Jruby prepends "SyntaxError in" to the output of "ruby -c". This breaks loc and qf lists being able to jump the error.
Add efm if the current interpreter is jruby because it prepends
"SyntaxError in" to errors from "ruby -c"
Is there a ruby executable available if jruby is used (e.g. on windows)? I included your change in commit 1ef9ab8 anyway.