In this example https://github.com/hibernate/hibernate- ... ridge.java
dynamic fields are added to indexed document:

public class DateSplitBridge implements FieldBridge {
...
public void set(String name, Object value, Document document, LuceneOptions luceneOptions) {
...
luceneOptions.addFieldToDocument( name + ".year", String.valueOf( year ), document);
...

How do I configure Facet for such ad hoc fields?
Can it be done in FieldBridge itself?

You can add whatever kind of field you like to the passed Document instance directly, i.e. not using the LuceneOptions helper.

Hth,

--Gunnar