bug#20628: 25.0.50; Incorrect line height for some fonts

[Eli Zaretskii]

> Date: Fri, 22 May 2015 15:03:24 -0400
> From: Clément Pit--Claudel
>  <clement.pitclaudel@live.com>
> CC: 20628@debbugs.gnu.org
> 
> I believe you have something like the following line in mind:
> 
>   (set-fontset-font fontset 'unicode (font-spec :name "Symbola") nil 'append)

That's too radical.  You could be more selective, e.g.:

  (set-fontset-font "fontset-default"
                    '(#x1d400 . #x1d7ff)
                    "Symbola")

That's because you may wish using other fonts for other Unicode
blocks.

> Indeed, this fixes the problem. Unfortunately, this problem makes it hard for 
> package developers to make use of prettify-symbols-mode. Indeed, programming 
> languages like Agda or Gallina (Coq) would gain a lot from heavy 
> prettification, but since the default fallback font tends to be one of these 
> badly behaved TeX fonts, users of Adga and Coq packages will often run into 
> this problem if we enable prettification by default at the package level the 
> package level. IOW, it's currently hard to come up with a workaround that 
> does not involve user intervention at the moment.

Couldn't those package developers recommend fontset settings, of even
include ready-to-use .emacs snippets as part of the package?

> > (...)
> >> Is it possible for Emacs to do so by default?
> > 
> > You mean, have the default fontset set up to avoid the problem?  The
> > difficulty with that is that the fonts we'd need to put into the
> > default fontset are not free, and there's an understandable reluctance
> > to advertise them.
> 
> Symbola (in package ttf-ancient-fonts in Debian) actually seems to have good 
> coverage for the kind of math symbols that triggers fallback to TeX fonts.

Yes, and there are others (I mentioned them in my other message).