bug#5275: Malayalam file names not rendered correctly (conjuncts are not formed) in message window and buffer title

[YAMAMOTO Mitsuharu]

>>>>> On Fri, 15 Jan 2010 11:19:24 +0900, Kenichi Handa <handa@m17n.org> said:

>> Though this is not reliably reproducible, mode-line display seems
>> to become unstable occasionally when the buffer name containing
>> composition is short and requires trailing padding spaces.

> I tried various buffer names but couldn't reproduce it.  What does
> "unstable" mean exactly?  When you reproduce it, please let me know
> the buffer name and which font is used for it.

Unfortunately, I couldn't reproduce it on GNU/Linux.  But the
following examples spontaneously fail with the X11 build on Mac OS X
10.5.

  (switch-to-buffer-other-window (string ?e 769))
  (switch-to-buffer-other-window (string ?e 769 ?e 769))
  (switch-to-buffer-other-window (string ?e 769 ?e 769 ?e 769))
  (switch-to-buffer-other-window (string ?e 769 ?e 769 ?e 769 ?e 769))
  (switch-to-buffer-other-window (string ?e 769 ?e 769 ?e 769 ?e 769 ?e 769))

  ;; The following one always succeeds.
  (switch-to-buffer-other-window (string ?e 769 ?e 769 ?e 769 ?e 769 ?e 769 ?e 
769))

Sometimes the buffer name is rendered incorrectly (see the
attachment), and sometimes the mode line is not updated.  The latter
case often leads to crash afterwards.

The font used for the buffer name in the modeline is

  xft:-bitstream-Bank Gothic-normal-normal-normal-*-16-*-*-*-*-0-iso10646-1

I can see similar phenomena on the Mac port and also with ideographic
variation sequences.  So I don't think fonts or libotf is related to
this issue.

I suspect the problematic case is that `charpos + field_width' in
reseat_to_string exceeds the length of the given string.  The value of
`field_width' is 12 by default when displaying buffer names.

                                     YAMAMOTO Mitsuharu
                                mituharu@math.s.chiba-u.ac.jp