Features used to implement the example

• Boolean validator with math, date-time or text-string terms
• Copy a parsed text to a field

Example: Restrict parent issue from closing if it has sub-tasks that were created during a given parent issue status

If sub-tasks are raised while the parent is at a status of "Released", the parent cannot be moved to status "Closed" until all sub-tasks are closed. 

Create a "Text field (single line)" custom field in sub-task issue called "Parent status at sub-task's creation"

Insert post-function Copy a parsed text to a field into sub-task's "Create Issue" with the following configuration:

Note that:

• %{00042} is field code for "Parent's issue status" virtual field
• Beware to introduce that post-function after "Creates the issue originally" system post-function

Insert Boolean validator with math, date-time or text-string terms validator into "Close issue" transition in parent's workflow with the following configuration:

Boolean expression used is: count(filterByPredicate(subtasks(), ^%{11900} = "Released" AND ^%{00016} != "Closed")) = 0

Note that:

• %{11900} is field code for "Parent status at subtask's creation" custom field in my particular JIRA instance. You should replace 11900 with the field code in your Jira instance
• %{00016} is field code for "Issue status"