bug#64439: 28.2; auto-fill-mode gets turned on all over the place

[Jim Porter]

On 7/11/2023 4:31 AM, Eli Zaretskii wrote:
> > Date: Mon, 10 Jul 2023 16:53:41 -0700
> > From: Jim Porter <jporterbugs@gmail.com>
> > Cc: dhowells@redhat.com, Michael Albinus <michael.albinus@gmx.de>,
> >   64439@debbugs.gnu.org, Noam Postavsky <npostavs@gmail.com>
> >
> > On 7/10/2023 2:54 PM, Jim Porter wrote:
> > > Interestingly, I can't reproduce this on Emacs 30 (latest master), but I
> > > *can* on Emacs 28.2 and the latest rev on the Emacs 29 branch. I haven't
> > > dug any further yet to see which commit could have changed this though.
> >
> > ... and it looks like you're the one who fixed this, Stefan! Should this
> > get backported into the emacs-29 branch?
>
> Sorry, no.  We've lived with this subtle problem for 40 years, we can
> live another one or two.

Ok, just thought I'd ask. It's not too hard to work around anyway.

For anyone who's interested, here's what I did to work around the bug in 
Emacs 29 and earlier:

--------------------

(use-package text-mode
  :preface
  (defun user/turn-on-auto-fill (&optional recursive)
    "Turn on `auto-fill-mode', but fix things if it got set globally.
See <https://debbugs.gnu.org/cgi/bugreport.cgi?bug=64439>."
    (turn-on-auto-fill)
    (when (default-value 'auto-fill-function)
      (message "`auto-fill-function' got set globally; fixing it...")
      (setq-default auto-fill-function nil)
      (when recursive
        (error (concat "Recursively setting the default value of "
                       "`auto-fill-function'!")))
      (run-with-timer 0 nil
                      (lambda (buf)
                        (with-current-buffer buf
                          (user/turn-on-auto-fill)))
                      (current-buffer))))

  :init
  (add-hook 'text-mode-hook (if (< emacs-major-version 30)
                                #'user/turn-on-auto-fill
                              #'turn-on-auto-fill)))