Scratch.groovy

package examples

import com.atlassian.jira.component.ComponentAccessor
import com.atlassian.jira.issue.link.IssueLinkManager

def issueManager = ComponentAccessor.getIssueManager()
def issueLinkManager = ComponentAccessor.getComponent(IssueLinkManager)

log.debug("is subtask: ${issue.isSubTask()}")
if (issue.isSubTask()) {
    log.debug("issue id: ${issue.id}")
    log.debug("parent: ${issue.parentObject}")
    log.debug("sibs: ${issue.parentObject.subTaskObjects*.key}")

    issueLinkManager.createIssueLink(issue.id, issueManager.getIssueObject("SRTESTPRJ-14").id, 10000L, 0, ComponentAccessor.jiraAuthenticationContext.loggedInUser)
}