[cfe] Add always_declare_return_types lint

Change-Id: I206a7a8132b5ea79dc019acf5c2e0cd800307bcf
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/212161
Reviewed-by: Jens Johansen <jensj@google.com>
Commit-Queue: Johnni Winther <johnniwinther@google.com>

.dart_tool/package_config.json

@@ -11,7 +11,7 @@
     "constraint, update this by running tools/generate_package_config.dart."
   ],
   "configVersion": 2,
-  "generated": "2021-08-23T16:52:51.727804",
+  "generated": "2021-09-01T12:41:37.776425",
   "generator": "tools/generate_package_config.dart",
   "packages": [
     {
@@ -316,7 +316,7 @@
       "name": "front_end",
       "rootUri": "../pkg/front_end",
       "packageUri": "lib/",
-      "languageVersion": "2.12"
+      "languageVersion": "2.13"
     },
     {
       "name": "front_end_testcases",

pkg/front_end/analysis_options.yaml

@@ -19,4 +19,5 @@ linter:
     - lines_longer_than_80_chars
     - unrelated_type_equality_checks
     - annotate_overrides
+    - always_declare_return_types
     # - always_specify_types

pkg/front_end/benchmarks/ikg/dart2js.dart

@@ -6,4 +6,4 @@
 
 import 'package:compiler/src/dart2js.dart' as dart2js;
 
-main(args) => dart2js.main(args);
+void main(args) => dart2js.main(args);

pkg/front_end/benchmarks/ikg/hello.dart

@@ -2,4 +2,4 @@
 // 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.
 
-main() => print('hello world');
+void main() => print('hello world');

pkg/front_end/lib/src/base/libraries_specification.dart

@@ -137,20 +137,19 @@ class LibrariesSpecification {
       if (targetName.startsWith("comment:")) return null;
       Map<String, LibraryInfo> libraries = <String, LibraryInfo>{};
       if (targetData is! Map) {
-        return _reportError(
-            "target specification for '$targetName' is not a map");
+        _reportError("target specification for '$targetName' is not a map");
       }
       if (!targetData.containsKey("libraries")) {
-        return _reportError("target specification "
+        _reportError("target specification "
             "for '$targetName' doesn't have a libraries entry");
       }
       dynamic librariesData = targetData["libraries"];
       if (librariesData is! Map<String, dynamic>) {
-        return _reportError("libraries entry for '$targetName' is not a map");
+        _reportError("libraries entry for '$targetName' is not a map");
       }
       librariesData.forEach((String name, data) {
         if (data is! Map<String, dynamic>) {
-          return _reportError(
+          _reportError(
               "library data for '$name' in target '$targetName' is not a map");
         }
         Uri checkAndResolve(uriString) {
@@ -175,13 +174,12 @@ class LibrariesSpecification {
         } else if (data['patches'] == null) {
           patches = const [];
         } else {
-          return _reportError(
-              "patches entry for '$name' is not a list or a string");
+          _reportError("patches entry for '$name' is not a list or a string");
         }
 
         dynamic supported = data['supported'] ?? true;
         if (supported is! bool) {
-          return _reportError("\"supported\" entry: expected a 'bool' but "
+          _reportError("\"supported\" entry: expected a 'bool' but "
               "got a '${supported.runtimeType}' ('$supported')");
         }
         libraries[name] =
@@ -193,7 +191,7 @@ class LibrariesSpecification {
     return new LibrariesSpecification(targets);
   }
 
-  static _reportError(String error) =>
+  static Never _reportError(String error) =>
       throw new LibrariesSpecificationException(error);
 
   /// Serialize this specification to json.

pkg/front_end/lib/src/base/processed_options.dart

@@ -793,7 +793,7 @@ class ProcessedOptions {
 
   String debugString() {
     StringBuffer sb = new StringBuffer();
-    writeList(String name, List elements) {
+    void writeList(String name, List elements) {
       if (elements.isEmpty) {
         sb.writeln('$name: <empty>');
         return;

pkg/front_end/lib/src/fasta/crash.dart

@@ -50,7 +50,7 @@ void resetCrashReporting() {
 
 Future<T> reportCrash<T>(error, StackTrace trace,
     [Uri? uri, int? charOffset]) async {
-  note(String note) async {
+  Future<void> note(String note) async {
     stderr.write(note);
     await stderr.flush();
   }

pkg/front_end/lib/src/fasta/incremental_compiler.dart

@@ -2097,7 +2097,7 @@ class IncrementalCompiler implements IncrementalKernelGenerator {
       return false;
     }
 
-    addBuilderAndInvalidateUris(Uri uri, LibraryBuilder libraryBuilder) {
+    void addBuilderAndInvalidateUris(Uri uri, LibraryBuilder libraryBuilder) {
       if (uri.scheme == "dart" && !libraryBuilder.isSynthetic) {
         if (seenUris.add(libraryBuilder.importUri)) {
           reusedLibraries.add(libraryBuilder);

pkg/front_end/lib/src/fasta/incremental_serializer.dart

@@ -256,7 +256,7 @@ class IncrementalSerializer {
 
   /// Add the group but not its dependencies to the output if they weren't added
   /// already.
-  addDataButNotDependentData(SerializationGroup group,
+  void addDataButNotDependentData(SerializationGroup group,
       Set<SerializationGroup> cachedPackagesInOutput, Sink<List<int>> sink) {
     if (cachedPackagesInOutput.add(group)) {
       sink.add(group.serializedData);
@@ -265,7 +265,7 @@ class IncrementalSerializer {
 
   /// Add the group and its dependencies to the output if they weren't added
   /// already.
-  addDataAndDependentData(SerializationGroup group,
+  void addDataAndDependentData(SerializationGroup group,
       Set<SerializationGroup> cachedPackagesInOutput, Sink<List<int>> sink) {
     if (cachedPackagesInOutput.add(group)) {
       sink.add(group.serializedData);

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

@@ -1859,7 +1859,7 @@ class BodyBuilder extends ScopeListener<JumpTarget>
   }
 
   @override
-  /* Expression | Generator | Initializer */ finishSend(Object receiver,
+  Expression_Generator_Initializer finishSend(Object receiver,
       List<UnresolvedType>? typeArguments, Arguments arguments, int charOffset,
       {bool isTypeArgumentsInForest = false}) {
     if (receiver is Generator) {
@@ -2445,7 +2445,7 @@ class BodyBuilder extends ScopeListener<JumpTarget>
   /// implies that it shouldn't be turned into a [ThisPropertyAccessGenerator]
   /// if the name doesn't resolve in the scope).
   @override
-  /*Generator|Expression|Builder*/ scopeLookup(
+  Expression_Generator_Builder scopeLookup(
       Scope scope, String name, Token token,
       {bool isQualified: false, PrefixBuilder? prefix}) {
     int charOffset = offsetForToken(token);
@@ -7444,7 +7444,7 @@ class _BodyBuilderCloner extends CloneVisitorNotMembers {
   _BodyBuilderCloner(this.bodyBuilder);
 
   @override
-  visitStaticInvocation(StaticInvocation node) {
+  TreeNode visitStaticInvocation(StaticInvocation node) {
     if (node is FactoryConstructorInvocation) {
       FactoryConstructorInvocation result = new FactoryConstructorInvocation(
           node.target, clone(node.arguments),
@@ -7464,7 +7464,7 @@ class _BodyBuilderCloner extends CloneVisitorNotMembers {
   }
 
   @override
-  visitConstructorInvocation(ConstructorInvocation node) {
+  TreeNode visitConstructorInvocation(ConstructorInvocation node) {
     if (node is TypeAliasedConstructorInvocation) {
       TypeAliasedConstructorInvocation result =
           new TypeAliasedConstructorInvocation(
@@ -7478,7 +7478,7 @@ class _BodyBuilderCloner extends CloneVisitorNotMembers {
   }
 
   @override
-  visitArguments(Arguments node) {
+  TreeNode visitArguments(Arguments node) {
     if (node is ArgumentsImpl) {
       return ArgumentsImpl.clone(node, node.positional.map(clone).toList(),
           node.named.map(clone).toList(), node.types.map(visitType).toList());

pkg/front_end/lib/src/fasta/kernel/expression_generator.dart

@@ -215,11 +215,11 @@ abstract class Generator {
   ///
   /// If the invocation has explicit type arguments
   /// [buildTypeWithResolvedArguments] called instead.
-  /* Expression | Generator | Initializer */ doInvocation(
+  Expression_Generator_Initializer doInvocation(
       int offset, List<UnresolvedType>? typeArguments, Arguments arguments,
       {bool isTypeArgumentsInForest = false});
 
-  /* Expression | Generator */ buildSelectorAccess(
+  Expression_Generator buildSelectorAccess(
       Selector send, int operatorOffset, bool isNullAware) {
     if (send is InvocationSelector) {
       return _helper.buildMethodInvocation(buildSimpleRead(), send.name,
@@ -237,7 +237,7 @@ abstract class Generator {
     }
   }
 
-  /*Expression | Generator*/ buildEqualsOperation(Token token, Expression right,
+  Expression_Generator buildEqualsOperation(Token token, Expression right,
       {required bool isNot}) {
     // ignore: unnecessary_null_comparison
     assert(isNot != null);
@@ -245,18 +245,18 @@ abstract class Generator {
         isNot: isNot);
   }
 
-  /*Expression | Generator*/ buildBinaryOperation(
+  Expression_Generator buildBinaryOperation(
       Token token, Name binaryName, Expression right) {
     return _forest.createBinary(
         offsetForToken(token), buildSimpleRead(), binaryName, right);
   }
 
-  /*Expression | Generator*/ buildUnaryOperation(Token token, Name unaryName) {
+  Expression_Generator buildUnaryOperation(Token token, Name unaryName) {
     return _forest.createUnary(
         offsetForToken(token), unaryName, buildSimpleRead());
   }
 
-  /*Expression|Generator*/ applyTypeArguments(
+  Expression_Generator applyTypeArguments(
       int fileOffset, List<UnresolvedType>? typeArguments) {
     return new Instantiation(
         buildSimpleRead(), _helper.buildDartTypeArguments(typeArguments))
@@ -2625,8 +2625,9 @@ class ExplicitExtensionAccessGenerator extends Generator {
         isNullAware: isNullAware);
   }
 
-  /* Expression | Generator */ @override
-  buildSelectorAccess(Selector send, int operatorOffset, bool isNullAware) {
+  @override
+  Expression_Generator buildSelectorAccess(
+      Selector send, int operatorOffset, bool isNullAware) {
     if (_helper.constantContext != ConstantContext.none) {
       _helper.addProblem(
           messageNotAConstantExpression, fileOffset, token.length);
@@ -2643,7 +2644,8 @@ class ExplicitExtensionAccessGenerator extends Generator {
   }
 
   @override
-  buildBinaryOperation(Token token, Name binaryName, Expression right) {
+  Expression_Generator buildBinaryOperation(
+      Token token, Name binaryName, Expression right) {
     int fileOffset = offsetForToken(token);
     Generator generator = _createInstanceAccess(token, binaryName);
     return generator.doInvocation(fileOffset, null,
@@ -2651,7 +2653,7 @@ class ExplicitExtensionAccessGenerator extends Generator {
   }
 
   @override
-  buildUnaryOperation(Token token, Name unaryName) {
+  Expression_Generator buildUnaryOperation(Token token, Name unaryName) {
     int fileOffset = offsetForToken(token);
     Generator generator = _createInstanceAccess(token, unaryName);
     return generator.doInvocation(
@@ -2659,7 +2661,7 @@ class ExplicitExtensionAccessGenerator extends Generator {
   }
 
   @override
-  doInvocation(
+  Expression_Generator_Initializer doInvocation(
       int offset, List<UnresolvedType>? typeArguments, Arguments arguments,
       {bool isTypeArgumentsInForest = false}) {
     Generator generator = _createInstanceAccess(token, callName);
@@ -2860,7 +2862,8 @@ class DeferredAccessGenerator extends Generator {
   }
 
   @override
-  buildSelectorAccess(Selector send, int operatorOffset, bool isNullAware) {
+  Expression_Generator buildSelectorAccess(
+      Selector send, int operatorOffset, bool isNullAware) {
     Object propertyAccess =
         suffixGenerator.buildSelectorAccess(send, operatorOffset, isNullAware);
     if (propertyAccess is Generator) {
@@ -2914,7 +2917,7 @@ class DeferredAccessGenerator extends Generator {
   }
 
   @override
-  doInvocation(
+  Expression_Generator_Initializer doInvocation(
       int offset, List<UnresolvedType>? typeArguments, Arguments arguments,
       {bool isTypeArgumentsInForest = false}) {
     Object suffix = suffixGenerator.doInvocation(
@@ -3098,7 +3101,8 @@ class TypeUseGenerator extends AbstractReadOnlyAccessGenerator {
   }
 
   @override
-  buildSelectorAccess(Selector send, int operatorOffset, bool isNullAware) {
+  Expression_Generator buildSelectorAccess(
+      Selector send, int operatorOffset, bool isNullAware) {
     int nameOffset = offsetForToken(send.token);
     Name name = send.name;
     Arguments? arguments = send.arguments;
@@ -3326,7 +3330,7 @@ class TypeUseGenerator extends AbstractReadOnlyAccessGenerator {
   }
 
   @override
-  doInvocation(
+  Expression_Generator_Builder doInvocation(
       int offset, List<UnresolvedType>? typeArguments, Arguments arguments,
       {bool isTypeArgumentsInForest = false}) {
     if (declaration.isExtension) {
@@ -3363,7 +3367,8 @@ class TypeUseGenerator extends AbstractReadOnlyAccessGenerator {
   }
 
   @override
-  applyTypeArguments(int fileOffset, List<UnresolvedType>? typeArguments) {
+  Expression_Generator applyTypeArguments(
+      int fileOffset, List<UnresolvedType>? typeArguments) {
     return new TypeUseGenerator(_helper, token, declaration, targetName)
       ..typeArguments = typeArguments;
   }
@@ -3509,7 +3514,7 @@ abstract class AbstractReadOnlyAccessGenerator extends Generator {
   }
 
   @override
-  doInvocation(
+  Expression_Generator_Initializer doInvocation(
       int offset, List<UnresolvedType>? typeArguments, Arguments arguments,
       {bool isTypeArgumentsInForest = false}) {
     return _helper.forest.createExpressionInvocation(
@@ -3564,7 +3569,7 @@ abstract class ErroneousExpressionGenerator extends Generator {
   }
 
   @override
-  doInvocation(
+  Expression_Generator_Initializer doInvocation(
       int offset, List<UnresolvedType>? typeArguments, Arguments arguments,
       {bool isTypeArgumentsInForest = false}) {
     return buildError(arguments,
@@ -3572,7 +3577,8 @@ abstract class ErroneousExpressionGenerator extends Generator {
   }
 
   @override
-  buildSelectorAccess(Selector send, int operatorOffset, bool isNullAware) {
+  Expression_Generator buildSelectorAccess(
+      Selector send, int operatorOffset, bool isNullAware) {
     return send.withReceiver(buildSimpleRead(), operatorOffset,
         isNullAware: isNullAware);
   }
@@ -3765,7 +3771,7 @@ abstract class ContextAwareGenerator extends Generator {
   }
 
   @override
-  Expression doInvocation(
+  Never doInvocation(
       int charOffset, List<UnresolvedType>? typeArguments, Arguments arguments,
       {bool isTypeArgumentsInForest = false}) {
     return unhandled("${runtimeType}", "doInvocation", charOffset, _uri);
@@ -3804,7 +3810,7 @@ abstract class ContextAwareGenerator extends Generator {
   }
 
   @override
-  _makeInvalidRead([UnresolvedKind? unresolvedKind]) {
+  Never _makeInvalidRead([UnresolvedKind? unresolvedKind]) {
     return unsupported("makeInvalidRead", token.charOffset, _helper.uri);
   }
 
@@ -4011,7 +4017,7 @@ class PrefixUseGenerator extends Generator {
   }
 
   @override
-  /* Expression | Generator | Initializer */ doInvocation(
+  Expression doInvocation(
       int offset, List<UnresolvedType>? typeArguments, Arguments arguments,
       {bool isTypeArgumentsInForest = false}) {
     return _helper.wrapInLocatedProblem(
@@ -4022,7 +4028,7 @@ class PrefixUseGenerator extends Generator {
   }
 
   @override
-  /* Expression | Generator */ buildSelectorAccess(
+  Expression_Generator buildSelectorAccess(
       Selector send, int operatorOffset, bool isNullAware) {
     assert(send.name.text == send.token.lexeme,
         "'${send.name.text}' != ${send.token.lexeme}");
@@ -4400,7 +4406,8 @@ class ThisAccessGenerator extends Generator {
   }
 
   @override
-  buildSelectorAccess(Selector send, int operatorOffset, bool isNullAware) {
+  Expression_Generator buildSelectorAccess(
+      Selector send, int operatorOffset, bool isNullAware) {
     Name name = send.name;
     Arguments? arguments = send.arguments;
     int offset = offsetForToken(send.token);
@@ -4451,7 +4458,7 @@ class ThisAccessGenerator extends Generator {
   }
 
   @override
-  doInvocation(
+  Expression_Generator_Initializer doInvocation(
       int offset, List<UnresolvedType>? typeArguments, Arguments arguments,
       {bool isTypeArgumentsInForest = false}) {
     if (isInitializer) {
@@ -4465,7 +4472,8 @@ class ThisAccessGenerator extends Generator {
   }
 
   @override
-  buildEqualsOperation(Token token, Expression right, {required bool isNot}) {
+  Expression_Generator buildEqualsOperation(Token token, Expression right,
+      {required bool isNot}) {
     // ignore: unnecessary_null_comparison
     assert(isNot != null);
     if (isSuper) {
@@ -4485,7 +4493,8 @@ class ThisAccessGenerator extends Generator {
   }
 
   @override
-  buildBinaryOperation(Token token, Name binaryName, Expression right) {
+  Expression_Generator buildBinaryOperation(
+      Token token, Name binaryName, Expression right) {
     if (isSuper) {
       int offset = offsetForToken(token);
       return _helper.buildMethodInvocation(
@@ -4499,7 +4508,7 @@ class ThisAccessGenerator extends Generator {
   }
 
   @override
-  buildUnaryOperation(Token token, Name unaryName) {
+  Expression_Generator buildUnaryOperation(Token token, Name unaryName) {
     if (isSuper) {
       int offset = offsetForToken(token);
       return _helper.buildMethodInvocation(
@@ -4650,7 +4659,7 @@ class IncompleteErrorGenerator extends ErroneousExpressionGenerator {
   }
 
   @override
-  doInvocation(
+  Generator doInvocation(
           int offset, List<UnresolvedType>? typeArguments, Arguments arguments,
           {bool isTypeArgumentsInForest = false}) =>
       this;
@@ -4705,8 +4714,9 @@ class ParenthesizedExpressionGenerator extends AbstractReadOnlyAccessGenerator {
   @override
   String get _debugName => "ParenthesizedExpressionGenerator";
 
-  /* Expression | Generator */ @override
-  buildSelectorAccess(Selector send, int operatorOffset, bool isNullAware) {
+  @override
+  Expression_Generator buildSelectorAccess(
+      Selector send, int operatorOffset, bool isNullAware) {
     if (send is InvocationSelector) {
       return _helper.buildMethodInvocation(
           _createRead(), send.name, send.arguments, offsetForToken(send.token),
@@ -4763,8 +4773,7 @@ abstract class Selector {
   Name get name;
 
   /// Applies this selector to [receiver].
-  /* Expression | Generator */ withReceiver(
-      Object? receiver, int operatorOffset,
+  Expression_Generator withReceiver(Object? receiver, int operatorOffset,
       {bool isNullAware: false});
 
   List<UnresolvedType>? get typeArguments => null;
@@ -4826,7 +4835,7 @@ class InvocationSelector extends Selector {
   String get _debugName => 'InvocationSelector';
 
   @override
-  withReceiver(Object? receiver, int operatorOffset,
+  Expression_Generator withReceiver(Object? receiver, int operatorOffset,
       {bool isNullAware: false}) {
     if (receiver is Generator) {
       return receiver.buildSelectorAccess(this, operatorOffset, isNullAware);
@@ -4868,7 +4877,7 @@ class PropertySelector extends Selector {
   String get _debugName => 'PropertySelector';
 
   @override
-  withReceiver(Object? receiver, int operatorOffset,
+  Expression_Generator withReceiver(Object? receiver, int operatorOffset,
       {bool isNullAware: false}) {
     if (receiver is Generator) {
       return receiver.buildSelectorAccess(this, operatorOffset, isNullAware);

pkg/front_end/lib/src/fasta/kernel/expression_generator_helper.dart

@@ -44,6 +44,15 @@ import 'kernel_ast_api.dart'
         Typedef,
         VariableDeclaration;
 
+/// Alias for Expression | Generator
+typedef Expression_Generator = dynamic;
+
+/// Alias for Expression | Generator | Builder
+typedef Expression_Generator_Builder = dynamic;
+
+/// Alias for Expression | Generator | Initializer
+typedef Expression_Generator_Initializer = dynamic;
+
 abstract class ExpressionGeneratorHelper implements InferenceHelper {
   SourceLibraryBuilder get libraryBuilder;
 
@@ -66,11 +75,11 @@ abstract class ExpressionGeneratorHelper implements InferenceHelper {
 
   bool get enableConstructorTearOffsInLibrary;
 
-  /* Generator | Expression | Builder */ scopeLookup(
+  Expression_Generator_Builder scopeLookup(
       Scope scope, String name, Token token,
       {bool isQualified: false, PrefixBuilder? prefix});
 
-  /* Expression | Generator | Initializer */ finishSend(Object receiver,
+  Expression_Generator_Initializer finishSend(Object receiver,
       List<UnresolvedType>? typeArguments, Arguments arguments, int offset,
       {bool isTypeArgumentsInForest = false});
 

pkg/front_end/lib/src/fasta/kernel/forest.dart

@@ -885,17 +885,17 @@ class _VariablesDeclaration extends Statement {
   }
 
   @override
-  visitChildren(v) {
+  Never visitChildren(v) {
     throw unsupported("visitChildren", fileOffset, uri);
   }
 
   @override
-  transformChildren(v) {
+  Never transformChildren(v) {
     throw unsupported("transformChildren", fileOffset, uri);
   }
 
   @override
-  transformOrRemoveChildren(v) {
+  Never transformOrRemoveChildren(v) {
     throw unsupported("transformOrRemoveChildren", fileOffset, uri);
   }
 

pkg/front_end/lib/src/fasta/kernel/implicit_field_type.dart

@@ -48,7 +48,7 @@ abstract class ImplicitFieldType extends DartType {
   }
 
   @override
-  visitChildren(Visitor<dynamic> v) {
+  Never visitChildren(Visitor<dynamic> v) {
     unsupported("visitChildren", fieldBuilder.charOffset, fieldBuilder.fileUri);
   }
 

pkg/front_end/lib/src/fasta/kernel/implicit_type_argument.dart

@@ -37,7 +37,7 @@ class ImplicitTypeArgument extends DartType {
   }
 
   @override
-  visitChildren(Visitor v) {
+  Never visitChildren(Visitor v) {
     unhandled("$runtimeType", "${v.runtimeType}", -1, null);
   }
 

pkg/front_end/lib/src/fasta/kernel/verifier.dart

@@ -179,7 +179,7 @@ class FastaVerifyingVisitor extends VerifyingVisitor {
   }
 
   @override
-  problem(TreeNode? node, String details,
+  void problem(TreeNode? node, String details,
       {TreeNode? context, TreeNode? origin}) {
     node ??= (context ?? currentClassOrExtensionOrMember);
     int offset = node?.fileOffset ?? -1;
@@ -446,7 +446,7 @@ class FastaVerifyGetStaticType extends VerifyGetStaticType {
   FastaVerifyGetStaticType(TypeEnvironment env, this.skipPlatform) : super(env);
 
   @override
-  visitLibrary(Library node) {
+  void visitLibrary(Library node) {
     // 'dart:test' is used in the unit tests and isn't an actual part of the
     // platform.
     if (skipPlatform &&

pkg/front_end/lib/src/fasta/modifier.dart

@@ -89,7 +89,7 @@ class Modifier {
   }
 
   @override
-  toString() => "modifier(${'$kind'.substring('ModifierEnum.'.length)})";
+  String toString() => "modifier(${'$kind'.substring('ModifierEnum.'.length)})";
 
   static int toMask(List<Modifier>? modifiers) {
     int result = 0;

pkg/front_end/lib/src/fasta/problems.dart

@@ -35,7 +35,7 @@ class DebugAbort {
                 .withoutLocation();
 
   @override
-  toString() => "DebugAbort: ${message.message}";
+  String toString() => "DebugAbort: ${message.message}";
 }
 
 /// Used to report an internal error.

pkg/front_end/lib/src/fasta/scope.dart

@@ -686,8 +686,6 @@ abstract class ProblemBuilder extends BuilderImpl {
 
   ProblemBuilder(this.name, this.builder, this.charOffset, this.fileUri);
 
-  get target => null;
-
   @override
   bool get hasProblem => true;
 

pkg/front_end/lib/src/fasta/source/directive_listener.dart

@@ -37,7 +37,7 @@ class DirectiveListener extends Listener {
   DirectiveListener();
 
   @override
-  beginExport(Token export) {
+  void beginExport(Token export) {
     _combinators = <NamespaceCombinator>[];
   }
 
@@ -47,7 +47,7 @@ class DirectiveListener extends Listener {
   }
 
   @override
-  beginImport(Token import) {
+  void beginImport(Token import) {
     _combinators = <NamespaceCombinator>[];
   }
 
@@ -59,7 +59,7 @@ class DirectiveListener extends Listener {
   }
 
   @override
-  beginPart(Token part) {
+  void beginPart(Token part) {
     _inPart = true;
   }
 
@@ -69,7 +69,7 @@ class DirectiveListener extends Listener {
   }
 
   @override
-  endExport(Token export, Token semicolon) {
+  void endExport(Token export, Token semicolon) {
     exports.add(new NamespaceDirective.export(_uri, _combinators));
     _uri = null;
     _combinators = null;
@@ -82,14 +82,14 @@ class DirectiveListener extends Listener {
   }
 
   @override
-  endImport(Token? import, Token? semicolon) {
+  void endImport(Token? import, Token? semicolon) {
     imports.add(new NamespaceDirective.import(_uri, _combinators));
     _uri = null;
     _combinators = null;
   }
 
   @override
-  endPart(Token part, Token semicolon) {
+  void endPart(Token part, Token semicolon) {
     parts.add(_uri);
     _uri = null;
     _inPart = false;

pkg/front_end/lib/src/fasta/source/stack_listener_impl.dart

@@ -63,7 +63,7 @@ abstract class StackListenerImpl extends StackListener {
 
   /// Used to report an internal error encountered in the stack listener.
   @override
-  internalProblem(Message message, int charOffset, Uri uri) {
+  Never internalProblem(Message message, int charOffset, Uri uri) {
     return problems.internalProblem(message, charOffset, uri);
   }
 

pkg/front_end/lib/src/fasta/type_inference/type_schema.dart

@@ -47,7 +47,7 @@ class TypeSchemaPrinter extends Printer {
             annotator: annotator);
 
   @override
-  defaultDartType(covariant UnknownType node) {
+  void defaultDartType(covariant UnknownType node) {
     writeWord('?');
   }
 }

pkg/front_end/lib/src/fasta/util/direct_parser_ast.dart

@@ -1152,7 +1152,7 @@ extension InitializerExtension on DirectParserASTContentInitializerEnd {
   }
 }
 
-main(List<String> args) {
+void main(List<String> args) {
   File f = new File(args[0]);
   Uint8List data = f.readAsBytesSync();
   DirectParserASTContent ast = getAST(data);

pkg/front_end/lib/src/fasta/util/textual_outline.dart

@@ -656,7 +656,7 @@ void outputUnknownChunk(
   _currentUnknown.interimEnd = null;
 }
 
-main(List<String> args) {
+void main(List<String> args) {
   File f = new File(args[0]);
   Uint8List data = f.readAsBytesSync();
   ScannerConfiguration scannerConfiguration = new ScannerConfiguration();
@@ -822,12 +822,12 @@ class TextualOutlineListener extends Listener {
   List<String>? _combinatorNames;
 
   @override
-  beginExport(Token export) {
+  void beginExport(Token export) {
     _combinators = <_NamespaceCombinator>[];
   }
 
   @override
-  beginImport(Token import) {
+  void beginImport(Token import) {
     _combinators = <_NamespaceCombinator>[];
   }
 

pkg/front_end/lib/src/testing/id_extractor.dart

@@ -167,19 +167,19 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  defaultNode(Node node) {
+  void defaultNode(Node node) {
     node.visitChildren(this);
   }
 
   @override
-  visitProcedure(Procedure node) {
+  void visitProcedure(Procedure node) {
     // Avoid visiting annotations.
     node.function.accept(this);
     computeForMember(node);
   }
 
   @override
-  visitConstructor(Constructor node) {
+  void visitConstructor(Constructor node) {
     // Avoid visiting annotations.
     visitList(node.initializers, this);
     node.function.accept(this);
@@ -187,13 +187,13 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  visitField(Field node) {
+  void visitField(Field node) {
     // Avoid visiting annotations.
     node.initializer?.accept(this);
     computeForMember(node);
   }
 
-  _visitInvocation(Expression node, Name name) {
+  void _visitInvocation(Expression node, Name name) {
     if (name.text == '[]') {
       computeForNode(node, computeDefaultNodeId(node));
     } else if (name.text == '[]=') {
@@ -208,31 +208,31 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  visitDynamicInvocation(DynamicInvocation node) {
+  void visitDynamicInvocation(DynamicInvocation node) {
     _visitInvocation(node, node.name);
     super.visitDynamicInvocation(node);
   }
 
   @override
-  visitFunctionInvocation(FunctionInvocation node) {
+  void visitFunctionInvocation(FunctionInvocation node) {
     _visitInvocation(node, node.name);
     super.visitFunctionInvocation(node);
   }
 
   @override
-  visitLocalFunctionInvocation(LocalFunctionInvocation node) {
+  void visitLocalFunctionInvocation(LocalFunctionInvocation node) {
     computeForNode(node, createInvokeId(node));
     super.visitLocalFunctionInvocation(node);
   }
 
   @override
-  visitEqualsCall(EqualsCall node) {
+  void visitEqualsCall(EqualsCall node) {
     _visitInvocation(node, Name.equalsName);
     super.visitEqualsCall(node);
   }
 
   @override
-  visitEqualsNull(EqualsNull node) {
+  void visitEqualsNull(EqualsNull node) {
     Expression receiver = node.expression;
     if (receiver is VariableGet && receiver.variable.name == null) {
       // This is a desugared `?.`.
@@ -243,48 +243,48 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  visitInstanceInvocation(InstanceInvocation node) {
+  void visitInstanceInvocation(InstanceInvocation node) {
     _visitInvocation(node, node.name);
     super.visitInstanceInvocation(node);
   }
 
   @override
-  visitInstanceGetterInvocation(InstanceGetterInvocation node) {
+  void visitInstanceGetterInvocation(InstanceGetterInvocation node) {
     _visitInvocation(node, node.name);
     super.visitInstanceGetterInvocation(node);
   }
 
   @override
-  visitLoadLibrary(LoadLibrary node) {
+  void visitLoadLibrary(LoadLibrary node) {
     computeForNode(node, createInvokeId(node));
   }
 
   @override
-  visitDynamicGet(DynamicGet node) {
+  void visitDynamicGet(DynamicGet node) {
     computeForNode(node, computeDefaultNodeId(node));
     super.visitDynamicGet(node);
   }
 
   @override
-  visitFunctionTearOff(FunctionTearOff node) {
+  void visitFunctionTearOff(FunctionTearOff node) {
     computeForNode(node, computeDefaultNodeId(node));
     super.visitFunctionTearOff(node);
   }
 
   @override
-  visitInstanceGet(InstanceGet node) {
+  void visitInstanceGet(InstanceGet node) {
     computeForNode(node, computeDefaultNodeId(node));
     super.visitInstanceGet(node);
   }
 
   @override
-  visitInstanceTearOff(InstanceTearOff node) {
+  void visitInstanceTearOff(InstanceTearOff node) {
     computeForNode(node, computeDefaultNodeId(node));
     super.visitInstanceTearOff(node);
   }
 
   @override
-  visitVariableDeclaration(VariableDeclaration node) {
+  void visitVariableDeclaration(VariableDeclaration node) {
     if (node.name != null && node.parent is! FunctionDeclaration) {
       // Skip synthetic variables and function declaration variables.
       computeForNode(node, computeDefaultNodeId(node));
@@ -294,7 +294,7 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  visitFunctionDeclaration(FunctionDeclaration node) {
+  void visitFunctionDeclaration(FunctionDeclaration node) {
     computeForNode(
         node,
         computeDefaultNodeId(node,
@@ -305,13 +305,13 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  visitFunctionExpression(FunctionExpression node) {
+  void visitFunctionExpression(FunctionExpression node) {
     computeForNode(node, computeDefaultNodeId(node));
     super.visitFunctionExpression(node);
   }
 
   @override
-  visitVariableGet(VariableGet node) {
+  void visitVariableGet(VariableGet node) {
     if (node.variable.name != null && !node.variable.isFieldFormal) {
       // Skip use of synthetic variables.
       computeForNode(node, computeDefaultNodeId(node));
@@ -320,19 +320,19 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  visitDynamicSet(DynamicSet node) {
+  void visitDynamicSet(DynamicSet node) {
     computeForNode(node, createUpdateId(node));
     super.visitDynamicSet(node);
   }
 
   @override
-  visitInstanceSet(InstanceSet node) {
+  void visitInstanceSet(InstanceSet node) {
     computeForNode(node, createUpdateId(node));
     super.visitInstanceSet(node);
   }
 
   @override
-  visitVariableSet(VariableSet node) {
+  void visitVariableSet(VariableSet node) {
     if (node.variable.name != null) {
       // Skip use of synthetic variables.
       computeForNode(node, createUpdateId(node));
@@ -341,43 +341,43 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  visitExpressionStatement(ExpressionStatement node) {
+  void visitExpressionStatement(ExpressionStatement node) {
     computeForNode(node, createExpressionStatementId(node));
     return super.visitExpressionStatement(node);
   }
 
   @override
-  visitIfStatement(IfStatement node) {
+  void visitIfStatement(IfStatement node) {
     computeForNode(node, computeDefaultNodeId(node));
     return super.visitIfStatement(node);
   }
 
   @override
-  visitTryCatch(TryCatch node) {
+  void visitTryCatch(TryCatch node) {
     computeForNode(node, computeDefaultNodeId(node));
     return super.visitTryCatch(node);
   }
 
   @override
-  visitTryFinally(TryFinally node) {
+  void visitTryFinally(TryFinally node) {
     computeForNode(node, computeDefaultNodeId(node));
     return super.visitTryFinally(node);
   }
 
   @override
-  visitDoStatement(DoStatement node) {
+  void visitDoStatement(DoStatement node) {
     computeForNode(node, createLoopId(node));
     super.visitDoStatement(node);
   }
 
   @override
-  visitForStatement(ForStatement node) {
+  void visitForStatement(ForStatement node) {
     computeForNode(node, createLoopId(node));
     super.visitForStatement(node);
   }
 
   @override
-  visitForInStatement(ForInStatement node) {
+  void visitForInStatement(ForInStatement node) {
     computeForNode(node, createLoopId(node));
     computeForNode(node, createIteratorId(node));
     computeForNode(node, createCurrentId(node));
@@ -386,32 +386,32 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  visitWhileStatement(WhileStatement node) {
+  void visitWhileStatement(WhileStatement node) {
     computeForNode(node, createLoopId(node));
     super.visitWhileStatement(node);
   }
 
   @override
-  visitLabeledStatement(LabeledStatement node) {
+  void visitLabeledStatement(LabeledStatement node) {
     // TODO(johnniwinther): Call computeForNode for label statements that are
     // not placeholders for loop and switch targets.
     super.visitLabeledStatement(node);
   }
 
   @override
-  visitBreakStatement(BreakStatement node) {
+  void visitBreakStatement(BreakStatement node) {
     computeForNode(node, createGotoId(node));
     super.visitBreakStatement(node);
   }
 
   @override
-  visitSwitchStatement(SwitchStatement node) {
+  void visitSwitchStatement(SwitchStatement node) {
     computeForNode(node, createSwitchId(node));
     super.visitSwitchStatement(node);
   }
 
   @override
-  visitSwitchCase(SwitchCase node) {
+  void visitSwitchCase(SwitchCase node) {
     if (node.expressionOffsets.isNotEmpty) {
       computeForNode(node, createSwitchCaseId(node));
     }
@@ -419,13 +419,13 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  visitContinueSwitchStatement(ContinueSwitchStatement node) {
+  void visitContinueSwitchStatement(ContinueSwitchStatement node) {
     computeForNode(node, createGotoId(node));
     super.visitContinueSwitchStatement(node);
   }
 
   @override
-  visitConstantExpression(ConstantExpression node) {
+  void visitConstantExpression(ConstantExpression node) {
     // Implicit constants (for instance omitted field initializers, implicit
     // default values) and synthetic constants (for instance in noSuchMethod
     // forwarders) have no offset.
@@ -435,7 +435,7 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  visitNullLiteral(NullLiteral node) {
+  void visitNullLiteral(NullLiteral node) {
     // Synthetic null literals, for instance in locals and fields without
     // initializers, have no offset.
     computeForNode(
@@ -444,13 +444,13 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  visitBoolLiteral(BoolLiteral node) {
+  void visitBoolLiteral(BoolLiteral node) {
     computeForNode(node, computeDefaultNodeId(node));
     super.visitBoolLiteral(node);
   }
 
   @override
-  visitIntLiteral(IntLiteral node) {
+  void visitIntLiteral(IntLiteral node) {
     // Synthetic ints literals, for instance in enum fields, have no offset.
     computeForNode(
         node, computeDefaultNodeId(node, skipNodeWithNoOffset: true));
@@ -458,13 +458,13 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  visitDoubleLiteral(DoubleLiteral node) {
+  void visitDoubleLiteral(DoubleLiteral node) {
     computeForNode(node, computeDefaultNodeId(node));
     super.visitDoubleLiteral(node);
   }
 
   @override
-  visitStringLiteral(StringLiteral node) {
+  void visitStringLiteral(StringLiteral node) {
     // Synthetic string literals, for instance in enum fields, have no offset.
     computeForNode(
         node, computeDefaultNodeId(node, skipNodeWithNoOffset: true));
@@ -472,7 +472,7 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  visitListLiteral(ListLiteral node) {
+  void visitListLiteral(ListLiteral node) {
     // Synthetic list literals,for instance in noSuchMethod forwarders, have no
     // offset.
     computeForNode(
@@ -481,7 +481,7 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  visitMapLiteral(MapLiteral node) {
+  void visitMapLiteral(MapLiteral node) {
     // Synthetic map literals, for instance in noSuchMethod forwarders, have no
     // offset.
     computeForNode(
@@ -490,13 +490,13 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  visitSetLiteral(SetLiteral node) {
+  void visitSetLiteral(SetLiteral node) {
     computeForNode(node, computeDefaultNodeId(node));
     super.visitSetLiteral(node);
   }
 
   @override
-  visitThisExpression(ThisExpression node) {
+  void visitThisExpression(ThisExpression node) {
     TreeNode parent = node.parent!;
     if (node.fileOffset == TreeNode.noOffset ||
         (parent is InstanceGet ||
@@ -511,13 +511,13 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  visitAwaitExpression(AwaitExpression node) {
+  void visitAwaitExpression(AwaitExpression node) {
     computeForNode(node, computeDefaultNodeId(node));
     super.visitAwaitExpression(node);
   }
 
   @override
-  visitConstructorInvocation(ConstructorInvocation node) {
+  void visitConstructorInvocation(ConstructorInvocation node) {
     // Skip synthetic constructor invocations like for enum constants.
     // TODO(johnniwinther): Can [skipNodeWithNoOffset] be removed when dart2js
     // no longer test with cfe constants?
@@ -527,43 +527,43 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  visitStaticGet(StaticGet node) {
+  void visitStaticGet(StaticGet node) {
     computeForNode(node, computeDefaultNodeId(node));
     super.visitStaticGet(node);
   }
 
   @override
-  visitStaticTearOff(StaticTearOff node) {
+  void visitStaticTearOff(StaticTearOff node) {
     computeForNode(node, computeDefaultNodeId(node));
     super.visitStaticTearOff(node);
   }
 
   @override
-  visitStaticSet(StaticSet node) {
+  void visitStaticSet(StaticSet node) {
     computeForNode(node, createUpdateId(node));
     super.visitStaticSet(node);
   }
 
   @override
-  visitStaticInvocation(StaticInvocation node) {
+  void visitStaticInvocation(StaticInvocation node) {
     computeForNode(node, createInvokeId(node));
     super.visitStaticInvocation(node);
   }
 
   @override
-  visitThrow(Throw node) {
+  void visitThrow(Throw node) {
     computeForNode(node, computeDefaultNodeId(node));
     super.visitThrow(node);
   }
 
   @override
-  visitRethrow(Rethrow node) {
+  void visitRethrow(Rethrow node) {
     computeForNode(node, computeDefaultNodeId(node));
     super.visitRethrow(node);
   }
 
   @override
-  visitAsExpression(AsExpression node) {
+  void visitAsExpression(AsExpression node) {
     if (node.isTypeError) {
       computeForNode(node, createImplicitAsId(node));
     } else {
@@ -573,33 +573,33 @@ abstract class DataExtractor<T> extends Visitor<void>
   }
 
   @override
-  visitArguments(Arguments node) {
+  void visitArguments(Arguments node) {
     computeForNode(
         node, computeDefaultNodeId(node, skipNodeWithNoOffset: true));
     return super.visitArguments(node);
   }
 
   @override
-  visitBlock(Block node) {
+  void visitBlock(Block node) {
     computeForNode(
         node, computeDefaultNodeId(node, skipNodeWithNoOffset: true));
     return super.visitBlock(node);
   }
 
   @override
-  visitConditionalExpression(ConditionalExpression node) {
+  void visitConditionalExpression(ConditionalExpression node) {
     computeForNode(node, computeDefaultNodeId(node));
     return super.visitConditionalExpression(node);
   }
 
   @override
-  visitLogicalExpression(LogicalExpression node) {
+  void visitLogicalExpression(LogicalExpression node) {
     computeForNode(node, computeDefaultNodeId(node));
     return super.visitLogicalExpression(node);
   }
 
   @override
-  visitInvalidExpression(InvalidExpression node) {
+  void visitInvalidExpression(InvalidExpression node) {
     // Invalid expressions produced in the constant evaluator don't have a
     // file offset.
     computeForNode(

pkg/front_end/pubspec.yaml

@@ -6,7 +6,7 @@ name: front_end
 publish_to: none
 
 environment:
-  sdk: '>=2.12.0 <3.0.0'
+  sdk: '>=2.13.0 <3.0.0'
 
 dependencies:
   _fe_analyzer_shared:

pkg/front_end/test/ast_nodes_has_to_string_test.dart

@@ -10,7 +10,7 @@ import 'package:kernel/class_hierarchy.dart';
 
 import 'incremental_suite.dart' as helper;
 
-main(List<String> args) async {
+void main(List<String> args) async {
   exitCode = 1;
   Map<Uri, List<Class>> classMap = {};
   Map<Uri, List<Class>> classMapWithOne = {};
@@ -24,11 +24,8 @@ main(List<String> args) async {
     Uri input = Platform.script.resolve("../tool/_fasta/compile.dart");
     CompilerOptions options = helper.getOptions();
     helper.TestIncrementalCompiler compiler =
-        new helper.TestIncrementalCompiler(
-            options,
-            input,
-            /*Uri initializeFrom*/ null,
-            /*bool outlineOnly*/ true);
+        new helper.TestIncrementalCompiler(options, input,
+            /*Uri initializeFrom*/ null, /*bool outlineOnly*/ true);
     c = await compiler.computeDelta();
     classHierarchy = compiler.getClassHierarchy()!;
     List<Library> libraries = c.libraries

pkg/front_end/test/binary_md_dill_reader.dart

@@ -167,7 +167,7 @@ class BinaryMdDillReader {
   /// Initial setup of a "class definition" in the binary.md file.
   /// This includes parsing the name, setting up any "extends"-relationship,
   /// generics etc.
-  _binaryMdHandlePossibleClassStart(String s) {
+  void _binaryMdHandlePossibleClassStart(String s) {
     if (s.startsWith("type Byte =")) return;
     if (s.startsWith("type UInt32 =")) return;
 

pkg/front_end/test/binary_md_vm_tags_and_version_git_test.dart

@@ -29,7 +29,7 @@ final RegExp tagParser = new RegExp(r"V\((\w*),\s*(\d+)\)");
 // Match stuff like "kNullConstant = 0,"
 final RegExp constantTagParser = new RegExp(r"k(\w*)\s*=\s*(\d+)");
 
-main() async {
+void main() async {
   File binaryMd = new File("$repoDir/pkg/kernel/binary.md");
   String binaryMdContent = binaryMd.readAsStringSync();
 

pkg/front_end/test/class_hierarchy/class_hierarchy_test.dart

@@ -13,7 +13,7 @@ import 'package:front_end/src/fasta/kernel/class_hierarchy_builder.dart';
 import 'package:front_end/src/testing/id_extractor.dart';
 import 'package:kernel/ast.dart';
 
-main(List<String> args) async {
+void main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve('data'));
   await runTests<Features>(dataDir,
       args: args,

pkg/front_end/test/compile_benchmark.dart

@@ -22,7 +22,7 @@ import "simple_stats.dart";
 final Uri benchmarkHelper =
     Platform.script.resolve("compile_benchmark_helper.dart");
 
-main(List<String> args) {
+void main(List<String> args) {
   List<String> arguments;
   bool tryToAnnotate = false;
   bool tryToSlowDown = false;
@@ -363,7 +363,7 @@ class RegisterCallTransformer extends RecursiveVisitor {
   List<Procedure> procedures = [];
 
   @override
-  visitLibrary(Library node) {
+  void visitLibrary(Library node) {
     if (node.importUri.scheme == "package" &&
         node.importUri.pathSegments.first == "front_end") {
       super.visitLibrary(node);
@@ -371,7 +371,7 @@ class RegisterCallTransformer extends RecursiveVisitor {
   }
 
   @override
-  visitProcedure(Procedure node) {
+  void visitProcedure(Procedure node) {
     if (node.function.body == null) return;
     int procedureNum = procedures.length;
     procedures.add(node);
@@ -395,7 +395,7 @@ class RegisterTimeTransformer extends RecursiveVisitor {
   List<Procedure> procedures = [];
 
   @override
-  visitLibrary(Library node) {
+  void visitLibrary(Library node) {
     if (node.importUri.scheme == "package" &&
         node.importUri.pathSegments.first == "front_end") {
       super.visitLibrary(node);
@@ -403,7 +403,7 @@ class RegisterTimeTransformer extends RecursiveVisitor {
   }
 
   @override
-  visitProcedure(Procedure node) {
+  void visitProcedure(Procedure node) {
     if (node.function.body == null) return;
     if (node.function.dartAsyncMarker != AsyncMarker.Sync) return;
     int procedureNum = procedures.length;

pkg/front_end/test/compile_benchmark_helper.dart

@@ -4,7 +4,7 @@
 
 import '../tool/_fasta/entry_points.dart' show compileEntryPoint;
 
-main(List<String> arguments) async {
+void main(List<String> arguments) async {
   await compileEntryPoint(arguments);
   if (numCalls.isNotEmpty) {
     print("[");

pkg/front_end/test/compile_dart2js_with_no_sdk_test.dart

@@ -6,7 +6,7 @@ import 'package:front_end/src/api_prototype/compiler_options.dart';
 
 import 'incremental_suite.dart' show TestIncrementalCompiler, getOptions;
 
-main() async {
+void main() async {
   final Uri dart2jsUrl = Uri.base.resolve("pkg/compiler/bin/dart2js.dart");
   CompilerOptions options = getOptions();
   options.sdkSummary = options.sdkSummary!.resolve("nonexisting.dill");

pkg/front_end/test/compile_with_no_sdk_test.dart

@@ -7,7 +7,7 @@ import 'package:front_end/src/api_prototype/memory_file_system.dart';
 
 import 'incremental_suite.dart' show TestIncrementalCompiler, getOptions;
 
-main() async {
+void main() async {
   await compile("import 'foo.dart' if (dart.library.bar) 'baz.dart';");
 }
 

pkg/front_end/test/constant_evaluator_benchmark.dart

@@ -130,7 +130,7 @@ class SilentErrorReporter implements constants.ErrorReporter {
 
 late IncrementalCompiler incrementalCompiler;
 
-main(List<String> arguments) async {
+void main(List<String> arguments) async {
   Uri? platformUri;
   Uri mainUri;
   bool nnbd = false;

pkg/front_end/test/covariance_check/covariance_check_test.dart

@@ -11,7 +11,7 @@ import 'package:front_end/src/testing/id_testing_helper.dart';
 import 'package:front_end/src/testing/id_testing_utils.dart';
 import 'package:kernel/ast.dart';
 
-main(List<String> args) async {
+void main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve('data'));
   await runTests<String>(dataDir,
       args: args,

pkg/front_end/test/crashing_test_case_minimizer.dart

@@ -19,7 +19,7 @@ import 'crashing_test_case_minimizer_impl.dart';
 // 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.
 
-main(List<String> arguments) async {
+void main(List<String> arguments) async {
   String filename;
   Uri loadJson;
   for (String arg in arguments) {

pkg/front_end/test/crashing_test_case_minimizer_impl.dart

@@ -132,7 +132,7 @@ class TestMinimizerSettings {
     };
   }
 
-  initializeFromJson(Map<String, dynamic> json) {
+  void initializeFromJson(Map<String, dynamic> json) {
     mainUri = Uri.parse(json["mainUri"]);
     platformUri = Uri.parse(json["platformUri"]);
     noPlatform = json["noPlatform"];
@@ -2109,7 +2109,7 @@ class _FakeFileSystem extends FileSystem {
     return new _FakeFileSystemEntity(this, uri);
   }
 
-  initializeFromJson(Map<String, dynamic> json) {
+  void initializeFromJson(Map<String, dynamic> json) {
     _initialized = true;
     _redirectAndRecord = json['_redirectAndRecord'];
     data.clear();

pkg/front_end/test/dartdoc_test_test.dart

@@ -9,7 +9,7 @@ import 'package:front_end/src/fasta/hybrid_file_system.dart';
 
 import "../tool/dart_doctest_impl.dart" as impl;
 
-main() async {
+void main() async {
   expectCategory = "comment extraction";
   testCommentExtraction();
 

pkg/front_end/test/dartdoctest_suite.dart

@@ -9,7 +9,7 @@ import 'package:testing/testing.dart'
 
 import '../tool/dart_doctest_impl.dart';
 
-main([List<String> arguments = const []]) =>
+void main([List<String> arguments = const []]) =>
     runMe(arguments, createContext, configurationPath: "../testing.json");
 
 Future<Context> createContext(

pkg/front_end/test/desugar_test.dart

@@ -23,7 +23,7 @@ import 'package:front_end/src/testing/compiler_common.dart';
 import 'package:kernel/ast.dart' as ir;
 import 'package:kernel/binary/ast_from_binary.dart' show BinaryBuilder;
 
-main() async {
+void main() async {
   await asyncTest(() async {
     await testRedirectingFactoryDirect();
     await testRedirectingFactorySerialized();
@@ -32,13 +32,13 @@ main() async {
   });
 }
 
-testRedirectingFactoryDirect() async {
+Future<void> testRedirectingFactoryDirect() async {
   var component = await compileUnit(['a.dart'], {'a.dart': aSource});
   checkIsRedirectingFactory(component, 'a.dart', 'A', 'foo');
   checkIsRedirectingFactory(component, 'core', 'Uri', 'file');
 }
 
-testRedirectingFactorySerialized() async {
+Future<void> testRedirectingFactorySerialized() async {
   var component = await compileUnit(['a.dart'], {'a.dart': aSource});
   var bytes = serializeComponent(component);
   component = new ir.Component();
@@ -49,7 +49,7 @@ testRedirectingFactorySerialized() async {
 
 // regression test: redirecting factories from patch files don't have the
 // redirecting-factory flag stored in kernel.
-testRedirectingFactoryPatchFile() async {
+Future<void> testRedirectingFactoryPatchFile() async {
   var componentUri =
       computePlatformBinariesLocation().resolve('dart2js_platform.dill');
   var component = new ir.Component();
@@ -81,7 +81,7 @@ class _B implements A {
 }
 ''';
 
-testExtensionMemberKind() async {
+Future<void> testExtensionMemberKind() async {
   var component = await compileUnit(['e.dart'], {'e.dart': extensionSource});
   var library = component.libraries
       .firstWhere((l) => l.importUri.path.endsWith('e.dart'));

pkg/front_end/test/dill_round_trip_test.dart

@@ -15,7 +15,7 @@ import 'package:kernel/target/targets.dart' show NoneTarget, TargetFlags;
 import 'incremental_suite.dart'
     show checkIsEqual, getOptions, normalCompilePlain;
 
-main() async {
+void main() async {
   final Uri dart2jsUrl = Uri.base.resolve("pkg/compiler/bin/dart2js.dart");
   Stopwatch stopwatch = new Stopwatch()..start();
   Component compiledComponent = await normalCompilePlain(dart2jsUrl,

pkg/front_end/test/enable_non_nullable/enable_non_nullable_test.dart

@@ -20,7 +20,7 @@ const Version experimentReleaseVersion = const Version(2, 9);
 /// The version used in this test as the experiment enabled version.
 const Version experimentEnabledVersion = const Version(2, 10);
 
-main() async {
+void main() async {
   print('--------------------------------------------------------------------');
   print('Test off-by-default with command-line flag');
   print('--------------------------------------------------------------------');
@@ -58,7 +58,7 @@ main() async {
       versionOptsInAllowed: experimentReleaseVersion);
 }
 
-test(
+void test(
     {bool enableNonNullableByDefault,
     bool enableNonNullableExplicitly,
     Version versionImpliesOptIn,

pkg/front_end/test/extensions/extensions_test.dart

@@ -23,7 +23,7 @@ import 'package:front_end/src/testing/id_testing_helper.dart';
 import 'package:front_end/src/testing/id_testing_utils.dart';
 import 'package:kernel/ast.dart';
 
-main(List<String> args) async {
+void main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve('data'));
   await runTests<Features>(dataDir,
       args: args,

pkg/front_end/test/fasta/ambiguous_export_test.dart

@@ -20,7 +20,7 @@ import 'package:front_end/src/fasta/dill/dill_target.dart' show DillTarget;
 import 'package:kernel/ast.dart'
     show Field, Library, Name, Component, StringLiteral;
 
-main() async {
+void main() async {
   await asyncTest(() async {
     Uri uri = Uri.parse("org.dartlang.fasta:library");
     Library library = new Library(uri, fileUri: uri);

pkg/front_end/test/fasta/analyze_git_test.dart

@@ -8,7 +8,7 @@ import 'dart:io' show exitCode;
 
 import "package:testing/src/run_tests.dart" as testing show main;
 
-main() async {
+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

pkg/front_end/test/fasta/analyze_src_with_lints_git_test.dart

@@ -8,7 +8,7 @@ import 'dart:io' show exitCode;
 
 import "package:testing/src/run_tests.dart" as testing show main;
 
-main() async {
+void main() async {
   await testing.main(<String>[
     "--config=pkg/front_end/testing_with_lints.json",
     "--verbose",

pkg/front_end/test/fasta/assert_locations_test.dart

@@ -115,7 +115,7 @@ class VerifyingVisitor extends RecursiveVisitor {
   VerifyingVisitor(this.test);
 
   @override
-  visitProcedure(Procedure node) {
+  void visitProcedure(Procedure node) {
     expectedSpan = test.spans[node.name.text];
     if (expectedSpan != null) {
       super.visitProcedure(node);
@@ -125,7 +125,7 @@ class VerifyingVisitor extends RecursiveVisitor {
   }
 
   @override
-  visitAssertStatement(AssertStatement node) {
+  void visitAssertStatement(AssertStatement node) {
     Expect.equals(expectedSpan.startOffset, node.conditionStartOffset);
     Expect.equals(expectedSpan.endOffset, node.conditionEndOffset);
   }

pkg/front_end/test/fasta/bootstrap_test.dart

@@ -107,5 +107,5 @@ class ComparisonFailed {
   ComparisonFailed(this.a, this.b);
 
   @override
-  toString() => "Error: $a is different from $b";
+  String toString() => "Error: $a is different from $b";
 }

pkg/front_end/test/fasta/expression_suite.dart

@@ -439,5 +439,5 @@ Future<Context> createContext(
   return new Context(compilerContext, errors, updateExpectations);
 }
 
-main([List<String> arguments = const []]) =>
+void main([List<String> arguments = const []]) =>
     runMe(arguments, createContext, configurationPath: "../../testing.json");

pkg/front_end/test/fasta/generator_to_string_test.dart

@@ -66,7 +66,7 @@ void check(String expected, Object generator) {
   Expect.stringEquals(expected, "$generator");
 }
 
-main() async {
+void main() async {
   await CompilerContext.runWithDefaultOptions((CompilerContext c) async {
     Token token = scanString("    myToken").tokens;
     Uri uri = Uri.parse("org-dartlang-test:my_library.dart");

pkg/front_end/test/fasta/incremental_dartino_suite.dart

@@ -244,5 +244,5 @@ Future<Context> createContext(
   return new Context(new CompilerContext(options), errors);
 }
 
-main([List<String> arguments = const []]) =>
+void main([List<String> arguments = const []]) =>
     runMe(arguments, createContext, configurationPath: "../../testing.json");

pkg/front_end/test/fasta/incremental_expectations.dart

@@ -41,7 +41,7 @@ class IncrementalExpectation {
         hasCompileTimeError: extractHasCompileTimeError(data));
   }
 
-  toJson() {
+  dynamic toJson() {
     if (!commitChangesShouldFail && !hasCompileTimeError) {
       return messages.length == 1 ? messages.first : messages;
     }

pkg/front_end/test/fasta/incremental_hello_test.dart

@@ -34,7 +34,7 @@ void diagnosticMessageHandler(DiagnosticMessage message) {
   throw "Unexpected message: ${message.plainTextFormatted.join('\n')}";
 }
 
-test({bool sdkFromSource}) async {
+Future<void> test({bool sdkFromSource}) async {
   final CompilerOptions optionBuilder = new CompilerOptions()
     ..packagesFileUri = Uri.base.resolve(".packages")
     ..target = new VmTarget(new TargetFlags())

pkg/front_end/test/fasta/link_test.dart

@@ -8,12 +8,14 @@ import 'package:_fe_analyzer_shared/src/util/link.dart' show Link, LinkBuilder;
 
 import 'package:expect/expect.dart' show Expect;
 
-main() {
+void main() {
   Link<String> strings = const Link<String>().prepend("B").prepend("A");
   Expect.stringEquals("[ A, B ]", "${strings}");
   Expect.stringEquals("[ B, A ]", "${strings.reverse(const Link<String>())}");
 
-  strings = (new LinkBuilder<String>()..addLast("A")..addLast("B"))
+  strings = (new LinkBuilder<String>()
+        ..addLast("A")
+        ..addLast("B"))
       .toLink(const Link<String>());
 
   Expect.stringEquals("[ A, B ]", "${strings}");
@@ -34,7 +36,9 @@ main() {
   Expect.stringEquals("[ A, B ]", "${strings}");
   Expect.stringEquals("[ B, A ]", "${strings.reverse(const Link<String>())}");
 
-  strings = (new LinkBuilder<String>()..addLast("A")..addLast("B"))
+  strings = (new LinkBuilder<String>()
+        ..addLast("A")
+        ..addLast("B"))
       .toLink(const Link<String>());
 
   Expect.stringEquals("[ A, B ]", "${strings}");

pkg/front_end/test/fasta/messages_suite.dart

@@ -876,5 +876,5 @@ class Script {
   }
 }
 
-main([List<String> arguments = const []]) =>
+void main([List<String> arguments = const []]) =>
     runMe(arguments, createContext, configurationPath: "../../testing.json");

pkg/front_end/test/fasta/object_supertype_test.dart

@@ -75,12 +75,12 @@ Future<List<DiagnosticMessage>> outline(String objectHeader) async {
   return messages;
 }
 
-test() async {
+Future<void> test() async {
   Set<String> normalErrors = (await outline("class Object {"))
       .map((DiagnosticMessage message) => getMessageCodeObject(message).name)
       .toSet();
 
-  check(String objectHeader, List<Code> expectedCodes) async {
+  void check(String objectHeader, List<Code> expectedCodes) async {
     List<DiagnosticMessage> messages = (await outline(objectHeader))
         .where((DiagnosticMessage message) =>
             !normalErrors.contains(getMessageCodeObject(message).name))
@@ -100,6 +100,6 @@ test() async {
       <Code>[codeObjectExtends, codeObjectMixesIn]);
 }
 
-main() {
+void main() {
   asyncTest(test);
 }

pkg/front_end/test/fasta/outline_suite.dart

@@ -13,5 +13,5 @@ Future<FastaContext> createContext(
   return FastaContext.create(suite, environment);
 }
 
-main([List<String> arguments = const []]) =>
+void main([List<String> arguments = const []]) =>
     runMe(arguments, createContext, configurationPath: "../../testing.json");

pkg/front_end/test/fasta/parser/literal_entry_info_test.dart

@@ -12,7 +12,7 @@ import 'package:front_end/src/fasta/source/diet_parser.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
-main() {
+void main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(CollectionElementTest);
     defineReflectiveTests(MapElementTest);
@@ -21,7 +21,7 @@ main() {
 
 @reflectiveTest
 class CollectionElementTest {
-  test_closingBrace() {
+  void test_closingBrace() {
     parseEntry(
       '[ }',
       [
@@ -36,7 +36,7 @@ class CollectionElementTest {
     );
   }
 
-  test_comma() {
+  void test_comma() {
     parseEntry(
       '[ ,',
       [
@@ -50,7 +50,7 @@ class CollectionElementTest {
     );
   }
 
-  test_expression() {
+  void test_expression() {
     parseEntry(
       '[ x',
       [
@@ -63,7 +63,7 @@ class CollectionElementTest {
     );
   }
 
-  test_for() {
+  void test_for() {
     parseEntry(
       '[ for (var i = 0; i < 10; ++i) 2',
       [
@@ -101,7 +101,7 @@ class CollectionElementTest {
     );
   }
 
-  test_forForFor() {
+  void test_forForFor() {
     parseEntry(
       '[ for (var i = 0; i < 10; ++i) for (x in y) for (var a in [6]) 2',
       [
@@ -178,7 +178,7 @@ class CollectionElementTest {
     );
   }
 
-  test_forIfForElse() {
+  void test_forIfForElse() {
     parseEntry(
       '[ await for (var x in y) if (a) for (b in c) 2 else 7',
       [
@@ -241,7 +241,7 @@ class CollectionElementTest {
     );
   }
 
-  test_forIn() {
+  void test_forIn() {
     parseEntry(
       '[ await for (var x in y) 2',
       [
@@ -271,7 +271,7 @@ class CollectionElementTest {
     );
   }
 
-  test_forInSpread() {
+  void test_forInSpread() {
     parseEntry(
       '[ for (var x in y) ...[2]',
       [
@@ -303,7 +303,7 @@ class CollectionElementTest {
     );
   }
 
-  test_forSpreadQ() {
+  void test_forSpreadQ() {
     parseEntry(
       '[ for (i = 0; i < 10; ++i) ...[2]',
       [
@@ -339,7 +339,7 @@ class CollectionElementTest {
     );
   }
 
-  test_if() {
+  void test_if() {
     parseEntry(
       '[ if (true) 2',
       [
@@ -354,7 +354,7 @@ class CollectionElementTest {
     );
   }
 
-  test_ifElse() {
+  void test_ifElse() {
     parseEntry(
       '[ if (true) 2 else 5',
       [
@@ -371,7 +371,7 @@ class CollectionElementTest {
     );
   }
 
-  test_ifFor() {
+  void test_ifFor() {
     parseEntry(
       '[ if (true) for (x in y) 2',
       [
@@ -405,7 +405,7 @@ class CollectionElementTest {
     );
   }
 
-  test_ifForElseIfFor() {
+  void test_ifForElseIfFor() {
     parseEntry(
       '[ if (true) for (a in b) 2 else if (c) for (d in e) 5',
       [
@@ -469,7 +469,7 @@ class CollectionElementTest {
     );
   }
 
-  test_ifSpreadQ() {
+  void test_ifSpreadQ() {
     parseEntry(
       '[ if (true) ...?[2]',
       [
@@ -487,7 +487,7 @@ class CollectionElementTest {
     );
   }
 
-  test_ifElseSpreadQ() {
+  void test_ifElseSpreadQ() {
     parseEntry(
       '[ if (true) ...?[2] else ... const {5}',
       [
@@ -512,14 +512,14 @@ class CollectionElementTest {
     );
   }
 
-  test_intLiteral() {
+  void test_intLiteral() {
     parseEntry('[ 1', [
       'handleLiteralInt 1',
       'handleLiteralList 1, [, null, ]',
     ]);
   }
 
-  test_spread() {
+  void test_spread() {
     parseEntry('[ ...[1]', [
       'handleNoTypeArguments [',
       'handleLiteralInt 1',
@@ -529,7 +529,7 @@ class CollectionElementTest {
     ]);
   }
 
-  test_spreadQ() {
+  void test_spreadQ() {
     parseEntry('[ ...?[1]', [
       'handleNoTypeArguments [',
       'handleLiteralInt 1',
@@ -565,7 +565,7 @@ class CollectionElementTest {
 
 @reflectiveTest
 class MapElementTest {
-  test_closingBrace() {
+  void test_closingBrace() {
     parseEntry(
       'before }',
       [
@@ -588,7 +588,7 @@ class MapElementTest {
     );
   }
 
-  test_comma() {
+  void test_comma() {
     parseEntry(
       'before ,',
       [
@@ -611,7 +611,7 @@ class MapElementTest {
     );
   }
 
-  test_expression() {
+  void test_expression() {
     parseEntry(
       'before x:y',
       [
@@ -628,7 +628,7 @@ class MapElementTest {
     );
   }
 
-  test_for() {
+  void test_for() {
     parseEntry(
       'before for (var i = 0; i < 10; ++i) 2:3',
       [
@@ -667,7 +667,7 @@ class MapElementTest {
     );
   }
 
-  test_forIn() {
+  void test_forIn() {
     parseEntry(
       'before await for (var x in y) 2:3',
       [
@@ -698,7 +698,7 @@ class MapElementTest {
     );
   }
 
-  test_forInSpread() {
+  void test_forInSpread() {
     parseEntry(
       'before for (var x in y) ...{2:3}',
       [
@@ -731,7 +731,7 @@ class MapElementTest {
     );
   }
 
-  test_forSpreadQ() {
+  void test_forSpreadQ() {
     parseEntry(
       'before for (i = 0; i < 10; ++i) ...?{2:7}',
       [
@@ -768,7 +768,7 @@ class MapElementTest {
     );
   }
 
-  test_if() {
+  void test_if() {
     parseEntry(
       'before if (true) 2:3',
       [
@@ -784,7 +784,7 @@ class MapElementTest {
     );
   }
 
-  test_ifSpread() {
+  void test_ifSpread() {
     parseEntry(
       'before if (true) ...{2:3}',
       [
@@ -803,7 +803,7 @@ class MapElementTest {
     );
   }
 
-  test_intLiteral() {
+  void test_intLiteral() {
     parseEntry('before 1:2', [
       'handleLiteralInt 1',
       'handleLiteralInt 2',
@@ -811,7 +811,7 @@ class MapElementTest {
     ]);
   }
 
-  test_spread() {
+  void test_spread() {
     parseEntry('before ...const {1:2}', [
       'beginConstLiteral {',
       'handleNoTypeArguments {',
@@ -824,7 +824,7 @@ class MapElementTest {
     ]);
   }
 
-  test_spreadQ() {
+  void test_spreadQ() {
     parseEntry('before ...?const {1:3}', [
       'beginConstLiteral {',
       'handleNoTypeArguments {',
@@ -1101,7 +1101,7 @@ class TestInfoListener implements Listener {
   }
 
   @override
-  noSuchMethod(Invocation invocation) {
+  dynamic noSuchMethod(Invocation invocation) {
     throw '${invocation.memberName} should not be called.';
   }
 }

pkg/front_end/test/fasta/parser/parser_suite.dart

@@ -46,5 +46,5 @@ class Parse extends Step<ScannedFile, Null, ChainContext> {
   }
 }
 
-main(List<String> arguments) =>
+void main(List<String> arguments) =>
     runMe(arguments, createContext, configurationPath: "../../../testing.json");

pkg/front_end/test/fasta/parser/token_stream_rewriter_test.dart

@@ -13,7 +13,7 @@ import 'package:_fe_analyzer_shared/src/scanner/token_impl.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
-main() {
+void main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(TokenStreamRewriterTest_NoPrevious);
     defineReflectiveTests(TokenStreamRewriterTest_UsingPrevious);

pkg/front_end/test/fasta/parser/type_info_test.dart

@@ -15,7 +15,7 @@ import 'package:front_end/src/fasta/source/diet_parser.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
-main() {
+void main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(NoTypeInfoTest);
     defineReflectiveTests(PrefixedTypeInfoTest);
@@ -304,7 +304,7 @@ class PrefixedTypeInfoTest {
     expect(prefixedType.couldBeExpression, isTrue);
 
     TypeInfoListener listener;
-    assertResult(Token actualEnd) {
+    void assertResult(Token actualEnd) {
       expect(actualEnd, expectedEnd);
       expect(listener.calls, [
         'handleIdentifier C prefixedTypeReference',
@@ -380,7 +380,7 @@ class SimpleNullableTypeTest {
     expect(simpleNullableType.couldBeExpression, isTrue);
 
     TypeInfoListener listener;
-    assertResult(Token actualEnd) {
+    void assertResult(Token actualEnd) {
       expect(actualEnd, expectedEnd);
       expect(listener.calls, [
         'handleIdentifier C typeReference',
@@ -431,7 +431,7 @@ class SimpleNullableTypeWith1ArgumentTest {
     expect(simpleNullableTypeWith1Argument.couldBeExpression, isFalse);
 
     TypeInfoListener listener;
-    assertResult(Token actualEnd) {
+    void assertResult(Token actualEnd) {
       expect(actualEnd, expectedEnd);
       expect(listener.calls, [
         'handleIdentifier C typeReference',
@@ -501,7 +501,7 @@ class SimpleTypeTest {
     expect(simpleType.couldBeExpression, isTrue);
 
     TypeInfoListener listener;
-    assertResult(Token actualEnd) {
+    void assertResult(Token actualEnd) {
       expect(actualEnd, expectedEnd);
       expect(listener.calls, [
         'handleIdentifier C typeReference',
@@ -575,7 +575,7 @@ class SimpleTypeWith1ArgumentTest {
     expect(simpleTypeWith1Argument.couldBeExpression, isFalse);
 
     TypeInfoListener listener;
-    assertResult(Token actualEnd) {
+    void assertResult(Token actualEnd) {
       expect(actualEnd, expectedEnd);
       expect(listener.calls, [
         'handleIdentifier C typeReference',
@@ -619,7 +619,7 @@ class SimpleTypeWith1ArgumentTest {
     expect(simpleTypeWith1ArgumentGtEq.couldBeExpression, isFalse);
 
     TypeInfoListener listener;
-    assertResult(Token actualEnd) {
+    void assertResult(Token actualEnd) {
       expect(actualEnd.lexeme, '>');
       expect(actualEnd.next.lexeme, '=');
       expect(actualEnd.next.next, semicolon);
@@ -664,7 +664,7 @@ class SimpleTypeWith1ArgumentTest {
     expect(simpleTypeWith1ArgumentGtGt.couldBeExpression, isFalse);
 
     TypeInfoListener listener;
-    assertResult(Token actualEnd) {
+    void assertResult(Token actualEnd) {
       expect(actualEnd.lexeme, '>');
       expect(actualEnd.next.lexeme, '>');
       expect(actualEnd.next.next, semicolon);
@@ -3019,11 +3019,11 @@ class TypeInfoListener implements Listener {
   }
 
   @override
-  noSuchMethod(Invocation invocation) {
+  dynamic noSuchMethod(Invocation invocation) {
     throw '${invocation.memberName} should not be called.';
   }
 
-  assertTokenInStream(Token match) {
+  void assertTokenInStream(Token match) {
     if (firstToken != null && match != null && !match.isEof) {
       Token token = firstToken;
       while (!token.isEof) {

pkg/front_end/test/fasta/reexport_test.dart

@@ -11,7 +11,7 @@ import "package:front_end/src/testing/compiler_common.dart" show compileUnit;
 import "package:front_end/src/api_prototype/front_end.dart"
     show CompilerOptions;
 
-main() {
+void main() {
   asyncTest(() async {
     var sources = <String, dynamic>{
       "a.dart": """

pkg/front_end/test/fasta/scanner/scanner_suite.dart

@@ -21,5 +21,5 @@ class ScannerContext extends ChainContext {
   ];
 }
 
-main(List<String> arguments) =>
+void main(List<String> arguments) =>
     runMe(arguments, createContext, configurationPath: "../../../testing.json");

pkg/front_end/test/fasta/sdk_test.dart

@@ -17,4 +17,5 @@ Future<FastaContext> createContext(
   return FastaContext.create(suite, environment);
 }
 
-main([List<String> arguments = const []]) => runMe(arguments, createContext);
+void main([List<String> arguments = const []]) =>
+    runMe(arguments, createContext);

pkg/front_end/test/fasta/strong_suite.dart

@@ -15,11 +15,11 @@ Future<FastaContext> createContext(
   return FastaContext.create(suite, environment);
 }
 
-main(List<String> arguments) {
+void main(List<String> arguments) {
   internalMain(arguments: arguments);
 }
 
-internalMain(
+void internalMain(
     {List<String> arguments = const [], int shards = 1, int shard = 0}) {
   runMe(arguments, createContext,
       configurationPath: "../../testing.json", shards: shards, shard: shard);

pkg/front_end/test/fasta/super_mixins_test.dart

@@ -90,7 +90,7 @@ DiagnosticMessageHandler _makeDiagnosticMessageHandler(Set<String> names) {
 /// Check that by default an error is reported for all unresolved super
 /// invocations: independently of weather they target abstract super members
 /// or nonexistent targets.
-testDisabledSuperMixins() async {
+Future<void> testDisabledSuperMixins() async {
   var missingSuperMethodNames = new Set<String>();
   var options = new CompilerOptions()
     ..onDiagnostic = _makeDiagnosticMessageHandler(missingSuperMethodNames);
@@ -103,7 +103,7 @@ testDisabledSuperMixins() async {
 /// super-invocation that targets an non-existent method, a super-invocation
 /// that targets an abstract member of the super-class should not be reported.
 /// In non-abstract class we should report both cases as an error.
-testEnabledSuperMixins() async {
+Future<void> testEnabledSuperMixins() async {
   var missingSuperMethodNames = new Set<String>();
   var options = new CompilerOptions()
     ..onDiagnostic = _makeDiagnosticMessageHandler(missingSuperMethodNames)

pkg/front_end/test/fasta/testing/suite.dart

@@ -2059,6 +2059,7 @@ mixin TestTarget on Target {
 }
 
 class TestVmTarget extends VmTarget with TestTarget, TestTargetMixin {
+  @override
   final TestTargetFlags flags;
 
   TestVmTarget(this.flags) : super(flags);
@@ -2136,6 +2137,7 @@ class NoneConstantsBackendWithJs extends NoneConstantsBackend {
 }
 
 class TestDart2jsTarget extends Dart2jsTarget with TestTarget, TestTargetMixin {
+  @override
   final TestTargetFlags flags;
 
   TestDart2jsTarget(String name, this.flags) : super(name, flags);
@@ -2143,6 +2145,7 @@ class TestDart2jsTarget extends Dart2jsTarget with TestTarget, TestTargetMixin {
 
 class TestDevCompilerTarget extends DevCompilerTarget
     with TestTarget, TestTargetMixin {
+  @override
   final TestTargetFlags flags;
 
   TestDevCompilerTarget(this.flags) : super(flags);

pkg/front_end/test/fasta/text_serialization_suite.dart

@@ -15,11 +15,11 @@ Future<FastaContext> createContext(
   return FastaContext.create(suite, environment);
 }
 
-main(List<String> arguments) {
+void main(List<String> arguments) {
   internalMain(arguments: arguments);
 }
 
-internalMain(
+void internalMain(
     {List<String> arguments = const [], int shards = 1, int shard = 0}) {
   runMe(arguments, createContext,
       configurationPath: "../../testing.json", shards: shards, shard: shard);

pkg/front_end/test/fasta/textual_outline_suite.dart

@@ -52,7 +52,7 @@ Future<Context> createContext(
   return new Context(environment["updateExpectations"] == "true");
 }
 
-main([List<String> arguments = const []]) =>
+void main([List<String> arguments = const []]) =>
     runMe(arguments, createContext, configurationPath: "../../testing.json");
 
 class Context extends ChainContext with MatchContext {

pkg/front_end/test/fasta/tool_git_test.dart

@@ -47,7 +47,7 @@ const List<String> unsafeTools = const <String>[
   "testing",
 ];
 
-main() {
+void main() {
   if (!Platform.isMacOS && !Platform.isLinux) {
     // The tool is a shell script and only works on Mac and Linux.
     return;

pkg/front_end/test/fasta/type_inference/factor_type_test.dart

@@ -102,7 +102,7 @@ class FactorTypeTest extends FactorTypeTestMixin<DartType> {
       typeToText(type, TypeRepresentation.analyzerNonNullableByDefault);
 }
 
-main() async {
+void main() async {
   CompilerOptions options = new CompilerOptions()
     ..explicitExperimentalFlags[ExperimentalFlag.nonNullable] = true;
   InternalCompilerResult result = await compileScript('',

pkg/front_end/test/fasta/type_inference/type_constraint_gatherer_nnbd_test.dart

@@ -14,7 +14,7 @@ import 'package:kernel/testing/type_parser_environment.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
-main() {
+void main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(TypeConstraintGathererTest);
   });

pkg/front_end/test/fasta/type_inference/type_constraint_gatherer_test.dart

@@ -14,7 +14,7 @@ import 'package:kernel/testing/type_parser_environment.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
-main() {
+void main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(TypeConstraintGathererTest);
   });

pkg/front_end/test/fasta/type_inference/type_inference_engine_test.dart

@@ -9,7 +9,7 @@ import 'package:kernel/ast.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
-main() {
+void main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(IncludesTypeParametersCovariantlyTest);
   });

pkg/front_end/test/fasta/type_inference/type_schema_elimination_nnbd_test.dart

@@ -12,7 +12,7 @@ import 'package:kernel/testing/type_parser_environment.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
-main() {
+void main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(TypeSchemaEliminationTest);
   });

pkg/front_end/test/fasta/type_inference/type_schema_elimination_test.dart

@@ -12,7 +12,7 @@ import 'package:kernel/testing/type_parser_environment.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
-main() {
+void main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(TypeSchemaEliminationTest);
   });

pkg/front_end/test/fasta/type_inference/type_schema_environment_nnbd_test.dart

@@ -13,7 +13,7 @@ import 'package:kernel/testing/type_parser_environment.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
-main() {
+void main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(TypeSchemaEnvironmentTest);
   });

pkg/front_end/test/fasta/type_inference/type_schema_environment_test.dart

@@ -13,7 +13,7 @@ import 'package:kernel/testing/type_parser_environment.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
-main() {
+void main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(TypeSchemaEnvironmentTest);
   });

pkg/front_end/test/fasta/type_inference/type_schema_test.dart

@@ -9,7 +9,7 @@ import 'package:kernel/ast.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
-main() {
+void main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(UnknownTypeTest);
   });

pkg/front_end/test/fasta/types/dart2js_benchmark.dart

@@ -8,5 +8,5 @@ import "dart:io" show Platform;
 
 import "subtypes_benchmark.dart" show run;
 
-main() =>
+void main() =>
     run(Platform.script.resolve("benchmark_data/dart2js.json.gz"), "Dart2js");

pkg/front_end/test/fasta/types/dart2js_benchmark_test.dart

@@ -6,4 +6,4 @@
 
 import "dart2js_benchmark.dart" as bench show main;
 
-main() => bench.main();
+void main() => bench.main();

pkg/front_end/test/fasta/types/dill_hierachy_test.dart

@@ -14,7 +14,8 @@ import "package:kernel/core_types.dart" show CoreTypes;
 
 import "package:kernel/target/targets.dart" show NoneTarget, TargetFlags;
 
-import 'package:kernel/testing/type_parser_environment.dart' show parseComponent;
+import 'package:kernel/testing/type_parser_environment.dart'
+    show parseComponent;
 
 import "package:front_end/src/api_prototype/compiler_options.dart"
     show CompilerOptions;
@@ -100,7 +101,7 @@ F:
   interfaceSetters:
 """;
 
-main() {
+void main() {
   final Ticker ticker = new Ticker(isVerbose: false);
   final Component component = parseComponent("""
 class A;

pkg/front_end/test/fasta/types/fasta_legacy_upper_bound_test.dart

@@ -63,7 +63,7 @@ class FastaLegacyUpperBoundTest extends LegacyUpperBoundTest {
   }
 }
 
-main() {
+void main() {
   final Ticker ticker = new Ticker();
   final CompilerContext context = new CompilerContext(new ProcessedOptions(
       options: new CompilerOptions()

pkg/front_end/test/fasta/types/fasta_types_test.dart

@@ -40,7 +40,7 @@ import 'kernel_type_parser_test.dart' show parseSdk;
 
 import "shared_type_tests.dart" show SubtypeTest;
 
-main() {
+void main() {
   final Ticker ticker = new Ticker(isVerbose: false);
   final CompilerContext context = new CompilerContext(new ProcessedOptions(
       options: new CompilerOptions()

pkg/front_end/test/fasta/types/hashcode_test.dart

@@ -21,7 +21,7 @@ FunctionType createTTo_VoidToR() {
       typeParameters: [T]);
 }
 
-test1() {
+void test1() {
   DartType voidToR1 = createVoidToR();
   DartType voidToR2 = createVoidToR();
   DartType voidToR3 = createTTo_VoidToR().returnType;
@@ -48,7 +48,7 @@ FunctionType createVoidTo_VoidToR() {
       typeParameters: [R]);
 }
 
-test2() {
+void test2() {
   FunctionType outer1 = createVoidTo_VoidToR();
   FunctionType outer2 = createVoidTo_VoidToR();
   DartType voidToR1 = outer1.returnType;
@@ -61,6 +61,6 @@ test2() {
       "Hash code mismatch for outer1 vs outer2."); // false, on no!
 }
 
-main() {
+void main() {
   test2();
 }

pkg/front_end/test/fasta/types/kernel_legacy_upper_bound_test.dart

@@ -30,6 +30,6 @@ class KernelLegacyUpperBoundTest extends LegacyUpperBoundTest {
   }
 }
 
-main() {
+void main() {
   new KernelLegacyUpperBoundTest().test();
 }

pkg/front_end/test/fasta/types/kernel_type_parser_test.dart

@@ -114,7 +114,7 @@ Component parseSdk(Uri uri, TypeParserEnvironment environment) {
   return new Component(libraries: <Library>[library]);
 }
 
-main() {
+void main() {
   Uri uri = Uri.parse("dart:core");
   TypeParserEnvironment environment = new TypeParserEnvironment(uri, uri);
   Component component = parseSdk(uri, environment);

pkg/front_end/test/fasta/types/large_app_benchmark.dart

@@ -8,5 +8,5 @@ import "dart:io" show Platform;
 
 import "subtypes_benchmark.dart" show run;
 
-main() => run(
+void main() => run(
     Platform.script.resolve("benchmark_data/large_app.json.gz"), "LargeApp");

pkg/front_end/test/fasta/types/large_app_benchmark_test.dart

@@ -6,4 +6,4 @@
 
 import "large_app_benchmark.dart" as bench show main;
 
-main() => bench.main();
+void main() => bench.main();

pkg/front_end/test/fasta/types/subtypes_benchmark.dart

@@ -178,4 +178,4 @@ Future<void> run(Uri benchmarkInput, String name) async {
       "${fastaWatch.elapsedMilliseconds / runs} ms");
 }
 
-main() => run(Uri.base.resolve("type_checks.json"), "***");
+void main() => run(Uri.base.resolve("type_checks.json"), "***");

pkg/front_end/test/fasta/uri_translator_test.dart

@@ -10,7 +10,7 @@ import 'package:package_config/package_config.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
-main() {
+void main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(UriTranslatorImplTest);
   });

pkg/front_end/test/fasta/util/direct_parser_ast_test.dart

@@ -12,7 +12,7 @@ import 'package:front_end/src/fasta/util/direct_parser_ast_helper.dart';
 
 Uri base;
 
-main(List<String> args) {
+void main(List<String> args) {
   File script = new File.fromUri(Platform.script);
   base = script.parent.uri;
 

pkg/front_end/test/fasta/weak_suite.dart

@@ -14,11 +14,11 @@ Future<FastaContext> createContext(
   return FastaContext.create(suite, environment);
 }
 
-main(List<String> arguments) {
+void main(List<String> arguments) {
   internalMain(arguments: arguments);
 }
 
-internalMain(
+void internalMain(
         {List<String> arguments = const [], int shards = 1, int shard = 0}) =>
     runMe(arguments, createContext,
         configurationPath: "../../testing.json", shard: shard, shards: shards);

pkg/front_end/test/ffi_test.dart

@@ -6,7 +6,7 @@
 
 import 'package:expect/expect.dart';
 
-main() {
+void main() {
   // TODO(dacoharkes): implement dart:ffi tests
   Expect.isTrue(true);
 }

pkg/front_end/test/flutter_gallery_leak_tester.dart

@@ -26,7 +26,7 @@ Set<String> files = {};
 // but assumes that flutter has been setup as by the script
 // `tools/bots/flutter/compile_flutter.sh`.
 
-main(List<String> args) async {
+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 "

pkg/front_end/test/generated_files_up_to_date_git_test.dart

@@ -20,7 +20,7 @@ import 'utils/io_utils.dart' show computeRepoDirUri;
 
 final Uri repoDir = computeRepoDirUri();
 
-main() async {
+void main() async {
   messages();
   experimentalFlags();
   directParserAstHelper();

pkg/front_end/test/hot_reload_e2e_test.dart

@@ -66,7 +66,7 @@ abstract class TestCase {
     }
   }
 
-  setUp() async {
+  Future<void> setUp() async {
     outDir = Directory.systemTemp.createTempSync('hotreload_test');
     outputUri = outDir.uri.resolve('test.dill');
     var root = Uri.parse('org-dartlang-test:///');
@@ -81,7 +81,7 @@ abstract class TestCase {
     await rebuild(compiler, outputUri); // this is a full compile.
   }
 
-  tearDown() async {
+  Future<void> tearDown() async {
     outDir.deleteSync(recursive: true);
     lines = null;
   }
@@ -102,7 +102,7 @@ abstract class TestCase {
 
   /// Start the VM with the first version of the program compiled by the
   /// incremental compiler.
-  startProgram(int reloadCount) async {
+  Future<void> startProgram(int reloadCount) async {
     var vmArgs = [
       '--enable-vm-service=0', // Note: use 0 to avoid port collisions.
       '--pause_isolates_on_start',
@@ -289,7 +289,7 @@ class ReloadToplevelField extends TestCase {
   }
 }
 
-main() {
+void main() {
   asyncTest(() async {
     await new InitialProgramIsValid().test();
     await new ReloadAfterLeafLibraryModification().test();

pkg/front_end/test/id_testing/id_testing_test.dart

@@ -30,7 +30,7 @@ import 'package:kernel/ast.dart'
         Library,
         TreeNode;
 
-main(List<String> args) async {
+void main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve('data'));
   await runTests<String>(dataDir,
       args: args,

pkg/front_end/test/id_tests/assigned_variables_test.dart

@@ -19,7 +19,7 @@ import 'package:front_end/src/testing/id_testing_helper.dart';
 import 'package:front_end/src/testing/id_testing_utils.dart';
 import 'package:kernel/ast.dart' hide Variance;
 
-main(List<String> args) async {
+void main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve(
       '../../../_fe_analyzer_shared/test/flow_analysis/assigned_variables/'
       'data'));