bug#14838: 24.3.50; repeating next-line or previous-line is broken

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 11 Jul 2013 23:25:05 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 14838@debbugs.gnu.org
> 
> > From: Stephen Berman <stephen.berman@gmx.net>
> > Cc: jan.h.d@swipnet.se,  14838@debbugs.gnu.org
> > Date: Thu, 11 Jul 2013 22:04:07 +0200
> > 
> > > I don't believe the aref part.  I think the real culprit is font-info.
> > > Let's conduct an experiment: if you modify default-font-height so that
> > > it always just calls frame-char-height, does the problem go away?
> > 
> > Yep, that it does.  And no trace messages are emitted.
> 
> Thanks, I will come up with a change that will refrain from calling
> font-info unless it's strictly necessary.

I'm unsure what test(s) to use to detect reliably the situation where
the font of the default face is different from the frame's default.
The two candidates I thought about are:

  . See if face-remapping-alist is non-nil and includes an association
    for the 'default' face

  . Compare

      (frame-parameter 'font)

    with

      (face-font 'default)

Regarding the 1st candidate, I'm not sure the condition will always
hold whenever the font of the default face was modified in some way.

Regarding the 2nd candidate, I'm not sure (frame-parameter 'font) will
always return a non-trivial value.  Can it return nil, for example?

Any other suggestions?

Stephen, can you test both of the above in your case?

Thanks.