Re: Question about display engine

[Ergus]

On Sun, Oct 13, 2019 at 08:04:02PM +0300, Eli Zaretskii wrote:
> > Date: Sun, 13 Oct 2019 18:44:24 +0200
> > From: Ergus <address@hidden>
> > Cc: address@hidden, address@hidden
> >
> > >Could it be that redisplay_window_0, or some function it calls,
> > >signals an error, which is caught by internal_condition_case_1?  What
> > >happens if you put a breakpoint in signal_or_quit, does it get called
> > >from redisplay_window or some other function called by
> > >redisplay_windows?
> >
> > Yes, actually:
> >
> > #0  0x00005597732a0380 in signal_or_quit (error_symbol=0x2cd0, 
> > data=0x559775ee2633, keyboard_quit=false) at ../../src/eval.c:1586
> > #1  0x000055977314c308 in Fsignal (error_symbol=<optimized out>, 
> > error_symbol@entry=0x2cd0, data=<optimized out>) at ../../src/eval.c:1568
> > #2  0x000055977314c4c9 in xsignal (data=<optimized out>, error_symbol=0x2cd0) 
> > at ../../src/lisp.h:4139
> > #3  0x000055977314c4c9 in xsignal2 (error_symbol=error_symbol@entry=0x2cd0, 
> > arg1=<optimized out>, arg2=<optimized out>) at ../../src/eval.c:1713
> > #4  0x000055977314b76e in args_out_of_range (a1=<optimized out>, a2=<optimized 
> > out>) at ../../src/lisp.h:1032
> > #5  0x000055977314e97b in validate_interval_range (object=0x559775cee0d5, 
> > begin=0x7fff35ec34b8, end=0x7fff35ec34b8, force=<optimized out>) at 
> > ../../src/textprop.c:158
> > #6  0x00005597732f4050 in Ftext_properties_at (position=<optimized out>, 
> > object=<optimized out>) at ../../src/textprop.c:572
> > #7  0x00005597732f40bc in Fget_text_property (position=<optimized out>, prop=0x5d30, 
> > object=<optimized out>) at ../../src/textprop.c:592
> > #8  0x00005597731f8eec in face_at_buffer_position
> >     (w=0x5597758e7620, pos=0, endptr=endptr@entry=0x7fff35ec3650, limit=100, 
> > mouse=mouse@entry=false, base_face_id=1, attr_filter=LFACE_EXTEND_INDEX)
> >     at ../../src/xfaces.c:6090
>
> Then looking at the position that causes the error will probably tell
> you what's wrong.  (Is OBJECT passed to Fget_text_property a string?
> if not, position of zero is invalid.)

That's exactly the problem. IT_CHARPOS (*it), is returning zero in
face_at_pos and !STRINGP (it->string). Could you tell me whats going on
please.