Re: FACE_FROM_ID vs FACE_OPT_FROM_ID

[Paul Eggert]

On 06/23/2016 10:03 PM, Eli Zaretskii wrote:
> What was the GCC 6.1 complaint that led you to this change?
Diagnostics like this one (there were quite a few):

> xdisp.c: In function 'fill_image_glyph_string':
> xdisp.c:24916:20: error: potential null pointer dereference 
> [-Werror=null-dereference]
>    s->font = s->face->font;
>              ~~~~~~~^~~~~~

The problem being that s->face was set from FACE_FROM_ID, which (before 
the change) might return a null pointer.

The intent is that FACE_FROM_ID returns a face (a non-null pointer), 
whereas FACE_OPT_FROM_ID returns a face option (either a face or a null 
pointer). Similarly for IMAGE_FROM_ID. I installed the attached patch to 
try to make this clearer.

0001-Clarify-intent-of-FACE_FROM_ID-and-IMAGE_FROM_ID.txt
Description: Text document