bug#25216: 26.0.50 [regression]; Curly quotes are not found in some sizes of ‘Terminus’ font

[Eli Zaretskii <eliz@gnu.org>]

> From: Dmitry Alexandrov <321942@gmail.com>
> Date: Sat, 17 Dec 2016 04:03:07 +0300
> 
> Steps to reproduce:
> 
>    $ emacs --quick --font '-*-terminus-medium-r-*-*-20-*-*-*-*-*-*-*'
> 
> Find some document with curly quotes: ‘’ and “”.  GNU Emacs Manual (‘<f1> r’) uses them heavily, for instance.
> 
> It looks wrong:

What is wrong with how it looks?  Info mode uses several fonts anyway,
so seeing a different font used for quotes shouldn't be a disaster.

> ‘C-u C-x =’ says that instead of Terminus ‘x:-misc-fixed-medium-r-normal--20-200-75-75-c-100-iso10646-1’ font is used for rendering quotes.  When I request 24th size, I got yet another font — ‘x:-efont-fixed-medium-r-normal--24-240-75-75-c-240-iso10646-1’.
> 
> In a strange way there is no such a problem with some other sizes:
> 
>    $ emacs --quick --font '-*-terminus-medium-r-*-*-16-*-*-*-*-*-*-*'
> 
> is okay, for example.  ‘C-u C-x =’ says that ‘xft:-xos4-Terminus-normal-normal-normal-*-16-*-*-*-c-80-iso10646-1’ is used in that case.

Emacs 25 should prefer the default font for symbol and punctuation
characters, as long as the default font supports them.  So I don't
understand why you see these character displayed using another font,
if the default one has the corresponding glyphs.

> The reason is *not* that Terminus just does not have these glyphs — it does.  Moreover — GNU Emacs 24.4.1 finds and renders them correctly:

Emacs 25 has different settings of the default fontset, see
fontset.el.  It instructs Emacs to use fixed-medium fonts for symbols
and punctuation characters that are absent from the default font.
Emacs 24 didn't have those settings.

I think you should be able to force Emacs to use your font for these
characters by using set-fontset-font for the range of codepoints you
want to be displayed by the Terminus font.

Of course, if you or someone can explain why Emacs doesn't use the
default font, as it should have, for these characters, that would be
even better, since we might then be able to fix the problem without
any need for user customizations.

One idea I have is that the way you specify the font on the Emacs
command line doesn't specify a registry.  Did you try using iso10646-1
as the registry?