[ddc] Adding error messages for illegal enum conversions after a hot reload.

Fixes: #60102, #60104
Change-Id: I5b89edffc3aa753d0882c2b9fd6aefd9bfef7175
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/416080
Reviewed-by: Nate Biggs <[email protected]>
Reviewed-by: Nicholas Shahan <[email protected]>
Commit-Queue: Mark Zhou <[email protected]>

Author: Markzipan

pkg/dev_compiler/lib/src/kernel/hot_reload_delta_inspector.dart

@@ -40,6 +40,9 @@ class HotReloadDeltaInspector {
           continue;
         }
         _checkClassTypeParametersCountChange(acceptedClass, deltaClass);
+        if (acceptedClass.isEnum || deltaClass.isEnum) {
+          _checkEnumIllegalConversion(acceptedClass, deltaClass);
+        }
         if (acceptedClass.hasConstConstructor) {
           _checkConstClassConsistency(acceptedClass, deltaClass);
           _checkConstClassDeletedFields(acceptedClass, deltaClass);
@@ -110,6 +113,21 @@ class HotReloadDeltaInspector {
           'Class: ${deltaClass.name}');
     }
   }
+
+  /// Records a rejection error when a class is redefined as or from an [Enum].
+  ///
+  /// [acceptedClass] and [deltaClass] must represent the same class in the
+  /// last known accepted and delta components respectively.
+  void _checkEnumIllegalConversion(Class acceptedClass, Class deltaClass) {
+    if (acceptedClass.isEnum && !deltaClass.isEnum) {
+      _rejectionMessages
+          .add('Enum class cannot be redefined to be a non-enum class.'
+              'Class: ${deltaClass.name}');
+    } else if (!acceptedClass.isEnum && deltaClass.isEnum) {
+      _rejectionMessages.add('Class cannot be redefined to be a enum class.'
+          'Class: ${deltaClass.name}');
+    }
+  }
 }
 
 const hotReloadLibraryMetadataTag = 'ddc.hot-reload-library.metadata';