Re: \documentclass does not activate latex-mode

[jfbu]

Hi Keita,

Le 18/08/2022 à 09:40, Ikumi Keita a écrit :
> Hi Jean, sorry for late response. I just came back from my summer
> vacation.

no worries whatsoever
thanks for all your volunteer work on AUCTeX !

> > > > > > jfbu <jfbu@free.fr> writes:
> > when I open a buffer on this file
>
> > ----
> > \def\foo{bar}
> > \documentclass{foobar}
> > \begin{document}
> > hello
> > \end{document}
> > ----
>
> > there is no activation of latex-mode.
>
> > I have to manually type-in M-x latex-mode.
>
> [...]
>
> > Any hint to make my life less miserable?
>
> Actually, AUCTeX is able to activate latex mode correctly, but emacs
> built-in tex-mode.el interferes with it, due to the change installed in
> emacs 28. :-(


oh well... yes indeed I am currently using a build of GNU Emacs 28.1...

in retrospect it is easy for me to say that somewhere inside me a little voice 
was telling me that in the past I had been working under same circumstances and 
didn't experience the reported problems... but your detective work is much more 
accurate!

> For the time being, you can work around by
> (let (entry)
>    (while (setq entry (rassq 'tex-mode auto-mode-alist))
>      (setcdr entry #'TeX-tex-mode)))
> in your personal init file.

wow it does work! Now that's quite magic to me. I have delayed for two decades 
learning e-Lisp...

> > But IMHO, should'nt \documentclass by itself trigger latex-mode?
> > It is relatively frequent to have to put code before the
> > \documentclass.
>
> Yes. As I wrote above, there was no problem until emacs 27.

I knew it! (subconsciously ;-))

Thanks for your help!

Best,

Jean-François

> [To developpers]
> In emacs 28, tex-mode.el changed `tex-mode' activation like this:
> ----------------------------------------------------------------------
> (define-derived-mode tex-mode text-mode "generic-TeX"
>    "...doc string..."
>    (tex-common-initialization))
>
> (advice-add 'tex-mode :around #'tex--redirect-to-submode)
> (defvar tex-mode--recursing nil)
> (defun tex--redirect-to-submode (orig-fun)
>    "Redirect to one of the submodes when called directly."
>    ;; The file may have "mode: tex" in the local variable
>    ;; block, in which case we'll be called recursively
>    ;; infinitely.  Inhibit that.
>    (let ((tex-mode--recursing tex-mode--recursing))
>      (funcall (if (or delay-mode-hooks tex-mode--recursing)
>                   ;; We're called from one of the children already.
>                   orig-fun
>                 (setq tex-mode--recursing t)
>                 (tex--guess-mode)))))
> ----------------------------------------------------------------------
> This around advice for `tex-mode' broke AUCTeX's intention. At emacs
> startup, AUCTeX adds override advice `TeX-tex-mode' to `tex-mode' in
> tex-site.el. However, when tex-mode.el is autoloaded, it futher adds
> around advice `tex--redirect-to-submode'.
> By the nature of around advice, it bypasses the `orig-fun' (which is
> essentially `TeX-tex-mode' by the override advice) and calls
> `tex--guess-mode'. `tex--guess-mode' in tex-mode.el is not smart enough
> to guess that Jean's example is latex document, ending up with calling
> `plain-tex-mode'.
>
> Why on earth does tex-mode.el use advice for its own function? The whole
> above piece of code can just be composed up as
> ----------------------------------------------------------------------
> (defvar tex-mode--recursing nil)
> (define-derived-mode tex-mode text-mode "generic-TeX"
>    "...doc string..."
>
>    ;; The file may have "mode: tex" in the local variable
>    ;; block, in which case we'll be called recursively
>    ;; infinitely.  Inhibit that.
>    (let ((tex-mode--recursing tex-mode--recursing))
>      (if (or delay-mode-hooks tex-mode--recursing)
>          ;; We're called from one of the children already.
>          (tex-common-initialization)
>        (setq tex-mode--recursing t)
>        (tex--guess-mode))))
> ----------------------------------------------------------------------
> without any advice, if I understand correctly.
>
> I think we should file bug report for tex-mode.el. What do others think?
>
> Regards,
> Ikumi Keita
> #StandWithUkraine #StopWarInUkraine