As of 0.5.0, rcodetools can show additional information about the completion candidates. rcodetools includes elisp and vimscript code for emacs and vim, but it can be used with any editor.
EMACS
VIM
What's new
--dev: adds project directories to $:
--completion-class-info: list completion candidates and class info
display completion candidates with description, both in emacs and vim (using the menu+preview window).