bug#26980: 25.2; Freeze & redisplay_internal & macOS

[Eli Zaretskii]

> From: Robert Vojta <rvojta@me.com>
> Date: Mon, 29 May 2017 11:37:42 +0200
> Cc: alan@idiocy.org, 26980@debbugs.gnu.org
> 
> It’s caused by unicode character number 9448 (ⓨ). In 99% of cases, ascent of 
> this character is 16, descent is 4, thus the sum is 20 and it equals to 
> desired mode line height (20). Works like a charm.
> 
> What troubles me is that sometimes the descent is 5. Sometimes means it’s 
> totally random. For the whole week, it’s always 4, works. And boom, it’s 5 -> 
> 16 + 5 -> 21 -> 21 != 20 and never ending loop is here.

Can you see if those instances with descent of 5 are because the
character is displayed using a different font, by any chance?

Another, perhaps more probable cause could be that in some cases
CURRENT_MODE_LINE_HEIGHT uses the value of w->mode_line_height, and
sometimes it needs to estimate the height by calling
estimate_mode_line_height.  Maybe something is inconsistent between
the estimation and the actual value.

Also, the offending character is displayed on the mode line, right?
Could you please show a screenshot of a window with the mode line
formatted as it should when Emacs freezes?

Thanks.