Check labels in smerge-mode

* lisp/vc/diff.el (diff-check-labels): Separated out into its own
function (bug#18850)...
(diff-no-select): ... from here.

* lisp/vc/smerge-mode.el (smerge-diff): Use diff-check-labels.

2 files changed, 17 insertions, 8 deletions

diff --git a/lisp/vc/diff.el b/lisp/vc/diff.el
index 523be87bc49..5fa771f5f1e 100644
--- a/lisp/vc/diff.el
+++ b/lisp/vc/diff.el
@@ -123,6 +123,15 @@ Possible values are:
 
 (defvar diff-default-directory)
 
+(defun diff-check-labels (&optional force)
+  (if (not (or force (eq 'check diff-use-labels)))
+      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))))))
+
 (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)))
@@ -130,11 +139,7 @@ Possible values are:
   (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)))))
+  (diff-check-labels)
   (let* ((old-alt (diff-file-local-copy old))
 	 (new-alt (diff-file-local-copy new))
 	 (command
diff --git a/lisp/vc/smerge-mode.el b/lisp/vc/smerge-mode.el
index 6b1df6603df..f032b084167 100644
--- a/lisp/vc/smerge-mode.el
+++ b/lisp/vc/smerge-mode.el
@@ -44,6 +44,7 @@
 ;;; Code:
 
 (eval-when-compile (require 'cl-lib))
+(require 'diff)				;For diff-check-labels.
 (require 'diff-mode)                    ;For diff-refine.
 (require 'newcomment)
 
@@ -1243,9 +1244,12 @@ spacing of the \"Lower\" chunk."
 	    (let ((status
 		   (apply 'call-process diff-command nil t nil
 			  (append smerge-diff-switches
-				  (list "-L" (concat name1 "/" file)
-					"-L" (concat name2 "/" file)
-					file1 file2)))))
+				  (and (diff-check-labels)
+				       (list "--label"
+					     (concat name1 "/" file)
+					     "--label"
+					     (concat name2 "/" file)))
+				  (list file1 file2)))))
 	      (if (eq status 0) (insert "No differences found.\n"))))
 	  (goto-char (point-min))
 	  (diff-mode)