Codenarc is a static code analysis tool for Groovy. It's been around for quite a while but one feature it lacked was the ability to see the rule violations right inside of IntelliJ.

Luckily one of my co-workers saw that Daniel Demus recently updated the IntelliJ plugin that was originally created by Cédric Champeau.

An example of a rule violation right inside IntelliJ:

You can get the plugin here and check out the code or file a bug on the Github project

One caveat is the plugin currently does not automatically import your codenarc.groovy|xml rule files - you have to enable rules manually in the inspection settings dialog. Though there is a feature request open to do just that.