[ddc] Add hot reload rejection for type parameters

Changing the number of type parameters on a class is not supported
in a hot reload.

Issue: #60101
Change-Id: I3e397f26ca80e655dcb3d2807ddefd59c89adddb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/409381
Commit-Queue: Nicholas Shahan <[email protected]>
Reviewed-by: Mark Zhou <[email protected]>

Author: nshahan

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

@@ -39,6 +39,7 @@ class HotReloadDeltaInspector {
           // No previous version of the class to compare with.
           continue;
         }
+        _checkClassTypeParametersCountChange(acceptedClass, deltaClass);
         if (acceptedClass.hasConstConstructor) {
           _checkConstClassConsistency(acceptedClass, deltaClass);
           _checkConstClassDeletedFields(acceptedClass, deltaClass);
@@ -93,6 +94,22 @@ class HotReloadDeltaInspector {
           'Class: ${deltaClass.name}');
     }
   }
+
+  /// Records a rejection error when the number of [TypeParameter]s on a class
+  /// changes between [acceptedClass] and [deltaClass].
+  ///
+  /// [acceptedClass] and [deltaClass] must represent the same class in the
+  /// last known accepted and delta components respectively.
+  void _checkClassTypeParametersCountChange(
+      Class acceptedClass, Class deltaClass) {
+    if (acceptedClass.typeParameters.length !=
+        deltaClass.typeParameters.length) {
+      _rejectionMessages.add(
+          'Limitation: changing type parameters does not work with hot reload.'
+          "Library:'${deltaClass.enclosingLibrary.importUri}' "
+          'Class: ${deltaClass.name}');
+    }
+  }
 }
 
 const hotReloadLibraryMetadataTag = 'ddc.hot-reload-library.metadata';