Re: Question about display engine

[Eli Zaretskii]

> Cc: Eli Zaretskii <address@hidden>
> From: martin rudalics <address@hidden>
> Date: Thu, 8 Aug 2019 15:05:37 +0200
> 
>  > Yes, that's exactly the point. The only face I see that needs to be
>  > extended so far is the region. If only the region is extended
>  > (assuming we won't stop extending that one too) you won't need your
>  > workarounds, extra settings, another flag in the face structure, or
>  > call extend face to end of line most of the time.
> 
> I'm afraid things are not that simple.  We have at least the secondary
> selection and 'hl-line-mode' to take care of.

Indeed, nothing is ever as simple in the display code, due to the
sheer amount of different use cases.  I think at least one other face
attribute that's special in this regard is :box, in particular (but
not only) because extend_face_to_end_of_line is called from the
function which redisplays the mode line and the header line.

> Moreover, there might be users who do prefer the current way of
> extending (and not extending) faces to window edges.  And I have no
> idea whether image or rectangular regions require special treatment
> too.

Yes, I think we will have to provide some backward compatibility shims
for these and other use cases.