Subject: 27.0.50; [PATCH] avoid calling vc backend if vc-display-status is nil

From: Andy Moreton <[email-masked]>
Date: Fri, 20 Jul 2018 17:45:09 +0100

If the user sets `vc-display-status' to nil then the VC backend is still
called to get a revision number, even though it will not be displayed.

The following patch avoids this unneeded work.

Do not call VC backend to update mode line if vc-display-status is nil

2018-07-20  Andy Moreton  <[email-masked]>

	* lisp/vc/vc-hooks.el (vc-mode-line): Avoid calling VC backend if
	vc-display-status is nil.

diff --git a/lisp/vc/vc-hooks.el b/lisp/vc/vc-hooks.el
index 55c0132bf2..f1b622b54a 100644
--- a/lisp/vc/vc-hooks.el
+++ b/lisp/vc/vc-hooks.el
@@ -692,24 +692,26 @@ vc-mode-line
  If BACKEND is passed use it as the VC backend when computing the result."
    (interactive (list buffer-file-name))
    (setq backend (or backend (vc-backend file)))
-  (if (not backend)
-      (setq vc-mode nil)
+  (cond
+   ((not backend)
+    (setq vc-mode nil))
+   ((null vc-display-status)
+    (setq vc-mode (concat " " (symbol-name backend))))
+   (t
      (let* ((ml-string (vc-call-backend backend 'mode-line-string file))
  	   (ml-echo (get-text-property 0 'help-echo ml-string)))
        (setq vc-mode
  	    (concat
  	     " "
-	     (if (null vc-display-status)
-		 (symbol-name backend)
-	       (propertize
-		ml-string
-		'mouse-face 'mode-line-highlight
-		'help-echo
-		(concat (or ml-echo
-			    (format "File under the %s version control system"
-				    backend))
-			"\nmouse-1: Version Control menu")
-		'local-map vc-mode-line-map)))))
+	     (propertize
+	      ml-string
+	      'mouse-face 'mode-line-highlight
+	      'help-echo
+	      (concat (or ml-echo
+			  (format "File under the %s version control system"
+				  backend))
+		      "\nmouse-1: Version Control menu")
+	      'local-map vc-mode-line-map))))
      ;; If the user is root, and the file is not owner-writable,
      ;; then pretend that we can't write it
      ;; even though we can (because root can write anything).
@@ -718,7 +720,7 @@ vc-mode-line
  	 (not buffer-read-only)
  	 (zerop (user-real-uid))
  	 (zerop (logand (file-modes buffer-file-name) 128))
-	 (setq buffer-read-only t)))
+	 (setq buffer-read-only t))))
    (force-mode-line-update)
    backend)

In GNU Emacs 27.0.50 (build 21, x86_64-w64-mingw32)
  of 2018-07-20 built on AJM-DESKTOP2
Repository revision: 249606fb539bd1a7dc95129277c1684826fc068f
Windowing system distributor 'Microsoft Corp.', version 10.0.16299
Recent messages:
Finding changes in c:/emacs/git/emacs/master/lisp/vc/vc-hooks.el...
Running in foreground: git --no-pager diff-index --exit-code -p HEAD  -- 
vc-hooks.el
Done (status=1): git --no-pager diff-index --exit-code -p HEAD  -- vc-hooks.el
Finding changes in c:/emacs/git/emacs/master/lisp/vc/vc-hooks.el...done
Mark activated
Mark set
Saved text from "diff --git a/lisp/vc/vc-hooks.el b/lisp/"
Mark set
Saving file c:/home/ajm/sandbox/emacs/vc-mode-line.patch...
Wrote c:/home/ajm/sandbox/emacs/vc-mode-line.patch

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