Eclipse mars m2e & groovy eclipse compiler?: no source folders

I tried to import a maven multimodule project that worked with eclipse luna into eclipse mars. This multi-module maven project has no source folder in eclipse mars, the dependencies are also not present:

I can't add the src/main/java folder as a source folder:

Other maven multi module projects do work. The difference with this project is that it uses the groovy-eclipse-compiler:

<plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.3</version>
        <dependencies>
          <dependency>
            <groupId>org.codehaus.groovy</groupId>
            <artifactId>groovy-eclipse-compiler</artifactId>
            <version>2.9.2-01</version>
            <scope>compile</scope>
          </dependency>
          <dependency>
            <groupId>org.codehaus.groovy</groupId>
            <artifactId>groovy-eclipse-batch</artifactId>
            <version>2.4.3-01</version>
            <scope>compile</scope>
          </dependency>
        </dependencies>
        <configuration>
          <compilerId>groovy-eclipse-compiler</compilerId>
          <fork>true</fork>
          <verbose>false</verbose>
          <source>1.7</source>
          <target>1.7</target>
          <encoding>UTF-8</encoding>
          <showDeprecation>true</showDeprecation>
          <verbose />
        </configuration>
      </plugin>

To have the correct groovy tooling in eclipse I installed groovy-eclipse from the update site:

Groovy Eclipse 2.9.2 snapshot builds for Eclipse 4.5 are available, update site http://dist.springsource.org/snapshot/GRECLIPSE/e4.5/

What can I do so eclipse mars recognizes this maven project correctly?

This seems to be a groovy-eclipse bug. I opened an issue on the github page: github.com/groovy/groovy-eclipse/issues/130 , but I guess the project has been orphaned, which is a real shame :( !