diff --git a/pkg/front_end/analysis_options.yaml b/pkg/front_end/analysis_options.yaml
index b82914b..907c504 100644
--- a/pkg/front_end/analysis_options.yaml
+++ b/pkg/front_end/analysis_options.yaml
@@ -9,6 +9,7 @@
     - curly_braces_in_flow_control_structures
     - prefer_adjacent_string_concatenation
     - unawaited_futures
+    - avoid_void_async
     - recursive_getters
     - avoid_empty_else
     - empty_statements
diff --git a/pkg/front_end/test/ast_nodes_has_to_string_test.dart b/pkg/front_end/test/ast_nodes_has_to_string_test.dart
index 705ed30..d9ddaba 100644
--- a/pkg/front_end/test/ast_nodes_has_to_string_test.dart
+++ b/pkg/front_end/test/ast_nodes_has_to_string_test.dart
@@ -10,7 +10,7 @@
 
 import 'incremental_suite.dart' as helper;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   exitCode = 1;
   Map<Uri, List<Class>> classMap = {};
   Map<Uri, List<Class>> classMapWithOne = {};
diff --git a/pkg/front_end/test/binary_md_vm_tags_and_version_git_test.dart b/pkg/front_end/test/binary_md_vm_tags_and_version_git_test.dart
index 537c165..fb3e464 100644
--- a/pkg/front_end/test/binary_md_vm_tags_and_version_git_test.dart
+++ b/pkg/front_end/test/binary_md_vm_tags_and_version_git_test.dart
@@ -29,7 +29,7 @@
 // Match stuff like "kNullConstant = 0,"
 final RegExp constantTagParser = new RegExp(r"k(\w*)\s*=\s*(\d+)");
 
-void main() async {
+Future<void> main() async {
   File binaryMd = new File("$repoDir/pkg/kernel/binary.md");
   String binaryMdContent = binaryMd.readAsStringSync();
 
diff --git a/pkg/front_end/test/class_hierarchy/class_hierarchy_test.dart b/pkg/front_end/test/class_hierarchy/class_hierarchy_test.dart
index 15e0fa5..4acaf78 100644
--- a/pkg/front_end/test/class_hierarchy/class_hierarchy_test.dart
+++ b/pkg/front_end/test/class_hierarchy/class_hierarchy_test.dart
@@ -13,7 +13,7 @@
 import 'package:kernel/ast.dart';
 import 'package:kernel/core_types.dart';
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve('data'));
   await runTests<Features>(dataDir,
       args: args,
diff --git a/pkg/front_end/test/compile_benchmark_helper.dart b/pkg/front_end/test/compile_benchmark_helper.dart
index 823a7bc..95a8f54 100644
--- a/pkg/front_end/test/compile_benchmark_helper.dart
+++ b/pkg/front_end/test/compile_benchmark_helper.dart
@@ -4,7 +4,7 @@
 
 import '../tool/_fasta/entry_points.dart' show compileEntryPoint;
 
-void main(List<String> arguments) async {
+Future<void> main(List<String> arguments) async {
   await compileEntryPoint(arguments);
   if (numCalls.isNotEmpty) {
     print("[");
diff --git a/pkg/front_end/test/compile_dart2js_with_no_sdk_test.dart b/pkg/front_end/test/compile_dart2js_with_no_sdk_test.dart
index 74bafaa..3e51713 100644
--- a/pkg/front_end/test/compile_dart2js_with_no_sdk_test.dart
+++ b/pkg/front_end/test/compile_dart2js_with_no_sdk_test.dart
@@ -6,7 +6,7 @@
 
 import 'incremental_suite.dart' show TestIncrementalCompiler, getOptions;
 
-void main() async {
+Future<void> main() async {
   final Uri dart2jsUrl = Uri.base.resolve("pkg/compiler/bin/dart2js.dart");
   CompilerOptions options = getOptions();
   options.sdkSummary = options.sdkSummary!.resolve("nonexisting.dill");
diff --git a/pkg/front_end/test/compile_with_no_sdk_test.dart b/pkg/front_end/test/compile_with_no_sdk_test.dart
index d8f45308..0b34d97 100644
--- a/pkg/front_end/test/compile_with_no_sdk_test.dart
+++ b/pkg/front_end/test/compile_with_no_sdk_test.dart
@@ -7,7 +7,7 @@
 
 import 'incremental_suite.dart' show TestIncrementalCompiler, getOptions;
 
-void main() async {
+Future<void> main() async {
   await compile("import 'foo.dart' if (dart.library.bar) 'baz.dart';");
 }
 
diff --git a/pkg/front_end/test/constant_evaluator_benchmark.dart b/pkg/front_end/test/constant_evaluator_benchmark.dart
index 1d6eddd..5a817a6 100644
--- a/pkg/front_end/test/constant_evaluator_benchmark.dart
+++ b/pkg/front_end/test/constant_evaluator_benchmark.dart
@@ -131,7 +131,7 @@
 
 late IncrementalCompiler incrementalCompiler;
 
-void main(List<String> arguments) async {
+Future<void> main(List<String> arguments) async {
   Uri? platformUri;
   Uri mainUri;
   bool nnbd = false;
diff --git a/pkg/front_end/test/covariance_check/covariance_check_test.dart b/pkg/front_end/test/covariance_check/covariance_check_test.dart
index eb7cc24..4f59ddc 100644
--- a/pkg/front_end/test/covariance_check/covariance_check_test.dart
+++ b/pkg/front_end/test/covariance_check/covariance_check_test.dart
@@ -11,7 +11,7 @@
 import 'package:front_end/src/testing/id_testing_utils.dart';
 import 'package:kernel/ast.dart';
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve('data'));
   await runTests<String>(dataDir,
       args: args,
diff --git a/pkg/front_end/test/crashing_test_case_minimizer.dart b/pkg/front_end/test/crashing_test_case_minimizer.dart
index 980721c..c5e60d5 100644
--- a/pkg/front_end/test/crashing_test_case_minimizer.dart
+++ b/pkg/front_end/test/crashing_test_case_minimizer.dart
@@ -19,7 +19,7 @@
 // TODO(jensj): Add asserts or similar where - after each rewrite - we run the
 // parser on it and verifies that no syntax errors have been introduced.
 
-void main(List<String> arguments) async {
+Future<void> main(List<String> arguments) async {
   String filename;
   Uri loadJson;
   for (String arg in arguments) {
diff --git a/pkg/front_end/test/dartdoc_test_test.dart b/pkg/front_end/test/dartdoc_test_test.dart
index a3570f1..455a8cf 100644
--- a/pkg/front_end/test/dartdoc_test_test.dart
+++ b/pkg/front_end/test/dartdoc_test_test.dart
@@ -9,7 +9,7 @@
 
 import "../tool/dart_doctest_impl.dart" as impl;
 
-void main() async {
+Future<void> main() async {
   expectCategory = "comment extraction";
   testCommentExtraction();
 
@@ -20,7 +20,7 @@
   await testRunningTests();
 }
 
-void testRunningTests() async {
+Future<void> testRunningTests() async {
   MemoryFileSystem memoryFileSystem =
       new MemoryFileSystem(new Uri(scheme: "darttest", path: "/"));
   HybridFileSystem hybridFileSystem = new HybridFileSystem(memoryFileSystem);
diff --git a/pkg/front_end/test/desugar_test.dart b/pkg/front_end/test/desugar_test.dart
index 5b7539b2..31089ed 100644
--- a/pkg/front_end/test/desugar_test.dart
+++ b/pkg/front_end/test/desugar_test.dart
@@ -23,7 +23,7 @@
 import 'package:kernel/ast.dart' as ir;
 import 'package:kernel/binary/ast_from_binary.dart' show BinaryBuilder;
 
-void main() async {
+Future<void> main() async {
   await asyncTest(() async {
     await testRedirectingFactoryDirect();
     await testRedirectingFactorySerialized();
diff --git a/pkg/front_end/test/dill_round_trip_test.dart b/pkg/front_end/test/dill_round_trip_test.dart
index 17bbe1d..32d5759 100644
--- a/pkg/front_end/test/dill_round_trip_test.dart
+++ b/pkg/front_end/test/dill_round_trip_test.dart
@@ -15,7 +15,7 @@
 import 'incremental_suite.dart'
     show checkIsEqual, getOptions, normalCompilePlain;
 
-void main() async {
+Future<void> main() async {
   final Uri dart2jsUrl = Uri.base.resolve("pkg/compiler/bin/dart2js.dart");
   Stopwatch stopwatch = new Stopwatch()..start();
   Component compiledComponent = await normalCompilePlain(dart2jsUrl,
diff --git a/pkg/front_end/test/enable_non_nullable/enable_non_nullable_test.dart b/pkg/front_end/test/enable_non_nullable/enable_non_nullable_test.dart
index b15d91f..f5fb221 100644
--- a/pkg/front_end/test/enable_non_nullable/enable_non_nullable_test.dart
+++ b/pkg/front_end/test/enable_non_nullable/enable_non_nullable_test.dart
@@ -20,7 +20,7 @@
 /// The version used in this test as the experiment enabled version.
 const Version experimentEnabledVersion = const Version(2, 10);
 
-void main() async {
+Future<void> main() async {
   print('--------------------------------------------------------------------');
   print('Test off-by-default with command-line flag');
   print('--------------------------------------------------------------------');
@@ -58,7 +58,7 @@
       versionOptsInAllowed: experimentReleaseVersion);
 }
 
-void test(
+Future<void> test(
     {bool enableNonNullableByDefault,
     bool enableNonNullableExplicitly,
     Version versionImpliesOptIn,
diff --git a/pkg/front_end/test/extensions/extensions_test.dart b/pkg/front_end/test/extensions/extensions_test.dart
index c811201..2666476 100644
--- a/pkg/front_end/test/extensions/extensions_test.dart
+++ b/pkg/front_end/test/extensions/extensions_test.dart
@@ -23,7 +23,7 @@
 import 'package:front_end/src/testing/id_testing_utils.dart';
 import 'package:kernel/ast.dart';
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve('data'));
   await runTests<Features>(dataDir,
       args: args,
diff --git a/pkg/front_end/test/fasta/ambiguous_export_test.dart b/pkg/front_end/test/fasta/ambiguous_export_test.dart
index 579a3f8..fa0ef8f 100644
--- a/pkg/front_end/test/fasta/ambiguous_export_test.dart
+++ b/pkg/front_end/test/fasta/ambiguous_export_test.dart
@@ -20,7 +20,7 @@
 import 'package:kernel/ast.dart'
     show Field, Library, Name, Component, StringLiteral;
 
-void main() async {
+Future<void> main() async {
   await asyncTest(() async {
     Uri uri = Uri.parse("org.dartlang.fasta:library");
     Library library = new Library(uri, fileUri: uri);
diff --git a/pkg/front_end/test/fasta/analyze_git_test.dart b/pkg/front_end/test/fasta/analyze_git_test.dart
index 7ccff17..c649729 100644
--- a/pkg/front_end/test/fasta/analyze_git_test.dart
+++ b/pkg/front_end/test/fasta/analyze_git_test.dart
@@ -8,7 +8,7 @@
 
 import "package:testing/src/run_tests.dart" as testing show main;
 
-void main() async {
+Future<void> main() async {
   // This method is async, but keeps a port open to prevent the VM from exiting
   // prematurely.
   // Note: if you change this file, also change
diff --git a/pkg/front_end/test/fasta/analyze_src_with_lints_git_test.dart b/pkg/front_end/test/fasta/analyze_src_with_lints_git_test.dart
index 34ca1e2..b4b0e5f 100644
--- a/pkg/front_end/test/fasta/analyze_src_with_lints_git_test.dart
+++ b/pkg/front_end/test/fasta/analyze_src_with_lints_git_test.dart
@@ -8,7 +8,7 @@
 
 import "package:testing/src/run_tests.dart" as testing show main;
 
-void main() async {
+Future<void> main() async {
   await testing.main(<String>[
     "--config=pkg/front_end/testing_with_lints.json",
     "--verbose",
diff --git a/pkg/front_end/test/fasta/expression_suite.dart b/pkg/front_end/test/fasta/expression_suite.dart
index 793aeb0..d6159f9 100644
--- a/pkg/front_end/test/fasta/expression_suite.dart
+++ b/pkg/front_end/test/fasta/expression_suite.dart
@@ -327,7 +327,7 @@
 
   // Compile [test.expression], update [test.errors] with results.
   // As a side effect - verify that generated procedure can be serialized.
-  void compileExpression(TestCase test, IncrementalCompiler compiler,
+  Future<void> compileExpression(TestCase test, IncrementalCompiler compiler,
       Component component, Context context) async {
     Map<String, DartType> definitions = {};
     for (String name in test.definitions) {
@@ -386,7 +386,7 @@
         context.fileSystem.entityForUri(dillFileUri).writeAsBytesSync(
             await new File.fromUri(dillFileUri).readAsBytes());
       }
-      compileExpression(test, sourceCompiler, component, context);
+      await compileExpression(test, sourceCompiler, component, context);
 
       var dillCompiler =
           new IncrementalCompiler(context.compilerContext, dillFileUri);
@@ -399,7 +399,7 @@
       // Since it compiled successfully from source, the bootstrap-from-Dill
       // should also succeed without errors.
       assert(errors.isEmpty);
-      compileExpression(test, dillCompiler, component, context);
+      await compileExpression(test, dillCompiler, component, context);
     }
     return new Result.pass(tests);
   }
diff --git a/pkg/front_end/test/fasta/generator_to_string_test.dart b/pkg/front_end/test/fasta/generator_to_string_test.dart
index 2888840..b2c4f52 100644
--- a/pkg/front_end/test/fasta/generator_to_string_test.dart
+++ b/pkg/front_end/test/fasta/generator_to_string_test.dart
@@ -65,7 +65,7 @@
   Expect.stringEquals(expected, "$generator");
 }
 
-void main() async {
+Future<void> main() async {
   await CompilerContext.runWithDefaultOptions((CompilerContext c) async {
     Token token = scanString("    myToken").tokens;
     Uri uri = Uri.parse("org-dartlang-test:my_library.dart");
diff --git a/pkg/front_end/test/fasta/object_supertype_test.dart b/pkg/front_end/test/fasta/object_supertype_test.dart
index 62b9210..b588191 100644
--- a/pkg/front_end/test/fasta/object_supertype_test.dart
+++ b/pkg/front_end/test/fasta/object_supertype_test.dart
@@ -80,7 +80,7 @@
       .map((DiagnosticMessage message) => getMessageCodeObject(message).name)
       .toSet();
 
-  void check(String objectHeader, List<Code> expectedCodes) async {
+  Future<void> check(String objectHeader, List<Code> expectedCodes) async {
     List<DiagnosticMessage> messages = (await outline(objectHeader))
         .where((DiagnosticMessage message) =>
             !normalErrors.contains(getMessageCodeObject(message).name))
diff --git a/pkg/front_end/test/fasta/type_inference/factor_type_test.dart b/pkg/front_end/test/fasta/type_inference/factor_type_test.dart
index 65243ed..a365e93 100644
--- a/pkg/front_end/test/fasta/type_inference/factor_type_test.dart
+++ b/pkg/front_end/test/fasta/type_inference/factor_type_test.dart
@@ -102,7 +102,7 @@
       typeToText(type, TypeRepresentation.analyzerNonNullableByDefault);
 }
 
-void main() async {
+Future<void> main() async {
   CompilerOptions options = new CompilerOptions()
     ..explicitExperimentalFlags[ExperimentalFlag.nonNullable] = true;
   InternalCompilerResult result = await compileScript('',
diff --git a/pkg/front_end/test/flutter_gallery_leak_tester.dart b/pkg/front_end/test/flutter_gallery_leak_tester.dart
index 1b5e46b..973961d 100644
--- a/pkg/front_end/test/flutter_gallery_leak_tester.dart
+++ b/pkg/front_end/test/flutter_gallery_leak_tester.dart
@@ -26,7 +26,7 @@
 // but assumes that flutter has been setup as by the script
 // `tools/bots/flutter/compile_flutter.sh`.
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   if (Platform.isWindows) {
     throw "This script cannot run on Windows as it uses non-Windows "
         "assumptions both for the placement of pub packages and the presence "
diff --git a/pkg/front_end/test/generated_files_up_to_date_git_test.dart b/pkg/front_end/test/generated_files_up_to_date_git_test.dart
index 17773be..5161eef 100644
--- a/pkg/front_end/test/generated_files_up_to_date_git_test.dart
+++ b/pkg/front_end/test/generated_files_up_to_date_git_test.dart
@@ -20,7 +20,7 @@
 
 final Uri repoDir = computeRepoDirUri();
 
-void main() async {
+Future<void> main() async {
   messages();
   experimentalFlags();
   directParserAstHelper();
diff --git a/pkg/front_end/test/id_testing/id_testing_test.dart b/pkg/front_end/test/id_testing/id_testing_test.dart
index f3f465f..873dc8e 100644
--- a/pkg/front_end/test/id_testing/id_testing_test.dart
+++ b/pkg/front_end/test/id_testing/id_testing_test.dart
@@ -29,7 +29,7 @@
         Library,
         TreeNode;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve('data'));
   await runTests<String>(dataDir,
       args: args,
diff --git a/pkg/front_end/test/id_tests/assigned_variables_test.dart b/pkg/front_end/test/id_tests/assigned_variables_test.dart
index 53e04d5..1b325de 100644
--- a/pkg/front_end/test/id_tests/assigned_variables_test.dart
+++ b/pkg/front_end/test/id_tests/assigned_variables_test.dart
@@ -18,7 +18,7 @@
 import 'package:front_end/src/testing/id_testing_utils.dart';
 import 'package:kernel/ast.dart' hide Variance;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve(
       '../../../_fe_analyzer_shared/test/flow_analysis/assigned_variables/'
       'data'));
diff --git a/pkg/front_end/test/id_tests/constant_test.dart b/pkg/front_end/test/id_tests/constant_test.dart
index cdf28c3..54eccdb 100644
--- a/pkg/front_end/test/id_tests/constant_test.dart
+++ b/pkg/front_end/test/id_tests/constant_test.dart
@@ -22,7 +22,7 @@
 import 'package:front_end/src/testing/id_testing_utils.dart';
 import 'package:kernel/ast.dart';
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script
       .resolve('../../../_fe_analyzer_shared/test/constants/data'));
   await runTests<String>(dataDir,
diff --git a/pkg/front_end/test/id_tests/definite_assignment_test.dart b/pkg/front_end/test/id_tests/definite_assignment_test.dart
index 09b7584..74afe1e 100644
--- a/pkg/front_end/test/id_tests/definite_assignment_test.dart
+++ b/pkg/front_end/test/id_tests/definite_assignment_test.dart
@@ -14,7 +14,7 @@
 import 'package:front_end/src/testing/id_testing_utils.dart';
 import 'package:kernel/ast.dart' hide Variance;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve(
       '../../../_fe_analyzer_shared/test/flow_analysis/definite_assignment/'
       'data'));
diff --git a/pkg/front_end/test/id_tests/definite_unassignment_test.dart b/pkg/front_end/test/id_tests/definite_unassignment_test.dart
index 2d25641..30d0fb5 100644
--- a/pkg/front_end/test/id_tests/definite_unassignment_test.dart
+++ b/pkg/front_end/test/id_tests/definite_unassignment_test.dart
@@ -14,7 +14,7 @@
 import 'package:front_end/src/testing/id_testing_utils.dart';
 import 'package:kernel/ast.dart' hide Variance;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve(
       '../../../_fe_analyzer_shared/test/flow_analysis/definite_unassignment/'
       'data'));
diff --git a/pkg/front_end/test/id_tests/inferred_type_arguments_test.dart b/pkg/front_end/test/id_tests/inferred_type_arguments_test.dart
index 32f5603..6c5aedc 100644
--- a/pkg/front_end/test/id_tests/inferred_type_arguments_test.dart
+++ b/pkg/front_end/test/id_tests/inferred_type_arguments_test.dart
@@ -14,7 +14,7 @@
 import 'package:front_end/src/testing/id_testing_utils.dart';
 import 'package:kernel/ast.dart' hide Variance;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(
       Platform.script.resolve('../../../_fe_analyzer_shared/test/'
           'inference/inferred_type_arguments/data'));
diff --git a/pkg/front_end/test/id_tests/inferred_variable_types_test.dart b/pkg/front_end/test/id_tests/inferred_variable_types_test.dart
index 3049cb9..91c4800 100644
--- a/pkg/front_end/test/id_tests/inferred_variable_types_test.dart
+++ b/pkg/front_end/test/id_tests/inferred_variable_types_test.dart
@@ -14,7 +14,7 @@
 import 'package:front_end/src/testing/id_testing_utils.dart';
 import 'package:kernel/ast.dart' hide Variance;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(
       Platform.script.resolve('../../../_fe_analyzer_shared/test/'
           'inference/inferred_variable_types/data'));
diff --git a/pkg/front_end/test/id_tests/inheritance_test.dart b/pkg/front_end/test/id_tests/inheritance_test.dart
index f6cdbe5..3d6aba4 100644
--- a/pkg/front_end/test/id_tests/inheritance_test.dart
+++ b/pkg/front_end/test/id_tests/inheritance_test.dart
@@ -20,7 +20,7 @@
 
 const String cfeFromBuilderMarker = 'cfe:builder';
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script
       .resolve('../../../_fe_analyzer_shared/test/inheritance/data'));
   await runTests<String>(dataDir,
diff --git a/pkg/front_end/test/id_tests/nullability_test.dart b/pkg/front_end/test/id_tests/nullability_test.dart
index de14982..d77f169 100644
--- a/pkg/front_end/test/id_tests/nullability_test.dart
+++ b/pkg/front_end/test/id_tests/nullability_test.dart
@@ -10,7 +10,7 @@
 import 'package:front_end/src/testing/id_testing_helper.dart';
 import 'package:kernel/ast.dart' hide Variance;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve(
       '../../../_fe_analyzer_shared/test/flow_analysis/nullability/data'));
   await runTests<String>(dataDir,
diff --git a/pkg/front_end/test/id_tests/reachability_test.dart b/pkg/front_end/test/id_tests/reachability_test.dart
index 288bee9..d486fde 100644
--- a/pkg/front_end/test/id_tests/reachability_test.dart
+++ b/pkg/front_end/test/id_tests/reachability_test.dart
@@ -15,7 +15,7 @@
 import 'package:front_end/src/testing/id_testing_utils.dart';
 import 'package:kernel/ast.dart' hide Variance;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve(
       '../../../_fe_analyzer_shared/test/flow_analysis/reachability/data'));
   await runTests<Set<_ReachabilityAssertion>>(dataDir,
diff --git a/pkg/front_end/test/id_tests/type_promotion_test.dart b/pkg/front_end/test/id_tests/type_promotion_test.dart
index 52e0ec2..fed4245 100644
--- a/pkg/front_end/test/id_tests/type_promotion_test.dart
+++ b/pkg/front_end/test/id_tests/type_promotion_test.dart
@@ -12,7 +12,7 @@
 import 'package:front_end/src/testing/id_testing_utils.dart';
 import 'package:kernel/ast.dart' hide Variance;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script
       .resolve('../../../_fe_analyzer_shared/test/flow_analysis/type_promotion/'
           'data'));
diff --git a/pkg/front_end/test/id_tests/why_not_promoted_test.dart b/pkg/front_end/test/id_tests/why_not_promoted_test.dart
index 8b8d215..ed82ac1 100644
--- a/pkg/front_end/test/id_tests/why_not_promoted_test.dart
+++ b/pkg/front_end/test/id_tests/why_not_promoted_test.dart
@@ -15,7 +15,7 @@
 import 'package:front_end/src/testing/id_testing_utils.dart';
 import 'package:kernel/ast.dart' hide Variance, MapLiteralEntry;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(
       Platform.script.resolve('../../../_fe_analyzer_shared/test/flow_analysis/'
           'why_not_promoted/data'));
diff --git a/pkg/front_end/test/incremental_compiler_leak_test.dart b/pkg/front_end/test/incremental_compiler_leak_test.dart
index 675bee9..a9f3b81 100644
--- a/pkg/front_end/test/incremental_compiler_leak_test.dart
+++ b/pkg/front_end/test/incremental_compiler_leak_test.dart
@@ -12,10 +12,10 @@
 
 const int limit = 10;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   LeakFinder heapHelper = new LeakFinder();
 
-  heapHelper.start([
+  await heapHelper.start([
     "--disable-dart-dev",
     "--enable-asserts",
     Platform.script.resolve("incremental_dart2js_tester.dart").toString(),
diff --git a/pkg/front_end/test/incremental_dart2js_load_from_dill_test.dart b/pkg/front_end/test/incremental_dart2js_load_from_dill_test.dart
index d335bf9..f4b0342 100644
--- a/pkg/front_end/test/incremental_dart2js_load_from_dill_test.dart
+++ b/pkg/front_end/test/incremental_dart2js_load_from_dill_test.dart
@@ -22,7 +22,7 @@
 
 Directory outDir;
 
-void main() async {
+Future<void> main() async {
   outDir =
       Directory.systemTemp.createTempSync("incremental_load_from_dill_test");
   try {
diff --git a/pkg/front_end/test/incremental_dart2js_test.dart b/pkg/front_end/test/incremental_dart2js_test.dart
index be9f6f5..3a36586 100644
--- a/pkg/front_end/test/incremental_dart2js_test.dart
+++ b/pkg/front_end/test/incremental_dart2js_test.dart
@@ -6,7 +6,7 @@
 
 import "incremental_dart2js_tester.dart";
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   bool fast = true;
   bool useExperimentalInvalidation = true;
   bool addDebugBreaks = false;
diff --git a/pkg/front_end/test/incremental_dart2js_tester.dart b/pkg/front_end/test/incremental_dart2js_tester.dart
index 8837c39..3428af3 100644
--- a/pkg/front_end/test/incremental_dart2js_tester.dart
+++ b/pkg/front_end/test/incremental_dart2js_tester.dart
@@ -18,7 +18,7 @@
 
 import "incremental_utils.dart" as util;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   bool fast = false;
   bool useExperimentalInvalidation = false;
   bool addDebugBreaks = false;
@@ -59,7 +59,7 @@
   Dart2jsTester(this.useExperimentalInvalidation, this.fast,
       this.addDebugBreaks, this.limit);
 
-  void test() async {
+  Future<void> test() async {
     helper.TestIncrementalCompiler compiler = await setup();
     if (addDebugBreaks) {
       debugger();
diff --git a/pkg/front_end/test/incremental_flutter_tester.dart b/pkg/front_end/test/incremental_flutter_tester.dart
index 5ebaf9a..3663d30 100644
--- a/pkg/front_end/test/incremental_flutter_tester.dart
+++ b/pkg/front_end/test/incremental_flutter_tester.dart
@@ -46,7 +46,7 @@
   exit(1);
 }
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   bool fast = false;
   bool useExperimentalInvalidation = false;
   File inputFile;
diff --git a/pkg/front_end/test/incremental_load_from_invalid_dill_test.dart b/pkg/front_end/test/incremental_load_from_invalid_dill_test.dart
index 5fd461d..ac40f6e 100644
--- a/pkg/front_end/test/incremental_load_from_invalid_dill_test.dart
+++ b/pkg/front_end/test/incremental_load_from_invalid_dill_test.dart
@@ -73,7 +73,7 @@
   CompilerOptions options;
   IncrementalCompiler compiler;
 
-  void compileExpectInitializeFailAndSpecificWarning(
+  Future<void> compileExpectInitializeFailAndSpecificWarning(
       Code expectedWarningCode, bool writeFileOnCrashReport) async {
     errorMessages.clear();
     warningMessages.clear();
diff --git a/pkg/front_end/test/language_versioning/language_versioning_test.dart b/pkg/front_end/test/language_versioning/language_versioning_test.dart
index c1a9f1c..359c265 100644
--- a/pkg/front_end/test/language_versioning/language_versioning_test.dart
+++ b/pkg/front_end/test/language_versioning/language_versioning_test.dart
@@ -26,7 +26,7 @@
 
 import 'package:kernel/ast.dart' show Component, Library, Version;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   // Fix default/max major and minor version so we can test it.
   // This config sets it to 2.8.
   TestConfigWithLanguageVersion cfeConfig =
diff --git a/pkg/front_end/test/language_versioning/language_versioning_up_to_date_git_test.dart b/pkg/front_end/test/language_versioning/language_versioning_up_to_date_git_test.dart
index 09ddce5..89c3833 100644
--- a/pkg/front_end/test/language_versioning/language_versioning_up_to_date_git_test.dart
+++ b/pkg/front_end/test/language_versioning/language_versioning_up_to_date_git_test.dart
@@ -16,7 +16,7 @@
 
 String get dartVm => Platform.executable;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   ProcessResult result = await Process.run(
       "python3", ["tools/make_version.py", "--no_git", "-q"],
       workingDirectory: repoDir);
diff --git a/pkg/front_end/test/memory_file_system_test.dart b/pkg/front_end/test/memory_file_system_test.dart
index 3792f40..5c20d45 100644
--- a/pkg/front_end/test/memory_file_system_test.dart
+++ b/pkg/front_end/test/memory_file_system_test.dart
@@ -41,18 +41,18 @@
     file = entityForPath(path);
   }
 
-  void test_createDirectory_doesNotExist() async {
+  Future<void> test_createDirectory_doesNotExist() async {
     file.createDirectory();
     expect(await file.exists(), true);
   }
 
-  void test_createDirectory_exists_asDirectory() async {
+  Future<void> test_createDirectory_exists_asDirectory() async {
     file.createDirectory();
     file.createDirectory();
     expect(await file.exists(), true);
   }
 
-  void test_createDirectory_exists_asFile() async {
+  Future<void> test_createDirectory_exists_asFile() async {
     file.writeAsStringSync('');
     await expectLater(file.createDirectory, _throwsFileSystemException);
   }
@@ -65,16 +65,16 @@
     expect(file == entityForPath(join(tempPath, 'file.txt')), isTrue);
   }
 
-  void test_exists_directory_exists() async {
+  Future<void> test_exists_directory_exists() async {
     file.createDirectory();
     expect(await file.exists(), true);
   }
 
-  void test_exists_doesNotExist() async {
+  Future<void> test_exists_doesNotExist() async {
     expect(await file.exists(), false);
   }
 
-  void test_exists_file_exists() async {
+  Future<void> test_exists_file_exists() async {
     file.writeAsStringSync('x');
     expect(await file.exists(), true);
   }
@@ -87,57 +87,57 @@
     expect(file.uri, context.toUri(path));
   }
 
-  void test_readAsBytes_badUtf8() async {
+  Future<void> test_readAsBytes_badUtf8() async {
     // A file containing invalid UTF-8 can still be read as raw bytes.
     List<int> bytes = [0xc0, 0x40]; // Invalid UTF-8
     file.writeAsBytesSync(bytes);
     expect(await file.readAsBytes(), bytes);
   }
 
-  void test_readAsBytes_doesNotExist() async {
+  Future<void> test_readAsBytes_doesNotExist() async {
     await expectLater(file.readAsBytes, _throwsFileSystemException);
   }
 
-  void test_readAsBytes_exists() async {
+  Future<void> test_readAsBytes_exists() async {
     var s = 'contents';
     file.writeAsStringSync(s);
     expect(await file.readAsBytes(), utf8.encode(s));
   }
 
-  void test_readAsString_badUtf8() async {
+  Future<void> test_readAsString_badUtf8() async {
     file.writeAsBytesSync([0xc0, 0x40]); // Invalid UTF-8
     await expectLater(file.readAsString, _throwsFileSystemException);
   }
 
-  void test_readAsString_doesNotExist() async {
+  Future<void> test_readAsString_doesNotExist() async {
     await expectLater(file.readAsString, _throwsFileSystemException);
   }
 
-  void test_readAsString_exists() async {
+  Future<void> test_readAsString_exists() async {
     var s = 'contents';
     file.writeAsStringSync(s);
     expect(await file.readAsString(), s);
   }
 
-  void test_readAsString_utf8() async {
+  Future<void> test_readAsString_utf8() async {
     file.writeAsBytesSync([0xe2, 0x82, 0xac]); // Unicode € symbol, in UTF-8
     expect(await file.readAsString(), '\u20ac');
   }
 
-  void test_writeAsBytesSync_directory() async {
+  Future<void> test_writeAsBytesSync_directory() async {
     file.createDirectory();
     await expectLater(
         () => file.writeAsBytesSync([0]), _throwsFileSystemException);
   }
 
-  void test_writeAsBytesSync_modifyAfterRead() async {
+  Future<void> test_writeAsBytesSync_modifyAfterRead() async {
     // For efficiency we do not make defensive copies.
     file.writeAsBytesSync([1]);
     (await file.readAsBytes())[0] = 2;
     expect(await file.readAsBytes(), [2]);
   }
 
-  void test_writeAsBytesSync_modifyAfterWrite_Uint8List() async {
+  Future<void> test_writeAsBytesSync_modifyAfterWrite_Uint8List() async {
     // For efficiency we do not make defensive copies.
     var bytes = new Uint8List.fromList([1]);
     file.writeAsBytesSync(bytes);
@@ -145,7 +145,7 @@
     expect(await file.readAsBytes(), [2]);
   }
 
-  void test_writeAsBytesSync_modifyAfterWrite() async {
+  Future<void> test_writeAsBytesSync_modifyAfterWrite() async {
     // For efficiency we generally do not make defensive copies, but on the
     // other hrand we keep everything as `Uint8List`s internally, so in this
     // case a copy is actually made.
@@ -155,25 +155,25 @@
     expect(await file.readAsBytes(), [1]);
   }
 
-  void test_writeAsBytesSync_overwrite() async {
+  Future<void> test_writeAsBytesSync_overwrite() async {
     file.writeAsBytesSync([1]);
     file.writeAsBytesSync([2]);
     expect(await file.readAsBytes(), [2]);
   }
 
-  void test_writeAsStringSync_directory() async {
+  Future<void> test_writeAsStringSync_directory() async {
     file.createDirectory();
     await expectLater(
         () => file.writeAsStringSync(''), _throwsFileSystemException);
   }
 
-  void test_writeAsStringSync_overwrite() async {
+  Future<void> test_writeAsStringSync_overwrite() async {
     file.writeAsStringSync('first');
     file.writeAsStringSync('second');
     expect(await file.readAsString(), 'second');
   }
 
-  void test_writeAsStringSync_utf8() async {
+  Future<void> test_writeAsStringSync_utf8() async {
     file.writeAsStringSync('\u20ac'); // Unicode € symbol
     expect(await file.readAsBytes(), [0xe2, 0x82, 0xac]);
   }
@@ -223,7 +223,7 @@
         Uri.parse('$tempUri/file.txt'));
   }
 
-  void test_entityForUri_fileUri_relative() async {
+  Future<void> test_entityForUri_fileUri_relative() async {
     // A weird quirk of the Uri class is that it doesn't seem possible to create
     // a `file:` uri with a relative path, no matter how many slashes you use or
     // if you populate the fields directly.  But just to be certain, try to do
diff --git a/pkg/front_end/test/multiple_simultaneous_compiles_test.dart b/pkg/front_end/test/multiple_simultaneous_compiles_test.dart
index e09aae3..df42515 100644
--- a/pkg/front_end/test/multiple_simultaneous_compiles_test.dart
+++ b/pkg/front_end/test/multiple_simultaneous_compiles_test.dart
@@ -18,7 +18,7 @@
 
 import 'incremental_suite.dart' show getOptions;
 
-void main() async {
+Future<void> main() async {
   Uri compileTarget = Platform.script.resolve("binary_md_dill_reader.dart");
   if (!(new File.fromUri(compileTarget)).existsSync()) {
     throw "$compileTarget doesn't exist";
diff --git a/pkg/front_end/test/patching/patching_test.dart b/pkg/front_end/test/patching/patching_test.dart
index 8ad7d4e..9b7d6d9 100644
--- a/pkg/front_end/test/patching/patching_test.dart
+++ b/pkg/front_end/test/patching/patching_test.dart
@@ -19,7 +19,7 @@
 import 'package:front_end/src/testing/id_testing_utils.dart';
 import 'package:kernel/ast.dart';
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve('data'));
   await runTests<Features>(dataDir,
       args: args,
diff --git a/pkg/front_end/test/predicates/predicate_test.dart b/pkg/front_end/test/predicates/predicate_test.dart
index 2660e72..ec7b50d 100644
--- a/pkg/front_end/test/predicates/predicate_test.dart
+++ b/pkg/front_end/test/predicates/predicate_test.dart
@@ -22,7 +22,7 @@
 const String isNullMarker = 'is-null';
 const String sentinelMarker = 'sentinel';
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve('data'));
   await runTests<Features>(dataDir,
       args: args,
diff --git a/pkg/front_end/test/read_dill_from_binary_md_git_test.dart b/pkg/front_end/test/read_dill_from_binary_md_git_test.dart
index 7d2da16..ec6277b 100644
--- a/pkg/front_end/test/read_dill_from_binary_md_git_test.dart
+++ b/pkg/front_end/test/read_dill_from_binary_md_git_test.dart
@@ -14,7 +14,7 @@
 
 import 'utils/io_utils.dart' show computeRepoDir;
 
-void main() async {
+Future<void> main() async {
   await testDart2jsCompile();
 }
 
diff --git a/pkg/front_end/test/split_dill_test.dart b/pkg/front_end/test/split_dill_test.dart
index f4ebb71..16484f2 100644
--- a/pkg/front_end/test/split_dill_test.dart
+++ b/pkg/front_end/test/split_dill_test.dart
@@ -22,7 +22,7 @@
 
 import 'utils/io_utils.dart' show computeRepoDir;
 
-void main() async {
+Future<void> main() async {
   final Uri dart2jsUrl = Uri.base.resolve("pkg/compiler/bin/dart2js.dart");
   Stopwatch stopwatch = new Stopwatch()..start();
   Component component = await normalCompileToComponent(dart2jsUrl,
diff --git a/pkg/front_end/test/src/base/processed_options_test.dart b/pkg/front_end/test/src/base/processed_options_test.dart
index 529e56b..b771f32 100644
--- a/pkg/front_end/test/src/base/processed_options_test.dart
+++ b/pkg/front_end/test/src/base/processed_options_test.dart
@@ -77,7 +77,7 @@
     expect(processed.fileSystem, same(fileSystem));
   }
 
-  void test_getSdkSummaryBytes_summaryLocationProvided() async {
+  Future<void> test_getSdkSummaryBytes_summaryLocationProvided() async {
     var uri = Uri.parse('org-dartlang-test:///sdkSummary');
 
     writeMockSummaryTo(uri);
@@ -95,7 +95,7 @@
         mockSummary.libraries.single.importUri);
   }
 
-  void test_getSdkSummary_summaryLocationProvided() async {
+  Future<void> test_getSdkSummary_summaryLocationProvided() async {
     var uri = Uri.parse('org-dartlang-test:///sdkSummary');
     writeMockSummaryTo(uri);
     await checkMockSummary(new CompilerOptions()
@@ -116,7 +116,7 @@
         mockSummary.libraries.single.importUri);
   }
 
-  void test_getUriTranslator_explicitLibrariesSpec() async {
+  Future<void> test_getUriTranslator_explicitLibrariesSpec() async {
     fileSystem
         .entityForUri(Uri.parse('org-dartlang-test:///.packages'))
         .writeAsStringSync('');
@@ -134,7 +134,7 @@
         '/bar.dart');
   }
 
-  void test_getUriTranslator_inferredLibrariesSpec() async {
+  Future<void> test_getUriTranslator_inferredLibrariesSpec() async {
     fileSystem
         .entityForUri(Uri.parse('org-dartlang-test:///.packages'))
         .writeAsStringSync('');
@@ -153,7 +153,7 @@
         '/mysdk/lib/bar.dart');
   }
 
-  void test_getUriTranslator_notInferredLibrariesSpec() async {
+  Future<void> test_getUriTranslator_notInferredLibrariesSpec() async {
     fileSystem
         .entityForUri(Uri.parse('org-dartlang-test:///.packages'))
         .writeAsStringSync('');
@@ -178,7 +178,7 @@
     expect(packages.resolve(input), expected);
   }
 
-  void test_getUriTranslator_explicitPackagesFile() async {
+  Future<void> test_getUriTranslator_explicitPackagesFile() async {
     // This .packages file should be ignored.
     fileSystem
         .entityForUri(Uri.parse('org-dartlang-test:///.packages'))
@@ -195,7 +195,8 @@
     checkPackageExpansion('foo', 'baz', uriTranslator.packages);
   }
 
-  void test_getUriTranslator_explicitPackagesFile_withBaseLocation() async {
+  Future<void>
+      test_getUriTranslator_explicitPackagesFile_withBaseLocation() async {
     // This .packages file should be ignored.
     fileSystem
         .entityForUri(Uri.parse('org-dartlang-test:///.packages'))
@@ -214,7 +215,7 @@
     checkPackageExpansion('foo', 'base/location/baz', uriTranslator.packages);
   }
 
-  void test_getUriTranslator_implicitPackagesFile_ambiguous() async {
+  Future<void> test_getUriTranslator_implicitPackagesFile_ambiguous() async {
     // This .packages file should be ignored.
     fileSystem
         .entityForUri(Uri.parse('org-dartlang-test:///.packages'))
@@ -231,7 +232,7 @@
     checkPackageExpansion('foo', 'baz', uriTranslator.packages);
   }
 
-  void test_getUriTranslator_implicitPackagesFile_nextToScript() async {
+  Future<void> test_getUriTranslator_implicitPackagesFile_nextToScript() async {
     // Create the base directory.
     fileSystem
         .entityForUri(Uri.parse('org-dartlang-test:///base/location/'))
@@ -256,7 +257,7 @@
     checkPackageExpansion('foo', 'base/location/baz', uriTranslator.packages);
   }
 
-  void test_getUriTranslator_implicitPackagesFile_searchAbove() async {
+  Future<void> test_getUriTranslator_implicitPackagesFile_searchAbove() async {
     // Create the base directory.
     fileSystem
         .entityForUri(Uri.parse('org-dartlang-test:///base/location/'))
@@ -277,7 +278,8 @@
     checkPackageExpansion('foo', 'base/baz', uriTranslator.packages);
   }
 
-  void test_getUriTranslator_implicitPackagesFile_packagesDirectory() async {
+  Future<void>
+      test_getUriTranslator_implicitPackagesFile_packagesDirectory() async {
     // Create the base directory.
     fileSystem
         .entityForUri(Uri.parse('org-dartlang-test:///base/location/'))
@@ -302,7 +304,7 @@
     checkPackageExpansion('foo', 'base/baz', uriTranslator.packages);
   }
 
-  void test_getUriTranslator_implicitPackagesFile_noPackages() async {
+  Future<void> test_getUriTranslator_implicitPackagesFile_noPackages() async {
     // Create the base directory.
     fileSystem
         .entityForUri(Uri.parse('org-dartlang-test:///base/location/'))
@@ -320,7 +322,7 @@
     expect(uriTranslator.packages.packages, isEmpty);
   }
 
-  void test_getUriTranslator_noPackages() async {
+  Future<void> test_getUriTranslator_noPackages() async {
     var errors = [];
     // .packages file should be ignored.
     fileSystem
@@ -337,7 +339,7 @@
         startsWith(_stringPrefixOf(templateCantReadFile)));
   }
 
-  void test_validateOptions_noInputs() async {
+  Future<void> test_validateOptions_noInputs() async {
     fileSystem
         .entityForUri(Uri.parse('org-dartlang-test:///foo.dart'))
         .writeAsStringSync('main(){}\n');
@@ -351,7 +353,7 @@
     expect(result, isFalse);
   }
 
-  void test_validateOptions_input_doesnt_exist() async {
+  Future<void> test_validateOptions_input_doesnt_exist() async {
     var errors = [];
     var raw = new CompilerOptions()
       ..fileSystem = fileSystem
@@ -363,7 +365,7 @@
     expect(result, isTrue);
   }
 
-  void test_validateOptions_root_exists() async {
+  Future<void> test_validateOptions_root_exists() async {
     var sdkRoot = Uri.parse('org-dartlang-test:///sdk/root/');
     fileSystem
         // Note: this test is a bit hackish because the memory file system
@@ -390,7 +392,7 @@
     expect(result, isTrue);
   }
 
-  void test_validateOptions_root_doesnt_exists() async {
+  Future<void> test_validateOptions_root_doesnt_exists() async {
     fileSystem
         .entityForUri(Uri.parse('org-dartlang-test:///foo.dart'))
         .writeAsStringSync('main(){}\n');
@@ -407,7 +409,7 @@
         startsWith(_stringPrefixOf(templateSdkRootNotFound)));
   }
 
-  void test_validateOptions_summary_exists() async {
+  Future<void> test_validateOptions_summary_exists() async {
     var sdkSummary = Uri.parse('org-dartlang-test:///sdk/root/outline.dill');
     fileSystem.entityForUri(sdkSummary).writeAsStringSync('\n');
     fileSystem
@@ -426,7 +428,7 @@
     expect(result, isTrue);
   }
 
-  void test_validateOptions_summary_doesnt_exists() async {
+  Future<void> test_validateOptions_summary_doesnt_exists() async {
     fileSystem
         .entityForUri(Uri.parse('org-dartlang-test:///foo.dart'))
         .writeAsStringSync('main(){}\n');
@@ -443,7 +445,7 @@
         startsWith(_stringPrefixOf(templateSdkSummaryNotFound)));
   }
 
-  void test_validateOptions_inferred_summary_exists() async {
+  Future<void> test_validateOptions_inferred_summary_exists() async {
     var sdkRoot = Uri.parse('org-dartlang-test:///sdk/root/');
     var sdkSummary =
         Uri.parse('org-dartlang-test:///sdk/root/vm_platform_strong.dill');
@@ -465,7 +467,7 @@
     expect(result, isTrue);
   }
 
-  void test_validateOptions_inferred_summary_doesnt_exists() async {
+  Future<void> test_validateOptions_inferred_summary_doesnt_exists() async {
     var sdkRoot = Uri.parse('org-dartlang-test:///sdk/root/');
     var sdkSummary = Uri.parse('org-dartlang-test:///sdk/root/outline.dill');
     fileSystem.entityForUri(sdkRoot).writeAsStringSync('\n');
diff --git a/pkg/front_end/test/standard_file_system_test.dart b/pkg/front_end/test/standard_file_system_test.dart
index 3769878..c22913c 100644
--- a/pkg/front_end/test/standard_file_system_test.dart
+++ b/pkg/front_end/test/standard_file_system_test.dart
@@ -49,16 +49,16 @@
     expect(dir == entityForPath(p.join(tempPath, 'dir')), isTrue);
   }
 
-  void test_exists_directoryExists() async {
+  Future<void> test_exists_directoryExists() async {
     await new io.Directory(path).create();
     expect(await dir.exists(), isTrue);
   }
 
-  void test_exists_doesNotExist() async {
+  Future<void> test_exists_doesNotExist() async {
     expect(await dir.exists(), isFalse);
   }
 
-  void test_readAsBytes() async {
+  Future<void> test_readAsBytes() async {
     await new io.Directory(path).create();
     await expectLater(dir.readAsBytes, _throwsFileSystemException);
   }
@@ -88,11 +88,11 @@
     expect(file == entityForPath(p.join(tempPath, 'file.txt')), isTrue);
   }
 
-  void test_exists_doesNotExist() async {
+  Future<void> test_exists_doesNotExist() async {
     expect(await file.exists(), isFalse);
   }
 
-  void test_exists_fileExists() async {
+  Future<void> test_exists_fileExists() async {
     new io.File(path).writeAsStringSync('contents');
     expect(await file.exists(), isTrue);
   }
@@ -101,39 +101,39 @@
     expect(file.hashCode, entityForPath(p.join(tempPath, 'file.txt')).hashCode);
   }
 
-  void test_readAsBytes_badUtf8() async {
+  Future<void> test_readAsBytes_badUtf8() async {
     // A file containing invalid UTF-8 can still be read as raw bytes.
     List<int> bytes = [0xc0, 0x40]; // Invalid UTF-8
     new io.File(path).writeAsBytesSync(bytes);
     expect(await file.readAsBytes(), bytes);
   }
 
-  void test_readAsBytes_doesNotExist() async {
+  Future<void> test_readAsBytes_doesNotExist() async {
     await expectLater(file.readAsBytes, _throwsFileSystemException);
   }
 
-  void test_readAsBytes_exists() async {
+  Future<void> test_readAsBytes_exists() async {
     var s = 'contents';
     new io.File(path).writeAsStringSync(s);
     expect(await file.readAsBytes(), utf8.encode(s));
   }
 
-  void test_readAsString_badUtf8() async {
+  Future<void> test_readAsString_badUtf8() async {
     new io.File(path).writeAsBytesSync([0xc0, 0x40]); // Invalid UTF-8
     await expectLater(file.readAsString, _throwsFileSystemException);
   }
 
-  void test_readAsString_doesNotExist() async {
+  Future<void> test_readAsString_doesNotExist() async {
     await expectLater(file.readAsString, _throwsFileSystemException);
   }
 
-  void test_readAsString_exists() async {
+  Future<void> test_readAsString_exists() async {
     var s = 'contents';
     new io.File(path).writeAsStringSync(s);
     expect(await file.readAsString(), s);
   }
 
-  void test_readAsString_utf8() async {
+  Future<void> test_readAsString_utf8() async {
     var bytes = [0xe2, 0x82, 0xac]; // Unicode € symbol (in UTF-8)
     new io.File(path).writeAsBytesSync(bytes);
     expect(await file.readAsString(), '\u20ac');
@@ -206,7 +206,7 @@
     }
   }
 
-  void test_entityForUri_nonFileUri() async {
+  Future<void> test_entityForUri_nonFileUri() async {
     await expectLater(
         () => StandardFileSystem.instance
             .entityForUri(Uri.parse('package:foo/bar.dart')),
@@ -242,7 +242,7 @@
     tempPath = tempDirectory.absolute.path;
   }
 
-  void tearDown() async {
+  Future<void> tearDown() async {
     try {
       tempDirectory.deleteSync(recursive: true);
     } on io.FileSystemException {
@@ -257,7 +257,7 @@
 
 @reflectiveTest
 class DataTest {
-  void test_Data_URIs() async {
+  Future<void> test_Data_URIs() async {
     String string = "<{[DART]}>";
     Uri string_uri = new Uri.dataFromString(string, base64: false);
     Uri string_uri_base64 = new Uri.dataFromString(string, base64: true);
diff --git a/pkg/front_end/test/static_types/analysis_helper.dart b/pkg/front_end/test/static_types/analysis_helper.dart
index 6b41b38..cdfdfcc 100644
--- a/pkg/front_end/test/static_types/analysis_helper.dart
+++ b/pkg/front_end/test/static_types/analysis_helper.dart
@@ -22,7 +22,7 @@
 import 'package:kernel/core_types.dart';
 import 'package:kernel/type_environment.dart';
 
-void run(Uri entryPoint, String allowedListPath,
+Future<void> run(Uri entryPoint, String allowedListPath,
     {bool verbose = false,
     bool generate = false,
     bool analyzedUrisFilter(Uri uri)}) async {
diff --git a/pkg/front_end/test/static_types/cfe_dynamic_test.dart b/pkg/front_end/test/static_types/cfe_dynamic_test.dart
index cda9ff6..ff5e01c 100644
--- a/pkg/front_end/test/static_types/cfe_dynamic_test.dart
+++ b/pkg/front_end/test/static_types/cfe_dynamic_test.dart
@@ -21,7 +21,7 @@
   return false;
 }
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   await run(Uri.base.resolve('pkg/front_end/tool/_fasta/compile.dart'),
       'pkg/front_end/test/static_types/cfe_allowed.json',
       analyzedUrisFilter: cfeOnly,
diff --git a/pkg/front_end/test/static_types/static_type_test.dart b/pkg/front_end/test/static_types/static_type_test.dart
index 7c2d21e..0f168be 100644
--- a/pkg/front_end/test/static_types/static_type_test.dart
+++ b/pkg/front_end/test/static_types/static_type_test.dart
@@ -12,7 +12,7 @@
 import 'package:kernel/ast.dart';
 import 'package:kernel/type_environment.dart';
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve('data'));
   await runTests<String>(dataDir,
       args: args,
diff --git a/pkg/front_end/test/test_generator_test.dart b/pkg/front_end/test/test_generator_test.dart
index f873a70..23c8f54 100644
--- a/pkg/front_end/test/test_generator_test.dart
+++ b/pkg/front_end/test/test_generator_test.dart
@@ -17,7 +17,7 @@
 
 import 'incremental_suite.dart' as helper;
 
-void main() async {
+Future<void> main() async {
   CompilerAndOptions compilerAndOptions = TestCompiler.initialize();
   TestCompiler compiler = compilerAndOptions.compiler;
   bool hasNewline = true;
diff --git a/pkg/front_end/test/text_representation/text_representation_test.dart b/pkg/front_end/test/text_representation/text_representation_test.dart
index ba24ec6..883ac09 100644
--- a/pkg/front_end/test/text_representation/text_representation_test.dart
+++ b/pkg/front_end/test/text_representation/text_representation_test.dart
@@ -64,7 +64,7 @@
   throw new UnsupportedError("Unexpected marker '${marker}'.");
 }
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve('data'));
   await runTests<String>(dataDir,
       args: args,
diff --git a/pkg/front_end/test/tool/reload.dart b/pkg/front_end/test/tool/reload.dart
index 7b783bc..40a94a5 100644
--- a/pkg/front_end/test/tool/reload.dart
+++ b/pkg/front_end/test/tool/reload.dart
@@ -107,7 +107,7 @@
 /// launched with `--observe` to enable the service protocol.
 ///
 // TODO(sigmund): provide flags to configure the vm-service port.
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   if (args.length == 0) {
     print('usage: reload <entry-uri>');
     return;
diff --git a/pkg/front_end/test/unit_test_suites_impl.dart b/pkg/front_end/test/unit_test_suites_impl.dart
index bd7f75f..3376bd2 100644
--- a/pkg/front_end/test/unit_test_suites_impl.dart
+++ b/pkg/front_end/test/unit_test_suites_impl.dart
@@ -495,7 +495,7 @@
   );
 }
 
-void runSuite(SuiteConfiguration configuration) async {
+Future<void> runSuite(SuiteConfiguration configuration) async {
   Suite suite = configuration.suite;
   String name = suite.prefix;
   String fullSuiteName = "$suiteNamePrefix/$name";
@@ -531,7 +531,7 @@
   await File.fromUri(uri).writeAsString(lines.map((line) => "$line\n").join());
 }
 
-void main([List<String> arguments = const <String>[]]) async {
+Future<void> main([List<String> arguments = const <String>[]]) async {
   Stopwatch totalRuntime = new Stopwatch()..start();
 
   List<String> results = [];
diff --git a/pkg/front_end/test/vm_service_coverage.dart b/pkg/front_end/test/vm_service_coverage.dart
index 31e61fe..0d4768a 100644
--- a/pkg/front_end/test/vm_service_coverage.dart
+++ b/pkg/front_end/test/vm_service_coverage.dart
@@ -8,7 +8,7 @@
 
 import 'vm_service_helper.dart' as vmService;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   CoverageHelper coverageHelper = new CoverageHelper();
 
   List<String> allArgs = <String>[];
@@ -19,7 +19,7 @@
   ]);
   allArgs.addAll(args);
 
-  coverageHelper.start(allArgs);
+  await coverageHelper.start(allArgs);
 }
 
 class CoverageHelper extends vmService.LaunchingVMServiceHelper {
diff --git a/pkg/front_end/test/vm_service_coverage_constant_evaluator.dart b/pkg/front_end/test/vm_service_coverage_constant_evaluator.dart
index 1fed414..56b167b 100644
--- a/pkg/front_end/test/vm_service_coverage_constant_evaluator.dart
+++ b/pkg/front_end/test/vm_service_coverage_constant_evaluator.dart
@@ -6,7 +6,7 @@
 
 import 'vm_service_coverage.dart' as helper;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   CoverageHelper coverageHelper = new CoverageHelper();
 
   List<String> allArgs = <String>[];
@@ -17,7 +17,7 @@
   ]);
   allArgs.addAll(args);
 
-  coverageHelper.start(allArgs);
+  await coverageHelper.start(allArgs);
 }
 
 class CoverageHelper extends helper.CoverageHelper {
diff --git a/pkg/front_end/test/vm_service_for_leak_detection.dart b/pkg/front_end/test/vm_service_for_leak_detection.dart
index bae1839..e5782a8 100644
--- a/pkg/front_end/test/vm_service_for_leak_detection.dart
+++ b/pkg/front_end/test/vm_service_for_leak_detection.dart
@@ -8,7 +8,7 @@
 
 import "vm_service_heap_helper.dart" as helper;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   List<helper.Interest> interests = <helper.Interest>[];
   interests.add(new helper.Interest(
     Uri.parse("package:front_end/src/fasta/source/source_library_builder.dart"),
@@ -45,7 +45,7 @@
   );
 
   if (args.length > 0 && args[0] == "--dart2js") {
-    heapHelper.start([
+    await heapHelper.start([
       "--enable-asserts",
       Platform.script.resolve("incremental_dart2js_tester.dart").toString(),
       "--addDebugBreaks",
@@ -53,13 +53,13 @@
       "--experimental",
     ]);
   } else if (args.length > 0 && args[0] == "--weekly") {
-    heapHelper.start([
+    await heapHelper.start([
       "--enable-asserts",
       Platform.script.resolve("incremental_suite.dart").toString(),
       "-DaddDebugBreaks=true",
     ]);
   } else {
-    heapHelper.start([
+    await heapHelper.start([
       "--enable-asserts",
       Platform.script.resolve("incremental_suite.dart").toString(),
       "-DaddDebugBreaks=true",
diff --git a/pkg/front_end/test/vm_service_heap_finder.dart b/pkg/front_end/test/vm_service_heap_finder.dart
index 13f18fc..a098317 100644
--- a/pkg/front_end/test/vm_service_heap_finder.dart
+++ b/pkg/front_end/test/vm_service_heap_finder.dart
@@ -15,7 +15,7 @@
   Foo(this.x, this.y);
 }
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   String connectTo;
   String classToFind;
   String whatToDo;
diff --git a/pkg/front_end/test/vm_service_heap_helper.dart b/pkg/front_end/test/vm_service_heap_helper.dart
index d7bf8d0..ac5e8d9 100644
--- a/pkg/front_end/test/vm_service_heap_helper.dart
+++ b/pkg/front_end/test/vm_service_heap_helper.dart
@@ -50,7 +50,7 @@
     }
   }
 
-  void pause() async {
+  Future<void> pause() async {
     await serviceClient.pause(_isolateRef.id);
   }
 
diff --git a/pkg/front_end/test/vm_service_heap_helper_test.dart b/pkg/front_end/test/vm_service_heap_helper_test.dart
index 470e114..8a7df50 100644
--- a/pkg/front_end/test/vm_service_heap_helper_test.dart
+++ b/pkg/front_end/test/vm_service_heap_helper_test.dart
@@ -49,7 +49,7 @@
     throwOnPossibleLeak: false,
   );
 
-  heapHelper.start(
+  await heapHelper.start(
     [
       "--enable-asserts",
       Platform.script.toString(),
diff --git a/pkg/front_end/test/vm_service_helper.dart b/pkg/front_end/test/vm_service_helper.dart
index f5adc3f..c796b41 100644
--- a/pkg/front_end/test/vm_service_helper.dart
+++ b/pkg/front_end/test/vm_service_helper.dart
@@ -155,7 +155,7 @@
 
   bool _started = false;
 
-  void start(List<String> scriptAndArgs,
+  Future<void> start(List<String> scriptAndArgs,
       {void stdoutReceiver(String line),
       void stderrReceiver(String line)}) async {
     if (_started) throw "Already started";
diff --git a/pkg/front_end/test/weekly_tester.dart b/pkg/front_end/test/weekly_tester.dart
index 6cdd65a..2fe9bbf 100644
--- a/pkg/front_end/test/weekly_tester.dart
+++ b/pkg/front_end/test/weekly_tester.dart
@@ -6,7 +6,7 @@
 import 'dart:convert' show LineSplitter, utf8;
 import 'dart:io' show File, Platform, Process, exitCode;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   // General idea: Launch - in separate processes - whatever we want to run
   // concurrently, capturing the stdout and stderr, printing it with some
   // prepended identification.
diff --git a/pkg/front_end/tool/_fasta/abcompile.dart b/pkg/front_end/tool/_fasta/abcompile.dart
index 26ad63a..2978ee2 100644
--- a/pkg/front_end/tool/_fasta/abcompile.dart
+++ b/pkg/front_end/tool/_fasta/abcompile.dart
@@ -18,7 +18,7 @@
 /// by alternately launching the compile application in this directory
 /// and the compile application location in the repo specified by "bRoot"
 /// via -DbRoot=/absolute/path/to/other/sdk/repo
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   print(args);
   if (bRootPath == null) {
     print('Expected -DbRoot=/absolute/path/to/other/sdk/repo');
diff --git a/pkg/front_end/tool/_fasta/entry_points.dart b/pkg/front_end/tool/_fasta/entry_points.dart
index f729ad1..6d05e95 100644
--- a/pkg/front_end/tool/_fasta/entry_points.dart
+++ b/pkg/front_end/tool/_fasta/entry_points.dart
@@ -86,7 +86,7 @@
   }
 }
 
-void outlineEntryPoint(List<String> arguments) async {
+Future<void> outlineEntryPoint(List<String> arguments) async {
   installAdditionalTargets();
 
   for (int i = 0; i < iterations; i++) {
@@ -97,7 +97,7 @@
   }
 }
 
-void depsEntryPoint(List<String> arguments) async {
+Future<void> depsEntryPoint(List<String> arguments) async {
   installAdditionalTargets();
 
   for (int i = 0; i < iterations; i++) {
@@ -108,7 +108,7 @@
   }
 }
 
-void compilePlatformEntryPoint(List<String> arguments) async {
+Future<void> compilePlatformEntryPoint(List<String> arguments) async {
   installAdditionalTargets();
   for (int i = 0; i < iterations; i++) {
     if (i > 0) {
@@ -118,7 +118,7 @@
   }
 }
 
-void batchEntryPoint(List<String> arguments) {
+Future<void> batchEntryPoint(List<String> arguments) {
   installAdditionalTargets();
   return new BatchCompiler(
           stdin.transform(utf8.decoder).transform(new LineSplitter()))
@@ -136,7 +136,7 @@
 
   BatchCompiler(this.lines);
 
-  void run() async {
+  Future<void> run() async {
     await for (String line in lines) {
       try {
         if (await batchCompileArguments(
@@ -207,7 +207,7 @@
   }
 }
 
-void incrementalEntryPoint(List<String> arguments) async {
+Future<void> incrementalEntryPoint(List<String> arguments) async {
   installAdditionalTargets();
   await withGlobalOptions("incremental", arguments, true,
       (CompilerContext c, _) {
diff --git a/pkg/front_end/tool/_fasta/log_analyzer.dart b/pkg/front_end/tool/_fasta/log_analyzer.dart
index 1fdbc7a..430b50b 100644
--- a/pkg/front_end/tool/_fasta/log_analyzer.dart
+++ b/pkg/front_end/tool/_fasta/log_analyzer.dart
@@ -8,7 +8,7 @@
 
 import 'package:testing/src/run_tests.dart' show CommandLine;
 
-void main(List<String> arguments) async {
+Future<void> main(List<String> arguments) async {
   CommandLine cl = CommandLine.parse(arguments);
   Set<String> fields = cl.commaSeparated("--fields=");
   if (fields.isEmpty) {
diff --git a/pkg/front_end/tool/_fasta/log_collector.dart b/pkg/front_end/tool/_fasta/log_collector.dart
index 3b0c717..c82af8f 100644
--- a/pkg/front_end/tool/_fasta/log_collector.dart
+++ b/pkg/front_end/tool/_fasta/log_collector.dart
@@ -30,7 +30,7 @@
   print("${request.uri}: $message");
 }
 
-void collectLog(DateTime time, HttpRequest request) async {
+Future<void> collectLog(DateTime time, HttpRequest request) async {
   String json = await request.cast<List<int>>().transform(utf8.decoder).join();
   var data;
   try {
@@ -81,7 +81,7 @@
 """);
 }
 
-void main(List<String> arguments) async {
+Future<void> main(List<String> arguments) async {
   RawReceivePort keepAlive = new RawReceivePort();
   Uri uri;
   if (arguments.length == 1) {
@@ -104,7 +104,7 @@
       badRequest(request, HttpStatus.notFound, "Not found.");
       continue;
     }
-    collectLog(new DateTime.now(), request);
+    await collectLog(new DateTime.now(), request);
   }
   keepAlive.close();
 }
diff --git a/pkg/front_end/tool/fasta_perf_test.dart b/pkg/front_end/tool/fasta_perf_test.dart
index 1671627..1d561b8 100644
--- a/pkg/front_end/tool/fasta_perf_test.dart
+++ b/pkg/front_end/tool/fasta_perf_test.dart
@@ -9,7 +9,7 @@
 import 'dart:io' show Platform;
 import 'fasta_perf.dart' as m show main;
 
-void main() async {
+Future<void> main() async {
   var benchIds = [
     'scan',
     'kernel_gen_e2e',
diff --git a/pkg/front_end/tool/generate_ast_coverage.dart b/pkg/front_end/tool/generate_ast_coverage.dart
index 516d5e1..d3a299b 100644
--- a/pkg/front_end/tool/generate_ast_coverage.dart
+++ b/pkg/front_end/tool/generate_ast_coverage.dart
@@ -13,7 +13,7 @@
   return repoDir.resolve('pkg/kernel/lib/src/coverage.dart');
 }
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Uri output = args.isEmpty
       ? computeCoverageUri(Uri.base)
       : new File(args[0]).absolute.uri;
diff --git a/pkg/front_end/tool/generate_ast_equivalence.dart b/pkg/front_end/tool/generate_ast_equivalence.dart
index 5a0c02b..beea310 100644
--- a/pkg/front_end/tool/generate_ast_equivalence.dart
+++ b/pkg/front_end/tool/generate_ast_equivalence.dart
@@ -11,7 +11,7 @@
   return repoDir.resolve('pkg/kernel/lib/src/equivalence.dart');
 }
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Uri output = args.isEmpty
       ? computeEquivalenceUri(Uri.base)
       : new File(args[0]).absolute.uri;
diff --git a/pkg/front_end/tool/incremental_perf_test.dart b/pkg/front_end/tool/incremental_perf_test.dart
index d24c01a..1be785ef 100644
--- a/pkg/front_end/tool/incremental_perf_test.dart
+++ b/pkg/front_end/tool/incremental_perf_test.dart
@@ -9,7 +9,7 @@
     show computePlatformBinariesLocation;
 import 'incremental_perf.dart' as m show main;
 
-void main() async {
+Future<void> main() async {
   var sdkOutline = computePlatformBinariesLocation(forceBuildDir: true).resolve(
       // TODO(sigmund): switch to `vm_outline.dill` (issue #29881).
       "vm_platform_strong.dill");
diff --git a/pkg/front_end/tool/perf_test.dart b/pkg/front_end/tool/perf_test.dart
index 495c9fb..6667553 100644
--- a/pkg/front_end/tool/perf_test.dart
+++ b/pkg/front_end/tool/perf_test.dart
@@ -7,7 +7,7 @@
 import 'dart:io' show Platform;
 import 'perf.dart' as m;
 
-void main() async {
+Future<void> main() async {
   var benchIds = ['scan', 'parse'];
   var inputFile =
       Platform.script.resolve('../lib/src/api_prototype/file_system.dart').path;
diff --git a/pkg/front_end/tool/smoke_test_quick.dart b/pkg/front_end/tool/smoke_test_quick.dart
index b6d94f8..12b77c3 100644
--- a/pkg/front_end/tool/smoke_test_quick.dart
+++ b/pkg/front_end/tool/smoke_test_quick.dart
@@ -10,7 +10,7 @@
 
 String get dartVm => Platform.executable;
 
-void main(List<String> args) async {
+Future<void> main(List<String> args) async {
   Stopwatch stopwatch = new Stopwatch()..start();
   List<Future> futures = <Future>[];
   futures.add(run("pkg/front_end/test/explicit_creation_git_test.dart",
diff --git a/pkg/front_end/tool/update_all.dart b/pkg/front_end/tool/update_all.dart
index e32686e..bffcf9f 100644
--- a/pkg/front_end/tool/update_all.dart
+++ b/pkg/front_end/tool/update_all.dart
@@ -23,7 +23,7 @@
   'pkg/front_end/test/static_types/static_type_test.dart',
 ];
 
-void main() async {
+Future<void> main() async {
   // Update all tests based on expectation files.
   await expectations.main(const <String>[]);
 
diff --git a/pkg/kernel/binary.md b/pkg/kernel/binary.md
index ab32dae..1a0a3a2 100644
--- a/pkg/kernel/binary.md
+++ b/pkg/kernel/binary.md
@@ -147,7 +147,7 @@
 
 type ComponentFile {
   UInt32 magic = 0x90ABCDEF;
-  UInt32 formatVersion = 71;
+  UInt32 formatVersion = 72;
   Byte[10] shortSdkHash;
   List<String> problemsAsJson; // Described in problems.md.
   Library[] libraries;
@@ -346,6 +346,10 @@
   Byte flags (isExtensionTypeDeclaration);
   List<TypeParameter> typeParameters;
   DartType onType;
+  Option<ExtensionTypeShowHideClause> showHideClause;
+}
+
+type ExtensionTypeShowHideClause {
   List<DartType> shownSupertypes;
   List<CanonicalNameReference> shownMembers;
   List<CanonicalNameReference> shownGetters;
diff --git a/pkg/kernel/lib/binary/ast_from_binary.dart b/pkg/kernel/lib/binary/ast_from_binary.dart
index 14eb7b8..1423d0d 100644
--- a/pkg/kernel/lib/binary/ast_from_binary.dart
+++ b/pkg/kernel/lib/binary/ast_from_binary.dart
@@ -529,14 +529,15 @@
         growable: useGrowableLists);
   }
 
-  List<Reference> readNonNullReferenceList() {
+  List<Reference> readNonNullReferenceList(List<Reference> result) {
     int length = readUInt30();
     if (!useGrowableLists && length == 0) {
       return emptyListOfReference;
     }
-    return new List<Reference>.generate(
-        length, (_) => readNonNullMemberReference(),
-        growable: useGrowableLists);
+    for (int i = 0; i < length; ++i) {
+      result.add(readNonNullMemberReference());
+    }
+    return result;
   }
 
   String? readStringOrNullIfEmpty() {
@@ -1458,32 +1459,27 @@
 
     readAndPushTypeParameterList(node.typeParameters, node);
     DartType onType = readDartType();
-    List<Supertype> shownSupertypes = readSupertypeList();
-    List<Reference> shownMembers = readNonNullReferenceList();
-    List<Reference> shownGetters = readNonNullReferenceList();
-    List<Reference> shownSetters = readNonNullReferenceList();
-    List<Reference> shownOperators = readNonNullReferenceList();
-    List<Supertype> hiddenSupertypes = readSupertypeList();
-    List<Reference> hiddenMembers = readNonNullReferenceList();
-    List<Reference> hiddenGetters = readNonNullReferenceList();
-    List<Reference> hiddenSetters = readNonNullReferenceList();
-    List<Reference> hiddenOperators = readNonNullReferenceList();
+
+    if (readAndCheckOptionTag()) {
+      ExtensionTypeShowHideClause showHideClause =
+          node.showHideClause = new ExtensionTypeShowHideClause();
+      readSupertypeList(showHideClause.shownSupertypes);
+      readNonNullReferenceList(showHideClause.shownMethods);
+      readNonNullReferenceList(showHideClause.shownGetters);
+      readNonNullReferenceList(showHideClause.shownSetters);
+      readNonNullReferenceList(showHideClause.shownOperators);
+      readSupertypeList(showHideClause.hiddenSupertypes);
+      readNonNullReferenceList(showHideClause.hiddenMethods);
+      readNonNullReferenceList(showHideClause.hiddenGetters);
+      readNonNullReferenceList(showHideClause.hiddenSetters);
+      readNonNullReferenceList(showHideClause.hiddenOperators);
+    }
+
     typeParameterStack.length = 0;
 
     node.name = name;
     node.fileUri = fileUri;
     node.onType = onType;
-    node.showHideClause = new ExtensionTypeShowHideClause()
-      ..shownSupertypes.addAll(shownSupertypes)
-      ..shownMethods.addAll(shownMembers)
-      ..shownGetters.addAll(shownGetters)
-      ..shownSetters.addAll(shownSetters)
-      ..shownOperators.addAll(shownOperators)
-      ..hiddenSupertypes.addAll(hiddenSupertypes)
-      ..hiddenMethods.addAll(hiddenMembers)
-      ..hiddenGetters.addAll(hiddenGetters)
-      ..hiddenSetters.addAll(hiddenSetters)
-      ..hiddenOperators.addAll(hiddenOperators);
 
     node.members = _readExtensionMemberDescriptorList();
 
@@ -2949,15 +2945,22 @@
     return readAndCheckOptionTag() ? readSupertype() : null;
   }
 
-  List<Supertype> readSupertypeList() {
+  List<Supertype> readSupertypeList([List<Supertype>? result]) {
     int length = readUInt30();
     if (!useGrowableLists && length == 0) {
       // When lists don't have to be growable anyway, we might as well use an
       // almost constant one for the empty list.
       return emptyListOfSupertype;
     }
-    return new List<Supertype>.generate(length, (_) => readSupertype(),
-        growable: useGrowableLists);
+    if (result != null) {
+      for (int i = 0; i < length; ++i) {
+        result.add(readSupertype());
+      }
+      return result;
+    } else {
+      return new List<Supertype>.generate(length, (_) => readSupertype(),
+          growable: useGrowableLists);
+    }
   }
 
   List<DartType> readDartTypeList() {
diff --git a/pkg/kernel/lib/binary/ast_to_binary.dart b/pkg/kernel/lib/binary/ast_to_binary.dart
index b0de73c..6cb1bd7 100644
--- a/pkg/kernel/lib/binary/ast_to_binary.dart
+++ b/pkg/kernel/lib/binary/ast_to_binary.dart
@@ -2451,18 +2451,24 @@
     enterScope(typeParameters: node.typeParameters);
     writeNodeList(node.typeParameters);
     writeDartType(node.onType);
-    ExtensionTypeShowHideClause showHideClause =
-        node.showHideClause ?? new ExtensionTypeShowHideClause();
-    writeNodeList(showHideClause.shownSupertypes);
-    writeList(showHideClause.shownMethods, writeNonNullReference);
-    writeList(showHideClause.shownGetters, writeNonNullReference);
-    writeList(showHideClause.shownSetters, writeNonNullReference);
-    writeList(showHideClause.shownOperators, writeNonNullReference);
-    writeNodeList(showHideClause.hiddenSupertypes);
-    writeList(showHideClause.hiddenMethods, writeNonNullReference);
-    writeList(showHideClause.hiddenGetters, writeNonNullReference);
-    writeList(showHideClause.hiddenSetters, writeNonNullReference);
-    writeList(showHideClause.hiddenOperators, writeNonNullReference);
+
+    ExtensionTypeShowHideClause? showHideClause = node.showHideClause;
+    if (showHideClause == null) {
+      writeByte(Tag.Nothing);
+    } else {
+      writeByte(Tag.Something);
+      writeNodeList(showHideClause.shownSupertypes);
+      writeList(showHideClause.shownMethods, writeNonNullReference);
+      writeList(showHideClause.shownGetters, writeNonNullReference);
+      writeList(showHideClause.shownSetters, writeNonNullReference);
+      writeList(showHideClause.shownOperators, writeNonNullReference);
+      writeNodeList(showHideClause.hiddenSupertypes);
+      writeList(showHideClause.hiddenMethods, writeNonNullReference);
+      writeList(showHideClause.hiddenGetters, writeNonNullReference);
+      writeList(showHideClause.hiddenSetters, writeNonNullReference);
+      writeList(showHideClause.hiddenOperators, writeNonNullReference);
+    }
+
     leaveScope(typeParameters: node.typeParameters);
 
     final int len = node.members.length;
diff --git a/pkg/kernel/lib/binary/tag.dart b/pkg/kernel/lib/binary/tag.dart
index 2fe1841..b628f87 100644
--- a/pkg/kernel/lib/binary/tag.dart
+++ b/pkg/kernel/lib/binary/tag.dart
@@ -176,7 +176,7 @@
   /// Internal version of kernel binary format.
   /// Bump it when making incompatible changes in kernel binaries.
   /// Keep in sync with runtime/vm/kernel_binary.h, pkg/kernel/binary.md.
-  static const int BinaryFormatVersion = 71;
+  static const int BinaryFormatVersion = 72;
 }
 
 abstract class ConstantTag {
diff --git a/runtime/vm/kernel_binary.h b/runtime/vm/kernel_binary.h
index 653c0fd..13f777c 100644
--- a/runtime/vm/kernel_binary.h
+++ b/runtime/vm/kernel_binary.h
@@ -20,8 +20,8 @@
 static const uint32_t kMagicProgramFile = 0x90ABCDEFu;
 
 // Both version numbers are inclusive.
-static const uint32_t kMinSupportedKernelFormatVersion = 71;
-static const uint32_t kMaxSupportedKernelFormatVersion = 71;
+static const uint32_t kMinSupportedKernelFormatVersion = 72;
+static const uint32_t kMaxSupportedKernelFormatVersion = 72;
 
 // Keep in sync with package:kernel/lib/binary/tag.dart
 #define KERNEL_TAG_LIST(V)                                                     \
diff --git a/runtime/vm/kernel_loader.cc b/runtime/vm/kernel_loader.cc
index 6efc565..6236cf3 100644
--- a/runtime/vm/kernel_loader.cc
+++ b/runtime/vm/kernel_loader.cc
@@ -1089,16 +1089,19 @@
       helper_.ReadByte();                    // skip flags.
       helper_.SkipTypeParametersList();      // skip type parameter list.
       helper_.SkipDartType();                // skip on-type.
-      helper_.SkipListOfDartTypes();         // skip shown types.
-      helper_.SkipListOfCanonicalNameReferences();  // skip shown members.
-      helper_.SkipListOfCanonicalNameReferences();  // skip shown getters.
-      helper_.SkipListOfCanonicalNameReferences();  // skip shown setters.
-      helper_.SkipListOfCanonicalNameReferences();  // skip shown operators.
-      helper_.SkipListOfDartTypes();                // skip hidden types.
-      helper_.SkipListOfCanonicalNameReferences();  // skip hidden members.
-      helper_.SkipListOfCanonicalNameReferences();  // skip hidden getters.
-      helper_.SkipListOfCanonicalNameReferences();  // skip hidden setters.
-      helper_.SkipListOfCanonicalNameReferences();  // skip hidden operators.
+      Tag tag = helper_.ReadTag();
+      if (tag != kNothing) {
+        helper_.SkipListOfDartTypes();                // skip shown types.
+        helper_.SkipListOfCanonicalNameReferences();  // skip shown members.
+        helper_.SkipListOfCanonicalNameReferences();  // skip shown getters.
+        helper_.SkipListOfCanonicalNameReferences();  // skip shown setters.
+        helper_.SkipListOfCanonicalNameReferences();  // skip shown operators.
+        helper_.SkipListOfDartTypes();                // skip hidden types.
+        helper_.SkipListOfCanonicalNameReferences();  // skip hidden members.
+        helper_.SkipListOfCanonicalNameReferences();  // skip hidden getters.
+        helper_.SkipListOfCanonicalNameReferences();  // skip hidden setters.
+        helper_.SkipListOfCanonicalNameReferences();  // skip hidden operators.
+      }
 
       const intptr_t extension_member_count = helper_.ReadListLength();
       for (intptr_t j = 0; j < extension_member_count; ++j) {
diff --git a/tools/VERSION b/tools/VERSION
index b752d93..aa58cf1 100644
--- a/tools/VERSION
+++ b/tools/VERSION
@@ -27,5 +27,5 @@
 MAJOR 2
 MINOR 15
 PATCH 0
-PRERELEASE 140
+PRERELEASE 141
 PRERELEASE_PATCH 0
\ No newline at end of file