diff --git a/pkg/analysis_server/lib/src/services/correction/dart/bind_to_field.dart b/pkg/analysis_server/lib/src/services/correction/dart/bind_to_field.dart
index 7bef682da9a..8dfc845cc9a 100644
--- a/pkg/analysis_server/lib/src/services/correction/dart/bind_to_field.dart
+++ b/pkg/analysis_server/lib/src/services/correction/dart/bind_to_field.dart
@@ -105,6 +105,8 @@ class BindToField extends ResolvedCorrectionProducer {
             ConstructorDeclaration() => false,
             FieldDeclaration() => false,
             MethodDeclaration() => member.name.lexeme == parameter.name?.lexeme,
+            // ignore: experimental_member_use
+            PrimaryConstructorBody() => false,
           },
         )) {
       return;
diff --git a/pkg/analysis_server/lib/src/services/correction/dart/create_method.dart b/pkg/analysis_server/lib/src/services/correction/dart/create_method.dart
index 8c133279787..e55987412e6 100644
--- a/pkg/analysis_server/lib/src/services/correction/dart/create_method.dart
+++ b/pkg/analysis_server/lib/src/services/correction/dart/create_method.dart
@@ -160,6 +160,8 @@ class CreateMethod extends ResolvedCorrectionProducer {
             fields: VariableDeclarationList(:var isLate),
           ) =>
             isStatic || !isLate,
+          // ignore: experimental_member_use
+          PrimaryConstructorBody() => false,
         };
       }
     } else {
diff --git a/pkg/analyzer/api.txt b/pkg/analyzer/api.txt
index 4db2bcd1c88..3c0a052d9f9 100644
--- a/pkg/analyzer/api.txt
+++ b/pkg/analyzer/api.txt
@@ -247,6 +247,7 @@ package:analyzer/analysis_rule/rule_visitor_registry.dart:
     addPostfixExpression (method: void Function(AbstractAnalysisRule, AstVisitor<dynamic>))
     addPrefixExpression (method: void Function(AbstractAnalysisRule, AstVisitor<dynamic>))
     addPrefixedIdentifier (method: void Function(AbstractAnalysisRule, AstVisitor<dynamic>))
+    addPrimaryConstructorBody (method: void Function(AbstractAnalysisRule, AstVisitor<dynamic>), experimental)
     addPrimaryConstructorDeclaration (method: void Function(AbstractAnalysisRule, AstVisitor<dynamic>), experimental)
     addPrimaryConstructorName (method: void Function(AbstractAnalysisRule, AstVisitor<dynamic>), experimental)
     addPropertyAccess (method: void Function(AbstractAnalysisRule, AstVisitor<dynamic>))
@@ -771,6 +772,7 @@ package:analyzer/dart/ast/ast.dart:
     visitPostfixExpression (method: R? Function(PostfixExpression))
     visitPrefixExpression (method: R? Function(PrefixExpression))
     visitPrefixedIdentifier (method: R? Function(PrefixedIdentifier))
+    visitPrimaryConstructorBody (method: R? Function(PrimaryConstructorBody), experimental)
     visitPrimaryConstructorDeclaration (method: R? Function(PrimaryConstructorDeclaration), experimental)
     visitPrimaryConstructorName (method: R? Function(PrimaryConstructorName), experimental)
     visitPropertyAccess (method: R? Function(PropertyAccess))
@@ -893,7 +895,7 @@ package:analyzer/dart/ast/ast.dart:
     sealedKeyword (getter: Token?)
     typeParameters (getter: TypeParameterList?)
     withClause (getter: WithClause?)
-  ClassMember (class extends Object implements Declaration, sealed (immediate subtypes: ClassMemberImpl, ConstructorDeclaration, FieldDeclaration, MethodDeclaration))
+  ClassMember (class extends Object implements Declaration, sealed (immediate subtypes: ClassMemberImpl, ConstructorDeclaration, FieldDeclaration, MethodDeclaration, PrimaryConstructorBody))
   ClassNamePart (class extends Object implements AstNode, sealed (immediate subtypes: ClassNamePartImpl, NameWithTypeParameters, PrimaryConstructorDeclaration), experimental):
     typeName (getter: Token)
     typeParameters (getter: TypeParameterList?)
@@ -1555,6 +1557,11 @@ package:analyzer/dart/ast/ast.dart:
     isDeferred (getter: bool)
     period (getter: Token)
     prefix (getter: SimpleIdentifier)
+  PrimaryConstructorBody (class extends Object implements ClassMember, experimental):
+    body (getter: FunctionBody)
+    colon (getter: Token?)
+    initializers (getter: NodeList<ConstructorInitializer>)
+    thisKeyword (getter: Token)
   PrimaryConstructorDeclaration (class extends Object implements ClassNamePart, experimental):
     constKeyword (getter: Token?)
     constructorName (getter: PrimaryConstructorName?)
@@ -2343,6 +2350,7 @@ package:analyzer/dart/ast/visitor.dart:
     visitPostfixExpression (method: R? Function(PostfixExpression))
     visitPrefixExpression (method: R? Function(PrefixExpression))
     visitPrefixedIdentifier (method: R? Function(PrefixedIdentifier))
+    visitPrimaryConstructorBody (method: R? Function(PrimaryConstructorBody), experimental)
     visitPrimaryConstructorDeclaration (method: R? Function(PrimaryConstructorDeclaration), experimental)
     visitPrimaryConstructorName (method: R? Function(PrimaryConstructorName), experimental)
     visitPropertyAccess (method: R? Function(PropertyAccess))
@@ -2534,6 +2542,7 @@ package:analyzer/dart/ast/visitor.dart:
     visitPostfixExpression (method: R? Function(PostfixExpression))
     visitPrefixExpression (method: R? Function(PrefixExpression))
     visitPrefixedIdentifier (method: R? Function(PrefixedIdentifier))
+    visitPrimaryConstructorBody (method: R? Function(PrimaryConstructorBody), experimental)
     visitPrimaryConstructorDeclaration (method: R? Function(PrimaryConstructorDeclaration), experimental)
     visitPrimaryConstructorName (method: R? Function(PrimaryConstructorName), experimental)
     visitPropertyAccess (method: R? Function(PropertyAccess))
@@ -2715,6 +2724,7 @@ package:analyzer/dart/ast/visitor.dart:
     visitPostfixExpression (method: R? Function(PostfixExpression))
     visitPrefixExpression (method: R? Function(PrefixExpression))
     visitPrefixedIdentifier (method: R? Function(PrefixedIdentifier))
+    visitPrimaryConstructorBody (method: R? Function(PrimaryConstructorBody), experimental)
     visitPrimaryConstructorDeclaration (method: R? Function(PrimaryConstructorDeclaration), experimental)
     visitPrimaryConstructorName (method: R? Function(PrimaryConstructorName), experimental)
     visitPropertyAccess (method: R? Function(PropertyAccess))
@@ -2896,6 +2906,7 @@ package:analyzer/dart/ast/visitor.dart:
     visitPostfixExpression (method: R? Function(PostfixExpression))
     visitPrefixExpression (method: R? Function(PrefixExpression))
     visitPrefixedIdentifier (method: R? Function(PrefixedIdentifier))
+    visitPrimaryConstructorBody (method: R? Function(PrimaryConstructorBody), experimental)
     visitPrimaryConstructorDeclaration (method: R? Function(PrimaryConstructorDeclaration), experimental)
     visitPrimaryConstructorName (method: R? Function(PrimaryConstructorName), experimental)
     visitPropertyAccess (method: R? Function(PropertyAccess))
@@ -3078,6 +3089,7 @@ package:analyzer/dart/ast/visitor.dart:
     visitPostfixExpression (method: T? Function(PostfixExpression))
     visitPrefixExpression (method: T? Function(PrefixExpression))
     visitPrefixedIdentifier (method: T? Function(PrefixedIdentifier))
+    visitPrimaryConstructorBody (method: T? Function(PrimaryConstructorBody), experimental)
     visitPrimaryConstructorDeclaration (method: T? Function(PrimaryConstructorDeclaration), experimental)
     visitPrimaryConstructorName (method: T? Function(PrimaryConstructorName), experimental)
     visitPropertyAccess (method: T? Function(PropertyAccess))
@@ -3260,6 +3272,7 @@ package:analyzer/dart/ast/visitor.dart:
     visitPostfixExpression (method: R? Function(PostfixExpression))
     visitPrefixExpression (method: R? Function(PrefixExpression))
     visitPrefixedIdentifier (method: R? Function(PrefixedIdentifier))
+    visitPrimaryConstructorBody (method: R? Function(PrimaryConstructorBody), experimental)
     visitPrimaryConstructorDeclaration (method: R? Function(PrimaryConstructorDeclaration), experimental)
     visitPrimaryConstructorName (method: R? Function(PrimaryConstructorName), experimental)
     visitPropertyAccess (method: R? Function(PropertyAccess))
diff --git a/pkg/analyzer/lib/analysis_rule/rule_visitor_registry.g.dart b/pkg/analyzer/lib/analysis_rule/rule_visitor_registry.g.dart
index bdbfb7307aa..7091d40782e 100644
--- a/pkg/analyzer/lib/analysis_rule/rule_visitor_registry.g.dart
+++ b/pkg/analyzer/lib/analysis_rule/rule_visitor_registry.g.dart
@@ -335,6 +335,9 @@ abstract class RuleVisitorRegistry {
 
   void addPrefixExpression(AbstractAnalysisRule rule, AstVisitor visitor);
 
+  @experimental
+  void addPrimaryConstructorBody(AbstractAnalysisRule rule, AstVisitor visitor);
+
   @experimental
   void addPrimaryConstructorDeclaration(
     AbstractAnalysisRule rule,
diff --git a/pkg/analyzer/lib/dart/ast/ast.dart b/pkg/analyzer/lib/dart/ast/ast.dart
index e7dd4e53e15..b025022d637 100644
--- a/pkg/analyzer/lib/dart/ast/ast.dart
+++ b/pkg/analyzer/lib/dart/ast/ast.dart
@@ -203,6 +203,7 @@ export 'package:analyzer/src/dart/ast/ast.dart'
         PostfixExpression,
         PrefixedIdentifier,
         PrefixExpression,
+        PrimaryConstructorBody,
         PrimaryConstructorDeclaration,
         PrimaryConstructorName,
         PropertyAccess,
diff --git a/pkg/analyzer/lib/dart/ast/visitor.g.dart b/pkg/analyzer/lib/dart/ast/visitor.g.dart
index 7323502d90c..dff248bc90e 100644
--- a/pkg/analyzer/lib/dart/ast/visitor.g.dart
+++ b/pkg/analyzer/lib/dart/ast/visitor.g.dart
@@ -535,6 +535,11 @@ class GeneralizingAstVisitor<R> implements AstVisitor<R> {
   @override
   R? visitPrefixExpression(PrefixExpression node) => visitExpression(node);
 
+  @experimental
+  @override
+  R? visitPrimaryConstructorBody(PrimaryConstructorBody node) =>
+      visitClassMember(node);
+
   @experimental
   @override
   R? visitPrimaryConstructorDeclaration(PrimaryConstructorDeclaration node) =>
@@ -1529,6 +1534,13 @@ class RecursiveAstVisitor<R> implements AstVisitor<R> {
     return null;
   }
 
+  @experimental
+  @override
+  R? visitPrimaryConstructorBody(PrimaryConstructorBody node) {
+    node.visitChildren(this);
+    return null;
+  }
+
   @experimental
   @override
   R? visitPrimaryConstructorDeclaration(PrimaryConstructorDeclaration node) {
@@ -2245,6 +2257,10 @@ class SimpleAstVisitor<R> implements AstVisitor<R> {
   @override
   R? visitPrefixExpression(PrefixExpression node) => null;
 
+  @experimental
+  @override
+  R? visitPrimaryConstructorBody(PrimaryConstructorBody node) => null;
+
   @experimental
   @override
   R? visitPrimaryConstructorDeclaration(PrimaryConstructorDeclaration node) =>
@@ -2825,6 +2841,10 @@ class ThrowingAstVisitor<R> implements AstVisitor<R> {
   @override
   R? visitPrefixExpression(PrefixExpression node) => _throw(node);
 
+  @experimental
+  @override
+  R? visitPrimaryConstructorBody(PrimaryConstructorBody node) => _throw(node);
+
   @experimental
   @override
   R? visitPrimaryConstructorDeclaration(PrimaryConstructorDeclaration node) =>
@@ -4054,6 +4074,15 @@ class TimedAstVisitor<T> implements AstVisitor<T> {
     return result;
   }
 
+  @experimental
+  @override
+  T? visitPrimaryConstructorBody(PrimaryConstructorBody node) {
+    stopwatch.start();
+    T? result = _baseVisitor.visitPrimaryConstructorBody(node);
+    stopwatch.stop();
+    return result;
+  }
+
   @experimental
   @override
   T? visitPrimaryConstructorDeclaration(PrimaryConstructorDeclaration node) {
@@ -4901,6 +4930,11 @@ class UnifyingAstVisitor<R> implements AstVisitor<R> {
   @override
   R? visitPrefixExpression(PrefixExpression node) => visitNode(node);
 
+  @experimental
+  @override
+  R? visitPrimaryConstructorBody(PrimaryConstructorBody node) =>
+      visitNode(node);
+
   @experimental
   @override
   R? visitPrimaryConstructorDeclaration(PrimaryConstructorDeclaration node) =>
diff --git a/pkg/analyzer/lib/src/dart/analysis/unlinked_api_signature.dart b/pkg/analyzer/lib/src/dart/analysis/unlinked_api_signature.dart
index 8cdc6298575..022a0cba5b1 100644
--- a/pkg/analyzer/lib/src/dart/analysis/unlinked_api_signature.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/unlinked_api_signature.dart
@@ -24,6 +24,7 @@ class _UnitApiSignatureComputer {
   static const int _kindConstructorDeclaration = 1;
   static const int _kindFieldDeclaration = 2;
   static const int _kindMethodDeclaration = 3;
+  static const int _kindPrimaryConstructorBody = 4;
   static const int _nullNode = 0;
   static const int _notNullNode = 1;
   static const int _nullToken = 0;
@@ -89,6 +90,8 @@ class _UnitApiSignatureComputer {
         _addFieldDeclaration(member, hasConstConstructor);
       } else if (member is MethodDeclaration) {
         _addMethodDeclaration(member);
+      } else if (member is PrimaryConstructorBody) {
+        _addPrimaryConstructorBody(member);
       } else {
         throw UnimplementedError('(${member.runtimeType}) $member');
       }
@@ -188,6 +191,11 @@ class _UnitApiSignatureComputer {
     }
   }
 
+  void _addPrimaryConstructorBody(PrimaryConstructorBody node) {
+    signature.addInt(_kindPrimaryConstructorBody);
+    _addTokens(node.beginToken, node.body.beginToken);
+  }
+
   void _addToken(Token? token) {
     if (token != null) {
       signature.addInt(_notNullToken);
diff --git a/pkg/analyzer/lib/src/dart/ast/ast.dart b/pkg/analyzer/lib/src/dart/ast/ast.dart
index 76b48d4e044..aef508af60f 100644
--- a/pkg/analyzer/lib/src/dart/ast/ast.dart
+++ b/pkg/analyzer/lib/src/dart/ast/ast.dart
@@ -20035,6 +20035,126 @@ final class PrefixExpressionImpl extends ExpressionImpl
   }
 }
 
+/// The body of a primary constructor.
+@AnalyzerPublicApi(message: 'exported by lib/dart/ast/ast.dart')
+@experimental
+// TODO(scheglov): This should not be a `Declaration`.
+abstract final class PrimaryConstructorBody implements ClassMember {
+  /// The body of the constructor.
+  FunctionBody get body;
+
+  /// The token for the separator before [initializers], or `null` if there
+  /// are no initializers.
+  Token? get colon;
+
+  /// The initializers associated with the constructor.
+  NodeList<ConstructorInitializer> get initializers;
+
+  /// The token for the `this` keyword.
+  Token get thisKeyword;
+}
+
+@GenerateNodeImpl(
+  childEntitiesOrder: [
+    GenerateNodeProperty('thisKeyword'),
+    GenerateNodeProperty('colon'),
+    GenerateNodeProperty('initializers'),
+    GenerateNodeProperty('body'),
+  ],
+)
+final class PrimaryConstructorBodyImpl extends ClassMemberImpl
+    implements PrimaryConstructorBody {
+  @generated
+  @override
+  final Token thisKeyword;
+
+  @generated
+  @override
+  final Token? colon;
+
+  @generated
+  @override
+  final NodeListImpl<ConstructorInitializerImpl> initializers =
+      NodeListImpl._();
+
+  @generated
+  FunctionBodyImpl _body;
+
+  @generated
+  PrimaryConstructorBodyImpl({
+    required super.comment,
+    required super.metadata,
+    required this.thisKeyword,
+    required this.colon,
+    required List<ConstructorInitializerImpl> initializers,
+    required FunctionBodyImpl body,
+  }) : _body = body {
+    this.initializers._initialize(this, initializers);
+    _becomeParentOf(body);
+  }
+
+  @generated
+  @override
+  FunctionBodyImpl get body => _body;
+
+  @generated
+  set body(FunctionBodyImpl body) {
+    _body = _becomeParentOf(body);
+  }
+
+  @generated
+  @override
+  Token get endToken {
+    return body.endToken;
+  }
+
+  @generated
+  @override
+  Token get firstTokenAfterCommentAndMetadata {
+    return thisKeyword;
+  }
+
+  @generated
+  @override
+  ChildEntities get _childEntities => super._childEntities
+    ..addToken('thisKeyword', thisKeyword)
+    ..addToken('colon', colon)
+    ..addNodeList('initializers', initializers)
+    ..addNode('body', body);
+
+  @generated
+  @override
+  E? accept<E>(AstVisitor<E> visitor) =>
+      visitor.visitPrimaryConstructorBody(this);
+
+  @override
+  dynamic noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
+
+  @generated
+  @override
+  void visitChildren(AstVisitor visitor) {
+    super.visitChildren(visitor);
+    initializers.accept(visitor);
+    body.accept(visitor);
+  }
+
+  @generated
+  @override
+  AstNodeImpl? _childContainingRange(int rangeOffset, int rangeEnd) {
+    if (super._childContainingRange(rangeOffset, rangeEnd) case var result?) {
+      return result;
+    }
+    if (initializers._elementContainingRange(rangeOffset, rangeEnd)
+        case var result?) {
+      return result;
+    }
+    if (body._containsOffset(rangeOffset, rangeEnd)) {
+      return body;
+    }
+    return null;
+  }
+}
+
 /// The declaration of a primary constructor.
 @AnalyzerPublicApi(message: 'exported by lib/dart/ast/ast.dart')
 @experimental
diff --git a/pkg/analyzer/lib/src/dart/ast/ast.g.dart b/pkg/analyzer/lib/src/dart/ast/ast.g.dart
index fa8d2626e25..cd149ab1d50 100644
--- a/pkg/analyzer/lib/src/dart/ast/ast.g.dart
+++ b/pkg/analyzer/lib/src/dart/ast/ast.g.dart
@@ -287,6 +287,9 @@ abstract class AstVisitor<R> {
 
   R? visitPrefixExpression(PrefixExpression node);
 
+  @experimental
+  R? visitPrimaryConstructorBody(PrimaryConstructorBody node);
+
   @experimental
   R? visitPrimaryConstructorDeclaration(PrimaryConstructorDeclaration node);
 
diff --git a/pkg/analyzer/lib/src/dart/ast/to_source_visitor.dart b/pkg/analyzer/lib/src/dart/ast/to_source_visitor.dart
index 0e7078c9597..41333c136cc 100644
--- a/pkg/analyzer/lib/src/dart/ast/to_source_visitor.dart
+++ b/pkg/analyzer/lib/src/dart/ast/to_source_visitor.dart
@@ -1151,6 +1151,17 @@ class ToSourceVisitor implements AstVisitor<void> {
     _writeOperand(node, node.operand);
   }
 
+  @override
+  void visitPrimaryConstructorBody(PrimaryConstructorBody node) {
+    _visitNodeList(node.metadata, separator: ' ', suffix: ' ');
+    _visitToken(node.thisKeyword);
+    if (node.initializers.isNotEmpty) {
+      _visitToken(node.colon, prefix: ' ', suffix: ' ');
+      _visitNodeList(node.initializers, separator: ', ');
+    }
+    _visitFunctionBody(node.body);
+  }
+
   @override
   void visitPrimaryConstructorDeclaration(PrimaryConstructorDeclaration node) {
     _visitToken(node.constKeyword, suffix: ' ');
diff --git a/pkg/analyzer/lib/src/error/duplicate_definition_verifier.dart b/pkg/analyzer/lib/src/error/duplicate_definition_verifier.dart
index 0cbad83a231..33e8aae046c 100644
--- a/pkg/analyzer/lib/src/error/duplicate_definition_verifier.dart
+++ b/pkg/analyzer/lib/src/error/duplicate_definition_verifier.dart
@@ -477,6 +477,9 @@ class MemberDuplicateDefinitionVerifier {
               _checkValuesDeclarationInEnum(member.name);
             }
           }
+        case PrimaryConstructorBodyImpl():
+          // TODO(scheglov): Handle this case.
+          throw UnimplementedError();
       }
     }
 
diff --git a/pkg/analyzer/lib/src/fasta/ast_builder.dart b/pkg/analyzer/lib/src/fasta/ast_builder.dart
index 33e8d024adc..b9f77444551 100644
--- a/pkg/analyzer/lib/src/fasta/ast_builder.dart
+++ b/pkg/analyzer/lib/src/fasta/ast_builder.dart
@@ -3167,15 +3167,24 @@ class AstBuilder extends StackListener {
     Token? beginInitializers,
     Token endToken,
   ) {
-    // TODO(declaring-constructors): Implement primary constructor body.
-    // ignore: unused_local_variable
-    var bodyObject = pop();
-    // ignore: unused_local_variable
+    assert(optional('this', beginToken));
+
+    var body = pop() as FunctionBodyImpl;
     var initializers = (pop() as List<ConstructorInitializerImpl>?) ?? const [];
-    // ignore: unused_local_variable
-    var separator = pop() as Token?;
-    // ignore: unused_local_variable
+    var colon = pop() as Token?;
     var metadata = pop() as List<AnnotationImpl>?;
+    var comment = _findComment(metadata, beginToken);
+
+    _classLikeBuilder!.members.add(
+      PrimaryConstructorBodyImpl(
+        comment: comment,
+        metadata: metadata,
+        thisKeyword: beginToken,
+        colon: colon,
+        initializers: initializers,
+        body: body,
+      ),
+    );
   }
 
   @override
diff --git a/pkg/analyzer/lib/src/lint/linter_visitor.g.dart b/pkg/analyzer/lib/src/lint/linter_visitor.g.dart
index 3feea101df4..999feb33637 100644
--- a/pkg/analyzer/lib/src/lint/linter_visitor.g.dart
+++ b/pkg/analyzer/lib/src/lint/linter_visitor.g.dart
@@ -804,6 +804,13 @@ class AnalysisRuleVisitor implements AstVisitor<void> {
     node.visitChildren(this);
   }
 
+  @experimental
+  @override
+  void visitPrimaryConstructorBody(PrimaryConstructorBody node) {
+    _runSubscriptions(node, _registry._forPrimaryConstructorBody);
+    node.visitChildren(this);
+  }
+
   @experimental
   @override
   void visitPrimaryConstructorDeclaration(PrimaryConstructorDeclaration node) {
@@ -1462,6 +1469,9 @@ class RuleVisitorRegistryImpl implements RuleVisitorRegistry {
 
   final List<_Subscription<PrefixExpression>> _forPrefixExpression = [];
 
+  final List<_Subscription<PrimaryConstructorBody>> _forPrimaryConstructorBody =
+      [];
+
   final List<_Subscription<PrimaryConstructorDeclaration>>
   _forPrimaryConstructorDeclaration = [];
 
@@ -2356,6 +2366,16 @@ class RuleVisitorRegistryImpl implements RuleVisitorRegistry {
     _forPrefixExpression.add(_Subscription(rule, visitor, _getTimer(rule)));
   }
 
+  @override
+  void addPrimaryConstructorBody(
+    AbstractAnalysisRule rule,
+    AstVisitor visitor,
+  ) {
+    _forPrimaryConstructorBody.add(
+      _Subscription(rule, visitor, _getTimer(rule)),
+    );
+  }
+
   @override
   void addPrimaryConstructorDeclaration(
     AbstractAnalysisRule rule,
diff --git a/pkg/analyzer/lib/src/test_utilities/find_node.dart b/pkg/analyzer/lib/src/test_utilities/find_node.dart
index 790a163c97c..daf157aa939 100644
--- a/pkg/analyzer/lib/src/test_utilities/find_node.dart
+++ b/pkg/analyzer/lib/src/test_utilities/find_node.dart
@@ -156,6 +156,8 @@ class FindNode {
 
   PrefixExpression get singlePrefixExpression => _single();
 
+  PrimaryConstructorBody get singlePrimaryConstructorBody => _single();
+
   PropertyAccess get singlePropertyAccess => _single();
 
   RecordLiteral get singleRecordLiteral => _single();
diff --git a/pkg/analyzer/test/src/dart/analysis/unlinked_api_signature_test.dart b/pkg/analyzer/test/src/dart/analysis/unlinked_api_signature_test.dart
index 10c642e9186..9d465629be3 100644
--- a/pkg/analyzer/test/src/dart/analysis/unlinked_api_signature_test.dart
+++ b/pkg/analyzer/test/src/dart/analysis/unlinked_api_signature_test.dart
@@ -3,7 +3,9 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analyzer/dart/analysis/utilities.dart';
+import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/src/dart/analysis/unlinked_api_signature.dart';
+import 'package:analyzer/src/dart/ast/ast.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
@@ -17,6 +19,10 @@ main() {
 
 @reflectiveTest
 class UnitApiSignatureTest {
+  void tearDown() {
+    useDeclaringConstructorsAst = default_useDeclaringConstructorsAst;
+  }
+
   test_class_annotation() async {
     _assertNotSameSignature(
       r'''
@@ -503,6 +509,57 @@ abstract class C {}
     );
   }
 
+  test_class_primaryConstructorBody_body() {
+    useDeclaringConstructorsAst = true;
+    _assertSameSignature(
+      r'''
+class C() {
+  this { 0; }
+}
+''',
+      r'''
+class C() {
+  this { 1; }
+}
+''',
+    );
+  }
+
+  test_class_primaryConstructorBody_initializer_const() {
+    useDeclaringConstructorsAst = true;
+    _assertNotSameSignature(
+      r'''
+class const C() {
+  final int f;
+  this: f = 1;
+}
+''',
+      r'''
+class const C() {
+  final int f;
+  this: f = 2;
+}
+''',
+    );
+  }
+
+  test_class_primaryConstructorBody_metadata() {
+    useDeclaringConstructorsAst = true;
+    _assertNotSameSignature(
+      r'''
+class C() {
+  this;
+}
+''',
+      r'''
+class C() {
+  @deprecated
+  this;
+}
+''',
+    );
+  }
+
   test_class_with() {
     _assertNotSameSignature(
       r'''
diff --git a/pkg/analyzer/test/src/dart/ast/to_source_visitor_test.dart b/pkg/analyzer/test/src/dart/ast/to_source_visitor_test.dart
index 160080c230b..2c4d9ad5cda 100644
--- a/pkg/analyzer/test/src/dart/ast/to_source_visitor_test.dart
+++ b/pkg/analyzer/test/src/dart/ast/to_source_visitor_test.dart
@@ -3953,6 +3953,48 @@ class ToSourceVisitorTest_declaringConstructors extends ToSourceVisitorTest {
     var findNode = _parseStringToFindNode(code);
     _assertSource(code, findNode.extensionTypeDeclaration(code));
   }
+
+  void test_visitPrimaryConstructorBody_block() {
+    var code = 'this {foo();}';
+    var findNode = _parseStringToFindNode('''
+class A() {
+  $code
+}
+''');
+    _assertSource(code, findNode.singlePrimaryConstructorBody);
+  }
+
+  void test_visitPrimaryConstructorBody_initializers() {
+    var code = 'this : x = 0, y = 1;';
+    var findNode = _parseStringToFindNode('''
+class A() {
+  final int x;
+  final int y;
+  $code
+}
+''');
+    _assertSource(code, findNode.singlePrimaryConstructorBody);
+  }
+
+  void test_visitPrimaryConstructorBody_metadata() {
+    var code = '@deprecated this;';
+    var findNode = _parseStringToFindNode('''
+class A() {
+  $code
+}
+''');
+    _assertSource(code, findNode.singlePrimaryConstructorBody);
+  }
+
+  void test_visitPrimaryConstructorBody_simple() {
+    var code = 'this;';
+    var findNode = _parseStringToFindNode('''
+class A() {
+  $code
+}
+''');
+    _assertSource(code, findNode.singlePrimaryConstructorBody);
+  }
 }
 
 @reflectiveTest
diff --git a/pkg/analyzer/test/src/dart/parser/class_test.dart b/pkg/analyzer/test/src/dart/parser/class_test.dart
index 7ba9484bfea..b6a5ae0b5c6 100644
--- a/pkg/analyzer/test/src/dart/parser/class_test.dart
+++ b/pkg/analyzer/test/src/dart/parser/class_test.dart
@@ -1156,6 +1156,108 @@ ClassDeclaration
 ''');
   }
 
+  test_primaryConstructorBody_body_blockFunctionBody() {
+    useDeclaringConstructorsAst = true;
+    var parseResult = parseStringWithErrors(r'''
+class A() {
+  this {
+    0;
+  }
+}
+''');
+    parseResult.assertNoErrors();
+
+    var node = parseResult.findNode.singlePrimaryConstructorBody;
+    assertParsedNodeText(node, r'''
+PrimaryConstructorBody
+  thisKeyword: this
+  body: BlockFunctionBody
+    block: Block
+      leftBracket: {
+      statements
+        ExpressionStatement
+          expression: IntegerLiteral
+            literal: 0
+          semicolon: ;
+      rightBracket: }
+''');
+  }
+
+  test_primaryConstructorBody_comment() {
+    useDeclaringConstructorsAst = true;
+    var parseResult = parseStringWithErrors(r'''
+class A() {
+  /// foo
+  /// bar
+  this;
+}
+''');
+    parseResult.assertNoErrors();
+
+    var node = parseResult.findNode.singlePrimaryConstructorBody;
+    assertParsedNodeText(node, r'''
+PrimaryConstructorBody
+  documentationComment: Comment
+    tokens
+      /// foo
+      /// bar
+  thisKeyword: this
+  body: EmptyFunctionBody
+    semicolon: ;
+''');
+  }
+
+  test_primaryConstructorBody_fieldInitializer() {
+    useDeclaringConstructorsAst = true;
+    var parseResult = parseStringWithErrors(r'''
+class A() {
+  final int x;
+  this : x = 0;
+}
+''');
+    parseResult.assertNoErrors();
+
+    var node = parseResult.findNode.singlePrimaryConstructorBody;
+    assertParsedNodeText(node, r'''
+PrimaryConstructorBody
+  thisKeyword: this
+  colon: :
+  initializers
+    ConstructorFieldInitializer
+      fieldName: SimpleIdentifier
+        token: x
+      equals: =
+      expression: IntegerLiteral
+        literal: 0
+  body: EmptyFunctionBody
+    semicolon: ;
+''');
+  }
+
+  test_primaryConstructorBody_metadata() {
+    useDeclaringConstructorsAst = true;
+    var parseResult = parseStringWithErrors(r'''
+class A() {
+  @deprecated
+  this;
+}
+''');
+    parseResult.assertNoErrors();
+
+    var node = parseResult.findNode.singlePrimaryConstructorBody;
+    assertParsedNodeText(node, r'''
+PrimaryConstructorBody
+  metadata
+    Annotation
+      atSign: @
+      name: SimpleIdentifier
+        token: deprecated
+  thisKeyword: this
+  body: EmptyFunctionBody
+    semicolon: ;
+''');
+  }
+
   test_setter_formalParameters_absent() {
     var parseResult = parseStringWithErrors(r'''
 class A {
diff --git a/pkg/analyzer/test/src/dart/parser/enum_test.dart b/pkg/analyzer/test/src/dart/parser/enum_test.dart
index 7c7267ba25b..897b1ea9fa0 100644
--- a/pkg/analyzer/test/src/dart/parser/enum_test.dart
+++ b/pkg/analyzer/test/src/dart/parser/enum_test.dart
@@ -626,6 +626,25 @@ EnumDeclaration
       EnumConstantDeclaration
         name: v
     rightBracket: }
+''');
+  }
+
+  test_primaryConstructorBody() {
+    useDeclaringConstructorsAst = true;
+    var parseResult = parseStringWithErrors(r'''
+enum E() {
+  v;
+  this;
+}
+''');
+    parseResult.assertNoErrors();
+
+    var node = parseResult.findNode.singlePrimaryConstructorBody;
+    assertParsedNodeText(node, r'''
+PrimaryConstructorBody
+  thisKeyword: this
+  body: EmptyFunctionBody
+    semicolon: ;
 ''');
   }
 }
diff --git a/pkg/analyzer/test/src/dart/parser/extension_test.dart b/pkg/analyzer/test/src/dart/parser/extension_test.dart
index 13e983cada5..f0269230936 100644
--- a/pkg/analyzer/test/src/dart/parser/extension_test.dart
+++ b/pkg/analyzer/test/src/dart/parser/extension_test.dart
@@ -289,4 +289,33 @@ ExtensionDeclaration
 ''');
     }
   }
+
+  test_primaryConstructorBody() {
+    useDeclaringConstructorsAst = true;
+    var parseResult = parseStringWithErrors(r'''
+extension A on int {
+  this;
+}
+''');
+    parseResult.assertNoErrors();
+
+    var node = parseResult.findNode.singleExtensionDeclaration;
+    assertParsedNodeText(node, r'''
+ExtensionDeclaration
+  extensionKeyword: extension
+  name: A
+  onClause: ExtensionOnClause
+    onKeyword: on
+    extendedType: NamedType
+      name: int
+  body: BlockClassBody
+    leftBracket: {
+    members
+      PrimaryConstructorBody
+        thisKeyword: this
+        body: EmptyFunctionBody
+          semicolon: ;
+    rightBracket: }
+''');
+  }
 }
diff --git a/pkg/analyzer/test/src/dart/parser/extension_type_test.dart b/pkg/analyzer/test/src/dart/parser/extension_type_test.dart
index 0a374167bb0..a5f7fc39b0b 100644
--- a/pkg/analyzer/test/src/dart/parser/extension_type_test.dart
+++ b/pkg/analyzer/test/src/dart/parser/extension_type_test.dart
@@ -2159,6 +2159,40 @@ ExtensionTypeDeclaration
     }
   }
 
+  test_primaryConstructorBody() {
+    useDeclaringConstructorsAst = true;
+    var parseResult = parseStringWithErrors(r'''
+extension type A(int it) {
+  this;
+}
+''');
+    parseResult.assertNoErrors();
+
+    var node = parseResult.findNode.singleExtensionTypeDeclaration;
+    assertParsedNodeText(node, r'''
+ExtensionTypeDeclaration
+  extensionKeyword: extension
+  typeKeyword: type
+  primaryConstructor: PrimaryConstructorDeclaration
+    typeName: A
+    formalParameters: FormalParameterList
+      leftParenthesis: (
+      parameter: SimpleFormalParameter
+        type: NamedType
+          name: int
+        name: it
+      rightParenthesis: )
+  body: BlockClassBody
+    leftBracket: {
+    members
+      PrimaryConstructorBody
+        thisKeyword: this
+        body: EmptyFunctionBody
+          semicolon: ;
+    rightBracket: }
+''');
+  }
+
   test_withImplementsClause() {
     var parseResult = parseStringWithErrors(r'''
 extension type A(int it) implements B, C {}
diff --git a/pkg/analyzer/test/src/dart/parser/mixin_test.dart b/pkg/analyzer/test/src/dart/parser/mixin_test.dart
index 1966f629551..5851e0e2618 100644
--- a/pkg/analyzer/test/src/dart/parser/mixin_test.dart
+++ b/pkg/analyzer/test/src/dart/parser/mixin_test.dart
@@ -287,6 +287,31 @@ MixinDeclaration
   name: A
   leftBracket: {
   rightBracket: }
+''');
+  }
+
+  test_primaryConstructorBody() {
+    useDeclaringConstructorsAst = true;
+    var parseResult = parseStringWithErrors(r'''
+mixin A {
+  this;
+}
+''');
+    parseResult.assertNoErrors();
+
+    var node = parseResult.findNode.singleMixinDeclaration;
+    assertParsedNodeText(node, r'''
+MixinDeclaration
+  mixinKeyword: mixin
+  name: A
+  body: BlockClassBody
+    leftBracket: {
+    members
+      PrimaryConstructorBody
+        thisKeyword: this
+        body: EmptyFunctionBody
+          semicolon: ;
+    rightBracket: }
 ''');
   }
 }
diff --git a/pkg/analyzer/test/src/summary/resolved_ast_printer.dart b/pkg/analyzer/test/src/summary/resolved_ast_printer.dart
index 33334856e19..ad2f51b4b84 100644
--- a/pkg/analyzer/test/src/summary/resolved_ast_printer.dart
+++ b/pkg/analyzer/test/src/summary/resolved_ast_printer.dart
@@ -1347,6 +1347,14 @@ class ResolvedAstPrinter extends ThrowingAstVisitor<void> {
     });
   }
 
+  @override
+  void visitPrimaryConstructorBody(PrimaryConstructorBody node) {
+    _sink.writeln('PrimaryConstructorBody');
+    _sink.withIndent(() {
+      _writeNamedChildEntities(node);
+    });
+  }
+
   @override
   void visitPrimaryConstructorDeclaration(PrimaryConstructorDeclaration node) {
     _sink.writeln('PrimaryConstructorDeclaration');
diff --git a/pkg/analyzer/tool/generators/ast_generator.dart b/pkg/analyzer/tool/generators/ast_generator.dart
index 2378d96adc8..da40e792de9 100644
--- a/pkg/analyzer/tool/generators/ast_generator.dart
+++ b/pkg/analyzer/tool/generators/ast_generator.dart
@@ -708,6 +708,8 @@ void visitChildren(AstVisitor visitor) {''');
               implClass.doNotGenerateLookupNames.add(memberName);
               continue;
             }
+          case PrimaryConstructorBodyImpl():
+            throw UnimplementedError();
         }
         if (implClass.generatedLookupNames.contains(memberName)) {
           replacements.add(_Replacement(member.offset, member.end, ''));
diff --git a/pkg/linter/lib/src/rules/analyzer_element_model_tracking.dart b/pkg/linter/lib/src/rules/analyzer_element_model_tracking.dart
index 3bea37c95fd..575753d452f 100644
--- a/pkg/linter/lib/src/rules/analyzer_element_model_tracking.dart
+++ b/pkg/linter/lib/src/rules/analyzer_element_model_tracking.dart
@@ -151,6 +151,10 @@ class _Visitor extends SimpleAstVisitor<void> {
                   trackingAnnotations.forEach(_reportBad);
                 }
             }
+          // ignore: experimental_member_use
+          case PrimaryConstructorBody():
+            // TODO(scheglov): Handle this case.
+            throw UnimplementedError();
         }
       }
     }
diff --git a/pkg/linter/lib/src/rules/unreachable_from_main.dart b/pkg/linter/lib/src/rules/unreachable_from_main.dart
index 8011236594f..452423e8a37 100644
--- a/pkg/linter/lib/src/rules/unreachable_from_main.dart
+++ b/pkg/linter/lib/src/rules/unreachable_from_main.dart
@@ -137,6 +137,10 @@ class _DeclarationGatherer {
               declarations.add(member);
             }
           }
+        // ignore: experimental_member_use
+        case PrimaryConstructorBody():
+          // TODO(scheglov): Handle this case.
+          throw UnimplementedError();
       }
     }
   }