Display the immediate representation type, not any erasure (#3685)

Author: srawlins

Diff for: lib/src/model/extension_type.dart

@@ -14,7 +14,7 @@ class ExtensionType extends InheritingContainer
   final ExtensionTypeElement element;
 
   late final ElementType representationType =
-      getTypeFor(element.typeErasure, library);
+      getTypeFor(element.representation.type, library);
 
   ExtensionType(this.element, super.library, super.packageGraph);
 

Diff for: test/templates/extension_type_test.dart

@@ -66,7 +66,7 @@ extension type One<E>(List<E> it) {
     ]);
   }
 
-  void test_representationType() async {
+  void test_representationType_class() async {
     await createPackageWithLibrary('''
 class Foo<E> {}
 extension type One<E>(Foo<E> it) {}
@@ -81,6 +81,19 @@ extension type One<E>(Foo<E> it) {}
     ]);
   }
 
+  void test_representationType_extensionType() async {
+    await createPackageWithLibrary('''
+extension type One(int one) {}
+extension type Two(One two) {}
+''');
+    var htmlLines = readLines(['lib', 'Two-extension-type.html']);
+
+    htmlLines.expectMainContentContainsAllInOrder([
+      matches('<dt>on</dt>'),
+      matches('<a href="../lib/One-extension-type.html">One</a>'),
+    ]);
+  }
+
   void test_classInterfaces() async {
     await createPackageWithLibrary('''
 class Base<E> {}