bug#35418: [PATCH] Don't poll auto-revert files that use notification

["Mattias Engdegård" <mattiase@acm.org>]

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Here is a detail that needs to be taken care of: we should not use notification on non-file buffers, since that is generally useless (consider the Buffer List buffer) and, with `auto-revert-avoid-polling', prevents these buffers from being polled and thus updated at all.

Patch attached. There is a hack for Dired buffers, since watching their directories happens to be just what we want. It would be nice to generalise this condition somehow, but meanwhile this will have to do, unless you can come up with something better.

A patch for global-auto-revert-mode will come shortly.


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From 23f8e60c110a372530a839948d7b17598517d928 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mattias=20Engdeg=C3=A5rd?= <mattiase@acm.org>
Date: Wed, 8 May 2019 00:02:59 +0200
Subject: [PATCH] Don't use file notification on non-file buffers

Most non-file buffers aren't served by file notification in
auto-revert mode; typically, they need to be polled, like the Buffer List.
With `auto-revert-avoid-polling', setting a useless notification means
that such buffers may never be updated at all (bug#35418).

An exception is made for Dired, as that mode works well with
notification on the directory.

* lisp/autorevert.el (auto-revert-buffers):
Modify condition for using notification.
---
 lisp/autorevert.el | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/lisp/autorevert.el b/lisp/autorevert.el
index 7cd5e7ee8b..5a62b5f6b9 100644
--- a/lisp/autorevert.el
+++ b/lisp/autorevert.el
@@ -858,8 +858,14 @@ the timer when no buffers need to be checked."
                   (auto-revert-remove-current-buffer))
               (when (auto-revert-active-p)
                 ;; Enable file notification.
+                ;; Don't bother creating a notifier for non-file buffers
+                ;; if there is a custom `revert-buffer-function'.
+                ;; An exception is made for Dired, since that mode works
+                ;; well with notifiers.
                 (when (and auto-revert-use-notify
-                           (not auto-revert-notify-watch-descriptor))
+                           (not auto-revert-notify-watch-descriptor)
+                           (or buffer-file-name
+                               (eq major-mode 'dired-mode)))
                   (auto-revert-notify-add-watch))
                 (auto-revert-handler)))))
 	(setq bufs (cdr bufs)))
-- 
2.20.1 (Apple Git-117)