don't create list for tagless collection binding, don't call set accessor in this case (collection will be used directly)

platform/util/src/com/intellij/util/xmlb/AbstractCollectionBinding.java

@@ -146,13 +146,23 @@ abstract class AbstractCollectionBinding implements Binding {
   public Object deserialize(Object o, @NotNull Object... nodes) {
     Collection result;
     if (getTagName(o) == null) {
-      result = new SmartList();
+      if (o instanceof Collection) {
+        result = (Collection)o;
+        result.clear();
+      }
+      else {
+        result = new SmartList();
+      }
       for (Object node : nodes) {
         if (!XmlSerializerImpl.isIgnoredNode(node)) {
           //noinspection unchecked
           result.add(getElementBinding(node).deserialize(o, node));
         }
       }
+
+      if (result == o) {
+        return result;
+      }
     }
     else {
       assert nodes.length == 1;

platform/util/src/com/intellij/util/xmlb/AccessorBindingWrapper.java

@@ -40,7 +40,11 @@ class AccessorBindingWrapper implements Binding {
   @Override
   @Nullable
   public Object deserialize(Object context, @NotNull Object... nodes) {
-    myAccessor.write(context, myBinding.deserialize(myAccessor.read(context), nodes));
+    Object currentValue = myAccessor.read(context);
+    Object deserializedValue = myBinding.deserialize(currentValue, nodes);
+    if (currentValue != deserializedValue) {
+      myAccessor.write(context, deserializedValue);
+    }
     return context;
   }