[parser] Handle empty class/extension type body

This is part of #61699

Change-Id: I93afc3426771c5a179fc77993433ae82aec05ff1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/459460
Commit-Queue: Johnni Winther <johnniwinther@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Erik Ernst <eernst@google.com>

Author: johnniwinther

pkg/_fe_analyzer_shared/lib/src/parser/forwarding_listener.dart

@@ -2115,11 +2115,21 @@ class ForwardingListener implements Listener {
     listener?.handleNoArguments(token);
   }
 
+  @override
+  void handleNoClassBody(Token semicolonToken) {
+    listener?.handleNoClassBody(semicolonToken);
+  }
+
   @override
   void handleNoConstructorReferenceContinuationAfterTypeArguments(Token token) {
     listener?.handleNoConstructorReferenceContinuationAfterTypeArguments(token);
   }
 
+  @override
+  void handleNoExtensionTypeBody(Token semicolonToken) {
+    listener?.handleNoExtensionTypeBody(semicolonToken);
+  }
+
   @override
   void handleNoFieldInitializer(Token token) {
     listener?.handleNoFieldInitializer(token);

pkg/_fe_analyzer_shared/lib/src/parser/listener.dart

@@ -208,6 +208,16 @@ abstract class Listener implements UnescapeErrorListener {
     logEvent("ClassDeclaration");
   }
 
+  /// Handle `;` as a class body.
+  void handleNoClassBody(Token semicolonToken) {
+    logEvent("NoClassBody");
+  }
+
+  /// Handle `;` as an extension type body.
+  void handleNoExtensionTypeBody(Token semicolonToken) {
+    logEvent("NoExtensionTypeBody");
+  }
+
   /// Handle the beginning of a mixin declaration.
   void beginMixinDeclaration(
     Token beginToken,

pkg/_fe_analyzer_shared/lib/src/parser/parser_impl.dart

@@ -3051,6 +3051,10 @@ class Parser {
   /// typeWithParameters
   ///     :    typeIdentifier typeParameters?
   ///     ;
+  /// classBody
+  ///     :    '{' (metadata memberDeclaration)* '}'
+  ///     |    ';'
+  ///     ;
   /// ```
   Token parseClass(
     Token token,
@@ -3066,16 +3070,28 @@ class Parser {
       /* forExtensionType = */ false,
     );
     token = parseClassHeaderOpt(token, beginToken, classKeyword);
-    if (!token.next!.isA(TokenType.OPEN_CURLY_BRACKET)) {
-      // Recovery
-      token = parseClassHeaderRecovery(start, beginToken, classKeyword);
-      ensureBlock(token, BlockKind.classDeclaration);
+    if (token.next!.isA(TokenType.SEMICOLON)) {
+      Token semicolonToken = token = token.next!;
+      if (!_isDeclaringConstructorsFeatureEnabled) {
+        reportExperimentNotEnabled(
+          ExperimentalFlag.declaringConstructors,
+          semicolonToken,
+          semicolonToken,
+        );
+      }
+      listener.handleNoClassBody(semicolonToken);
+    } else {
+      if (!token.next!.isA(TokenType.OPEN_CURLY_BRACKET)) {
+        // Recovery
+        token = parseClassHeaderRecovery(start, beginToken, classKeyword);
+        ensureBlock(token, BlockKind.classDeclaration);
+      }
+      token = parseClassOrMixinOrExtensionBody(
+        token,
+        DeclarationKind.Class,
+        className,
+      );
     }
-    token = parseClassOrMixinOrExtensionBody(
-      token,
-      DeclarationKind.Class,
-      className,
-    );
     listener.endClassDeclaration(beginToken, token);
     return token;
   }
@@ -3751,19 +3767,31 @@ class Parser {
     );
     Token start = token;
     token = parseClassOrMixinOrEnumImplementsOpt(token);
-    if (!token.next!.isA(TokenType.OPEN_CURLY_BRACKET)) {
-      // TODO(johnniwinther): Reuse logic from [parseClassHeaderRecovery] to
-      // handle `extends`, `with` and out-of-order/duplicate clauses.
-      token = parseExtensionTypeHeaderRecovery(start, extensionKeyword);
+    if (token.next!.isA(TokenType.SEMICOLON)) {
+      Token semicolonToken = token = token.next!;
+      if (!_isDeclaringConstructorsFeatureEnabled) {
+        reportExperimentNotEnabled(
+          ExperimentalFlag.declaringConstructors,
+          semicolonToken,
+          semicolonToken,
+        );
+      }
+      listener.handleNoExtensionTypeBody(semicolonToken);
+    } else {
+      if (!token.next!.isA(TokenType.OPEN_CURLY_BRACKET)) {
+        // TODO(johnniwinther): Reuse logic from [parseClassHeaderRecovery] to
+        // handle `extends`, `with` and out-of-order/duplicate clauses.
+        token = parseExtensionTypeHeaderRecovery(start, extensionKeyword);
 
-      // Recovery
-      ensureBlock(token, BlockKind.extensionTypeDeclaration);
+        // Recovery
+        ensureBlock(token, BlockKind.extensionTypeDeclaration);
+      }
+      token = parseClassOrMixinOrExtensionBody(
+        token,
+        DeclarationKind.ExtensionType,
+        name.lexeme,
+      );
     }
-    token = parseClassOrMixinOrExtensionBody(
-      token,
-      DeclarationKind.ExtensionType,
-      name.lexeme,
-    );
     listener.endExtensionTypeDeclaration(
       beginToken,
       augmentToken,

pkg/analyzer/lib/src/fasta/ast_builder.dart

@@ -5356,13 +5356,37 @@ class AstBuilder extends StackListener {
     }
   }
 
+  @override
+  void handleNoClassBody(Token semicolonToken) {
+    debugEvent("NoClassBody");
+    // TODO(scheglov): Handle omitted class body.
+    var builder = _classLikeBuilder;
+    if (builder != null) {
+      builder
+        ..leftBracket = semicolonToken
+        ..rightBracket = semicolonToken;
+    }
+  }
+
   @override
   void handleNoConstructorReferenceContinuationAfterTypeArguments(Token token) {
     debugEvent("NoConstructorReferenceContinuationAfterTypeArguments");
 
     push(NullValues.ConstructorReferenceContinuationAfterTypeArguments);
   }
 
+  @override
+  void handleNoExtensionTypeBody(Token semicolonToken) {
+    debugEvent("NoExtensionTypeBody");
+    // TODO(scheglov): Handle omitted extension type body.
+    var builder = _classLikeBuilder;
+    if (builder != null) {
+      builder
+        ..leftBracket = semicolonToken
+        ..rightBracket = semicolonToken;
+    }
+  }
+
   @override
   void handleNoFieldInitializer(Token token) {
     debugEvent("NoFieldInitializer");

pkg/front_end/lib/src/source/diet_listener.dart

@@ -1026,6 +1026,38 @@ class DietListener extends StackListenerImpl {
     _memberScope = currentDeclaration.bodyScope;
   }
 
+  @override
+  // Coverage-ignore(suite): Not run.
+  void handleNoClassBody(Token semicolonToken) {
+    assert(
+      checkState(semicolonToken, [
+        ValueKinds.Token,
+        ValueKinds.IdentifierOrParserRecoveryOrNull,
+        ValueKinds.TokenOrNull,
+      ]),
+    );
+    debugEvent("NoClassBody");
+    pop(); // Begin token
+    pop(); // Name
+    pop(); // Annotation begin token.
+  }
+
+  @override
+  // Coverage-ignore(suite): Not run.
+  void handleNoExtensionTypeBody(Token semicolonToken) {
+    assert(
+      checkState(semicolonToken, [
+        ValueKinds.Token,
+        ValueKinds.IdentifierOrParserRecoveryOrNull,
+        ValueKinds.TokenOrNull,
+      ]),
+    );
+    debugEvent("NoExtensionTypeBody");
+    pop(); // Begin token
+    pop(); // Name
+    pop(); // Annotation begin token.
+  }
+
   @override
   void endClassOrMixinOrExtensionBody(
     DeclarationKind kind,

pkg/front_end/lib/src/source/outline_builder.dart

@@ -4613,6 +4613,20 @@ class OutlineBuilder extends StackListenerImpl {
     nativeMethodName = null;
   }
 
+  @override
+  // Coverage-ignore(suite): Not run.
+  void handleNoClassBody(Token semicolonToken) {
+    debugEvent("NoClassBody");
+    _builderFactory.beginClassBody();
+  }
+
+  @override
+  // Coverage-ignore(suite): Not run.
+  void handleNoExtensionTypeBody(Token semicolonToken) {
+    debugEvent("NoExtensionTypeBody");
+    _builderFactory.beginExtensionTypeBody();
+  }
+
   @override
   void endClassOrMixinOrExtensionBody(
     DeclarationKind kind,

pkg/front_end/lib/src/util/parser_ast.dart

@@ -1167,13 +1167,23 @@ extension NamedMixinApplicationExtension on NamedMixinApplicationEnd {
 
 extension ClassDeclarationExtension on ClassDeclarationEnd {
   // Coverage-ignore(suite): Not run.
-  ClassOrMixinOrExtensionBodyEnd getClassOrMixinOrExtensionBody() {
+  ClassOrMixinOrExtensionBodyEnd? getClassOrMixinOrExtensionBody() {
     for (ParserAstNode child in children!) {
       if (child is ClassOrMixinOrExtensionBodyEnd) {
         return child;
       }
     }
-    throw "Not found.";
+    return null;
+  }
+
+  // Coverage-ignore(suite): Not run.
+  NoClassBodyHandle? getNoClassBody() {
+    for (ParserAstNode child in children!) {
+      if (child is NoClassBodyHandle) {
+        return child;
+      }
+    }
+    return null;
   }
 
   // Coverage-ignore(suite): Not run.
@@ -1212,12 +1222,15 @@ extension ClassDeclarationExtension on ClassDeclarationEnd {
 }
 
 // Coverage-ignore(suite): Not run.
-extension ClassOrMixinBodyExtension on ClassOrMixinOrExtensionBodyEnd {
+extension ClassOrMixinBodyExtension on ClassOrMixinOrExtensionBodyEnd? {
   List<MemberEnd> getMembers() {
     List<MemberEnd> members = [];
-    for (ParserAstNode child in children!) {
-      if (child is MemberEnd) {
-        members.add(child);
+    List<ParserAstNode>? children = this?.children;
+    if (children != null) {
+      for (ParserAstNode child in children) {
+        if (child is MemberEnd) {
+          members.add(child);
+        }
       }
     }
     return members;
@@ -1712,13 +1725,22 @@ extension ExtensionTypeDeclarationExtension on ExtensionTypeDeclarationEnd {
     return begin.name;
   }
 
-  ClassOrMixinOrExtensionBodyEnd getClassOrMixinOrExtensionBody() {
+  ClassOrMixinOrExtensionBodyEnd? getClassOrMixinOrExtensionBody() {
     for (ParserAstNode child in children!) {
       if (child is ClassOrMixinOrExtensionBodyEnd) {
         return child;
       }
     }
-    throw "Not found.";
+    return null;
+  }
+
+  NoExtensionTypeBodyHandle? getNoExtensionTypeBody() {
+    for (ParserAstNode child in children!) {
+      if (child is NoExtensionTypeBodyHandle) {
+        return child;
+      }
+    }
+    return null;
   }
 }