We could populate MQL's comment field by tapping into the following two possible sources:

• QueryOptions.getComment in org.hibernate.sql.ast.SqlAstTranslator.translate (see MongoTranslatorFactory.buildSelectTranslator and MongoTranslatorFactory.buildMutationTranslator)
• TableMutation.getMutationComment in org.hibernate.sql.ast.SqlAstTranslatorFactory.buildModelMutationTranslator

 
The former is passed when user is creating a select or mutation query statement by invoking comment setter method, and is also implicitly set by Hibernate ORM when HQL is used; the latter is hardcoded by Hibernate.

Addressing the source code notes tagged with TODO-HIBERNATE-53 is in scope of this ticket.