Migration: add FixBuilder support for enums

Change-Id: I2ab1fa367d17f827cd229ebfa0f1e7a055134ed7
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/131944
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Mike Fairhurst <mfairhurst@google.com>

pkg/nnbd_migration/lib/src/fix_builder.dart

@@ -150,7 +150,9 @@ class FixBuilder {
     element = element.declaration;
     if (element is ClassElement || element is TypeParameterElement) {
       return typeProvider.typeType;
-    } else if (element is PropertyAccessorElement && element.isSynthetic) {
+    } else if (element is PropertyAccessorElement &&
+        element.isSynthetic &&
+        !element.variable.isSynthetic) {
       var variableType = _variables
           .decoratedElementType(element.variable)
           .toFinalType(typeProvider);

pkg/nnbd_migration/test/api_test.dart

@@ -3903,10 +3903,6 @@ class _ProvisionalApiTestWithFixBuilder extends _ProvisionalApiTestBase
   @override
   bool get _usePermissiveMode => false;
 
-  @override
-  @FailingTest(issue: 'https://github.com/dart-lang/sdk/issues/38472')
-  Future<void> test_enum() => super.test_enum();
-
   @override
   @FailingTest(issue: 'https://github.com/dart-lang/sdk/issues/40023')
   Future<void> test_extension_nullableOnType_viaImplicitInvocation() =>

pkg/nnbd_migration/test/fix_builder_test.dart

@@ -1040,6 +1040,30 @@ f() => 1.0;
     visitSubexpression(findNode.doubleLiteral('1.0'), 'double');
   }
 
+  Future<void> test_enum_ref_index() async {
+    await analyze('''
+enum E { V }
+_f(E e) => e.index;
+''');
+    visitSubexpression(findNode.prefixed('e.index'), 'int');
+  }
+
+  Future<void> test_enum_ref_value() async {
+    await analyze('''
+enum E { V }
+_f() => E.V;
+''');
+    visitSubexpression(findNode.prefixed('E.V'), 'E');
+  }
+
+  Future<void> test_enum_ref_values() async {
+    await analyze('''
+enum E { V }
+_f() => E.values;
+''');
+    visitSubexpression(findNode.prefixed('E.values'), 'List<E>');
+  }
+
   Future<void> test_expressionStatement() async {
     await analyze('''
 _f(int/*!*/ x, int/*?*/ y) {