This is an extension library for ProjectBufferMode.
It provides commands to search and list all occurrences of a regexp in all marked files or in all files of the current project if no files are marked.
Also: using the prefix argument; the search will occur in all files listed in the buffer.
Put the following lines in your .emacs:
(eval-after-load "project-buffer-mode" '(progn (require 'project-buffer-occur) (define-key project-buffer-mode-map [(control ?f)] 'project-buffer-occur)))