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

[Zhang Haijun]

> It was a design decision, that filenotify.el implements directory watching. 
> Since kqueue does not support this, it must be emulated, somehow. 
> 

It seems that it is not true for kqueue on macOS 10.13.6.

Several weeks ago, I met a problem with emacs auto-revert. Some files in a 
directory can’t be auto reverted.  This directory was a soft link to another 
directory. I did some debug and  found that no event would be received if you 
use file watching for the files in a soft link directory. And use directory 
watching for these files worked well. So I modified filenotify.el like this:

diff --git a/lisp/filenotify.el b/lisp/filenotify.el
index 101ddb6be0..a4a0359328 100644
--- a/lisp/filenotify.el
+++ b/lisp/filenotify.el
@@ -363,7 +363,7 @@ file-notify-add-watch
       (setq desc (funcall
                   ;; kqueue does not report file changes in directory
                   ;; monitor.  So we must watch the file itself.
-                  func (if (eq file-notify--library 'kqueue) file dir)
+                  func (if (eq file-notify--library 'kqueue11) file dir)
                   l-flags 'file-notify-callback)))

     ;; Modify `file-notify-descriptors’.

It works well since then.

I don’t known from when the behavior of kqueue changed. There maybe need a user 
option to control whether to use file watching or directory watching for kqueue.