Note: This issue is about Java 8 and Scala interaction, so it should not be on the Scala plugin forum.
I’m using Idea 14.1.2 build #IC-141.173 with Scala plugin version 1.4.15. Scala version is 2.11.6.
It turns out Idea mischaracterizes passing a Java 8 closure into a Scala function IF the function has two overloads, one taking a Java 8 functional interface type and the other one taking a Scala function type. This works fine with the Scala compiler without even a warning, though.
This needs to work cleanly for providing APIs for both Java 8 and Scala uses. Tiny project demonstrating this issue is attached.