(diff-switches): New fun.

(diff, diff-backup): Use it.
(diff): Clean up the args construction.  Use backquote.
Use listp instead of consp to avoid putting a nil arg.

1 files changed, 44 insertions, 51 deletions

diff --git a/lisp/diff.el b/lisp/diff.el
index 5981e1888e1..c776e36dfdc 100644
--- a/lisp/diff.el
+++ b/lisp/diff.el
@@ -1,6 +1,6 @@
 ;;; diff.el --- run `diff' in compilation-mode
 
-;; Copyright (C) 1992, 1994, 1996, 2001 Free Software Foundation, Inc.
+;; Copyright (C) 1992, 1994, 1996, 2001, 2004 Free Software Foundation, Inc.
 
 ;; Maintainer: FSF
 ;; Keywords: unix, tools
@@ -185,39 +185,39 @@ is nil, REGEXP matches only half a hunk.")
                (t
                 (cons msg code))))))
 
+;; prompt if prefix arg present
+(defun diff-switches ()
+  (if current-prefix-arg
+      (read-string "Diff switches: "
+                   (if (stringp diff-switches)
+                       diff-switches
+                     (mapconcat 'identity diff-switches " ")))))
+
 ;;;###autoload
 (defun diff (old new &optional switches no-async)
   "Find and display the differences between OLD and NEW files.
 Interactively the current buffer's file name is the default for NEW
 and a backup file for NEW is the default for OLD.
-With prefix arg, prompt for diff switches.
-If NO-ASYNC is non-nil, call diff synchronously."
+If NO-ASYNC is non-nil, call diff synchronously.
+With prefix arg, prompt for diff switches."
   (interactive
-   (nconc
-    (let (oldf newf)
-      (nreverse
-       (list
-        (setq newf (buffer-file-name)
-              newf (if (and newf (file-exists-p newf))
-                       (read-file-name
-                        (concat "Diff new file: (default "
-                                (file-name-nondirectory newf) ") ")
-                        nil newf t)
-                     (read-file-name "Diff new file: " nil nil t)))
-        (setq oldf (file-newest-backup newf)
-              oldf (if (and oldf (file-exists-p oldf))
-                       (read-file-name
-                        (concat "Diff original file: (default "
-                                (file-name-nondirectory oldf) ") ")
-                        (file-name-directory oldf) oldf t)
-                     (read-file-name "Diff original file: "
-                                     (file-name-directory newf) nil t))))))
-    (if current-prefix-arg
-        (list (read-string "Diff switches: "
-                           (if (stringp diff-switches)
-                               diff-switches
-                             (mapconcat 'identity diff-switches " "))))
-      nil)))
+   (let (oldf newf)
+     (setq newf (buffer-file-name)
+           newf (if (and newf (file-exists-p newf))
+                    (read-file-name
+                     (concat "Diff new file: (default "
+                             (file-name-nondirectory newf) ") ")
+                     nil newf t)
+                  (read-file-name "Diff new file: " nil nil t)))
+     (setq oldf (file-newest-backup newf)
+           oldf (if (and oldf (file-exists-p oldf))
+                    (read-file-name
+                     (concat "Diff original file: (default "
+                             (file-name-nondirectory oldf) ") ")
+                     (file-name-directory oldf) oldf t)
+                  (read-file-name "Diff original file: "
+                                  (file-name-directory newf) nil t)))
+     (list oldf newf (diff-switches))))
   (setq new (expand-file-name new)
         old (expand-file-name old))
   (let ((old-alt (file-local-copy old))
@@ -227,21 +227,19 @@ If NO-ASYNC is non-nil, call diff synchronously."
         (let ((compilation-process-setup-function 'diff-process-setup)
               (command
                (mapconcat 'identity
-                          (append (list diff-command)
-                                  ;; Use explicitly specified switches
-                                  (if switches
-                                      (if (consp switches)
-                                          switches (list switches))
-                                    ;; If not specified, use default.
-                                    (if (consp diff-switches)
-                                        diff-switches
-                                      (list diff-switches)))
-                                  (if (or old-alt new-alt)
-                                      (list "-L" old "-L" new))
-                                  (list
-                                   (shell-quote-argument (or old-alt old)))
-                                  (list
-                                   (shell-quote-argument (or new-alt new))))
+                          `(,diff-command
+                            ;; Use explicitly specified switches
+                            ,@(if switches
+                                  (if (listp switches)
+                                      switches (list switches))
+                                ;; If not specified, use default.
+                                (if (listp diff-switches)
+                                    diff-switches
+                                  (list diff-switches)))
+                            ,@(if (or old-alt new-alt)
+                                  (list "-L" old "-L" new))
+                            ,(shell-quote-argument (or old-alt old))
+                            ,(shell-quote-argument (or new-alt new)))
                           " ")))
           (setq buf
                 (compile-internal command
@@ -270,15 +268,10 @@ If NO-ASYNC is non-nil, call diff synchronously."
   "Diff this file with its backup file or vice versa.
 Uses the latest backup, if there are several numerical backups.
 If this file is a backup, diff it with its original.
-The backup file is the first file given to `diff'."
+The backup file is the first file given to `diff'.
+With prefix arg, prompt for diff switches."
   (interactive (list (read-file-name "Diff (file with backup): ")
-                     (if current-prefix-arg
-                         (read-string "Diff switches: "
-                                      (if (stringp diff-switches)
-                                          diff-switches
-                                        (mapconcat 'identity
-                                                   diff-switches " ")))
-                       nil)))
+                     (diff-switches)))
   (let (bak ori)
     (if (backup-file-name-p file)
         (setq bak file