Display users associated to unchecked tasks in a user script field (ScriptRunner)

Prerequisites:

ScriptRunner running on your Jira.

Let's say you track tasks in an Elements Checklist panel and you want to list users that needs to take an action in a user field:

List users in unchecked tasks in user field

You can use the following script in a script field:

GROOVY

import com.atlassian.jira.component.ComponentAccessor
import com.atlassian.jira.issue.IssueManager
import com.atlassian.plugin.PluginAccessor
import com.atlassian.jira.user.ApplicationUser
 
PluginAccessor pluginAccessor = ComponentAccessor.getPluginAccessor()
Class panelContentServiceClass = pluginAccessor.getClassLoader().findClass("com.valiantys.software.elements.api.content.PanelContentService")
Class panelRefClass = pluginAccessor.getClassLoader().findClass("com.valiantys.software.elements.api.model.PanelRef")
Class attributeRefClass = pluginAccessor.getClassLoader().findClass("com.valiantys.software.elements.api.model.AttributeRef")
def userManager = ComponentAccessor.getUserManager() 

def panelContentService = ComponentAccessor.getOSGiComponentInstanceOfType(panelContentServiceClass)

// Constants to customize
def PANEL_NAME = "Tasks"
def CHECKBOX_ATTRIBUTE = "Done"
def USER_ATTRIBUTE = "Owner"

// Define Elements panel
def elementsPanel = panelContentService.getPanel(issue, panelRefClass.byName(PANEL_NAME))

// Get Elements panel items
Set<ApplicationUser> usersSet = new HashSet<ApplicationUser>()

for (def panelItem : elementsPanel.getPanelItems()) {
    def taskDone = panelItem.getAttributeContent(attributeRefClass.byName(CHECKBOX_ATTRIBUTE))?.getValue()
    if(!taskDone) {
        def owner = panelItem.getAttributeContent(attributeRefClass.byName(USER_ATTRIBUTE))?.getValue()
        if(owner != null) {
            usersSet.add(userManager.getUserByName(owner))
        }
    }

}

return usersSet

Notes:

Edit variables PANEL_NAME, CHECKBOX_ATTRIBUTE and USER_ATTRIBUTE to your needs.
The type of the script field must be User Picker (multiple users)
The Search of the field must be Multi User Picker Searcher