Extension type. Issue 53725. Use representationTypeErasure of the matched type.

Bug: #53725
Change-Id: Ia9ea1b964288f05a19b23562a5c1e08e8dff5aa0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/330981
Reviewed-by: Samuel Rawlins <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: scheglov

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

@@ -140,6 +140,10 @@ 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;
+    }
+
     // If one is `Null`, then the other must be nullable.
     final leftIsNullable = isPotentiallyNullable(left);
     final rightIsNullable = isPotentiallyNullable(right);

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

@@ -107,6 +107,32 @@ void f(double x) {
 ''');
   }
 
+  test_interfaceType2_matchedExtensionType_requiredRepresentation() async {
+    await assertNoErrorsInCode('''
+void f(A x) {
+  if (x case int _) {}
+}
+
+extension type A(int _) {}
+''');
+  }
+
+  test_interfaceType2_matchedExtensionTypeUnrelated_requiredFinal() async {
+    await assertErrorsInCode('''
+void f(A x) {
+  if (x case C _) {}
+}
+
+extension type A(B _) {}
+
+class B {}
+
+final class C {}
+''', [
+      error(WarningCode.PATTERN_NEVER_MATCHES_VALUE_TYPE, 27, 1),
+    ]);
+  }
+
   test_interfaceType2_matchedFinal_enumSubtype() async {
     await assertNoErrorsInCode('''
 void f(A x) {