This is a regression in JDK 9 b41:

$ idlj
com.sun.tools.corba.se.idl.InvalidArgument: Error reading Messages File.

Error reading Messages File.

From what I can tell, com.sun.tools.corba.se.idl.som.cff.FileLocator searches the class path by opening each directory as a ZIP file. This seems to be JDK 1.1 era code. We should change it to access the resources as resources file, this would allow the bulk of this code to be removed.