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.)