Re: auto-revert error on macOS when auto-revert-use-notify is t

[Eli Zaretskii <eliz@gnu.org>]

> From: Michael Albinus <michael.albinus@gmx.de>
> Date: Fri, 29 Dec 2017 11:02:10 +0100
> Cc: "emacs-devel@gnu.org" <emacs-devel@gnu.org>
> 
> > Emacs: 26.0.90 
> > OS: macOS 10.13.2
> >
> > 1. start Emacs with -Q
> > 2. open a test file (like 1.c)
> > 3. turn on auto-revert-mode by run global-auto-revert-mode
> > 4. add auto-revert-use-notify as a watcher variable by
> > debug-on-variable-change
> > 5. open the test file with vim
> > 6. modify the test file in vim and save it
> > 7. Emacs enter debug with the following msg:
> >
> > Debugger entered--setting auto-revert-use-notify in buffer 1.c to nil:
> >   debug--implement-debug-watch(auto-revert-use-notify nil set #<buffer
> > 1.c>)
> >   auto-revert-notify-handler((13 stopped "/Users/jun/test/1.c"))
> >   file-notify--rm-descriptor(13)
> >   file-notify-rm-watch(13)
> >   #f(compiled-function (key value) #<bytecode 0x40a952e1>)(13
> > (#<buffer 1.c>))
> >   maphash(#f(compiled-function (key value) #<bytecode 0x40a952e1>)
> > #<hash-table equal 7/65 0x40e7896d>)
> >   auto-revert-notify-rm-watch()
> >   auto-revert-notify-handler((13 stopped "/Users/jun/test/1.c"))
> >   file-notify--rm-descriptor(13)
> >   file-notify-rm-watch(13)
> >   file-notify-callback((13 (rename delete) "/Users/jun/test/1.c"))
> >   file-notify-handle-event((file-notify (13 (rename delete)
> > "/Users/jun/test/1.c") file-notify-callback))
> >   funcall-interactively(file-notify-handle-event (file-notify (13
> > (rename delete) "/Users/jun/test/1.c") file-notify-callback))
> >   call-interactively(file-notify-handle-event nil [(file-notify (13
> > (rename delete) "/Users/jun/test/1.c") file-notify-callback)])
> >   command-execute(file-notify-handle-event nil [(file-notify (13
> > (rename delete) "/Users/jun/test/1.c") file-notify-callback)] t)
> 
> Well, this is not an error. The watchdog over "/Users/jun/test/1.c"
> receives the `(rename delete)' events from writing the file. Due to
> this, the watchdog is removed, as you see in the backtrace.

Exactly, I think this is precisely the expected behavior: step 4
requests the debugger to be entered when auto-revert-use-notify is
modified, and auto-revert-notify-handler does modify it when the
watched file is deleted:

      (if (eq action 'stopped)
          ;; File notification has stopped.  Continue with polling.
          (cl-dolist (buffer
                      (if global-auto-revert-mode
                          (buffer-list) auto-revert-buffer-list))
            (with-current-buffer buffer
              (when (and (equal descriptor auto-revert-notify-watch-descriptor)
                         (or
                          ;; A buffer associated with a file.
                          (and (stringp buffer-file-name)
                               (string-equal
                                (file-name-nondirectory file)
                                (file-name-nondirectory buffer-file-name)))
                          ;; A buffer w/o a file, like dired.
                          (null buffer-file-name)))
                (auto-revert-notify-rm-watch)
                (setq-local auto-revert-use-notify nil))))  <<<<<<<<<<<<<