Ensure diff-hl-mode is bound and optimize diff-hl--update

Author: jamescherti

diff-hl.el

@@ -741,21 +741,25 @@ Return a list of line overlays used."
         (lambda (ref-changes)
           (when (buffer-live-p orig)
             (let ((ref-changes (diff-hl-adjust-changes ref-changes changes))
-                  (base (diff-hl--target-buffer orig)))
+                  (base (diff-hl--target-buffer orig))
+                  (has-changes (or changes ref-changes)))
               (dolist (buf (buffer-list))
                 (when (and (buffer-live-p buf)
-                           (eq (diff-hl--target-buffer buf) base)
-                           (buffer-local-value 'diff-hl-mode buf))
+                           (or (eq buf base)
+                               (eq (buffer-base-buffer buf) base)))
                   (with-current-buffer buf
-                    (let (reuse)
+                    (when (bound-and-true-p diff-hl-mode)
                       (diff-hl-remove-overlays)
-                      (let ((diff-hl-highlight-function
-                             diff-hl-highlight-reference-function)
-                            (diff-hl-fringe-face-function
-                             diff-hl-fringe-reference-face-function))
-                        (setq reuse (diff-hl--update-overlays ref-changes nil)))
-                      (diff-hl--update-overlays changes reuse)
-                      (when (not (or changes ref-changes))
+                      (let (reuse)
+                        (when ref-changes
+                          (let ((diff-hl-highlight-function
+                                 diff-hl-highlight-reference-function)
+                                (diff-hl-fringe-face-function
+                                 diff-hl-fringe-reference-face-function))
+                            (setq reuse (diff-hl--update-overlays ref-changes nil))))
+                        (when (or changes reuse)
+                          (diff-hl--update-overlays changes reuse)))
+                      (unless has-changes
                         (diff-hl--autohide-margin))))))))))))))
 
 (defun diff-hl--resolve (value-or-buffer cb)