Rubescript .rs files are very similar to C/C++ code. On my machines, I map .rs files to the C/C++ lexers in Eclipse as a result. To do this:
Windows > Preferences > C/C++ > File Types > New... > Pattern = *.rs, Type = C++ Source File.
It's not a 100% match, but is fairly close. Great for CTRL+SHIFT+F to auto-format your code.
--tim