Extension type. Perform ExtensionTypeErasure recursively, move to API.

Bug: #54057
Change-Id: Ib1bb67ae98d49f98f3b70c5c19744f1b74a386da
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/337261
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>

Author: scheglov

pkg/analyzer/lib/dart/element/type.dart

@@ -44,6 +44,17 @@ abstract class DartType {
   @Deprecated('Use element instead')
   Element? get element2;
 
+  /// The extension type erasure of this type.
+  ///
+  /// The extension type erasure of a type `V` is obtained by recursively
+  /// replacing every subterm of `V` which is an extension type with the
+  /// corresponding representation type.
+  ///
+  /// This getter can be used on any type, not necessary on a type that has
+  /// an extension type as a subterm. If there are no extension types, the
+  /// same type is returned.
+  DartType get extensionTypeErasure;
+
   /// Return `true` if this type represents the bottom type.
   bool get isBottom;
 

pkg/analyzer/lib/src/dart/constant/evaluation.dart

@@ -26,8 +26,7 @@ import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/member.dart';
 import 'package:analyzer/src/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/type_algebra.dart';
-import 'package:analyzer/src/dart/element/type_system.dart'
-    show ExtensionTypeErasure, TypeSystemImpl;
+import 'package:analyzer/src/dart/element/type_system.dart' show TypeSystemImpl;
 import 'package:analyzer/src/diagnostic/diagnostic.dart';
 import 'package:analyzer/src/error/codes.dart';
 import 'package:analyzer/src/generated/engine.dart';
@@ -3140,7 +3139,7 @@ extension RuntimeExtensions on TypeSystemImpl {
     DartObjectImpl obj,
     DartType type,
   ) {
-    type = ExtensionTypeErasure().perform(type);
+    type = type.extensionTypeErasure;
     if (!isNonNullableByDefault) {
       type = toLegacyTypeIfOptOut(type);
     }

pkg/analyzer/lib/src/dart/constant/value.dart

@@ -187,7 +187,7 @@ class DartObjectImpl implements DartObject, Constant {
     InstanceState state, {
     VariableElementImpl? variable,
   }) {
-    type = ExtensionTypeErasure().perform(type);
+    type = type.extensionTypeErasure;
     return DartObjectImpl._(
       typeSystem,
       type,
@@ -2506,7 +2506,7 @@ class ListState extends InstanceState {
     required List<DartObjectImpl> elements,
     bool isUnknown = false,
   }) {
-    elementType = ExtensionTypeErasure().perform(elementType);
+    elementType = elementType.extensionTypeErasure;
     return ListState._(
       elementType: elementType,
       elements: elements,
@@ -3105,9 +3105,7 @@ class TypeState extends InstanceState {
   final DartType? _type;
 
   factory TypeState(DartType? type) {
-    if (type != null) {
-      type = ExtensionTypeErasure().perform(type);
-    }
+    type = type?.extensionTypeErasure;
     return TypeState._(type);
   }
 

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

@@ -6,7 +6,6 @@ import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/nullability_suffix.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/element.dart';
-import 'package:analyzer/src/dart/element/type.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
 import 'package:collection/collection.dart';
 import 'package:meta/meta_meta.dart';
@@ -15,16 +14,6 @@ extension DartTypeExtension on DartType {
   bool get isExtensionType {
     return element is ExtensionTypeElement;
   }
-
-  /// If `this` is an [InterfaceType] that is an instantiation of an extension
-  /// type, returns its representation type erasure. Otherwise, returns self.
-  DartType get representationTypeErasureOrSelf {
-    final self = this;
-    if (self is InterfaceTypeImpl) {
-      return self.representationTypeErasure ?? self;
-    }
-    return self;
-  }
 }
 
 extension ElementAnnotationExtensions on ElementAnnotation {

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

@@ -666,17 +666,6 @@ class InterfaceTypeImpl extends TypeImpl implements InterfaceType {
     return null;
   }
 
-  /// The instantiated representation type erasure, if [element] is an
-  /// extension type.
-  DartType? get representationTypeErasure {
-    if (element case ExtensionTypeElement element) {
-      final substitution = Substitution.fromInterfaceType(this);
-      final typeErasure = element.typeErasure;
-      return substitution.substituteType(typeErasure);
-    }
-    return null;
-  }
-
   @override
   InterfaceType? get superclass {
     var supertype = element.supertype;
@@ -1269,6 +1258,11 @@ abstract class TypeImpl implements DartType {
   /// Initialize a newly created type.
   TypeImpl({this.alias});
 
+  @override
+  DartType get extensionTypeErasure {
+    return const ExtensionTypeErasure().perform(this);
+  }
+
   @override
   bool get isBottom => false;
 

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

@@ -36,15 +36,16 @@ import 'package:analyzer/src/utilities/extensions/collection.dart';
 import 'package:meta/meta.dart';
 
 class ExtensionTypeErasure extends ReplacementVisitor {
+  const ExtensionTypeErasure();
+
   DartType perform(DartType type) {
     return type.accept(this) ?? type;
   }
 
   @override
   DartType? visitInterfaceType(covariant InterfaceTypeImpl type) {
-    final typeErasure = type.representationTypeErasure;
-    if (typeErasure != null) {
-      return typeErasure;
+    if (type.representationType case final representationType?) {
+      return representationType.accept(this) ?? representationType;
     }
 
     return super.visitInterfaceType(type);
@@ -156,9 +157,7 @@ class TypeSystemImpl implements TypeSystem {
   /// type that implements both [left] and [right], regardless of whether
   /// [left] is a subtype of [right], or [right] is a subtype of [left].
   bool canBeSubtypeOf(DartType left, DartType right) {
-    if (left case InterfaceTypeImpl(:final representationTypeErasure?)) {
-      left = representationTypeErasure;
-    }
+    left = left.extensionTypeErasure;
 
     // If one is `Null`, then the other must be nullable.
     final leftIsNullable = isPotentiallyNullable(left);

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

@@ -20,7 +20,6 @@ import 'package:analyzer/src/dart/ast/ast.dart';
 import 'package:analyzer/src/dart/ast/extensions.dart';
 import 'package:analyzer/src/dart/element/class_hierarchy.dart';
 import 'package:analyzer/src/dart/element/element.dart';
-import 'package:analyzer/src/dart/element/extensions.dart';
 import 'package:analyzer/src/dart/element/inheritance_manager3.dart';
 import 'package:analyzer/src/dart/element/non_covariant_type_parameter_position.dart';
 import 'package:analyzer/src/dart/element/type.dart';
@@ -4904,7 +4903,7 @@ class ErrorVerifier extends RecursiveAstVisitor<void>
           final boundNode = current.bound;
           if (boundNode is NamedType) {
             var boundType = boundNode.typeOrThrow;
-            boundType = boundType.representationTypeErasureOrSelf;
+            boundType = boundType.extensionTypeErasure;
             current = elementToNode[boundType.element];
           } else {
             current = null;

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

@@ -8,7 +8,6 @@ import 'package:analyzer/src/dart/ast/ast.dart';
 import 'package:analyzer/src/dart/ast/extensions.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/type.dart';
-import 'package:analyzer/src/dart/element/type_system.dart';
 import 'package:analyzer/src/dart/element/type_visitor.dart';
 import 'package:analyzer/src/summary2/link.dart';
 import 'package:analyzer/src/utilities/extensions/collection.dart';
@@ -151,7 +150,7 @@ class _Node extends graph.Node<_Node> {
     final typeSystem = element.library.typeSystem;
 
     element.representation.type = type;
-    element.typeErasure = ExtensionTypeErasure().perform(type);
+    element.typeErasure = type.extensionTypeErasure;
 
     final interfaces = node.implementsClause?.interfaces
         .map((e) => e.type)

pkg/analyzer/test/src/dart/constant/evaluation_test.dart

@@ -601,6 +601,20 @@ const v = int;
     _assertHasPrimitiveEqualityTrue('v');
   }
 
+  test_identical_extensionType_types_recursive() async {
+    await assertNoErrorsInCode('''
+const c = identical(ExList<ExInt>, List<int>);
+
+extension type const ExInt(int value) implements int {}
+extension type const ExList<T>(List<T> value) implements List<T> {}
+''');
+    final result = _topLevelVar('c');
+    assertDartObjectText(result, r'''
+bool true
+  variable: self::@variable::c
+''');
+  }
+
   test_identical_typeLiteral_explicitTypeArgs_differentTypeArgs() async {
     await assertNoErrorsInCode('''
 class C<T> {}