bug#10159: auto-complete causes crash in emacs HEAD

[Eli Zaretskii <eliz@gnu.org>]

> From: Christopher Monsanto <chris@monsan.to>
> Date: Sat, 22 Sep 2012 08:19:11 -0400
> Cc: 10159@debbugs.gnu.org
> 
> Same here.
> 
> (gdb) pp string
> #("                                    " 0 36 (face popup-tip-face
> keymap nil popup-item ""))

That's good to know, thanks.

> Thanks. Seems to me that this value is coming from xdisp.c,
> display_line, var n_glyphs_before, derived from row->used[TEXT_AREA]
> (line 19425).

No, it comes from it->end_charpos, the length of the previous overlay
string, because when the next overlay string is loaded, its length was
not reflected in the value of it->end_charpos.  Should be fixed now in
revision 110135 on the trunk.

> (I wish I knew what a "struct it" is, not the most
> descriptive name! :-))

"it" stands for "iterator".  'struct it' is an object used by the
display engine to iterate over buffers or strings to be displayed, one
character at a time, with the purpose of generating the information
required by the display back-end (X, TTY, etc.) to update the screen.
See dispextern.h around line 1925, for more about that.

Please test revision 110135 thoroughly with auto-complete, and if you
find no problems, I will close this bug.