Update copyright year to 2015

[gnu-emacs] / lisp / vc / diff.el

diff --git a/lisp/vc/diff.el b/lisp/vc/diff.el
index 8b4ff7929692c99c3e40b178729d3ac883dfba7e..062248c8f14e5350d844e77982245b64aa3371b3 100644 (file)
--- a/lisp/vc/diff.el
+++ b/lisp/vc/diff.el
@@ -1,11 +1,11 @@
 ;;; diff.el --- run `diff'  -*- lexical-binding: t -*-
 
-;; Copyright (C) 1992, 1994, 1996, 2001-2013 Free Software Foundation,
+;; Copyright (C) 1992, 1994, 1996, 2001-2015 Free Software Foundation,
 ;; Inc.
 
 ;; Author: Frank Bresz
 ;; (according to authors.el)
-;; Maintainer: FSF
+;; Maintainer: emacs-devel@gnu.org
 ;; Keywords: unix, vc, tools
 
 ;; This file is part of GNU Emacs.
@@ -114,6 +114,13 @@ specified in the variable `diff-switches' are passed to the diff command."
           tempfile))
     (file-local-copy file-or-buf)))
 
+(defvar diff-use-labels 'check
+  "Whether `diff-command' understands the \"--label\" option.
+Possible values are:
+  t     -- yes, it does
+  nil   -- no, it does not
+  check -- try to probe whether it does")
+
 (defun diff-no-select (old new &optional switches no-async buf)
   ;; Noninteractive helper for creating and reverting diff buffers
   (unless (bufferp new) (setq new (expand-file-name new)))
@@ -121,6 +128,11 @@ specified in the variable `diff-switches' are passed to the diff command."
   (or switches (setq switches diff-switches)) ; If not specified, use default.
   (unless (listp switches) (setq switches (list switches)))
   (or buf (setq buf (get-buffer-create "*Diff*")))
+  (when (eq 'check diff-use-labels)
+    (setq diff-use-labels
+         (with-temp-buffer
+           (when (ignore-errors (call-process diff-command nil t nil "--help"))
+             (if (search-backward "--label" nil t) t)))))
   (let* ((old-alt (diff-file-local-copy old))
         (new-alt (diff-file-local-copy new))
         (command
@@ -130,11 +142,14 @@ specified in the variable `diff-switches' are passed to the diff command."
                       ,@switches
                        ,@(mapcar #'shell-quote-argument
                                  (nconc
-                                  (when (or old-alt new-alt)
-                                    (list "-L" (if (stringp old)
-                                                   old (prin1-to-string old))
-                                          "-L" (if (stringp new)
-                                                   new (prin1-to-string new))))
+                                  (and (or old-alt new-alt)
+                                      (eq diff-use-labels t)
+                                      (list "--label"
+                                            (if (stringp old) old
+                                              (prin1-to-string old))
+                                            "--label"
+                                            (if (stringp new) new
+                                              (prin1-to-string new))))
                                   (list (or old-alt old)
                                         (or new-alt new)))))
                     " "))