How to enable scalameta for Gatling 2.3?

#1

I am trying to enable the scalameta compiler plugin for Gatling and added the corresponding statements to the build.sbt file of my forked project/branch: https://github.com/tdauth/gatling/blob/tamino-2.3/build.sbt

However, it does not produce any semanticdb folders when compiling it.
Do I have to add the compiler plugin to the root variable or somewhere else?