bug#48732: 28.0.50; lisp_string_width segfaults on startup under macOS

[Eli Zaretskii]

> From: Naofumi Yasufuku <naofumi@yasufuku.dev>
> Date: Mon, 31 May 2021 23:27:02 +0900
> Cc: 48732@debbugs.gnu.org
> 
> This workaround works fine.  I think this issue can be closed.
> 
> Access to unrealized 'face->lface' Lisp_Object is not seen anymore
> on startup, and no segfault happens with both simple reproducing
> 'tramp-syntax’ init.el and my daily-use more complicated init.el.
> 
> I comfirmed it on two intel macs which this segfault was observed:
>   - MacBook running the latest macOS 11.4
>   - Mac mini running macOS 10.14
> 
> At the same time, font corruption issue with some themes is also disappeared
> as Pankaj said on emacs-devel list.
> (After autocmp string-width commits, I had seen the font corruption
> issue frequently with doom-tomorrow-night of doom-themes package.)

Thanks for testing.

I think the problem was in styled_format: it keeps C pointers to Lisp
string data around the call to lisp_string_width, which could cause
GC, which could relocate Lisp strings.  But after the last change,
lisp_string_width as called from styled_format can no longer cause GC,
so that problem is gone.  And there are other valid reasons why
'format' and 'format-message' are better without this feature, so I
think we will leave it at that.