Query can't be index sorted by lucene function property

[Piotr Tajduś]

I have index with lowercase function property. In debug I can see that 
index plan sort order is:

{ propertyName : 
function*lower*@metadane/korespondent/nadawca/nadawca/nazwa, 
propertyType : STRING, order : ASCENDING }

Ordering from query is:

lower([d].[metadane/korespondent/nadawca/nadawca/nazwa]) ASCENDING


Problem is in org.apache.jackrabbit.oak.query.QueryImpl.canSortByIndex() :

                        if (!(op instanceof PropertyValueImpl)) {
                            // ordered by a function: currently not 
supported
                            canSortByIndex = false;
                            break;
                        }

Operand is instance of LowerCaseImpl and it disqualifies such query from 
index sorting.


Best regards,

Piotr