Extension types. Report self reference in implements clause.

Change-Id: Icd26dcd6cf7521e075d6a8f13a985f3185c02369
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/319584
Reviewed-by: Phil Quitslund <pquitslund@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

pkg/analysis_server/lib/src/services/correction/error_fix_status.yaml

@@ -652,6 +652,8 @@ CompileTimeErrorCode.EXTENSION_TYPE_DECLARES_MEMBER_OF_OBJECT:
     Offer to delete the invalid member.
 CompileTimeErrorCode.EXTENSION_TYPE_IMPLEMENTS_DISALLOWED_TYPE:
   status: noFix
+CompileTimeErrorCode.EXTENSION_TYPE_IMPLEMENTS_ITSELF:
+  status: noFix
 CompileTimeErrorCode.EXTENSION_TYPE_INHERITED_MEMBER_CONFLICT:
   status: noFix
 CompileTimeErrorCode.EXTENSION_TYPE_REPRESENTATION_DEPENDS_ON_ITSELF:

pkg/analyzer/lib/src/dart/analysis/driver.dart

@@ -87,7 +87,7 @@ import 'package:analyzer/src/utilities/uri_cache.dart';
 /// TODO(scheglov) Clean up the list of implicitly analyzed files.
 class AnalysisDriver implements AnalysisDriverGeneric {
   /// The version of data format, should be incremented on every format change.
-  static const int DATA_VERSION = 296;
+  static const int DATA_VERSION = 297;
 
   /// The number of exception contexts allowed to write. Once this field is
   /// zero, we stop writing any new exception contexts in this process.

pkg/analyzer/lib/src/dart/element/element.dart

@@ -2967,8 +2967,13 @@ class ExtensionTypeElementImpl extends InterfaceElementImpl
   @override
   late final DartType typeErasure;
 
-  /// Whether the element has direct or indirect reference to itself.
-  bool hasSelfReference = false;
+  /// Whether the element has direct or indirect reference to itself,
+  /// in representation.
+  bool hasRepresentationSelfReference = false;
+
+  /// Whether the element has direct or indirect reference to itself,
+  /// in implemented superinterfaces.
+  bool hasImplementsSelfReference = false;
 
   ExtensionTypeElementImpl(super.name, super.nameOffset);
 

pkg/analyzer/lib/src/error/codes.g.dart

@@ -1642,6 +1642,15 @@ class CompileTimeErrorCode extends AnalyzerErrorCode {
         "Try specifying a different type, or remove the type from the list.",
   );
 
+  ///  No parameters.
+  static const CompileTimeErrorCode EXTENSION_TYPE_IMPLEMENTS_ITSELF =
+      CompileTimeErrorCode(
+    'EXTENSION_TYPE_IMPLEMENTS_ITSELF',
+    "The extension type can't implement itself.",
+    correctionMessage:
+        "Try removing the superinterface that references this extension type.",
+  );
+
   ///  Parameters:
   ///  0: the name of the extension type
   ///  1: the name of the conflicting member

pkg/analyzer/lib/src/error/error_code_values.g.dart

@@ -196,6 +196,7 @@ const List<ErrorCode> errorCodeValues = [
   CompileTimeErrorCode.EXTENSION_TYPE_DECLARES_INSTANCE_FIELD,
   CompileTimeErrorCode.EXTENSION_TYPE_DECLARES_MEMBER_OF_OBJECT,
   CompileTimeErrorCode.EXTENSION_TYPE_IMPLEMENTS_DISALLOWED_TYPE,
+  CompileTimeErrorCode.EXTENSION_TYPE_IMPLEMENTS_ITSELF,
   CompileTimeErrorCode.EXTENSION_TYPE_INHERITED_MEMBER_CONFLICT,
   CompileTimeErrorCode.EXTENSION_TYPE_REPRESENTATION_DEPENDS_ON_ITSELF,
   CompileTimeErrorCode.EXTERNAL_FIELD_CONSTRUCTOR_INITIALIZER,

pkg/analyzer/lib/src/generated/error_verifier.dart

@@ -711,6 +711,7 @@ class ErrorVerifier extends RecursiveAstVisitor<void>
       _checkForNonCovariantTypeParameterPositionInRepresentationType(
           node, element);
       _checkForExtensionTypeRepresentationDependsOnItself(node, element);
+      _checkForExtensionTypeImplementsItself(node, element);
       _checkForExtensionTypeMemberConflicts(
         node: node,
         element: element,
@@ -2915,6 +2916,18 @@ class ErrorVerifier extends RecursiveAstVisitor<void>
     }
   }
 
+  void _checkForExtensionTypeImplementsItself(
+    ExtensionTypeDeclarationImpl node,
+    ExtensionTypeElementImpl element,
+  ) {
+    if (element.hasImplementsSelfReference) {
+      errorReporter.reportErrorForToken(
+        CompileTimeErrorCode.EXTENSION_TYPE_IMPLEMENTS_ITSELF,
+        node.name,
+      );
+    }
+  }
+
   void _checkForExtensionTypeMemberConflicts({
     required ExtensionTypeDeclaration node,
     required ExtensionTypeElement element,
@@ -2958,7 +2971,7 @@ class ErrorVerifier extends RecursiveAstVisitor<void>
     ExtensionTypeDeclarationImpl node,
     ExtensionTypeElementImpl element,
   ) {
-    if (element.hasSelfReference) {
+    if (element.hasRepresentationSelfReference) {
       errorReporter.reportErrorForToken(
         CompileTimeErrorCode.EXTENSION_TYPE_REPRESENTATION_DEPENDS_ON_ITSELF,
         node.name,

pkg/analyzer/lib/src/summary2/element_flags.dart

@@ -97,16 +97,24 @@ class EnumElementFlags {
 }
 
 class ExtensionTypeElementFlags {
-  static const int _hasSelfReference = 1 << 0;
+  static const int _hasRepresentationSelfReference = 1 << 0;
+  static const int _hasImplementsSelfReference = 1 << 1;
 
   static void read(SummaryDataReader reader, ExtensionTypeElementImpl element) {
     var byte = reader.readByte();
-    element.hasSelfReference = (byte & _hasSelfReference) != 0;
+    element.hasRepresentationSelfReference =
+        (byte & _hasRepresentationSelfReference) != 0;
+    element.hasImplementsSelfReference =
+        (byte & _hasImplementsSelfReference) != 0;
   }
 
   static void write(BufferedSink sink, ExtensionTypeElementImpl element) {
     var result = 0;
-    result |= element.hasSelfReference ? _hasSelfReference : 0;
+    result |= element.hasRepresentationSelfReference
+        ? _hasRepresentationSelfReference
+        : 0;
+    result |=
+        element.hasImplementsSelfReference ? _hasImplementsSelfReference : 0;
     sink.writeByte(result);
   }
 }

pkg/analyzer/lib/src/summary2/extension_type.dart

@@ -3,7 +3,6 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:_fe_analyzer_shared/src/util/dependency_walker.dart' as graph;
-import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/ast/ast.dart';
 import 'package:analyzer/src/dart/ast/extensions.dart';
@@ -19,16 +18,29 @@ import 'package:analyzer/src/utilities/extensions/collection.dart';
 void buildExtensionTypes(Linker linker, List<AstNode> declarations) {
   final walker = _Walker(linker);
   final nodes = <_Node>[];
+  final elements = <ExtensionTypeElementImpl>[];
   for (final declaration in declarations) {
     if (declaration is ExtensionTypeDeclarationImpl) {
       final node = walker.getNode(declaration);
       nodes.add(node);
+      elements.add(node.element);
     }
   }
 
   for (final node in nodes) {
     walker.walk(node);
   }
+
+  _breakImplementsCycles(elements);
+}
+
+/// Clears interfaces for extension types that have cycles.
+void _breakImplementsCycles(List<ExtensionTypeElementImpl> elements) {
+  final walker = _ImplementsWalker();
+  for (final element in elements) {
+    final node = walker.getNode(element);
+    walker.walk(node);
+  }
 }
 
 /// Collector of referenced extension types in a type.
@@ -62,6 +74,62 @@ class _ExtensionTypeErasure extends ReplacementVisitor {
   }
 }
 
+class _ImplementsNode extends graph.Node<_ImplementsNode> {
+  final _ImplementsWalker walker;
+  final ExtensionTypeElementImpl element;
+
+  @override
+  bool isEvaluated = false;
+
+  _ImplementsNode(this.walker, this.element);
+
+  @override
+  List<_ImplementsNode> computeDependencies() {
+    return element.interfaces
+        .map((interface) => interface.element)
+        .whereType<ExtensionTypeElementImpl>()
+        .map(walker.getNode)
+        .toList();
+  }
+
+  void _evaluate() {
+    isEvaluated = true;
+  }
+
+  void _markCircular() {
+    isEvaluated = true;
+    element.hasImplementsSelfReference = true;
+
+    final representationType = element.representation.type;
+    final typeSystem = element.library.typeSystem;
+
+    final superInterface = typeSystem.isNonNullable(representationType)
+        ? typeSystem.objectNone
+        : typeSystem.objectQuestion;
+    element.interfaces = [superInterface];
+  }
+}
+
+class _ImplementsWalker extends graph.DependencyWalker<_ImplementsNode> {
+  final Map<ExtensionTypeElementImpl, _ImplementsNode> nodeMap = Map.identity();
+
+  @override
+  void evaluate(_ImplementsNode v) {
+    v._evaluate();
+  }
+
+  @override
+  void evaluateScc(List<_ImplementsNode> scc) {
+    for (final node in scc) {
+      node._markCircular();
+    }
+  }
+
+  _ImplementsNode getNode(ExtensionTypeElementImpl element) {
+    return nodeMap[element] ??= _ImplementsNode(this, element);
+  }
+}
+
 class _Node extends graph.Node<_Node> {
   final _Walker walker;
   final ExtensionTypeDeclarationImpl node;
@@ -122,14 +190,14 @@ class _Node extends graph.Node<_Node> {
   }
 
   void _markCircular() {
-    element.hasSelfReference = true;
+    element.hasRepresentationSelfReference = true;
     _evaluateWithType(InvalidTypeImpl.instance);
   }
 }
 
 class _Walker extends graph.DependencyWalker<_Node> {
   final Linker linker;
-  final Map<ExtensionTypeElement, _Node> nodeMap = Map.identity();
+  final Map<ExtensionTypeElementImpl, _Node> nodeMap = Map.identity();
 
   _Walker(this.linker);
 

pkg/analyzer/messages.yaml

@@ -5078,6 +5078,10 @@ CompileTimeErrorCode:
     comment: |-
       Parameters:
       0: the display string of the disallowed type
+  EXTENSION_TYPE_IMPLEMENTS_ITSELF:
+    problemMessage: "The extension type can't implement itself."
+    correctionMessage: Try removing the superinterface that references this extension type.
+    comment: No parameters.
   EXTENSION_TYPE_INHERITED_MEMBER_CONFLICT:
     problemMessage: "The extension type '{0}' has more than one distinct member named '{1}' from implemented types."
     correctionMessage: Try redeclaring the corresponding member in this extension type.

pkg/analyzer/test/src/diagnostics/extension_type_implements_itself_test.dart

@@ -0,0 +1,35 @@
+// Copyright (c) 2023, the Dart project authors. Please see the AUTHORS file
+// 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.
+
+import 'package:analyzer/src/error/codes.dart';
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+import '../dart/resolution/context_collection_resolution.dart';
+
+main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(ExtensionTypeImplementsItselfTest);
+  });
+}
+
+@reflectiveTest
+class ExtensionTypeImplementsItselfTest extends PubPackageResolutionTest {
+  test_hasCycle2() async {
+    await assertErrorsInCode('''
+extension type A(int it) implements B {}
+extension type B(int it) implements A {}
+''', [
+      error(CompileTimeErrorCode.EXTENSION_TYPE_IMPLEMENTS_ITSELF, 15, 1),
+      error(CompileTimeErrorCode.EXTENSION_TYPE_IMPLEMENTS_ITSELF, 56, 1),
+    ]);
+  }
+
+  test_hasCycle_self() async {
+    await assertErrorsInCode('''
+extension type A(int it) implements A {}
+''', [
+      error(CompileTimeErrorCode.EXTENSION_TYPE_IMPLEMENTS_ITSELF, 15, 1),
+    ]);
+  }
+}

pkg/analyzer/test/src/diagnostics/test_all.dart

@@ -248,6 +248,8 @@ import 'extension_type_declares_member_of_object_test.dart'
     as extension_type_declares_member_of_object;
 import 'extension_type_implements_disallowed_type_test.dart'
     as extension_type_implements_disallowed_type;
+import 'extension_type_implements_itself_test.dart'
+    as extension_type_implements_itself;
 import 'extension_type_inherited_member_conflict_test.dart'
     as extension_type_inherited_member_conflict;
 import 'extension_type_representation_depends_on_itself_test.dart'
@@ -1055,6 +1057,7 @@ main() {
     extension_type_declares_instance_field.main();
     extension_type_declares_member_of_object.main();
     extension_type_implements_disallowed_type.main();
+    extension_type_implements_itself.main();
     extension_type_inherited_member_conflict.main();
     extension_type_representation_depends_on_itself.main();
     external_field_constructor_initializer.main();

pkg/analyzer/test/src/summary/element_text.dart

@@ -500,7 +500,14 @@ class _ElementWriter {
 
   void _writeExtensionTypeElement(ExtensionTypeElementImpl e) {
     _sink.writeIndentedLine(() {
-      _sink.writeIf(e.hasSelfReference, 'hasSelfReference ');
+      _sink.writeIf(
+        e.hasRepresentationSelfReference,
+        'hasRepresentationSelfReference ',
+      );
+      _sink.writeIf(
+        e.hasImplementsSelfReference,
+        'hasImplementsSelfReference ',
+      );
       _writeName(e);
     });
 

pkg/analyzer/test/src/summary/elements_test.dart

@@ -47202,6 +47202,66 @@ library
 ''');
   }
 
+  test_interfaces_cycle2() async {
+    var library = await buildLibrary(r'''
+extension type A(int it) implements B {}
+extension type B(int it) implements A {}
+''');
+
+    configuration.withConstructors = false;
+    checkElementText(library, r'''
+library
+  definingUnit
+    extensionTypes
+      hasImplementsSelfReference A @15
+        representation: self::@extensionType::A::@field::it
+        typeErasure: int
+        interfaces
+          Object
+        fields
+          final it @21
+            type: int
+        accessors
+          synthetic get it @-1
+            returnType: int
+      hasImplementsSelfReference B @56
+        representation: self::@extensionType::B::@field::it
+        typeErasure: int
+        interfaces
+          Object
+        fields
+          final it @62
+            type: int
+        accessors
+          synthetic get it @-1
+            returnType: int
+''');
+  }
+
+  test_interfaces_cycle_self() async {
+    var library = await buildLibrary(r'''
+extension type A(int it) implements A {}
+''');
+
+    configuration.withConstructors = false;
+    checkElementText(library, r'''
+library
+  definingUnit
+    extensionTypes
+      hasImplementsSelfReference A @15
+        representation: self::@extensionType::A::@field::it
+        typeErasure: int
+        interfaces
+          Object
+        fields
+          final it @21
+            type: int
+        accessors
+          synthetic get it @-1
+            returnType: int
+''');
+  }
+
   test_interfaces_extensionType() async {
     var library = await buildLibrary(r'''
 extension type A(num it) {}
@@ -47510,7 +47570,7 @@ extension type B(A it) {}
 library
   definingUnit
     extensionTypes
-      hasSelfReference A @15
+      hasRepresentationSelfReference A @15
         representation: self::@extensionType::A::@field::it
         typeErasure: InvalidType
         interfaces
@@ -47521,7 +47581,7 @@ library
         accessors
           synthetic get it @-1
             returnType: InvalidType
-      hasSelfReference B @42
+      hasRepresentationSelfReference B @42
         representation: self::@extensionType::B::@field::it
         typeErasure: InvalidType
         interfaces
@@ -47558,7 +47618,7 @@ library
         accessors
           synthetic get it @-1
             returnType: B
-      hasSelfReference B @42
+      hasRepresentationSelfReference B @42
         representation: self::@extensionType::B::@field::it
         typeErasure: InvalidType
         interfaces
@@ -47582,7 +47642,7 @@ extension type A(A it) {}
 library
   definingUnit
     extensionTypes
-      hasSelfReference A @15
+      hasRepresentationSelfReference A @15
         representation: self::@extensionType::A::@field::it
         typeErasure: InvalidType
         interfaces