Bug fixes for hot reload

runtime/vm/object_reload.cc

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/object.h"
 
 #include "vm/isolate_reload.h"
 #include "vm/log.h"
 #include "vm/resolver.h"
 #include "vm/symbols.h"
@@ skipping 426 matching lines @@
   ASSERT(is_finalized() == replacement.is_finalized());
 
   if (is_finalized()) {
     // Get the field maps for both classes. These field maps walk the class
     // hierarchy.
     const Array& fields =
         Array::Handle(OffsetToFieldMap());
     const Array& replacement_fields =
         Array::Handle(replacement.OffsetToFieldMap());
 
-    // Check that we have the same number of fields.
+    // Check that the size of the instance is the same.
     if (fields.Length() != replacement_fields.Length()) {
       IRC->ReportError(String::Handle(String::NewFormatted(
           "Number of instance fields changed in %s", ToCString())));
       return false;
     }
 
+    // Check that we have the same next field offset. This check is not
+    // redundant with the one above because the instance OffsetToFieldMap
+    // array length is based on the instance size (which may be aligned up).
+    if (next_field_offset() != replacement.next_field_offset()) {
+      IRC->ReportError(String::Handle(String::NewFormatted(
+          "Number of instance fields changed in %s", ToCString())));
+      return false;
+    }
+
     if (NumTypeArguments() != replacement.NumTypeArguments()) {
       IRC->ReportError(String::Handle(String::NewFormatted(
           "Number of type arguments changed in %s", ToCString())));
       return false;
     }
 
     // Verify that field names / offsets match across the entire hierarchy.
     Field& field = Field::Handle();
     String& field_name = String::Handle();
     Field& replacement_field = Field::Handle();
@@ skipping 12 matching lines @@
             "Name of instance field changed ('%s' vs '%s') in '%s'",
             field_name.ToCString(),
             replacement_field_name.ToCString(),
             ToCString())));
         return false;
       }
     }
   } else if (is_prefinalized()) {
     if (!replacement.is_prefinalized()) {
       IRC->ReportError(String::Handle(String::NewFormatted(
-          "Original class ('%s') is prefinalized and replacement class ('%s')",
+          "Original class ('%s') is prefinalized and replacement class "
+          "('%s') is not ",
           ToCString(), replacement.ToCString())));
       return false;
     }
     if (instance_size() != replacement.instance_size()) {
      IRC->ReportError(String::Handle(String::NewFormatted(
          "Instance size mismatch between '%s' (%" Pd ") and replacement "
          "'%s' ( %" Pd ")",
          ToCString(),
          instance_size(),
          replacement.ToCString(),
@@ skipping 53 matching lines @@
     }
     ClearAndSetStaticTarget(new_target);
   } else {
     ClearWithSentinel();
   }
 }
 
 #endif  // !PRODUCT
 
 }   // namespace dart.