Every new version of Grails brings some enhancements, and challenges on developer side too. Starting Grails 2.3.x we used different approach to debug our application, and now we are again on same place with Grails 3.0.x.
As Grails is now using Spring Boot and Gradle, we have to hook into bootRun gradle task that gets added by Spring Boot Gradle plugin. You won't find this task anywhere in your build.gradle file but inside Gradle tool window of IntelliJ IDEA. To facilitate debugging again we just need to hook into this bootRun task as follows:
addResources = false
jvmArgs = ["-Xdebug", "-Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=5005"]