Re: Emacs26: Quick thoughts on display-line-numbers-mode

[Matthew Plant <maplant95@gmail.com>]

On Thu, 2017-10-05 at 22:50 +0300, Eli Zaretskii wrote:
> > From: Matthew Plant <maplant95@gmail.com>
> > Date: Thu, 05 Oct 2017 12:35:29 -0700
> > 
> > My apologies, I did not notice that line-number face existed
> > because it
> > is not part of the display line numbers group. This does exactly
> > what I
> > want.
> > 
> > That being said, shouldn't this face be part of the group display-
> > line-
> > number? Faces for compilation errors are part of the the
> > compilation
> > group. 
> 
> My reasoning was that this is one of the basic faces we provide, so
> it's in the basic faces group.
> 
Hmm... Ok.

> > Being able to specify which side the line numbers appear I imagine
> > would be useful for editing right to left languages.
> 
> When the paragraph direction is right-to-left, the numbers
> automatically appear on the right.  You should be able to see that if
> you visit TUTORIAL.he with display-line-numbers-mode turned on.
> 
> > That being said I can't find one editor that supports this feature
> 
> Well, Emacs does ;-)
> 

I was silently wondering if this was the case. Oops, my bad.

> > You said in a separate reply that separation between the numbers
> > and
> > the text is kept with a white-space glyph. Why not just let this be
> > a
> > buffer or mode local string specified by the user?
> 
> There's a technical problem with doing that, which I couldn't solve.
> It would also slow down redisplay, while performance was high on my
> priority list when working on this feature.

If you can elaborate on the technical problem I can give it a look.
If the glyph is limited to one character and is properly cached I don't
see why this would be a specificaly worrisome performance hit. I can
see it being an issue if the glyph is changed a lot, but I don't think
this is a common use case.

I'm making some assumptions about the display code, I'll take a look at
the implementation.