bug#45898: 27.1; wedged in redisplay again

[Eli Zaretskii <eliz@gnu.org>]

[I've redirected the discussion here, since emacs-diffs isn't the
right place for it.]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: emacs-diffs@gnu.org
> Date: Fri, 24 Jun 2022 21:02:59 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> > I cannot reproduce this.  Does it happen with the latest master?  If
> >> > so, can you put a breakpoint in xdisp.c here:
> >> >
> >> >       if (w && w->desired_matrix)
> >> > 	w->desired_matrix->no_scrolling_p = true;
> >> >       error ("Window showing buffer %s takes too long to redisplay", bufname);
> >> >
> >> > on the line that calls 'error', and when it breaks, show the
> >> > backtrace, both the C backtrace and Lisp backtrace?
> 
> (gdb) bt
> #0  update_redisplay_ticks (ticks=1, w=0x55555619b040) at xdisp.c:17256
> #1  0x00005555555d894e in set_iterator_to_next (it=0x7fffffff6d40, reseat_p=true) at xdisp.c:8189
> #2  0x00005555555ddabd in move_it_in_display_line_to (it=0x7fffffff6d40, to_charpos=69407, to_x=-1, op=MOVE_TO_POS) at xdisp.c:9967
> #3  0x00005555555de979 in move_it_to (it=0x7fffffff6d40, to_charpos=69407, to_x=-1, to_y=1494, to_vpos=-1, op=10) at xdisp.c:10221
> #4  0x00005555555e06c8 in partial_line_height (it_origin=0x7fffffff80b0) at xdisp.c:10852
> #5  0x00005555555f8cd5 in try_window (window=XIL(0x55555619b045), pos=..., flags=1) at xdisp.c:20229
> #6  0x00005555555f5e16 in redisplay_window (window=XIL(0x55555619b045), just_this_one_p=false) at xdisp.c:19606
> #7  0x00005555555ee563 in redisplay_window_0 (window=XIL(0x55555619b045)) at xdisp.c:17184
> #8  0x00005555557e6222 in internal_condition_case_1 (bfun=0x5555555ee521 <redisplay_window_0>, arg=XIL(0x55555619b045), handlers=XIL(0x7ffff17549f3), hfun=0x5555555ee43a <redisplay_window_error>) at eval.c:1509
> #9  0x00005555555ee410 in redisplay_windows (window=XIL(0x55555619b045)) at xdisp.c:17154
> #10 0x00005555555ed2ce in redisplay_internal () at xdisp.c:16609
> #11 0x00005555555edd94 in redisplay_preserve_echo_area (from_where=9) at xdisp.c:16967
> #12 0x000055555584c9f5 in wait_reading_process_output (time_limit=45, nsecs=0, read_kbd=-1, do_display=true, wait_for_cell=XIL(0), wait_proc=0x0, just_wait_proc=0) at process.c:5334
> #13 0x00005555555aa9f8 in sit_for (timeout=make_fixnum(45), reading=true, display_option=1) at dispnew.c:6238
> #14 0x000055555572aa94 in read_char (commandflag=1, map=XIL(0x55555941e113), prev_event=XIL(0), used_mouse_menu=0x7fffffffd9df, end_time=0x0) at keyboard.c:2840
> #15 0x000055555573ab2b in read_key_sequence (keybuf=0x7fffffffdbe0, prompt=XIL(0), dont_downcase_last=false, can_return_switch_frame=true, fix_current_buffer=true, prevent_redisplay=false) at keyboard.c:9988
> #16 0x0000555555726f35 in command_loop_1 () at keyboard.c:1391
> #17 0x00005555557e617b in internal_condition_case (bfun=0x555555726adf <command_loop_1>, handlers=XIL(0x90), hfun=0x5555557260e7 <cmd_error>) at eval.c:1485
> #18 0x000055555572678f in command_loop_2 (handlers=XIL(0x90)) at keyboard.c:1132
> #19 0x00005555557e583d in internal_catch (tag=XIL(0xf660), func=0x555555726765 <command_loop_2>, arg=XIL(0x90)) at eval.c:1208
> #20 0x0000555555726721 in command_loop () at keyboard.c:1110
> #21 0x0000555555725c89 in recursive_edit_1 () at keyboard.c:719
> #22 0x0000555555725e35 in Frecursive_edit () at keyboard.c:802
> #23 0x0000555555722188 in main (argc=3, argv=0x7fffffffe0f8) at emacs.c:2517
> 
> Lisp Backtrace:
> "redisplay_internal (C function)" (0x0)
> (gdb) 

Thanks.  I tried to fix this on master, please see if the problem is
gone.