childProject gradle depending on master.buildSrc: How to?

Noob making the initial step into buildSrc code and I was inspired by Move versions to java constants as a good first step. My structure is an eclipse multi-project using includeFlat.

It was easy to define a java class in master.buildSrc and add references to it in my master and child build.gradle files. However, it lacked auto-complete ability, i.e., I could not click on a reference in build.gradle and follow it to the corresponding java class.

Obviously, the projects need groovy nature and mine were merely java projects. Adding that allowed auto-complete to work in the master build.gradle file. However, auto-complete did not work for the child projects. Obviously because the child projects do not depend on the master project.

And cannot! Gradle does not (should not?) provide a way for a child project to depend on its master.

So how can I support this? Is there an easy way for child project gradle code to reference the master.buildSrc code in a manner exposed to the IDE?

Or do I need to abandon buildSrc and settle for a standalone project for my custom gradle tasks, perhaps with a composite project structure?