bug#17813: 24.3.91; bad linum display with `text-scale-adjust'

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Date: Thu, 19 Jun 2014 14:46:48 -0400
> Cc: 17813@debbugs.gnu.org, miles@gnu.org
> 
> I think the right solution is to scale the margin width by the ratio
> "linum font size / base font size".  Then users can set their `linum'
> face the way want and choose between (1) and (2).
> 
> But it turns out that face-attribute can't be used for that because it
> does not pay attention to face-remapping-alist.

Not sure what you mean by that: attributes don't care about remapping,
because remapping doesn't change the attributes, it only changes their
values.

> Miles, Eli, others, do you know of a function that returns "the font
> size, including face-remapping-alist effects"?

I think you want

  (aref (font-info (face-font 'default)) 2)

But note that font's size and its "width" (which is actually the
average width recorded in the font file) are not identical.  We don't
have a Lisp API to get the average width of a non-default font;
perhaps we should.