Re: emacs-28 c05864dd25: Avoid another segfault in 'face_at_buffer_position'

[Eli Zaretskii <eliz@gnu.org>]

> From: Robert Pluim <rpluim@gmail.com>
> Cc: Eli Zaretskii <eliz@gnu.org>
> Date: Fri, 14 Jan 2022 16:01:34 +0100
> 
>     Eli> diff --git a/src/xfaces.c b/src/xfaces.c
>     Eli> index b9fb7c0ac1..dff5ae346d 100644
>     Eli> --- a/src/xfaces.c
>     Eli> +++ b/src/xfaces.c
>     Eli> @@ -6425,8 +6425,12 @@ face_at_buffer_position (struct window *w, ptrdiff_t pos,
>  
>     Eli>      default_face = FACE_FROM_ID_OR_NULL (f, face_id);
>     Eli>      if (!default_face)
>     Eli> -      default_face = FACE_FROM_ID (f,
>     Eli> -				   lookup_basic_face (w, f, DEFAULT_FACE_ID));
>     Eli> +      {
>     Eli> +	if (FRAME_FACE_CACHE (f)->used == 0)
>     Eli> +	  recompute_basic_faces (f);
>     Eli> +	default_face = FACE_FROM_ID (f,
>     Eli> +				     lookup_basic_face (w, f, DEFAULT_FACE_ID));
>     Eli> +      }
>     Eli>    }
> 
> If youʼre going to need to check the face cache, how about doing that
> unconditionally? ie removing FACE_FROM_ID_OR_NULL and the
> !default_face bit?

I want the "usual" case, where default_face is non-NULL, to work as
quickly as possible.  The face cache being cleared is a relatively
rare exception.