
+    String? nameClue = namedObject.first;
     T object = namedObject.second;
     String distinctName =
         state.environment.addBinder(object, nameClue: nameClue);
diff --git a/pkg/kernel/lib/text/text_serializer.dart b/pkg/kernel/lib/text/text_serializer.dart
index 374cfc4..2c80120 100644
--- a/pkg/kernel/lib/text/text_serializer.dart
+++ b/pkg/kernel/lib/text/text_serializer.dart
@@ -1706,7 +1706,7 @@
         (ls) => Tuple2(ls, ls.body),
         (t) => t.first..body = t.second,
         Bind(
-            Wrapped<Tuple2<String, LabeledStatement>, LabeledStatement>(
+            Wrapped<Tuple2<String?, LabeledStatement>, LabeledStatement>(
                 (ls) => Tuple2("L", ls),
                 (t) => t.second,
                 Binder(Wrapped(
@@ -1775,7 +1775,7 @@
 }
 
 TextSerializer<SwitchCase> switchCaseCaseSerializer =
-    Wrapped<Tuple2<String, SwitchCase>, SwitchCase>(
+    Wrapped<Tuple2<String?, SwitchCase>, SwitchCase>(
         (w) => Tuple2("L", w),
         (u) => u.second,
         Binder(Wrapped<List<Expression>, SwitchCase>(
@@ -1784,7 +1784,7 @@
             ListSerializer(expressionSerializer))));
 
 TextSerializer<SwitchCase> switchCaseDefaultSerializer = Wrapped<
-        Tuple2<String, SwitchCase>, SwitchCase>(
+        Tuple2<String?, SwitchCase>, SwitchCase>(
     (w) => Tuple2("L", w),
     (u) => u.second,
     Binder(
diff --git a/pkg/kernel/test/ast_membench.dart b/pkg/kernel/test/ast_membench.dart
index baf8245..bd448d0 100644
--- a/pkg/kernel/test/ast_membench.dart
+++ b/pkg/kernel/test/ast_membench.dart
@@ -3,8 +3,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:kernel/kernel.dart';
 import 'dart:io';
 
diff --git a/pkg/kernel/test/binary/can_read_platform_test.dart b/pkg/kernel/test/binary/can_read_platform_test.dart
index 2c8d827..2b447bc 100644
--- a/pkg/kernel/test/binary/can_read_platform_test.dart
+++ b/pkg/kernel/test/binary/can_read_platform_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'dart:io';
 
 import 'package:kernel/binary/ast_from_binary.dart';
diff --git a/pkg/kernel/test/binary/component_mode_test.dart b/pkg/kernel/test/binary/component_mode_test.dart
index 2358e2f..c036b67 100644
--- a/pkg/kernel/test/binary/component_mode_test.dart
+++ b/pkg/kernel/test/binary/component_mode_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:kernel/binary/ast_from_binary.dart';
 
 import 'utils.dart';
diff --git a/pkg/kernel/test/binary/invalid_index_size.dart b/pkg/kernel/test/binary/invalid_index_size.dart
index 2722ee4..893c14b 100644
--- a/pkg/kernel/test/binary/invalid_index_size.dart
+++ b/pkg/kernel/test/binary/invalid_index_size.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:kernel/binary/ast_from_binary.dart' show ParseError;
 
 import 'utils.dart';
diff --git a/pkg/kernel/test/binary/lazy_reading_test.dart b/pkg/kernel/test/binary/lazy_reading_test.dart
index 9d8d45c..f8bec83 100644
--- a/pkg/kernel/test/binary/lazy_reading_test.dart
+++ b/pkg/kernel/test/binary/lazy_reading_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:kernel/binary/ast_from_binary.dart';
 import 'package:kernel/src/tool/find_referenced_libraries.dart';
 import 'utils.dart';
@@ -47,9 +45,9 @@
     final Library loadedLib = loadedComponent.libraries.single;
     final Class loadedClassA = loadedLib.classes.first;
     final ExpressionStatement loadedConstructorA =
-        loadedClassA.constructors.single.function.body;
+        loadedClassA.constructors.single.function.body as ExpressionStatement;
     final ConstructorInvocation loadedConstructorInvocation =
-        loadedConstructorA.expression;
+        loadedConstructorA.expression as ConstructorInvocation;
     final Class pointedToClass =
         loadedConstructorInvocation.target.enclosingClass;
     final Library pointedToLib =
@@ -81,9 +79,9 @@
     final Library loadedLib = loadedComponent2.libraries.single;
     final Class loadedClassA = loadedLib.classes.first;
     final ExpressionStatement loadedConstructorA =
-        loadedClassA.constructors.single.function.body;
+        loadedClassA.constructors.single.function.body as ExpressionStatement;
     final ConstructorInvocation loadedConstructorInvocation =
-        loadedConstructorA.expression;
+        loadedConstructorA.expression as ConstructorInvocation;
     final Class pointedToClass =
         loadedConstructorInvocation.target.enclosingClass;
     final Library pointedToLib =
diff --git a/pkg/kernel/test/binary/library_flags_test.dart b/pkg/kernel/test/binary/library_flags_test.dart
index c930c3c..d8776d6 100644
--- a/pkg/kernel/test/binary/library_flags_test.dart
+++ b/pkg/kernel/test/binary/library_flags_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'utils.dart';
 
 /// Test that library flags are serialized and read correctly.
diff --git a/pkg/kernel/test/binary/utils.dart b/pkg/kernel/test/binary/utils.dart
index 4253db8..1005909 100644
--- a/pkg/kernel/test/binary/utils.dart
+++ b/pkg/kernel/test/binary/utils.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'dart:io' show BytesBuilder;
 
 import 'package:kernel/binary/ast_to_binary.dart' show BinaryPrinter;
diff --git a/pkg/kernel/test/binary_bench.dart b/pkg/kernel/test/binary_bench.dart
index 75834e6..3c63ecd 100644
--- a/pkg/kernel/test/binary_bench.dart
+++ b/pkg/kernel/test/binary_bench.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 // This files contains methods for benchmarking Kernel binary serialization
 // and deserialization routines.
 
@@ -35,8 +33,8 @@
   },
 };
 
-Benchmark benchmark;
-File sourceDill;
+Benchmark? benchmark;
+late File sourceDill;
 bool forGolem = false;
 bool forRaw = false;
 
@@ -47,7 +45,7 @@
   }
 
   final bytes = sourceDill.readAsBytesSync();
-  benchmark(bytes);
+  benchmark!(bytes);
 }
 
 const warmupIterations = 100;
@@ -64,7 +62,8 @@
   }
   final warmupUs = sw.elapsedMicroseconds / warmupIterations;
 
-  final runsUs = new List<int>.filled(benchmarkIterations, null);
+  final runsUs =
+      new List<int>.filled(benchmarkIterations, /* dummy value = */ 0);
   for (var i = 0; i < benchmarkIterations; i++) {
     sw.reset();
     _fromBinary(bytes, eager: eager);
@@ -88,7 +87,8 @@
   }
   final warmupUs = sw.elapsedMicroseconds / warmupIterations;
 
-  final runsUs = new List<int>.filled(benchmarkIterations, null);
+  final runsUs =
+      new List<int>.filled(benchmarkIterations, /* dummy value = */ 0);
   for (var i = 0; i < benchmarkIterations; i++) {
     sw.reset();
     _toBinary(p);
@@ -106,7 +106,7 @@
 
   BenchmarkResult(this.name, this.coldRunUs, this.warmupUs, this.runsUs);
 
-  static T add<T extends num>(T x, T y) => x + y;
+  static T add<T extends num>(T x, T y) => x + y as T;
 
   void report() {
     runsUs.sort();
diff --git a/pkg/kernel/test/class_hierarchy_basic.dart b/pkg/kernel/test/class_hierarchy_basic.dart
index 1a9b34e..78ca0c5 100644
--- a/pkg/kernel/test/class_hierarchy_basic.dart
+++ b/pkg/kernel/test/class_hierarchy_basic.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 library kernel.class_hierarchy_basic;
 
 import 'package:kernel/class_hierarchy.dart';
@@ -97,19 +95,19 @@
     superMixtures[node] = new Set<Class>()..add(node);
     supertypes[node] = new Set<Class>()..add(node);
     if (node.supertype != null) {
-      buildSuperTypeSets(node.supertype.classNode);
-      superclasses[node].addAll(superclasses[node.supertype.classNode]);
-      superMixtures[node].addAll(superMixtures[node.supertype.classNode]);
-      supertypes[node].addAll(supertypes[node.supertype.classNode]);
+      buildSuperTypeSets(node.supertype!.classNode);
+      superclasses[node]!.addAll(superclasses[node.supertype!.classNode]!);
+      superMixtures[node]!.addAll(superMixtures[node.supertype!.classNode]!);
+      supertypes[node]!.addAll(supertypes[node.supertype!.classNode]!);
     }
     if (node.mixedInType != null) {
-      buildSuperTypeSets(node.mixedInType.classNode);
-      superMixtures[node].addAll(superMixtures[node.mixedInType.classNode]);
-      supertypes[node].addAll(supertypes[node.mixedInType.classNode]);
+      buildSuperTypeSets(node.mixedInType!.classNode);
+      superMixtures[node]!.addAll(superMixtures[node.mixedInType!.classNode]!);
+      supertypes[node]!.addAll(supertypes[node.mixedInType!.classNode]!);
     }
     for (var supertype in node.implementedTypes) {
       buildSuperTypeSets(supertype.classNode);
-      supertypes[node].addAll(supertypes[supertype.classNode]);
+      supertypes[node]!.addAll(supertypes[supertype.classNode]!);
     }
     classes.add(node);
     classIndex[node] = classes.length - 1;
@@ -125,8 +123,8 @@
       buildSuperTypeInstantiations(superclass);
       var substitution = Substitution.fromPairs(
           superclass.typeParameters, supertype.typeArguments);
-      supertypeInstantiations[superclass].forEach((key, type) {
-        supertypeInstantiations[node][key] =
+      supertypeInstantiations[superclass]!.forEach((key, type) {
+        supertypeInstantiations[node]![key] =
             substitution.substituteSupertype(type);
       });
     }
@@ -137,25 +135,26 @@
     gettersAndCalls[node] = <Name, Member>{};
     setters[node] = <Name, Member>{};
     if (node.supertype != null) {
-      buildDispatchTable(node.supertype.classNode);
-      gettersAndCalls[node].addAll(gettersAndCalls[node.supertype.classNode]);
-      setters[node].addAll(setters[node.supertype.classNode]);
+      buildDispatchTable(node.supertype!.classNode);
+      gettersAndCalls[node]!
+          .addAll(gettersAndCalls[node.supertype!.classNode]!);
+      setters[node]!.addAll(setters[node.supertype!.classNode]!);
     }
     // Overwrite map entries with declared members.
     Class mixin = node.mixedInType?.classNode ?? node;
     for (Procedure procedure in mixin.procedures) {
       if (procedure.isStatic || procedure.isAbstract) continue;
       if (procedure.kind == ProcedureKind.Setter) {
-        setters[node][procedure.name] = procedure;
+        setters[node]![procedure.name] = procedure;
       } else {
-        gettersAndCalls[node][procedure.name] = procedure;
+        gettersAndCalls[node]![procedure.name] = procedure;
       }
     }
     for (Field field in mixin.fields) {
       if (field.isStatic) continue;
-      gettersAndCalls[node][field.name] = field;
+      gettersAndCalls[node]![field.name] = field;
       if (!field.isFinal) {
-        setters[node][field.name] = field;
+        setters[node]![field.name] = field;
       }
     }
   }
@@ -163,7 +162,7 @@
   void mergeMaps(
       Map<Name, List<Member>> source, Map<Name, List<Member>> destination) {
     for (var name in source.keys) {
-      destination.putIfAbsent(name, () => <Member>[]).addAll(source[name]);
+      destination.putIfAbsent(name, () => <Member>[]).addAll(source[name]!);
     }
   }
 
@@ -171,12 +170,12 @@
     if (interfaceGettersAndCalls.containsKey(node)) return;
     interfaceGettersAndCalls[node] = <Name, List<Member>>{};
     interfaceSetters[node] = <Name, List<Member>>{};
-    void inheritFrom(Supertype type) {
+    void inheritFrom(Supertype? type) {
       if (type == null) return;
       buildInterfaceTable(type.classNode);
-      mergeMaps(interfaceGettersAndCalls[type.classNode],
-          interfaceGettersAndCalls[node]);
-      mergeMaps(interfaceSetters[type.classNode], interfaceSetters[node]);
+      mergeMaps(interfaceGettersAndCalls[type.classNode]!,
+          interfaceGettersAndCalls[node]!);
+      mergeMaps(interfaceSetters[type.classNode]!, interfaceSetters[node]!);
     }
 
     inheritFrom(node.supertype);
@@ -186,70 +185,70 @@
     for (Procedure procedure in node.mixin.procedures) {
       if (procedure.isStatic) continue;
       if (procedure.kind == ProcedureKind.Setter) {
-        interfaceSetters[node][procedure.name] = <Member>[procedure];
+        interfaceSetters[node]![procedure.name] = <Member>[procedure];
       } else {
-        interfaceGettersAndCalls[node][procedure.name] = <Member>[procedure];
+        interfaceGettersAndCalls[node]![procedure.name] = <Member>[procedure];
       }
     }
     for (Field field in node.mixin.fields) {
       if (field.isStatic) continue;
-      interfaceGettersAndCalls[node][field.name] = <Member>[field];
+      interfaceGettersAndCalls[node]![field.name] = <Member>[field];
       if (!field.isFinal) {
-        interfaceSetters[node][field.name] = <Member>[field];
+        interfaceSetters[node]![field.name] = <Member>[field];
       }
     }
   }
 
   bool isSubclassOf(Class subtype, Class supertype) {
-    return superclasses[subtype].contains(supertype);
+    return superclasses[subtype]!.contains(supertype);
   }
 
   bool isSubmixtureOf(Class subtype, Class supertype) {
-    return superMixtures[subtype].contains(supertype);
+    return superMixtures[subtype]!.contains(supertype);
   }
 
   bool isSubtypeOf(Class subtype, Class supertype) {
-    return supertypes[subtype].contains(supertype);
+    return supertypes[subtype]!.contains(supertype);
   }
 
-  Supertype getClassAsInstanceOf(Class type, Class supertype) {
-    return supertypeInstantiations[type][supertype];
+  Supertype? getClassAsInstanceOf(Class type, Class supertype) {
+    return supertypeInstantiations[type]![supertype];
   }
 
-  Member getDispatchTarget(Class class_, Name name, {bool setter: false}) {
-    return setter ? setters[class_][name] : gettersAndCalls[class_][name];
+  Member? getDispatchTarget(Class class_, Name name, {bool setter: false}) {
+    return setter ? setters[class_]![name] : gettersAndCalls[class_]![name];
   }
 
   List<Member> getDispatchTargets(Class class_, {bool setters: false}) {
     return setters
-        ? this.setters[class_].values
-        : gettersAndCalls[class_].values;
+        ? this.setters[class_]!.values.toList()
+        : gettersAndCalls[class_]!.values.toList();
   }
 
-  Member tryFirst(List<Member> members) {
-    return (members == null || members.isEmpty) ? null : members[0];
+  Member? tryFirst(Iterable<Member>? members) {
+    return (members == null || members.isEmpty) ? null : members.first;
   }
 
-  Member getInterfaceMember(Class class_, Name name, {bool setter: false}) {
+  Member? getInterfaceMember(Class class_, Name name, {bool setter: false}) {
     return tryFirst(getInterfaceMembersByName(class_, name, setter: setter));
   }
 
   Iterable<Member> getInterfaceMembersByName(Class class_, Name name,
       {bool setter: false}) {
     var iterable = setter
-        ? interfaceSetters[class_][name]
-        : interfaceGettersAndCalls[class_][name];
+        ? interfaceSetters[class_]![name]
+        : interfaceGettersAndCalls[class_]![name];
     return iterable == null ? const <Member>[] : iterable;
   }
 
   List<Member> getInterfaceMembers(Class class_, {bool setters: false}) {
     return setters
-        ? interfaceSetters[class_].values.expand((x) => x)
-        : interfaceGettersAndCalls[class_].values.expand((x) => x);
+        ? interfaceSetters[class_]!.values.expand((x) => x).toList()
+        : interfaceGettersAndCalls[class_]!.values.expand((x) => x).toList();
   }
 
   int getClassIndex(Class node) {
-    return classIndex[node];
+    return classIndex[node]!;
   }
 
   List<int> getExpenseHistogram() => <int>[];
diff --git a/pkg/kernel/test/class_hierarchy_bench.dart b/pkg/kernel/test/class_hierarchy_bench.dart
index 97d3dcd..f6bf037 100644
--- a/pkg/kernel/test/class_hierarchy_bench.dart
+++ b/pkg/kernel/test/class_hierarchy_bench.dart
@@ -3,8 +3,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:kernel/kernel.dart';
 import 'package:kernel/class_hierarchy.dart';
 import 'package:kernel/core_types.dart';
@@ -61,7 +59,8 @@
   int hierarchyCount = int.parse(options['cycle']);
   var hierarchies = <ClosedWorldClassHierarchy>[];
   for (int i = 0; i < hierarchyCount; i++) {
-    hierarchies.add(buildHierarchy());
+    // TODO(johnniwinther): This doesn't work for the [BasicClassHierarchy].
+    hierarchies.add(buildHierarchy() as ClosedWorldClassHierarchy);
   }
 
   List<Class> classes = hierarchies.first.classes.toList();
@@ -246,13 +245,13 @@
     classIds[class_] = classIds.length;
   }
 
-  List<int> depth = new List.filled(classes.length, null);
+  List<int> depth = new List.filled(classes.length, /* dummy value = */ 0);
   for (int i = 0; i < depth.length; ++i) {
     int parentDepth = 0;
     var classNode = classes[i];
     for (var supertype in classNode.supers) {
       var superclass = supertype.classNode;
-      int index = classIds[superclass];
+      int index = classIds[superclass]!;
       if (!(index < i)) {
         throw '${classNode.name}($i) extends ${superclass.name}($index)';
       }
@@ -264,7 +263,7 @@
   List<int> depthHistogram = getHistogramOf(depth);
   double averageDepth = average(depth);
   double medianDepth = median(depth);
-  int totalDepth = sum(depth);
+  int totalDepth = sum(depth) as int;
 
   int numberOfClasses = classes.length;
   String expenseHistogram =
diff --git a/pkg/kernel/test/class_hierarchy_membench.dart b/pkg/kernel/test/class_hierarchy_membench.dart
index 2c65048..0e6aefa 100644
--- a/pkg/kernel/test/class_hierarchy_membench.dart
+++ b/pkg/kernel/test/class_hierarchy_membench.dart
@@ -3,8 +3,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:kernel/kernel.dart';
 import 'package:kernel/class_hierarchy.dart';
 import 'package:kernel/core_types.dart';
@@ -53,7 +51,8 @@
 
   List<ClosedWorldClassHierarchy> keepAlive = <ClosedWorldClassHierarchy>[];
   for (int i = 0; i < copyCount; ++i) {
-    keepAlive.add(buildHierarchy());
+    // TODO(johnniwinther): This doesn't work for the [BasicClassHierarchy].
+    keepAlive.add(buildHierarchy() as ClosedWorldClassHierarchy);
   }
 
   print('$copyCount copies built');
diff --git a/pkg/kernel/test/class_hierarchy_self_check.dart b/pkg/kernel/test/class_hierarchy_self_check.dart
index 182a2b7..4cea403 100644
--- a/pkg/kernel/test/class_hierarchy_self_check.dart
+++ b/pkg/kernel/test/class_hierarchy_self_check.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:kernel/kernel.dart';
 import 'package:kernel/class_hierarchy.dart';
 import 'package:kernel/core_types.dart';
@@ -23,7 +21,7 @@
   BasicClassHierarchy basic = new BasicClassHierarchy(component);
   CoreTypes coreTypes = new CoreTypes(component);
   ClosedWorldClassHierarchy classHierarchy =
-      new ClassHierarchy(component, coreTypes);
+      new ClassHierarchy(component, coreTypes) as ClosedWorldClassHierarchy;
   int total = classHierarchy.numberOfClasses;
   int progress = 0;
   for (var class1 in classHierarchy.classes) {
@@ -60,18 +58,18 @@
   progress = 0;
   for (var classNode in classHierarchy.classes) {
     Iterable<Name> candidateNames = <Iterable<Name>>[
-      basic.gettersAndCalls[classNode].keys,
-      basic.setters[classNode].keys,
+      basic.gettersAndCalls[classNode]!.keys,
+      basic.setters[classNode]!.keys,
       pickRandom(nameList, 100)
     ].expand((x) => x);
     for (Name name in candidateNames) {
-      Member expectedGetter =
+      Member? expectedGetter =
           basic.getDispatchTarget(classNode, name, setter: false);
-      Member expectedSetter =
+      Member? expectedSetter =
           basic.getDispatchTarget(classNode, name, setter: true);
-      Member actualGetter =
+      Member? actualGetter =
           classHierarchy.getDispatchTarget(classNode, name, setter: false);
-      Member actualSetter =
+      Member? actualSetter =
           classHierarchy.getDispatchTarget(classNode, name, setter: true);
       if (actualGetter != expectedGetter) {
         fail('lookupGetter($classNode, $name) returned '
@@ -90,18 +88,18 @@
   progress = 0;
   for (var classNode in classHierarchy.classes) {
     Iterable<Name> candidateNames = [
-      basic.interfaceGettersAndCalls[classNode].keys,
-      basic.interfaceSetters[classNode].keys,
+      basic.interfaceGettersAndCalls[classNode]!.keys,
+      basic.interfaceSetters[classNode]!.keys,
       pickRandom(nameList, 100)
     ].expand((x) => x);
     for (Name name in candidateNames) {
-      Member expectedGetter =
+      Member? expectedGetter =
           basic.getInterfaceMember(classNode, name, setter: false);
-      Member expectedSetter =
+      Member? expectedSetter =
           basic.getInterfaceMember(classNode, name, setter: true);
-      Member actualGetter =
+      Member? actualGetter =
           classHierarchy.getInterfaceMember(classNode, name, setter: false);
-      Member actualSetter =
+      Member? actualSetter =
           classHierarchy.getInterfaceMember(classNode, name, setter: true);
       if (actualGetter != expectedGetter) {
         fail('getInterfaceMember($classNode, $name) returned '
diff --git a/pkg/kernel/test/class_hierarchy_test.dart b/pkg/kernel/test/class_hierarchy_test.dart
index 65b263d..f5a2bc5 100644
--- a/pkg/kernel/test/class_hierarchy_test.dart
+++ b/pkg/kernel/test/class_hierarchy_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import "package:expect/minitest.dart";
 
 import "package:kernel/ast.dart";
@@ -82,11 +80,11 @@
 
 class ClosedWorldClassHierarchyTest {
   final Component component = createMockSdkComponent();
-  CoreTypes coreTypes;
+  late CoreTypes coreTypes;
 
-  Library library;
+  late Library library;
 
-  ClassHierarchy _hierarchy;
+  ClassHierarchy? _hierarchy;
 
   ClosedWorldClassHierarchyTest() {
     coreTypes = new CoreTypes(component);
@@ -335,8 +333,9 @@
   /// The [TypeParameterType]s corresponding to [typeParameterNames] are
   /// passed to optional [extends_] and [implements_] callbacks.
   Class addGenericClass(String name, List<String> typeParameterNames,
-      {Supertype extends_(List<DartType> typeParameterTypes),
-      List<Supertype> implements_(List<DartType> typeParameterTypes)}) {
+      {Supertype Function(List<DartType> typeParameterTypes)? extends_,
+      List<Supertype> Function(List<DartType> typeParameterTypes)?
+          implements_}) {
     var typeParameters = typeParameterNames
         .map((name) => new TypeParameter(
             name, coreTypes.objectLegacyRawType, coreTypes.objectLegacyRawType))
diff --git a/pkg/kernel/test/class_hierarchy_test_disabled.dart b/pkg/kernel/test/class_hierarchy_test_disabled.dart
index 5cba5d7..40155b0 100644
--- a/pkg/kernel/test/class_hierarchy_test_disabled.dart
+++ b/pkg/kernel/test/class_hierarchy_test_disabled.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:kernel/kernel.dart';
 import 'package:test/test.dart';
 import 'class_hierarchy_self_check.dart';
diff --git a/pkg/kernel/test/convert_field_to_setter_getter.dart b/pkg/kernel/test/convert_field_to_setter_getter.dart
index d7e7fd7..900dbf4 100644
--- a/pkg/kernel/test/convert_field_to_setter_getter.dart
+++ b/pkg/kernel/test/convert_field_to_setter_getter.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:kernel/binary/ast_from_binary.dart';
 import 'package:kernel/binary/ast_to_binary.dart';
 import 'binary/utils.dart';
@@ -42,14 +40,14 @@
   // Canonical names are now set: Verify that the field is marked as such,
   // canonical-name-wise.
   String getterCanonicalName = '${field.getterReference.canonicalName}';
-  if (field.getterReference.canonicalName.parent.name != "@getters") {
+  if (field.getterReference.canonicalName!.parent!.name != "@getters") {
     throw "Expected @getters parent, but had "
-        "${field.getterReference.canonicalName.parent.name}";
+        "${field.getterReference.canonicalName!.parent!.name}";
   }
-  String setterCanonicalName = '${field.setterReference.canonicalName}';
-  if (field.setterReference.canonicalName.parent.name != "@setters") {
+  String setterCanonicalName = '${field.setterReference!.canonicalName}';
+  if (field.setterReference!.canonicalName!.parent!.name != "@setters") {
     throw "Expected @setters parent, but had "
-        "${field.setterReference.canonicalName.parent.name}";
+        "${field.setterReference!.canonicalName!.parent!.name}";
   }
 
   // Replace the field with a setter/getter pair.
@@ -65,7 +63,7 @@
   // a setter/getter), the reference wouldn't (because of the way `bindTo` is
   // implemented) actually have it's canonical name set, and serialization
   // wouldn't work.)
-  field.getterReference?.canonicalName?.unbind();
+  field.getterReference.canonicalName?.unbind();
   lib1.addProcedure(getter);
 
   FunctionNode setterFunction = new FunctionNode(new Block([]),
@@ -82,18 +80,18 @@
   List<int> writtenBytesGetterSetter = serialize(lib1, lib2);
   // Canonical names are now set: Verify that the getter/setter is marked as
   // such, canonical-name-wise.
-  if (getter.reference.canonicalName.parent.name != "@getters") {
+  if (getter.reference.canonicalName!.parent!.name != "@getters") {
     throw "Expected @getters parent, but had "
-        "${getter.reference.canonicalName.parent.name}";
+        "${getter.reference.canonicalName!.parent!.name}";
   }
   if ('${getter.reference.canonicalName}' != getterCanonicalName) {
     throw "Unexpected getter canonical name. "
         "Expected $getterCanonicalName, "
         "actual ${getter.reference.canonicalName}.";
   }
-  if (setter.reference.canonicalName.parent.name != "@setters") {
+  if (setter.reference.canonicalName!.parent!.name != "@setters") {
     throw "Expected @setters parent, but had "
-        "${setter.reference.canonicalName.parent.name}";
+        "${setter.reference.canonicalName!.parent!.name}";
   }
   if ('${setter.reference.canonicalName}' != setterCanonicalName) {
     throw "Unexpected setter canonical name. "
@@ -110,7 +108,7 @@
       fileUri: lib1Uri);
   // Important: Unbind any old canonical name
   // (nulling out the canonical name is not enough, see above).
-  fieldReplacement.getterReference?.canonicalName?.unbind();
+  fieldReplacement.getterReference.canonicalName?.unbind();
   fieldReplacement.setterReference?.canonicalName?.unbind();
   lib1.addField(fieldReplacement);
 
@@ -119,15 +117,15 @@
   List<int> writtenBytesFieldNew = serialize(lib1, lib2);
   // Canonical names are now set: Verify that the field is marked as such,
   // canonical-name-wise.
-  if (fieldReplacement.getterReference.canonicalName.parent.name !=
+  if (fieldReplacement.getterReference.canonicalName!.parent!.name !=
       "@getters") {
     throw "Expected @getters parent, but had "
-        "${fieldReplacement.getterReference.canonicalName.parent.name}";
+        "${fieldReplacement.getterReference.canonicalName!.parent!.name}";
   }
-  if (fieldReplacement.setterReference.canonicalName.parent.name !=
+  if (fieldReplacement.setterReference!.canonicalName!.parent!.name !=
       "@setters") {
     throw "Expected @setters parent, but had "
-        "${fieldReplacement.setterReference.canonicalName.parent.name}";
+        "${fieldReplacement.setterReference!.canonicalName!.parent!.name}";
   }
 
   // Load the written stuff and ensure it is as expected.
@@ -188,15 +186,16 @@
 }
 
 Member getSetTarget(Procedure p) {
-  Block block = p.function.body;
-  ExpressionStatement getterStatement = block.statements[0];
-  StaticSet staticSet = getterStatement.expression;
+  Block block = p.function.body as Block;
+  ExpressionStatement getterStatement =
+      block.statements[0] as ExpressionStatement;
+  StaticSet staticSet = getterStatement.expression as StaticSet;
   return staticSet.target;
 }
 
 Member getGetTarget(Procedure p) {
-  Block block = p.function.body;
-  ReturnStatement setterStatement = block.statements[1];
-  StaticGet staticGet = setterStatement.expression;
+  Block block = p.function.body as Block;
+  ReturnStatement setterStatement = block.statements[1] as ReturnStatement;
+  StaticGet staticGet = setterStatement.expression as StaticGet;
   return staticGet.target;
 }
diff --git a/pkg/kernel/test/dart_type_equivalence_test.dart b/pkg/kernel/test/dart_type_equivalence_test.dart
index acf4b96..41a7a01 100644
--- a/pkg/kernel/test/dart_type_equivalence_test.dart
+++ b/pkg/kernel/test/dart_type_equivalence_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import "package:expect/expect.dart" show Expect;
 
 import 'package:kernel/ast.dart';
diff --git a/pkg/kernel/test/flatten_test.dart b/pkg/kernel/test/flatten_test.dart
index 2dd50b8..2c5c656 100644
--- a/pkg/kernel/test/flatten_test.dart
+++ b/pkg/kernel/test/flatten_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import "package:expect/expect.dart" show Expect;
 
 import 'package:kernel/ast.dart';
@@ -62,7 +60,7 @@
 class Test {
   final String input;
   final String output;
-  final String typeParameters;
+  final String? typeParameters;
 
   const Test(this.input, this.output, [this.typeParameters]);
 }
diff --git a/pkg/kernel/test/future_value_type_test.dart b/pkg/kernel/test/future_value_type_test.dart
index f256cfe..9d0e32e 100644
--- a/pkg/kernel/test/future_value_type_test.dart
+++ b/pkg/kernel/test/future_value_type_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import "package:expect/expect.dart" show Expect;
 
 import 'package:kernel/ast.dart';
diff --git a/pkg/kernel/test/graph_test.dart b/pkg/kernel/test/graph_test.dart
index 28668f6..1dc79f9 100644
--- a/pkg/kernel/test/graph_test.dart
+++ b/pkg/kernel/test/graph_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
-// @dart = 2.9
-
 library kernel.test.graph_test;
 
 import 'package:expect/expect.dart' show Expect;
@@ -17,7 +15,7 @@
 
   Iterable<String> get vertices => graph.keys;
 
-  Iterable<String> neighborsOf(String vertex) => graph[vertex];
+  Iterable<String> neighborsOf(String vertex) => graph[vertex]!;
 }
 
 void test(String expected, Map<String, List<String>> graph) {
diff --git a/pkg/kernel/test/heap_test.dart b/pkg/kernel/test/heap_test.dart
index 07f5245..32b294e 100644
--- a/pkg/kernel/test/heap_test.dart
+++ b/pkg/kernel/test/heap_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:kernel/src/heap.dart';
 import 'package:test/test.dart';
 
@@ -36,7 +34,5 @@
 }
 
 class _intHeap extends Heap<int> {
-  _intHeap() : super(0);
-
   bool sortsBefore(int a, int b) => a < b;
 }
diff --git a/pkg/kernel/test/import_table_test.dart b/pkg/kernel/test/import_table_test.dart
index 62c10f0..c64f614 100644
--- a/pkg/kernel/test/import_table_test.dart
+++ b/pkg/kernel/test/import_table_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:kernel/import_table.dart';
 
 main() {
diff --git a/pkg/kernel/test/legacy_erasure_test.dart b/pkg/kernel/test/legacy_erasure_test.dart
index 4e14b3b..24b1a33 100644
--- a/pkg/kernel/test/legacy_erasure_test.dart
+++ b/pkg/kernel/test/legacy_erasure_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import "package:expect/expect.dart" show Expect;
 
 import 'package:kernel/ast.dart';
diff --git a/pkg/kernel/test/load_concat_dill_keeps_source_test.dart b/pkg/kernel/test/load_concat_dill_keeps_source_test.dart
index 0c2dc97..e8debc6 100644
--- a/pkg/kernel/test/load_concat_dill_keeps_source_test.dart
+++ b/pkg/kernel/test/load_concat_dill_keeps_source_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 // Test that 79cc54e51924cd5a6bdc2bd1771f2d0ee7af8899 works as intended.
 
 import 'dart:convert';
@@ -67,16 +65,16 @@
   builder.readComponent(tmp);
   if (tmp.uriToSource[uri1] == null) throw "No data for $uri1";
   if (tmp.uriToSource[uri2] == null) throw "No data for $uri2";
-  if (expect1 && tmp.uriToSource[uri1].source.isEmpty) {
+  if (expect1 && tmp.uriToSource[uri1]!.source.isEmpty) {
     throw "No data for $uri1";
   }
-  if (!expect1 && tmp.uriToSource[uri1].source.isNotEmpty) {
+  if (!expect1 && tmp.uriToSource[uri1]!.source.isNotEmpty) {
     throw "Unexpected data for $uri1";
   }
-  if (expect2 && tmp.uriToSource[uri2].source.isEmpty) {
+  if (expect2 && tmp.uriToSource[uri2]!.source.isEmpty) {
     throw "No data data for $uri2";
   }
-  if (!expect2 && tmp.uriToSource[uri2].source.isNotEmpty) {
+  if (!expect2 && tmp.uriToSource[uri2]!.source.isNotEmpty) {
     throw "Unexpected data for $uri2";
   }
 }
diff --git a/pkg/kernel/test/metadata_test.dart b/pkg/kernel/test/metadata_test.dart
index ed46532..16418c6 100644
--- a/pkg/kernel/test/metadata_test.dart
+++ b/pkg/kernel/test/metadata_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'dart:convert';
 import 'dart:io';
 
@@ -21,10 +19,10 @@
 /// * type representing the first type parameter of its enclosing function
 class Metadata {
   final String string;
-  final Reference _memberRef;
+  final Reference? _memberRef;
   final DartType type;
 
-  Member get member => _memberRef?.asMember;
+  Member? get member => _memberRef?.asMember;
 
   Metadata.forNode(TreeNode n)
       : this(
@@ -36,7 +34,7 @@
   Metadata(this.string, this._memberRef, this.type);
 }
 
-Member getMemberForMetadata(TreeNode node) {
+Member? getMemberForMetadata(TreeNode node) {
   final parent = node.parent;
   if (parent == null) return null;
   if (parent is Member) return parent;
@@ -67,7 +65,7 @@
     sink.writeByteList(utf8.encode(metadata.string));
     sink.writeStringReference(metadata.string);
     sink.writeNullAllowedCanonicalNameReference(
-        metadata.member?.reference?.canonicalName);
+        metadata.member?.reference.canonicalName);
     sink.writeDartType(metadata.type);
   }
 
@@ -116,7 +114,7 @@
 /// [shouldAnnotate] predicate.
 void annotate(Component p, NodePredicate shouldAnnotate) {
   globalDebuggingNames = new NameSystem();
-  final repository = p.metadata[TestMetadataRepository.kTag];
+  final repository = p.metadata[TestMetadataRepository.kTag]!;
   p.accept(new Visitor(shouldAnnotate, (node) {
     repository.mapping[node] = new Metadata.forNode(node);
   }));
@@ -126,7 +124,7 @@
 /// component matching [shouldAnnotate] predicate has correct metadata.
 void validate(Component p, NodePredicate shouldAnnotate) {
   globalDebuggingNames = new NameSystem();
-  final repository = p.metadata[TestMetadataRepository.kTag];
+  final repository = p.metadata[TestMetadataRepository.kTag]!;
   p.accept(new Visitor(shouldAnnotate, (node) {
     final m = repository.mapping[node];
     final expected = new Metadata.forNode(node);
@@ -168,7 +166,7 @@
     final component = fromBinary(platformBinary);
     annotate(component, shouldAnnotate);
     validate(component, shouldAnnotate);
-    expect(component.metadata[TestMetadataRepository.kTag].mapping.length,
+    expect(component.metadata[TestMetadataRepository.kTag]!.mapping.length,
         greaterThan(0));
 
     final annotatedComponentBinary = binaryTransformer(toBinary(component));
@@ -176,7 +174,7 @@
     validate(annotatedComponentFromBinary, shouldAnnotate);
     expect(
         annotatedComponentFromBinary
-            .metadata[TestMetadataRepository.kTag].mapping.length,
+            .metadata[TestMetadataRepository.kTag]!.mapping.length,
         greaterThan(0));
   }
 
diff --git a/pkg/kernel/test/nnbd_top_merge_test.dart b/pkg/kernel/test/nnbd_top_merge_test.dart
index 7fac29a..c6255f1 100644
--- a/pkg/kernel/test/nnbd_top_merge_test.dart
+++ b/pkg/kernel/test/nnbd_top_merge_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import "package:expect/expect.dart" show Expect;
 
 import 'package:kernel/ast.dart';
@@ -129,8 +127,8 @@
     List<String> parts = input.split(' vs ');
     DartType aType = env.parseType(parts[0]);
     DartType bType = env.parseType(parts[1]);
-    DartType expectedOutputType1;
-    DartType expectedOutputType2;
+    DartType? expectedOutputType1;
+    DartType? expectedOutputType2;
     if (output is List) {
       expectedOutputType1 = env.parseType(output[0]);
       expectedOutputType2 = env.parseType(output[1]);
@@ -138,8 +136,8 @@
       expectedOutputType1 = expectedOutputType2 = env.parseType(output);
     }
 
-    void test(DartType a, DartType b, DartType expectedOutputType) {
-      DartType actualOutputType = nnbdTopMerge(env.coreTypes, a, b);
+    void test(DartType a, DartType b, DartType? expectedOutputType) {
+      DartType? actualOutputType = nnbdTopMerge(env.coreTypes, a, b);
       print('nnbdTopMerge($a,$b) = '
           '$actualOutputType (expected=$expectedOutputType)');
       Expect.equals(
diff --git a/pkg/kernel/test/non_null_test.dart b/pkg/kernel/test/non_null_test.dart
index 5a3dca1..3fc2b89 100644
--- a/pkg/kernel/test/non_null_test.dart
+++ b/pkg/kernel/test/non_null_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import "package:expect/expect.dart" show Expect;
 
 import 'package:kernel/ast.dart';
diff --git a/pkg/kernel/test/norm_test.dart b/pkg/kernel/test/norm_test.dart
index 0f2cd38..0e1c9b1 100644
--- a/pkg/kernel/test/norm_test.dart
+++ b/pkg/kernel/test/norm_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import "package:expect/expect.dart" show Expect;
 
 import 'package:kernel/ast.dart';
diff --git a/pkg/kernel/test/regression_40662_test.dart b/pkg/kernel/test/regression_40662_test.dart
deleted file mode 100644
index 77eaf47..0000000
--- a/pkg/kernel/test/regression_40662_test.dart
+++ /dev/null
@@ -1,18 +0,0 @@
-// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-// @dart = 2.9
-
-// Regression test for https://github.com/dart-lang/sdk/issues/40662.
-
-import "package:expect/expect.dart" show Expect;
-
-bar(int a, List<int> b) {
-  Expect.equals(-1, a);
-  Expect.equals(-1, (b[0] - 2));
-}
-
-foo(int x) async => bar(x - 1, x != null ? [x + 1, x + 2, await null] : null);
-
-void main() async => await foo(0);
diff --git a/pkg/kernel/test/relink_test.dart b/pkg/kernel/test/relink_test.dart
index 3f4c9be..47da2a9 100644
--- a/pkg/kernel/test/relink_test.dart
+++ b/pkg/kernel/test/relink_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:kernel/binary/ast_from_binary.dart';
 import 'package:kernel/binary/ast_to_binary.dart';
 import 'package:kernel/src/tool/find_referenced_libraries.dart';
@@ -141,9 +139,11 @@
       Uri.parse('org-dartlang:///main.dart')) {
     throw "Expected main first, got ${component1Prime.libraries[0].importUri}";
   }
-  Block block = component1Prime.libraries[0].procedures[0].function.body;
-  ReturnStatement returnStatement = block.statements[0];
-  StaticInvocation staticInvocation = returnStatement.expression;
+  Block block =
+      component1Prime.libraries[0].procedures[0].function.body as Block;
+  ReturnStatement returnStatement = block.statements[0] as ReturnStatement;
+  StaticInvocation staticInvocation =
+      returnStatement.expression as StaticInvocation;
   Procedure target = staticInvocation.target;
   return target;
 }
diff --git a/pkg/kernel/test/round_trip.dart b/pkg/kernel/test/round_trip.dart
index 3766db0..188a2a1 100644
--- a/pkg/kernel/test/round_trip.dart
+++ b/pkg/kernel/test/round_trip.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 library kernel.round_trip;
 
 import 'dart:io';
@@ -30,7 +28,7 @@
   }
 }
 
-void testRoundTrip(List<int> bytes, List<int> sdkBytes) async {
+Future<void> testRoundTrip(List<int> bytes, List<int>? sdkBytes) async {
   var component = new Component();
   if (sdkBytes != null) {
     var sdk = new Component(nameRoot: component.root);
diff --git a/pkg/kernel/test/round_trip_self_check.dart b/pkg/kernel/test/round_trip_self_check.dart
index da2e0e1..058cef8 100644
--- a/pkg/kernel/test/round_trip_self_check.dart
+++ b/pkg/kernel/test/round_trip_self_check.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 library kernel.round_trip_test;
 
 import 'self_check_util.dart';
diff --git a/pkg/kernel/test/self_check_util.dart b/pkg/kernel/test/self_check_util.dart
index e742142..1ebdd39 100644
--- a/pkg/kernel/test/self_check_util.dart
+++ b/pkg/kernel/test/self_check_util.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'dart:async';
 
 import 'package:kernel/src/tool/batch_util.dart';
diff --git a/pkg/kernel/test/serialize_bench.dart b/pkg/kernel/test/serialize_bench.dart
index 0a413f9..72853ae 100644
--- a/pkg/kernel/test/serialize_bench.dart
+++ b/pkg/kernel/test/serialize_bench.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:kernel/kernel.dart';
 import 'dart:io';
 
diff --git a/pkg/kernel/test/text_serializer_from_kernel_nodes_test.dart b/pkg/kernel/test/text_serializer_from_kernel_nodes_test.dart
index ddc5c9f..fbdcefa 100644
--- a/pkg/kernel/test/text_serializer_from_kernel_nodes_test.dart
+++ b/pkg/kernel/test/text_serializer_from_kernel_nodes_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 library kernel.text_serializer_from_kernel_nodes_test;
 
 import 'package:kernel/ast.dart';
@@ -25,14 +23,17 @@
   final TextSerializer<T> serializer;
 
   TestCase(
-      {this.name,
-      this.node,
-      this.expectation,
-      this.serializer,
-      SerializationState Function() makeSerializationState,
-      DeserializationState Function() makeDeserializationState})
+      {required this.name,
+      required this.node,
+      required this.expectation,
+      required this.serializer,
+      SerializationState Function()? makeSerializationState,
+      DeserializationState Function()? makeDeserializationState})
+      // ignore: unnecessary_null_comparison
       : assert(node != null),
+        // ignore: unnecessary_null_comparison
         assert(expectation != null),
+        // ignore: unnecessary_null_comparison
         assert(serializer != null),
         this.makeSerializationState = makeSerializationState ??
             (() => new SerializationState(new SerializationEnvironment(null))),
@@ -75,12 +76,12 @@
     new TestCase<Statement>(
         name: 'let dynamic x = 42 in let Null x^0 = null in x;',
         node: () {
-          VariableDeclaration outterLetVar = new VariableDeclaration('x',
+          VariableDeclaration outerLetVar = new VariableDeclaration('x',
               type: const DynamicType(), initializer: new IntLiteral(42));
           VariableDeclaration innerLetVar = new VariableDeclaration('x',
               type: const NullType(), initializer: new NullLiteral());
-          return new ExpressionStatement(new Let(outterLetVar,
-              new Let(innerLetVar, new VariableGet(outterLetVar))));
+          return new ExpressionStatement(new Let(outerLetVar,
+              new Let(innerLetVar, new VariableGet(outerLetVar))));
         }(),
         expectation: ''
             '(expr (let "x^0" () (dynamic) (int 42) ()'
@@ -90,11 +91,11 @@
     new TestCase<Statement>(
         name: 'let dynamic x = 42 in let Null x^0 = null in x^0;',
         node: () {
-          VariableDeclaration outterLetVar = new VariableDeclaration('x',
+          VariableDeclaration outerLetVar = new VariableDeclaration('x',
               type: const DynamicType(), initializer: new IntLiteral(42));
           VariableDeclaration innerLetVar = new VariableDeclaration('x',
               type: const NullType(), initializer: new NullLiteral());
-          return new ExpressionStatement(new Let(outterLetVar,
+          return new ExpressionStatement(new Let(outerLetVar,
               new Let(innerLetVar, new VariableGet(innerLetVar))));
         }(),
         expectation: ''
@@ -133,9 +134,10 @@
           node: new ExpressionStatement(new StaticGet(field)),
           expectation: ''
               '(expr (get-static "package:foo/bar.dart::@getters::field"))',
-          makeSerializationState: () => new SerializationState(null),
-          makeDeserializationState: () =>
-              new DeserializationState(null, component.root),
+          makeSerializationState: () =>
+              new SerializationState(new SerializationEnvironment(null)),
+          makeDeserializationState: () => new DeserializationState(
+              new DeserializationEnvironment(null), component.root),
           serializer: statementSerializer);
     }(),
     () {
@@ -150,9 +152,10 @@
           node: new ExpressionStatement(new StaticGet(field)),
           expectation: ''
               '(expr (get-static "package:foo/bar.dart::@getters::field"))',
-          makeSerializationState: () => new SerializationState(null),
-          makeDeserializationState: () =>
-              new DeserializationState(null, component.root),
+          makeSerializationState: () =>
+              new SerializationState(new SerializationEnvironment(null)),
+          makeDeserializationState: () => new DeserializationState(
+              new DeserializationEnvironment(null), component.root),
           serializer: statementSerializer);
     }(),
     () {
@@ -169,9 +172,10 @@
           expectation: ''
               '(expr'
               ' (set-static "package:foo/bar.dart::@setters::field" (int 1)))',
-          makeSerializationState: () => new SerializationState(null),
-          makeDeserializationState: () =>
-              new DeserializationState(null, component.root),
+          makeSerializationState: () =>
+              new SerializationState(new SerializationEnvironment(null)),
+          makeDeserializationState: () => new DeserializationState(
+              new DeserializationEnvironment(null), component.root),
           serializer: statementSerializer);
     }(),
     () {
@@ -197,9 +201,10 @@
           expectation: ''
               '(expr (invoke-static "package:foo/bar.dart::@methods::foo"'
               ' () ((int 42)) ()))',
-          makeSerializationState: () => new SerializationState(null),
-          makeDeserializationState: () =>
-              new DeserializationState(null, component.root),
+          makeSerializationState: () =>
+              new SerializationState(new SerializationEnvironment(null)),
+          makeDeserializationState: () => new DeserializationState(
+              new DeserializationEnvironment(null), component.root),
           serializer: statementSerializer);
     }(),
     () {
@@ -222,9 +227,10 @@
               '(expr (invoke-const-static'
               ' "package:foo/bar.dart::A::@factories::foo"'
               ' () () ()))',
-          makeSerializationState: () => new SerializationState(null),
-          makeDeserializationState: () =>
-              new DeserializationState(null, component.root),
+          makeSerializationState: () =>
+              new SerializationState(new SerializationEnvironment(null)),
+          makeDeserializationState: () => new DeserializationState(
+              new DeserializationEnvironment(null), component.root),
           serializer: statementSerializer);
     }(),
     () {
@@ -365,9 +371,10 @@
               '(expr (invoke-constructor'
               ' "package:foo/bar.dart::A::@constructors::foo"'
               ' () () ()))',
-          makeSerializationState: () => new SerializationState(null),
-          makeDeserializationState: () =>
-              new DeserializationState(null, component.root),
+          makeSerializationState: () =>
+              new SerializationState(new SerializationEnvironment(null)),
+          makeDeserializationState: () => new DeserializationState(
+              new DeserializationEnvironment(null), component.root),
           serializer: statementSerializer);
     }(),
     () {
@@ -387,13 +394,14 @@
               '(expr (invoke-const-constructor'
               ' "package:foo/bar.dart::A::@constructors::foo"'
               ' () () ()))',
-          makeSerializationState: () => new SerializationState(null),
-          makeDeserializationState: () =>
-              new DeserializationState(null, component.root),
+          makeSerializationState: () =>
+              new SerializationState(new SerializationEnvironment(null)),
+          makeDeserializationState: () => new DeserializationState(
+              new DeserializationEnvironment(null), component.root),
           serializer: statementSerializer);
     }(),
     () {
-      TypeParameter outterParam =
+      TypeParameter outerParam =
           new TypeParameter('T', const DynamicType(), const DynamicType());
       TypeParameter innerParam =
           new TypeParameter('T', const DynamicType(), const DynamicType());
@@ -407,9 +415,9 @@
                     Nullability.legacy,
                     typeParameters: [innerParam])
               ],
-              new TypeParameterType(outterParam, Nullability.legacy),
+              new TypeParameterType(outerParam, Nullability.legacy),
               Nullability.legacy,
-              typeParameters: [outterParam]))),
+              typeParameters: [outerParam]))),
           expectation: ''
               '(expr (type (-> ("T^0") ((dynamic)) ((dynamic)) '
               '((-> ("T^1") ((dynamic)) ((dynamic)) () () () '
@@ -417,7 +425,7 @@
           makeSerializationState: () =>
               new SerializationState(new SerializationEnvironment(null)),
           makeDeserializationState: () => new DeserializationState(
-              new DeserializationEnvironment(null), null),
+              new DeserializationEnvironment(null), new CanonicalName.root()),
           serializer: statementSerializer);
     }(),
     () {
@@ -444,7 +452,7 @@
           makeSerializationState: () =>
               new SerializationState(new SerializationEnvironment(null)),
           makeDeserializationState: () => new DeserializationState(
-              new DeserializationEnvironment(null), null),
+              new DeserializationEnvironment(null), new CanonicalName.root()),
           serializer: statementSerializer);
     }(),
     () {
@@ -471,7 +479,7 @@
           makeSerializationState: () =>
               new SerializationState(new SerializationEnvironment(null)),
           makeDeserializationState: () => new DeserializationState(
-              new DeserializationEnvironment(null), null),
+              new DeserializationEnvironment(null), component.root),
           serializer: memberSerializer);
     }(),
     () {
@@ -588,7 +596,7 @@
           "  but expected:\n    ${testCase.expectation}");
     }
 
-    TreeNode deserialized =
+    Node deserialized =
         testCase.readNode(roundTripInput, testCase.makeDeserializationState());
     String roundTripOutput =
         testCase.writeNode(deserialized, testCase.makeSerializationState());
diff --git a/pkg/kernel/test/text_serializer_test.dart b/pkg/kernel/test/text_serializer_test.dart
index 0a3f209..ff8f0506 100644
--- a/pkg/kernel/test/text_serializer_test.dart
+++ b/pkg/kernel/test/text_serializer_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 library kernel.text_serializer_test;
 
 import 'package:kernel/ast.dart';
@@ -27,7 +25,9 @@
   TextIterator stream = new TextIterator(input, 0);
   stream.moveNext();
   Expression result = expressionSerializer.readFrom(
-      stream, new DeserializationState(null, new CanonicalName.root()));
+      stream,
+      new DeserializationState(
+          new DeserializationEnvironment(null), new CanonicalName.root()));
   if (stream.moveNext()) {
     throw StateError("extra cruft in basic literal");
   }
@@ -36,8 +36,8 @@
 
 String writeExpression(Expression expression) {
   StringBuffer buffer = new StringBuffer();
-  expressionSerializer.writeTo(
-      buffer, expression, new SerializationState(null));
+  expressionSerializer.writeTo(buffer, expression,
+      new SerializationState(new SerializationEnvironment(null)));
   return buffer.toString();
 }
 
diff --git a/pkg/kernel/test/type_hashcode_quality.dart b/pkg/kernel/test/type_hashcode_quality.dart
index f33541e..8bf1f34 100644
--- a/pkg/kernel/test/type_hashcode_quality.dart
+++ b/pkg/kernel/test/type_hashcode_quality.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:kernel/kernel.dart';
 import 'dart:io';
 
@@ -40,7 +38,7 @@
     if (hash == 0) {
       print('Type has a hash code of zero: $node');
     }
-    DartType existing = table[hash];
+    DartType? existing = table[hash];
     if (existing == null) {
       table[hash] = node;
     } else if (existing != node) {
diff --git a/pkg/kernel/test/type_hashcode_test.dart b/pkg/kernel/test/type_hashcode_test.dart
index 9a16a72..8d13fe6 100644
--- a/pkg/kernel/test/type_hashcode_test.dart
+++ b/pkg/kernel/test/type_hashcode_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:kernel/kernel.dart';
 import 'type_parser.dart';
 import 'package:test/test.dart';
@@ -55,11 +53,13 @@
   String type1;
   String type2;
   Iterable<String> quantifiedVariables;
-  Map<String, String> expectedSubstitution; // Null if unification should fail.
+  Map<String, String?>?
+      expectedSubstitution; // Null if unification should fail.
 
-  TestCase.success(this.type1, this.type2, this.expectedSubstitution) {
-    quantifiedVariables = expectedSubstitution.keys;
-  }
+  TestCase.success(
+      this.type1, this.type2, Map<String, String?> expectedSubstitution)
+      : this.expectedSubstitution = expectedSubstitution,
+        this.quantifiedVariables = expectedSubstitution.keys;
 
   TestCase.fail(this.type1, this.type2, this.quantifiedVariables);
 
@@ -68,7 +68,7 @@
   String toString() => '∃ ${quantifiedVariables.join(',')}. $type1 = $type2';
 }
 
-TestCase successCase(String type1, String type2, Map<String, String> expected,
+TestCase successCase(String type1, String type2, Map<String, String?> expected,
     {bool debug: false}) {
   return new TestCase.success(type1, type2, expected);
 }
diff --git a/pkg/kernel/test/type_parser.dart b/pkg/kernel/test/type_parser.dart
index 67a4c05..52401b9 100644
--- a/pkg/kernel/test/type_parser.dart
+++ b/pkg/kernel/test/type_parser.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 // A very simple parser for a subset of DartTypes for use in testing type
 // algebra.
 library kernel.test.type_parser;
@@ -41,14 +39,14 @@
 class DartTypeParser {
   final String string;
   int index = 0;
-  String tokenText;
+  String? tokenText;
   final TypeEnvironment environment;
   final Map<String, TypeParameter> localTypeParameters =
       <String, TypeParameter>{};
 
   DartTypeParser(this.string, this.environment);
 
-  TreeNode lookupType(String name) {
+  TreeNode? lookupType(String name) {
     return localTypeParameters[name] ?? environment(name);
   }
 
@@ -139,8 +137,8 @@
     }
   }
 
-  Nullability parseOptionalNullability(
-      [Nullability defaultNullability = Nullability.nonNullable]) {
+  Nullability? parseOptionalNullability(
+      [Nullability? defaultNullability = Nullability.nonNullable]) {
     int token = peekToken();
     switch (token) {
       case Token.QuestionMark:
@@ -159,23 +157,23 @@
     switch (token) {
       case Token.Name:
         scanToken();
-        String name = this.tokenText;
+        String name = this.tokenText!;
         if (name == 'void') return const VoidType();
         if (name == 'dynamic') return const DynamicType();
         var target = lookupType(name);
         if (target == null) {
           return fail('Unresolved type $name');
         } else if (target is Class) {
-          List<DartType> typeArguments = parseOptionalTypeArgumentList();
-          Nullability nullability = parseOptionalNullability();
+          List<DartType>? typeArguments = parseOptionalTypeArgumentList();
+          Nullability nullability = parseOptionalNullability()!;
           return new InterfaceType(target, nullability, typeArguments);
         } else if (target is Typedef) {
-          List<DartType> typeArguments = parseOptionalTypeArgumentList();
-          Nullability nullability = parseOptionalNullability();
+          List<DartType>? typeArguments = parseOptionalTypeArgumentList();
+          Nullability nullability = parseOptionalNullability()!;
           return new TypedefType(target, nullability, typeArguments);
         } else if (target is TypeParameter) {
-          Nullability nullability = parseOptionalNullability(null);
-          DartType promotedBound;
+          Nullability? nullability = parseOptionalNullability(null);
+          DartType? promotedBound;
           switch (peekToken()) {
             case Token.LeftAngle:
               return fail('Attempt to apply type arguments to a type variable');
@@ -199,7 +197,7 @@
         List<NamedType> namedParameters = <NamedType>[];
         parseParameterList(parameters, namedParameters);
         consumeString('=>');
-        Nullability nullability = parseOptionalNullability();
+        Nullability nullability = parseOptionalNullability()!;
         var returnType = parseType();
         return new FunctionType(parameters, returnType, nullability,
             namedParameters: namedParameters);
@@ -210,7 +208,7 @@
         List<NamedType> namedParameters = <NamedType>[];
         parseParameterList(parameters, namedParameters);
         consumeString('=>');
-        Nullability nullability = parseOptionalNullability();
+        Nullability nullability = parseOptionalNullability()!;
         var returnType = parseType();
         popTypeParameters(typeParameters);
         return new FunctionType(parameters, returnType, nullability,
@@ -246,7 +244,7 @@
     if (type is InterfaceType && type.typeArguments.isEmpty) {
       return type.classNode.name;
     } else if (type is TypeParameterType) {
-      return type.parameter.name;
+      return type.parameter.name!;
     } else {
       return fail('Unexpected colon after $type');
     }
@@ -267,12 +265,12 @@
     return types;
   }
 
-  List<DartType> parseOptionalList(int open, int close) {
+  List<DartType>? parseOptionalList(int open, int close) {
     if (peekToken() != open) return null;
     return parseTypeList(open, close);
   }
 
-  List<DartType> parseOptionalTypeArgumentList() {
+  List<DartType>? parseOptionalTypeArgumentList() {
     return parseOptionalList(Token.LeftAngle, Token.RightAngle);
   }
 
@@ -302,14 +300,14 @@
     if (localTypeParameters.containsKey(typeParameter.name)) {
       return fail('Shadowing a type parameter is not allowed');
     }
-    localTypeParameters[typeParameter.name] = typeParameter;
+    localTypeParameters[typeParameter.name!] = typeParameter;
     var next = peekToken();
     if (next == Token.Colon) {
       scanToken();
       typeParameter.bound = parseType();
     } else {
-      typeParameter.bound =
-          new InterfaceType(lookupType('Object'), Nullability.nullable);
+      typeParameter.bound = new InterfaceType(
+          lookupType('Object') as Class, Nullability.nullable);
     }
     return typeParameter;
   }
@@ -322,7 +320,7 @@
 class LazyTypeEnvironment {
   final Map<String, Class> classes = <String, Class>{};
   final Map<String, TypeParameter> typeParameters = <String, TypeParameter>{};
-  Library dummyLibrary;
+  late final Library dummyLibrary;
   final Component component = new Component();
 
   LazyTypeEnvironment() {
@@ -360,14 +358,14 @@
     for (var typeParameter
         in new DartTypeParser('<$typeParametersList>', lookup)
             .parseAndPushTypeParameterList()) {
-      typeParameters[typeParameter.name] = typeParameter;
+      typeParameters[typeParameter.name!] = typeParameter;
     }
   }
 
   DartType parse(String type) => parseDartType(type, lookup);
 
   Supertype parseSuper(String type) {
-    InterfaceType interfaceType = parse(type);
+    InterfaceType interfaceType = parse(type) as InterfaceType;
     return new Supertype(interfaceType.classNode, interfaceType.typeArguments);
   }
 
@@ -376,9 +374,9 @@
     return parse(type);
   }
 
-  TypeParameter getTypeParameter(String name) {
+  TypeParameter? getTypeParameter(String name) {
     if (name.length != 1) throw 'Type parameter names must have length 1';
-    return lookup(name);
+    return lookup(name) as TypeParameter?;
   }
 }
 
diff --git a/pkg/kernel/test/type_parser_test.dart b/pkg/kernel/test/type_parser_test.dart
index e015daa..5a2e651 100644
--- a/pkg/kernel/test/type_parser_test.dart
+++ b/pkg/kernel/test/type_parser_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:expect/expect.dart' show Expect;
 
 import 'package:kernel/testing/type_parser.dart';
diff --git a/pkg/kernel/test/type_substitute_bounds_test.dart b/pkg/kernel/test/type_substitute_bounds_test.dart
index c92d17a..ca16ac0 100644
--- a/pkg/kernel/test/type_substitute_bounds_test.dart
+++ b/pkg/kernel/test/type_substitute_bounds_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 library kernel.type_substitute_bounds_test;
 
 import 'package:kernel/kernel.dart';
@@ -45,7 +43,7 @@
 
   String toString() {
     var substitution = bounds.keys.map((key) {
-      var bound = bounds[key];
+      var bound = bounds[key]!;
       return '${bound.lower} <: $key <: ${bound.upper}';
     }).join(',');
     return '$type [$substitution] <: $expected';
@@ -72,7 +70,7 @@
       var upperBounds = <TypeParameter, DartType>{};
       var lowerBounds = <TypeParameter, DartType>{};
       testCase.bounds.forEach((String name, TypeBound bounds) {
-        var parameter = environment.getTypeParameter(name);
+        var parameter = environment.getTypeParameter(name)!;
         upperBounds[parameter] = environment.parse(bounds.upper);
         lowerBounds[parameter] = environment.parse(bounds.lower);
       });
diff --git a/pkg/kernel/test/type_substitution_identity_test.dart b/pkg/kernel/test/type_substitution_identity_test.dart
index 99d7fe7..d8fabbd 100644
--- a/pkg/kernel/test/type_substitution_identity_test.dart
+++ b/pkg/kernel/test/type_substitution_identity_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:kernel/kernel.dart';
 import 'package:kernel/type_algebra.dart';
 import 'type_parser.dart';
diff --git a/pkg/kernel/test/typedef_unalias_test.dart b/pkg/kernel/test/typedef_unalias_test.dart
index aded3c3..196ac3f 100644
--- a/pkg/kernel/test/typedef_unalias_test.dart
+++ b/pkg/kernel/test/typedef_unalias_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 library kernel.typedef_unalias_test;
 
 import 'package:kernel/ast.dart';
diff --git a/pkg/kernel/test/verify_bench.dart b/pkg/kernel/test/verify_bench.dart
index 6326b89..c5fc42e 100644
--- a/pkg/kernel/test/verify_bench.dart
+++ b/pkg/kernel/test/verify_bench.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'dart:io';
 
 import 'package:kernel/kernel.dart';
diff --git a/pkg/kernel/test/verify_self_check.dart b/pkg/kernel/test/verify_self_check.dart
index bb2cd02..bc9b184 100644
--- a/pkg/kernel/test/verify_self_check.dart
+++ b/pkg/kernel/test/verify_self_check.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:kernel/kernel.dart';
 import 'package:kernel/verifier.dart';
 
diff --git a/pkg/kernel/test/verify_test.dart b/pkg/kernel/test/verify_test.dart
index f1418df..3153b2e 100644
--- a/pkg/kernel/test/verify_test.dart
+++ b/pkg/kernel/test/verify_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:kernel/ast.dart';
 import 'package:kernel/text/ast_to_text.dart';
 import 'package:kernel/verifier.dart';
@@ -30,7 +28,7 @@
       test.addNode(VariableGet(node));
       return node;
     },
-    (Node node) => "Variable '$node' used out of scope.",
+    (Node? node) => "Variable '$node' used out of scope.",
   );
   negative1Test(
     'VariableSet out of scope',
@@ -39,7 +37,7 @@
       test.addNode(VariableSet(variable, new NullLiteral()));
       return variable;
     },
-    (Node node) => "Variable '$node' used out of scope.",
+    (Node? node) => "Variable '$node' used out of scope.",
   );
   negative1Test(
     'Variable block scope',
@@ -51,7 +49,7 @@
       ]));
       return variable;
     },
-    (Node node) => "Variable '$node' used out of scope.",
+    (Node? node) => "Variable '$node' used out of scope.",
   );
   negative1Test(
     'Variable let scope',
@@ -63,7 +61,7 @@
           new VariableGet(variable)));
       return variable;
     },
-    (Node node) => "Variable '$node' used out of scope.",
+    (Node? node) => "Variable '$node' used out of scope.",
   );
   negative1Test(
     'Variable redeclared',
@@ -72,7 +70,7 @@
       test.addNode(Block([variable, variable]));
       return variable;
     },
-    (Node node) => "Variable '$node' declared more than once.",
+    (Node? node) => "Variable '$node' declared more than once.",
   );
   negative1Test(
     'Member redeclared',
@@ -86,7 +84,7 @@
           fileUri: dummyUri));
       return field;
     },
-    (Node node) => "Member '$node' has been declared more than once.",
+    (Node? node) => "Member '$node' has been declared more than once.",
   );
   negative1Test(
     'Class redeclared',
@@ -96,7 +94,7 @@
           otherClass); // Test harness also adds otherClass to component.
       return test.otherClass;
     },
-    (Node node) => "Class '$node' declared more than once.",
+    (Node? node) => "Class '$node' declared more than once.",
   );
   negative1Test(
     'Class type parameter redeclared',
@@ -109,7 +107,7 @@
           fileUri: dummyUri));
       return parameter;
     },
-    (Node node) => "Type parameter '$node' redeclared.",
+    (Node? node) => "Type parameter '$node' redeclared.",
   );
   negative1Test(
     'Member type parameter redeclared',
@@ -124,7 +122,7 @@
 
       return parameter;
     },
-    (Node node) => "Type parameter '$node' redeclared.",
+    (Node? node) => "Type parameter '$node' redeclared.",
   );
   negative2Test(
     'Type parameter out of scope',
@@ -134,7 +132,7 @@
           typeArgument: new TypeParameterType(parameter, Nullability.legacy)));
       return [parameter, null];
     },
-    (Node node, Node parent) =>
+    (Node? node, Node? parent) =>
         "Type parameter '$node' referenced out of scope,"
         " owner is: '$parent'.",
   );
@@ -146,7 +144,7 @@
           TypeLiteral(new TypeParameterType(node, Nullability.legacy)));
       return [node, test.otherClass];
     },
-    (Node node, Node parent) =>
+    (Node? node, Node? parent) =>
         "Type parameter '$node' referenced out of scope,"
         " owner is: '$parent'.",
   );
@@ -164,7 +162,7 @@
 
       return [node, test.enclosingClass];
     },
-    (Node node, Node parent) =>
+    (Node? node, Node? parent) =>
         "Type parameter '$node' referenced from static context,"
         " parent is: '$parent'.",
   );
@@ -179,7 +177,7 @@
           fileUri: dummyUri));
       return [node, test.enclosingClass];
     },
-    (Node node, Node parent) =>
+    (Node? node, Node? parent) =>
         "Type parameter '$node' referenced from static context,"
         " parent is: '$parent'.",
   );
@@ -206,7 +204,7 @@
 
       return [parameter, parent];
     },
-    (Node node, Node parent) =>
+    (Node? node, Node? parent) =>
         "Type parameter '$node' referenced out of scope,"
         " owner is: '${(parent as TreeNode).parent}'.",
   );
@@ -218,7 +216,7 @@
       test.addNode(TypeLiteral(node));
       return node;
     },
-    (Node node) => "Type $node provides 0 type arguments,"
+    (Node? node) => "Type $node provides 0 type arguments,"
         " but the class declares 1 parameters.",
   );
   negative1Test(
@@ -229,7 +227,7 @@
       test.addNode(TypeLiteral(node));
       return node;
     },
-    (Node node) => "Type $node provides 2 type arguments,"
+    (Node? node) => "Type $node provides 2 type arguments,"
         " but the class declares 1 parameters.",
   );
   negative1Test(
@@ -240,7 +238,7 @@
           new TypeLiteral(new InterfaceType(orphan, Nullability.legacy)));
       return orphan;
     },
-    (Node node) => "Dangling reference to '$node', parent is: 'null'.",
+    (Node? node) => "Dangling reference to '$node', parent is: 'null'.",
   );
   negative1Test(
     'Dangling field get',
@@ -249,7 +247,7 @@
       test.addNode(new PropertyGet(new NullLiteral(), orphan.name, orphan));
       return orphan;
     },
-    (Node node) => "Dangling reference to '$node', parent is: 'null'.",
+    (Node? node) => "Dangling reference to '$node', parent is: 'null'.",
   );
   simpleNegativeTest(
     'Missing block parent pointer',
@@ -299,7 +297,7 @@
           StaticInvocation(method, new Arguments([new NullLiteral()])));
       return method;
     },
-    (Node node) => "StaticInvocation with incompatible arguments for"
+    (Node? node) => "StaticInvocation with incompatible arguments for"
         " '$node'.",
   );
   negative1Test(
@@ -316,7 +314,7 @@
       test.addNode(StaticInvocation(method, new Arguments.empty()));
       return method;
     },
-    (Node node) => "StaticInvocation with incompatible arguments for '$node'.",
+    (Node? node) => "StaticInvocation with incompatible arguments for '$node'.",
   );
   negative1Test(
     'StaticInvocation with unmatched named parameter',
@@ -331,7 +329,7 @@
               named: [new NamedExpression('p', new NullLiteral())])));
       return method;
     },
-    (Node node) => "StaticInvocation with incompatible arguments for"
+    (Node? node) => "StaticInvocation with incompatible arguments for"
         " '$node'.",
   );
   negative1Test(
@@ -348,7 +346,7 @@
       test.addNode(StaticInvocation(method, new Arguments.empty()));
       return method;
     },
-    (Node node) => "StaticInvocation with wrong number of type arguments for"
+    (Node? node) => "StaticInvocation with wrong number of type arguments for"
         " '$node'.",
   );
   negative1Test(
@@ -360,7 +358,7 @@
       test.addNode(ConstructorInvocation(constructor, new Arguments.empty()));
       return constructor;
     },
-    (Node node) =>
+    (Node? node) =>
         "ConstructorInvocation with wrong number of type arguments for"
         " '$node'.",
   );
@@ -433,7 +431,7 @@
       test.addNode(typedef_);
       return typedef_;
     },
-    (Node node) => "The typedef '$node' refers to itself",
+    (Node? node) => "The typedef '$node' refers to itself",
   );
   negative1Test(
     'Invalid typedef Foo = `(Foo) => void`',
@@ -446,7 +444,7 @@
       test.addNode(typedef_);
       return typedef_;
     },
-    (Node node) => "The typedef '$node' refers to itself",
+    (Node? node) => "The typedef '$node' refers to itself",
   );
   negative1Test(
     'Invalid typedef Foo = `() => Foo`',
@@ -457,7 +455,7 @@
       test.addNode(typedef_);
       return typedef_;
     },
-    (Node node) => "The typedef '$node' refers to itself",
+    (Node? node) => "The typedef '$node' refers to itself",
   );
   negative1Test(
     'Invalid typedef Foo = C<Foo>',
@@ -468,7 +466,7 @@
       test.addNode(typedef_);
       return typedef_;
     },
-    (Node node) => "The typedef '$node' refers to itself",
+    (Node? node) => "The typedef '$node' refers to itself",
   );
   negative1Test(
     'Invalid typedefs Foo = Bar, Bar = Foo',
@@ -481,7 +479,7 @@
       test.enclosingLibrary.addTypedef(bar);
       return foo;
     },
-    (Node foo) => "The typedef '$foo' refers to itself",
+    (Node? foo) => "The typedef '$foo' refers to itself",
   );
   negative1Test(
     'Invalid typedefs Foo = Bar, Bar = C<Foo>',
@@ -495,7 +493,7 @@
       test.enclosingLibrary.addTypedef(bar);
       return foo;
     },
-    (Node foo) => "The typedef '$foo' refers to itself",
+    (Node? foo) => "The typedef '$foo' refers to itself",
   );
   negative1Test(
     'Invalid typedefs Foo = C<Bar>, Bar = C<Foo>',
@@ -510,7 +508,7 @@
       test.enclosingLibrary.addTypedef(bar);
       return foo;
     },
-    (Node foo) => "The typedef '$foo' refers to itself",
+    (Node? foo) => "The typedef '$foo' refers to itself",
   );
   positiveTest(
     'Valid long typedefs C20 = C19 = ... = C1 = C0 = dynamic',
@@ -541,7 +539,7 @@
       first.type = new TypedefType(typedef_, Nullability.legacy);
       return firstTypedef;
     },
-    (Node node) => "The typedef '$node' refers to itself",
+    (Node? node) => "The typedef '$node' refers to itself",
   );
   positiveTest(
     'Valid typedef Foo<T extends C> = C<T>',
@@ -611,7 +609,7 @@
       test.enclosingLibrary.addTypedef(bar);
       return foo;
     },
-    (Node foo) => "The typedef '$foo' refers to itself",
+    (Node? foo) => "The typedef '$foo' refers to itself",
   );
   negative1Test(
     'Invalid typedef Foo<T extends Foo<dynamic> = C<T>',
@@ -628,7 +626,7 @@
       test.addNode(foo);
       return foo;
     },
-    (Node foo) => "The typedef '$foo' refers to itself",
+    (Node? foo) => "The typedef '$foo' refers to itself",
   );
   negative1Test(
     'Typedef arity error',
@@ -643,7 +641,7 @@
       test.enclosingLibrary.addField(field);
       return typedefType;
     },
-    (Node typedefType) =>
+    (Node? typedefType) =>
         "The typedef type $typedefType provides 0 type arguments,"
         " but the typedef declares 1 parameters.",
   );
@@ -659,7 +657,7 @@
       test.enclosingLibrary.addField(field);
       return foo;
     },
-    (Node foo) => "Dangling reference to '$foo', parent is: 'null'",
+    (Node? foo) => "Dangling reference to '$foo', parent is: 'null'",
   );
   negative1Test(
     'Non-static top-level field',
@@ -668,7 +666,7 @@
       test.enclosingLibrary.addField(field);
       return null;
     },
-    (Node node) => "The top-level field 'field' should be static",
+    (Node? node) => "The top-level field 'field' should be static",
   );
 }
 
@@ -683,21 +681,21 @@
 }
 
 class TestHarness {
-  Component component;
-  Class objectClass;
-  Library stubLibrary;
+  late Component component;
+  late Class objectClass;
+  late Library stubLibrary;
 
-  TypeParameter classTypeParameter;
+  late TypeParameter classTypeParameter;
 
-  Library enclosingLibrary;
-  Class enclosingClass;
-  Procedure enclosingMember;
+  late Library enclosingLibrary;
+  late Class enclosingClass;
+  late Procedure enclosingMember;
 
-  Class otherClass;
+  late Class otherClass;
 
-  InterfaceType objectLegacyRawType;
-  InterfaceType enclosingLegacyRawType;
-  InterfaceType otherLegacyRawType;
+  late InterfaceType objectLegacyRawType;
+  late InterfaceType enclosingLegacyRawType;
+  late InterfaceType otherLegacyRawType;
 
   void addNode(TreeNode node) {
     if (node is Expression) {
@@ -756,7 +754,7 @@
 
   VariableDeclaration makeVariable() => new VariableDeclaration(null);
 
-  TypeParameter makeTypeParameter([String name]) {
+  TypeParameter makeTypeParameter([String? name]) {
     return new TypeParameter(name, objectLegacyRawType, const DynamicType());
   }
 
@@ -802,10 +800,10 @@
   }
 }
 
-negative1Test(String name, Node Function(TestHarness test) nodeProvider,
-    dynamic Function(Node node) matcher) {
+negative1Test(String name, Node? Function(TestHarness test) nodeProvider,
+    dynamic Function(Node? node) matcher) {
   TestHarness testHarness = new TestHarness();
-  Node node = nodeProvider(testHarness);
+  Node? node = nodeProvider(testHarness);
   test(
     name,
     () {
@@ -818,10 +816,10 @@
   );
 }
 
-negative2Test(String name, List<Node> Function(TestHarness test) nodeProvider,
-    dynamic Function(Node node, Node other) matcher) {
+negative2Test(String name, List<Node?> Function(TestHarness test) nodeProvider,
+    dynamic Function(Node? node, Node? other) matcher) {
   TestHarness testHarness = new TestHarness();
-  List<Node> nodes = nodeProvider(testHarness);
+  List<Node?> nodes = nodeProvider(testHarness);
   if (nodes.length != 2) throw "Needs exactly 2 nodes: Node and other!";
   test(
     name,
diff --git a/pkg/kernel/tool/smoke_test_quick.dart b/pkg/kernel/tool/smoke_test_quick.dart
index 6ca6e19..b5a0b9a 100644
--- a/pkg/kernel/tool/smoke_test_quick.dart
+++ b/pkg/kernel/tool/smoke_test_quick.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'dart:io';
 
 final String repoDir = _computeRepoDir();
diff --git a/tools/VERSION b/tools/VERSION
index 69aef05..8235dad 100644
--- a/tools/VERSION
+++ b/tools/VERSION
@@ -27,5 +27,5 @@
 MAJOR 2
 MINOR 14
 PATCH 0
-PRERELEASE 356
+PRERELEASE 357
 PRERELEASE_PATCH 0
\ No newline at end of file