bug#24560: 25.1; With `--font 7x13', wrong font is used for Unicode characters

[Vladimir Panteleev <thecybershadow@gmail.com>]

On 2016-09-28 20:16, Eli Zaretskii wrote:
> Are you sure the 7x13 font installed on your system supports all those
> characters?  Emacs won't switch to a different font if the default
> font supports the character it needs to display.

As I mentioned in my bug report and as is visible in the screenshots,
the characters are indeed present in the font and are rendered correctly
in other applications. Only Emacs exhibits this problem.

> Or could it be that some customizations, either yours or site-wide,
> force Emacs to use other fonts for the above characters?

This problem is reproducible with "emacs -Q", without any
customizations, on all distributions I've tried.

Here is a complete recipe using a live CD, to remove any possibility of
user or site customization:

1. Get the Antergos live ISO (
https://antergos.com/download/antergos-live-iso/ ) and boot from it
(e.g. in a VM).
2. Choose "Start Antergos live".
3. Choose "Try It".
4. Install Emacs and urxvt (in a terminal, run "pacman -S emacs
rxvt-unicode").
5. Run "emacs -Q --font 7x13".
6. M-x view-hello-file
7. Observe that Cyrillic characters are rendered in a 12x13 font.
8. Run "urxvt -fn 7x13".
9. Copy some Cyrillic characters from Emacs and paste them in urxvt.
10. Observe that urxvt renders the Cyrillic characters correctly, in the
correct font.

This is not specific to Arch / Antegros: The problem is also
reproducible on Ubuntu and Fedora Workstation Live CDs, though you may
have to also install some font packages (xorg-x11-fonts-misc for
Fedora), and Emacs uses the 8x13 font for Cyrillic characters (so the
problem is less obvious). urxvt still uses the correct font there.

>> I have found that evaluating the Sexpr:
>>
>> (set-fontset-font "fontset-default" 'unicode "-misc-fixed-*-*-*--13-*-*-*-*-70-iso10646-1")
>>
> 
> Don't do that, this setting will cause all kinds of surprises.  To
> customize the fonts, use specific character codepoint ranges, and only
> specify font for a range if the font support most or all of that
> range.

Noted. However, immediately lacking a better concrete workaround, I
don't have a better option at my disposal.