Extension types. Report TYPE_PARAMETER_SUPERTYPE_OF_ITS_BOUND when via extension type.

Change-Id: I79d77e251fc4107e8d8496f9b4baea4b8a2b8bf0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/319200
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

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

@@ -5,10 +5,23 @@
 import 'package:analyzer/dart/element/element.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';
 
+extension DartTypeExtension on DartType {
+  /// 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 {
   static final Map<String, TargetKind> _targetKindsByName = {
     for (final kind in TargetKind.values) kind.name: kind,

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

@@ -20,6 +20,7 @@ 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';
@@ -4763,9 +4764,11 @@ class ErrorVerifier extends RecursiveAstVisitor<void>
 
         TypeParameter? current = parameter;
         for (var step = 0; current != null; step++) {
-          var bound = current.bound;
+          final boundNode = current.bound;
-          if (bound is NamedType) {
+          if (boundNode is NamedType) {
-            current = elementToNode[bound.element];
+            var boundType = boundNode.typeOrThrow;
+            boundType = boundType.representationTypeErasureOrSelf;
+            current = elementToNode[boundType.element];
           } else {
             current = null;
           }

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

@@ -17,7 +17,28 @@ main() {
 
 @reflectiveTest
 class TypeParameterSupertypeOfItsBoundTest extends PubPackageResolutionTest
-    with TypeParameterSupertypeOfItsBoundTestCases {}
+    with TypeParameterSupertypeOfItsBoundTestCases {
+  test_1of1_viaExtensionType() async {
+    await assertErrorsInCode(r'''
+extension type A<T>(T it) {}
+
+class B<U extends A<U>> {}
+''', [
+      error(CompileTimeErrorCode.TYPE_PARAMETER_SUPERTYPE_OF_ITS_BOUND, 38, 1),
+    ]);
+  }
+
+  test_2of2_viaExtensionType() async {
+    await assertErrorsInCode(r'''
+extension type A<T>(T it) {}
+
+class B<T1 extends A<T2>, T2 extends T1> {}
+''', [
+      error(CompileTimeErrorCode.TYPE_PARAMETER_SUPERTYPE_OF_ITS_BOUND, 38, 2),
+      error(CompileTimeErrorCode.TYPE_PARAMETER_SUPERTYPE_OF_ITS_BOUND, 56, 2),
+    ]);
+  }
+}
 
 mixin TypeParameterSupertypeOfItsBoundTestCases on PubPackageResolutionTest {
   test_1of1() async {