Groovy file does not compile in Intellij IDEA

I had the same issue and had to change in Idea the following setting: Settings->Compiler->Resource patterns

It was !?*.java

I changed it into !?.java;!?.form;!?.class;!?.groovy;!?.scala;!?.flex;!?.kt;!?.clj

It would be better to be able to specify it into the pom file though but haven't found a way yet.

GMaven plugin is only intended for maven compilation. Idea uses the Groovy compiler included in groovy-all jar. For Idea to get a hold of that add a project dependency, e.g.:

...
  <groupId>yourproject</groupId>
  <artifactId>yourproject</artifactId>
  <version>1.0.0-SNAPSHOT</version>

  <dependencies>
    <dependency>
      <groupId>org.codehaus.groovy</groupId>
      <artifactId>groovy-all</artifactId>
      <version>${groovy.version}</version>
    </dependency>
  </dependencies>
...

Solved by removing and creating from scratch IDEA project (ipr file)