bug#11464: 24.1.50; pos-visible-in-window-p returns a false positive with bidi text

[Ari Roponen]

The following code shows a problem with pos-visible-in-window-p
and bidirectional text. When there are right-to-left characters
at the beginning of the buffer, the function returns nil, as the
last line is not visible. However, when "a" is inserted into the
beginning of the buffer, the function returns t, which is
incorrect.

The bug happens in trunk and emacs-24, but not in emacs-23, so it
could be considered as a regression ;-)


(let (before after)
  (pop-to-buffer (get-buffer-create "test"))
  (erase-buffer)

  (dotimes (i (* 2 (window-height)))
    (insert "\u05d0\n"))                ; HEBREW LETTER ALEF
  (insert "Last line\n")
  (goto-char (point-min))

  (setq before (pos-visible-in-window-p (point-max)))

  (insert "a")
  (setq after (pos-visible-in-window-p (point-max)))
  (message "Visible: before: %S, after: %S" before after))


In GNU Emacs 24.1.50.8 (x86_64-unknown-linux-gnu, GTK+ Version 3.4.1)
 of 2012-05-13 on arirop
Bzr revision: 108213 monnier@iro.umontreal.ca-20120513030506-t7ggxqlr92y8yjw4
Windowing system distributor `Fedora Project', version 11.0.11200000
Configured using:
 `configure '--with-x-toolkit=gtk3''

-- 
Ari Roponen