I installed the patch and the bug was fixed.

Thanks.

On Sat, Jul 13, 2024 at 5:08 PM Eli Zaretskii <eliz@gnu.org> wrote:

> > From: Siyuan Chen <chansey97@gmail.com>
> > Date: Sat, 13 Jul 2024 01:52:11 +0800
> >
> > Reproduce steps:
> >
> > 1 Clone Emacs source code from https://github.com/emacs-mirror/emacs
> >
> > 2. Emacs -Q (Emacs 29.3 on Windows)
> >
> > 3. Open etc/NEWS.30 from the Emacs source code (by default Emacs will
> use emacs-news-mode)
> >
> > 4. M-x imenu and press TAB to complete
> >
> > Emacs shows 515 possible completions.
> >
> > 6. M-x emacs-news-view-mode
> >
> > 7. M-x imenu and press TAB to complete
> >
> > Emacs shows 202 possible completions.
> >
> > This is the problem, i.e. emacs-news-mode and emacs-news-view-mode
> return different imenu lists.
>
> This happens because emacs-news-view-mode derives from special-mode,
> and therefore has a different syntax table.  Which has the effect of
> duping imenu--generic-function into thinking some of the NEWS entries
> are in comments, and so it ignores them:
>
>                   ;; Insert the item unless it is already present.
>                   (unless (or (member item (cdr menu))
>                               (and imenu-generic-skip-comments-and-strings
>                                    (save-excursion
>                                      (goto-char start) (nth 8
> (syntax-ppss)))))
>                     (setcdr menu
>                             (cons item (cdr menu)))))
>
> Note the call to syntax-ppss there: it returns nil in 8th entry in
> emacs-news-mode when point is, e.g., on the final ^L in NEWS, but
> non-nil in emacs-news-view-mode.
>
> The simple and naïve change below seems to fix that.  The only problem
> with it is that one cannot move through the buffer with SPC, DEL, '<'
> etc.  For some reason I cannot get emacs-news-view-mode inherit the
> keymap of special-mode, nor even use its own keymap I defined in a
> defvar emacs-news-view-mode-map.  Stefan, any reason why a simple
> definition of emacs-news-view-mode-map doesn't work, as the ELisp
> manual promises it should (where it described define-derived-mode)?
>
> Also, any idea why syntax-ppss thinks the final ^L in NEWS, here:
>
>   ---
>   *** Emacs on MS-Windows now supports the ':stipple' face attribute.
>
>   ^L
>   ----------------------------------------------------------------------
>   This file is part of GNU Emacs.
>
> is in a comment when emacs-news-view-mode inherits from special-mode?
>
> Btw, I find our syntax-table introspection features not very helpful
> in these situations.  Once I figured out that syntax-ppss produces
> different results in these two modes, all the rest was pure guesswork,
> with no real way of investigating the differences and their reason(s).
> Do we have any ways of comparing two syntax tables and showing the
> differences in human-readable form?  Do we have a way of showing the
> source(s) f a syntax-table's information, like where it inherited from
> another and where it was modified by explicit modify-syntax-entry
> calls?  Do we have a way of making one mode use the syntax table of
> another mode without having a variable which holds the latter?  I
> needed all of these to investigate in this case, and was finally
> forced to treat the issue as a kind of "black box", making
> more-or-less random changes and looking at the results, which is very
> frustrating and a terrible waste of time...
>
>
> diff --git a/lisp/textmodes/emacs-news-mode.el
> b/lisp/textmodes/emacs-news-mode.el
> index 1dd017a..c87e7fa 100644
> --- a/lisp/textmodes/emacs-news-mode.el
> +++ b/lisp/textmodes/emacs-news-mode.el
> @@ -107,7 +107,7 @@ emacs-news-mode
>    (emacs-news--mode-common))
>
>  ;;;###autoload
> -(define-derived-mode emacs-news-view-mode special-mode "NEWS"
> +(define-derived-mode emacs-news-view-mode emacs-news-mode "NEWS"
>    "Major mode for viewing the Emacs NEWS file."
>    (setq buffer-read-only t)
>    (emacs-news--buttonize)
>