Module ... is not backed by gradle

The answer that worked for me is to restart IntelliJ - at startup build.gradle is identified and the project is set up.

The only thing that worked for me was to use the menu File > Close Project and reopen it. IDEA popped up a dialog saying "Import project from Gradle files" or something to that effect.

---

Dead ends: Below is a list of dead ends, so don't waste your time with them. I kept seeing "module is not backed by gradle" despite following all these proposed solutions:

1. There was no Gradle tool window, so I couldn't synchronize the project
2. Clicking File > Open gradle.build opens the file for editing and doesn't solve the issue
3. Creating a run configuration that runs gradle has no effect, even after I saw a build/ folder created
4. Runing ./gradlew from the commandline only creates files for gradle and doesn't fix IntelliJ

If you didn't set up the IDE project via "Import Project" and then pointing to a Gradle project, you may have to link the IDE project to the Gradle project. This can be done in the "Gradle" window.

I fixed this problem by clicking in the Menu

--> "Run" 
--> "Edit Configurations" 
--> [+] The little plus in the top left corner 
--> "Gradle"

With the new created run configuration it worked. I hope this will help some of you.