Either the RubyExecution.RUBY_COMPILER may be black-magically enhanced or we
could start to use more than one OutputRecognizer. E.g.

public class RubyExecution extends ExecutionService {
  ...
  psfs RE_BASE = "^((\\[|\\]|\\-|\\:|[0-9]|\\s|\\,)*)(\\s*from )";
  psfs RegexpOutputRecognizer RUBY_COMPILER_NO_EXT =
    new RegexpOutputRecognizer(RE_BASE + "?(\\S.*)\\:([0-9]+):in.*", // [1]
      4, 5, -1);
  psfs RegexpOutputRecognizer RUBY_COMPILER =
    new RegexpOutputRecognizer(RE_BASE + "?(\\S.*\\.(rb|rake))\\:([0-9]+).*",
      4, 6, -1);
  ...
} // + // NOI18N

[1] 'in' to prevent a lot of non-sense matches.

Also the RUBY_COMPILER recognizer is used (almost?) everywhere (probably 10+
places). So a method like ExecutionDescriptor.useDefaultRecognizers(boolean)
could be considered. Default would be true - in that case RUBY_COMPILER and
eventually RUBY_COMPILER_NO_EXT and others would be added by default -> no need
to call addOutputRecognizer(RubyExecution.RUBY_COMPILER) on all ED instances.