grepsource: Quick grepping when we have git-grep, find|xargs when we don't.

grepsource.el

(defconst grepsource-filetypes
  '("*.h" "*.hpp" "*.cpp" "*.c" "*.cc" "*.cpp" "*.inl" "*.grd" "*.idl" "*.m"
    "*.mm" "*.py" "*.sh" "*.cfg" "*SConscript" "SConscript*" "*.scons"
    "*.vcproj" "*.vsprops" "*.make" "*.gyp" "*.gypi")
  "A list of filetype patterns that grepsource will use.")

(defun grepsource (cmd-args)
  "Grep `default-directory' using git-grep for speed if we're in
a git repository and falling back to a big \"find | xargs grep\"
command if we aren't."
  (interactive (list (read-from-minibuffer "Grep project for string: ")))
  ;; When we're in a git repository, use git grep so we don't have to
  ;; find-files.
  (let ((quoted (replace-regexp-in-string "\"" "\\\\\"" cmd-args))
        (grep-use-null-device nil))
    (if (file-exists-p (concat default-directory "/.git"))
        ;; We can accelerate our grep using the local git stuff.
        (grep (concat "git --no-pager grep -n -e \"" quoted "\" -- "
                      (mapconcat 'identity grepsource-filetypes " ")))
      ;; Fallback to using find.
      (grep (concat "find . -path '*/.svn' -prune -o -name \""
                    (mapconcat 'identity grepsource-filetypes
                               "\" -or -name \"")
                    "\" | xargs grep -nH -e \"" quoted "\"")))))