Re: isearch, auto-composition-mode and display properties

[Juri Linkov]

> I hope others can reproduce this problem and someone can figure out
> what's going on.

Thank you for the detailed test case.  I was able to reproduce it.

To debug isearch, you can instrument one of the top isearch functions
(e.g. `isearch-repeat-forward'), open the isearch.el file in another
frame/buffer (another frame is more preferable when debugging display
problems like in your case), and start typing C-s in the original
buffer.  When it stops on an uninteresting place, just type `g' to
continue execution.  Use `i' to go to a deeper function.

The hardest part in debugging isearch is not forget not to use isearch
to navigate in the source buffer while edebug is active (e.g. to find
the next function to instrument, etc :)

Using this technique, it is possible to find that your trouble is cased
by the following part of `isearch-update':

          ;; Keep same hscrolling as at the start of the search when possible
          (let ((current-scroll (window-hscroll)))
            (set-window-hscroll (selected-window) isearch-start-hscroll)
            (unless (pos-visible-in-window-p)
              (set-window-hscroll (selected-window) current-scroll)))

Removing this part eliminates the bug you reported.  Unfortunately,
I have no idea how to fix this since this depends on the details
how the display engine works.

-- 
Juri Linkov
http://www.jurta.org/emacs/