void-variable revert-buffer-preserve-modes

[fleimgruber]

When follow-mode is enabled, I am seeing this error:

Debugger entered--Lisp error: (void-variable revert-buffer-preserve-modes)
  diff-hl-after-revert()
  auto-revert-tail-handler(70974)
  auto-revert-handler()
  auto-revert-buffer(#<buffer report.log>)
  #<subr auto-revert-buffers>()
  auto-revert-buffers--buffer-list-filter(#<subr auto-revert-buffers>)
  apply(auto-revert-buffers--buffer-list-filter #<subr auto-revert-buffers> nil)
  auto-revert-buffers()
  apply(auto-revert-buffers nil)
  timer-event-handler([t 26067 15968 683324 5 auto-revert-buffers nil nil 0 nil])

I am able to work around this via setting this in user config:

(setq revert-buffer-preserve-modes t)

I found related #205 (comment), and in particular calling diff-hl-after-revert outside of after-revert-hook is not supported, so I am figuring out why it gets called this way. Could not find anything related in my user config or Spacemacs setup.

[dgutov]

Hi!

It seems like the prerequisite was enabling auto-revert-tail-mode. It reuses the hook, whether that's a good idea or not, so we'll need to adapt.

I wonder whether it's a good idea to run diff-hl-after-revert every time auto-revert-tail-handler fires (supposedly it can fire quite often), but if we should revert as well, the fix would look like this:

diff --git a/diff-hl.el b/diff-hl.el
index 2a8bce5..4885b16 100644
--- a/diff-hl.el
+++ b/diff-hl.el
@@ -466,7 +466,8 @@ the current version of the file)."
 
 (defun diff-hl-after-revert ()
   (defvar revert-buffer-preserve-modes)
-  (when revert-buffer-preserve-modes
+  (when (or (not (boundp 'revert-buffer-preserve-modes))
+            revert-buffer-preserve-modes)
     (diff-hl-update)))
 
 (defun diff-hl-diff-goto-hunk-1 (historic)

Otherwise, it will be this:

diff --git a/diff-hl.el b/diff-hl.el
index 2a8bce5..56f66b4 100644
--- a/diff-hl.el
+++ b/diff-hl.el
@@ -465,8 +465,7 @@ the current version of the file)."
       (diff-hl-update))))
 
 (defun diff-hl-after-revert ()
-  (defvar revert-buffer-preserve-modes)
-  (when revert-buffer-preserve-modes
+  (when (bound-and-true-p revert-buffer-preserve-modes)
     (diff-hl-update)))
 
 (defun diff-hl-diff-goto-hunk-1 (historic)