grep-program and grep-command

["Lennart Borgman (gmail)" <lennart.borgman@gmail.com>]

The grep-command is a defcustom, but grep-program is a defvar. 
grep-command is computed by Emacs if its value is nil.

This seems a bit akward to me. It tells the user to customize 
grep-command if things does not work by default. Would it not be better 
if they instead set grep-program and let Emacs compute grep-command?

But since we want them to use customize we then should make grep-program 
into a defcustom. I suggest that grep-program is defined something like 
this (unfinished, and I I have renamed it to grep-program1 just for 
testing):


(defcustom grep-program1
   ;; Currently zgrep has trouble.  It runs egrep instead of grep,
   ;; and it doesn't pass along long options right.
   "grep"
   ;; (if (equal (condition-case nil	; in case "zgrep" isn't in exec-path
   ;; 		 (call-process "zgrep" nil nil nil
   ;; 			       "foo" null-device)
   ;; 	       (error nil))
   ;; 	     1)
   ;;     "zgrep"
   ;;   "grep")
   "The default grep program for `grep-command' and `grep-find-command'.
This variable's value takes effect when `grep-compute-defaults' is called."
   :type 'file
   :set (lambda(sym val)
          (unless (string= grep-command
                           (car (get 'grep-command 'customized-value)))
            (setq grep-command nil))
          ;; Add similar checks above for other computed values that
          ;; depends on this variable ...
          (set-default sym val))
   :group 'grep)