I have a filter to return a group of parent tasks based on some criteria.
I can use this as a group of issues to search further using filter = FilterName
What I would like to be able to do is to use this in the parent field search in something like
parent IN (filter = FilterName)
Is this possible?
The IN operator expects a comma-delimited list. While I'm not sure of a way to retrieve the information you're looking for solely using the built-in JQL, the question has been asked before and an answer was accepted based on using a plug-in.
Filter to show sub tasks of a filtered list of parent tasks
The good news is the Craftforge JQL plug-in referenced is free.
UPDATE: As Micky mentioned in the comments, this plugin is no longer free as of version 2.0 (16 Apr 2013)