Re: Emacs pretest: highlight line number in display-line-numbers-mode?

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 19 Oct 2017 13:43:06 -0700 (PDT)
> From: Drew Adams <drew.adams@oracle.com>
> 
> > This face is by default the same as line-number because of 2 reasons:
> > 
> >   . linum-mode did the same
> 
> ...chasing that rabbit: Why did `linum-mode' do that?

I don't know, but too many differences from a previous feature tend to
annoy people IME.

> >   . using a different face makes redisplay slightly slower
> >     (because it disallows some redisplay optimizations)
> 
> Would those optimizations still be available if a
> user chose the same face for both (but the faces
> were different by default)?
> 
> If so, I'd suggest making the faces different by
> default.

They are already different by default.  They just have the same
attributes.

> IOW, opt-in for the loss of a difference.

That's already so.

> > > To find the face used, I use `list-faces-display' and look
> > > for either a face name that is a likely candidate
> > > (`line-number' is pretty obvious, in this case) or a face
> > > appearance that matches what I see.
> > 
> > There are other places where this doesn't work, e.g. on the
> > mode line.
> 
> What do you mean by "this"?  Using `list-faces-display'
> or the fact that you can't use `C-u C-x =' to learn
> the face?

The latter.

> You gave that reply after my mention of the former. 
> Aren't all of the faces used in the mode line shown in
> `list-faces-display'?

They are, but so are the line-number faces.