[analysis_server] Add semantic highlighting for sealed class modifier.

Enable the 'sealed-class' experiment for the highlighting test and add the highlighting for the modifier.

Change-Id: I6affdab506c29ab9d92b2d6315a93d09396bafaa
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/277201
Reviewed-by: Samuel Rawlins <srawlins@google.com>
Commit-Queue: Kallen Tu <kallentu@google.com>

pkg/analysis_server/lib/src/computer/computer_highlights.dart

@@ -664,6 +664,7 @@ class _DartUnitHighlightsComputerVisitor extends RecursiveAstVisitor<void> {
   void visitClassDeclaration(ClassDeclaration node) {
     computer._addRegion_token(
         node.abstractKeyword, HighlightRegionType.BUILT_IN);
+    computer._addRegion_token(node.sealedKeyword, HighlightRegionType.BUILT_IN);
     computer._addRegion_token(node.classKeyword, HighlightRegionType.KEYWORD);
     computer._addRegion_token(node.name, HighlightRegionType.CLASS);
     super.visitClassDeclaration(node);
@@ -673,6 +674,7 @@ class _DartUnitHighlightsComputerVisitor extends RecursiveAstVisitor<void> {
   void visitClassTypeAlias(ClassTypeAlias node) {
     computer._addRegion_token(
         node.abstractKeyword, HighlightRegionType.BUILT_IN);
+    computer._addRegion_token(node.sealedKeyword, HighlightRegionType.BUILT_IN);
     super.visitClassTypeAlias(node);
   }
 
@@ -1079,6 +1081,7 @@ class _DartUnitHighlightsComputerVisitor extends RecursiveAstVisitor<void> {
 
   @override
   void visitMixinDeclaration(MixinDeclaration node) {
+    computer._addRegion_token(node.sealedKeyword, HighlightRegionType.BUILT_IN);
     computer._addRegion_token(node.mixinKeyword, HighlightRegionType.BUILT_IN);
     super.visitMixinDeclaration(node);
   }

pkg/analysis_server/test/analysis/notification_highlights2_test.dart

@@ -8,6 +8,7 @@ import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_constants.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analyzer/source/source_range.dart';
+import 'package:analyzer/src/dart/analysis/experiments.dart';
 import 'package:analyzer/src/test_utilities/test_code_format.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:collection/collection.dart';
@@ -25,6 +26,10 @@ void main() {
 
 @reflectiveTest
 class AnalysisNotificationHighlightsTest extends HighlightsTestSupport {
+  @override
+  List<String> get experiments =>
+      [...super.experiments, EnableString.sealed_class];
+
   void assertHighlightText(TestCode testCode, int index, String expected) {
     var actual = _getHighlightText(testCode, index);
     if (actual != expected) {
@@ -364,6 +369,22 @@ void f() {
     assertNoRegion(HighlightRegionType.BUILT_IN, 'of = 2');
   }
 
+  Future<void> test_BUILT_IN_sealed() async {
+    addTestFile('''
+sealed class A {}
+sealed mixin M {}
+sealed class B = Object with M;
+void f() {
+  var sealed = 42;
+}
+''');
+    await prepareHighlights();
+    assertHasRegion(HighlightRegionType.BUILT_IN, 'sealed class A');
+    assertHasRegion(HighlightRegionType.BUILT_IN, 'sealed mixin M');
+    assertHasRegion(HighlightRegionType.BUILT_IN, 'sealed class B');
+    assertNoRegion(HighlightRegionType.BUILT_IN, 'sealed = 42');
+  }
+
   Future<void> test_BUILT_IN_set() async {
     addTestFile('''
 set aaa(x) {}

pkg/analyzer/lib/dart/ast/ast.dart

@@ -1001,10 +1001,12 @@ abstract class ClassAugmentationDeclaration
 /// The declaration of a class.
 ///
 ///    classDeclaration ::=
-///        'abstract'? 'class' name [TypeParameterList]?
+///        classModifiers? 'class' name [TypeParameterList]?
 ///        [ExtendsClause]? [WithClause]? [ImplementsClause]?
 ///        '{' [ClassMember]* '}'
 ///
+///    classModifiers ::= 'sealed' | 'abstract'
+///
 /// Clients may not extend, implement or mix-in this class.
 abstract class ClassDeclaration implements ClassOrAugmentationDeclaration {
   @override
@@ -1090,6 +1092,9 @@ abstract class ClassOrAugmentationDeclaration
   /// Returns the right curly bracket.
   Token get rightBracket;
 
+  /// Return the 'sealed' keyword, or `null` if the keyword was absent.
+  Token? get sealedKeyword;
+
   /// Returns the type parameters for the class, or `null` if the class does
   /// not have any type parameters.
   TypeParameterList? get typeParameters;
@@ -1127,6 +1132,9 @@ abstract class ClassTypeAlias implements TypeAlias {
   /// implements clause.
   ImplementsClause? get implementsClause;
 
+  /// Return the 'sealed' keyword, or `null` if the keyword was absent.
+  Token? get sealedKeyword;
+
   /// Return the name of the superclass of the class being declared.
   NamedType get superclass;
 
@@ -3752,7 +3760,7 @@ abstract class MixinAugmentationDeclaration
 /// The declaration of a mixin.
 ///
 ///    mixinDeclaration ::=
-///        'mixin' name [TypeParameterList]?
+///        'sealed'? 'mixin' name [TypeParameterList]?
 ///        [OnClause]? [ImplementsClause]? '{' [ClassMember]* '}'
 ///
 /// Clients may not extend, implement or mix-in this class.
@@ -3821,6 +3829,9 @@ abstract class MixinOrAugmentationDeclaration
   /// Returns the right curly bracket.
   Token get rightBracket;
 
+  /// Return the 'sealed' keyword, or `null` if the keyword was absent.
+  Token? get sealedKeyword;
+
   /// Returns the type parameters for the mixin, or `null` if the mixin does
   /// not have any type parameters.
   TypeParameterList? get typeParameters;

pkg/analyzer/lib/src/dart/ast/ast.dart

@@ -1891,10 +1891,13 @@ class ChildEntity {
 /// The declaration of a class.
 ///
 ///    classDeclaration ::=
-///        'abstract'? 'class' [SimpleIdentifier] [TypeParameterList]?
+///        classModifiers? 'class' [SimpleIdentifier] [TypeParameterList]?
 ///        ([ExtendsClause] [WithClause]?)?
 ///        [ImplementsClause]?
 ///        '{' [ClassMember]* '}'
+///
+///    classModifiers ::= 'sealed' | 'abstract'
+///
 class ClassDeclarationImpl extends NamedCompilationUnitMemberImpl
     implements ClassDeclaration {
   /// The 'abstract' keyword, or `null` if the keyword was absent.
@@ -1908,6 +1911,7 @@ class ClassDeclarationImpl extends NamedCompilationUnitMemberImpl
   final Token? inlineKeyword;
 
   /// The 'sealed' keyword, or `null` if the keyword was absent.
+  @override
   final Token? sealedKeyword;
 
   /// The 'augment' keyword, or `null` if the keyword was absent.
@@ -2127,6 +2131,7 @@ class ClassTypeAliasImpl extends TypeAliasImpl implements ClassTypeAlias {
 
   /// The token for the 'sealed' keyword, or `null` if this is not defining a
   /// sealed class.
+  @override
   final Token? sealedKeyword;
 
   /// The token for the 'augment' keyword, or `null` if this is not defining an
@@ -8918,7 +8923,7 @@ class MethodInvocationImpl extends InvocationExpressionImpl
 /// The declaration of a mixin.
 ///
 ///    mixinDeclaration ::=
-///        metadata? 'mixin' [SimpleIdentifier] [TypeParameterList]?
+///        'sealed'? metadata? 'mixin' [SimpleIdentifier] [TypeParameterList]?
 ///        [RequiresClause]? [ImplementsClause]? '{' [ClassMember]* '}'
 class MixinDeclarationImpl extends NamedCompilationUnitMemberImpl
     implements MixinDeclaration {
@@ -8926,6 +8931,7 @@ class MixinDeclarationImpl extends NamedCompilationUnitMemberImpl
   final Token? augmentKeyword;
 
   /// Return the 'sealed' keyword, or `null` if the keyword was absent.
+  @override
   final Token? sealedKeyword;
 
   @override