GNU bug report logs - #62445
13.1.10; bug in preview-region applied to repeated math environments

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Paul Nelson <ultrono <at> gmail.com>
Subject: bug#62445: closed (Re: bug#62445: 13.1.10; bug in preview-region
 applied to repeated math environments)
Date: Mon, 08 Apr 2024 19:38:03 +0000

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Your bug report

#62445: 13.1.10; bug in preview-region applied to repeated math environments

which was filed against the auctex package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 62445 <at> debbugs.gnu.org.

-- 
62445: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=62445
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Arash Esbati <arash <at> gnu.org>
To: Paul Nelson <ultrono <at> gmail.com>
Cc: 62445-done <at> debbugs.gnu.org
Subject: Re: bug#62445: 13.1.10; bug in preview-region applied to repeated
 math environments
Date: Mon, 08 Apr 2024 21:37:06 +0200

Paul Nelson <ultrono <at> gmail.com> writes:

> I've adjusted the commit message as best I could (it wasn't 100% clear
> to me whether the summary line should appear "twice", both in the
> subject and in the first line of the commit message), and can't
> remember any reason not to just use setq, so I've changed it to that.
> Any further feedback is welcome.

Hi Paul,

thanks for considering my remarks.  I slightly changed your last
proposal and installed it on master (b4dde3e325); I hope it's Ok for
you.

Again, many thanks for your contribution and sorry for the delay at our
end.  I'm closing this report.

Best, Arash

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From: Paul Nelson <ultrono <at> gmail.com>
To: bug-auctex <at> gnu.org
Subject: 13.1.10; bug in preview-region applied to repeated math environments
Date: Sat, 25 Mar 2023 17:14:48 +0100

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Emacs  : GNU Emacs 29.0.50 (build 3, x86_64-apple-darwin21.6.0, NS
appkit-2113.60 Version 12.6 (Build 21G115))
 of 2022-11-06
Package: 13.1.10

Take the following document:

#+begin_src latex
\documentclass{amsart}
\begin{document}
 $x$ $x$
\end{document}
#+end_src

Run ~preview-region~ on the region consisting of the first $x$.  This works
as expected.

Next, run ~preview-region~ on the region consisting of just the second
$x$.  This does not preview the second $x$.  Instead, it refreshes the
overlay on the first $x$.

The relevant output:

#+begin_quote
./_region_.tex:5: Preview: Snippet 1 started.
<-><->

l.5 $
     x$
Preview: Tightpage -32891 -32891 32891 32891
./_region_.tex:5: Preview: Snippet 1 ended.(282168+0x374556).
<-><->

l.5 $x$

#+end_quote

The issue here is that there's not enough context for
~preview-parse-messages~ to determine which $x$ to overlay.

One workaround would be to apply ~preview-region~ to a region containing
both $x$'s (or to use ~preview-buffer~, etc).  This workaround wasn't ideal
for my use-case (see parenthetical comment at the bottom).

I think a fix would be to store the beginning of the region being previewed
in a buffer-local variable and, if needed, bump the point when searching
for where to place the overlay.  Details:

- Add the following line somewhere in preview.el:
  #+begin_src elisp
  (defvar-local preview-region--begin nil "Start of region being
processed.")
  #+end_src

- Add the following line to ~preview-region~, just before the invocation of
~preview-generate-preview~:
  #+begin_src elisp
  (setq-local preview-region--begin begin)
  #+end_src

- Add this to ~preview-parse-messages~, just before the second ~cond~ block:
  #+begin_src elisp
  (when (< (point) preview-region--begin)
    (goto-char preview-region--begin))
  #+end_src

I've made these changes in my local version and they have worked for me.

(This bug was an issue for me because I had set up a timer that searches
the visible portion of a TeX buffer for unrendered math environments and
runs ~preview-region~ on contiguous unpreviewed blocks.  This led to many
situations where  ~preview-region~ was called on math regions, such as the
second $x$ in the above example, that had already been previewed in the
current line.  My original workaround was to enlarge the region sent to
~preview-region~ to contain any repeated math regions that appear earlier
in a given line.  This worked, but often resulted in many fragments getting
unnecessarily refreshed.)

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