2018.2.1 update change log:
Added: When building the Java .jar, we now include everything in src/, not just .java files. For this reason, we now recommend you not store your music or movie collection in your robot code src/ folder.
http://wpilib.screenstepslive.com/s/currentCS/m/cpp/l/483574-c-java-plugin-changelog
Thank goodness. We can finally implement the robot based music streaming service we’ve been dreaming of.
inb4 someone starts off auton with STEAM POWER STEAM POWER on full blast
Watch for rule R08 (B), which this may or may not fall under 
. If only we followed Vex rules, which allows (used to allow when I was involved, at least) robot music only if the refs find it in good taste.
Just to double-check - this is a library update, and not an image update, correct?
Correct, but it’s ready for a future image update.
Is the update live from the online repository yet? Tried to update in Eclipse and it reported no updates available yet…
Yes, it’s online. Double-check the update sites setting in Eclipse is set to http://first.wpi.edu/FRC/roborio/release/eclipse/ (per http://wpilib.screenstepslive.com/s/currentCS/m/java/l/599681-installing-eclipse-c-java#installing-the-development-plugins-option-1-online-install). You can see what the update site is set to by going to Help | Install New Software, and clicking the down arrow–it should appear in that list. If it doesn’t, click Manage and enable / edit it in that dialog.
You may also have to manually check for updates (Help | Check for Updates).