[Emacs-diffs] /srv/bzr/emacs/trunk r111731: Check whether diff supports --label before using it

[Glenn Morris]

------------------------------------------------------------
revno: 111731
fixes bug: http://debbugs.gnu.org/11067
committer: Glenn Morris <address@hidden>
branch nick: trunk
timestamp: Mon 2013-02-11 00:28:08 -0800
message:
  Check whether diff supports --label before using it
  
  * lisp/vc/diff.el (diff-use-labels): New variable.
  (diff-no-select): Use --label rather than -L, and first
  check that it is supported.
modified:
  lisp/ChangeLog
  lisp/vc/diff.el

=== modified file 'lisp/ChangeLog'
--- a/lisp/ChangeLog    2013-02-11 01:50:45 +0000
+++ b/lisp/ChangeLog    2013-02-11 08:28:08 +0000
@@ -1,5 +1,9 @@
 2013-02-11  Glenn Morris  <address@hidden>
 
+       * vc/diff.el (diff-use-labels): New variable.
+       (diff-no-select): Use --label rather than -L, and first
+       check that it is supported.  (Bug#11067)
+
        * files.el (enable-dir-local-variables): New variable.
        (hack-dir-local-variables): Respect enable-dir-local-variables.
        * tutorial.el (help-with-tutorial):

=== modified file 'lisp/vc/diff.el'
--- a/lisp/vc/diff.el   2013-01-11 23:08:55 +0000
+++ b/lisp/vc/diff.el   2013-02-11 08:28:08 +0000
@@ -114,6 +114,13 @@
           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 @@
   (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 @@
                       ,@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)))))
                     " "))