There are various errors cloning and working with OpenJFX in IntelliJ IDE:

* The .idea/misc.xml needs to to use JDK_11 as language level instead of JDK_8.
For IntelliJ users: This is the language level shown inside the Project Structure. (File -> Project Structure...)

* The .idea/base.iml, .idea/controls.iml, .idea/fxml.iml, .idea/web.iml, .idea/graphics.iml are modified to include/recognize the shims (as test resource, this is very similar to the configuration inside the .classpath file from Eclipse)
* EDIT: The projects are now recognized by IntelliJ-gradle (.idea/gradle.xml, .idea/compiler.xml)

NOTE: This bug was filed on behalf of an OpenJFX contributor who has filed a PR to fix it at: https://github.com/openjdk/jfx/pull/506