bug#38731: 27.0.50; Unexpected redisplay behaviour. Cursor can’t be moved to end of line.

[Eli Zaretskii]

> Date: Thu, 26 Dec 2019 12:59:17 +0000
> From: Alan Third <alan@idiocy.org>
> Cc: HaiJun Zhang <netjune@outlook.com>, 38731@debbugs.gnu.org
> 
> In ns_draw_glyph_string I can see that s->x is correctly set to 136
> when the backtrace doesn’t contain expose_frame, but 178 when it does.

Isn't it the other way around?  The correct display should start at a
larger X coordinate.  Or maybe I don't understand what is s->x in this
context, i.e. what glyph string is S.

> The issue seems to rely on the combination of truncate lines mode,
> global hl mode and tabs on the left. The number of tabs seems to make
> no difference, the offset remains the same, and replacing tabs with
> spaces displays correctly.
> 
> Any thoughts on how to debug this further?

A TAB is displayed by a stretch glyph, so maybe start looking there.