March 8, 2025

Mask color font in st’s source code so st does not crash when trying to display emoji

I first downloaded st and compiled its source code.

However, st crashed when trying to display emails that contained emoji in Mutt, or when running $ khal interactive.

To fix this, I first tried to install libxft-bgra, in vain. I documented this there: https://yctct.com/st-install-libxft-bgra.

Next, I considered removing the package fonts-noto-color-emoji, but saw that it is tied to too many LaTeX packages. I did not want to touch that for now.

Then, finally, I went back to st’s FAQ and read this again:

## BadLength X error in Xft when trying to render emoji

Xft makes st crash when rendering color emojis with the following error:

"X Error of failed request:  BadLength (poly request too large or internal Xlib length error)"
Major opcode of failed request:  139 (RENDER)
Minor opcode of failed request:  20 (RenderAddGlyphs)
Serial number of failed request: 1595
Current serial number in output stream:  1818"

This is a known bug in Xft (not st) which happens on some platforms and
combination of particular fonts and fontconfig settings.

See also:
https://gitlab.freedesktop.org/xorg/lib/libxft/issues/6
https://bugs.freedesktop.org/show_bug.cgi?id=107534
https://bugzilla.redhat.com/show_bug.cgi?id=1498269

The solution is to remove color emoji fonts or disable this in the fontconfig
XML configuration.  As an ugly workaround (which may work only on newer
fontconfig versions (FC_COLOR)), the following code can be used to mask color
fonts:

FcPatternAddBool(fcpattern, FC_COLOR, FcFalse);

Please don't bother reporting this bug to st, but notify the upstream Xft
developers about fixing this bug.

As of 2022-09-05 this now seems to be finally fixed in libXft 2.3.5:
https://gitlab.freedesktop.org/xorg/lib/libxft/-/blob/libXft-2.3.5/NEWS

The bit that was useful to me is:

[...] or disable this in the fontconfig XML configuration.  As an ugly
workaround (which may work only on newer fontconfig versions (FC_COLOR)), the
following code can be used to mask color fonts:

FcPatternAddBool(fcpattern, FC_COLOR, FcFalse);

So I went into ~/bin/st, where I had extracted st’s source code, and grepped for FcPatternAddBool

$ grep FcPatternAddBool *
FAQ:    FcPatternAddBool(fcpattern, FC_COLOR, FcFalse);
grep: st: binary file matches
x.c:                    FcPatternAddBool(fcpattern, FC_SCALABLE, 1);
grep: x.o: binary file matches

Which showed me that the pattern FcPatternAddBool is in the file x.c.

In x.c I searched for FcPatternAddBool again, and replaced:

FcPatternAddBool(fcpattern, FC_SCALABLE, 1);

by:

FcPatternAddBool(fcpattern, FC_COLOR, FcFalse);

which I copied from st’s FAQ.

Then, still in ~/bin/st, I ran:

$ sudo make clean install 

to build st again.

To test, I opened st then Mutt. Searched for emails I had received containing emojis, and browsed through a few of them.

st did not crash.

Now, instead of crashing (or trying to display an emoji) st shows a small square.

PS: at the time of writing, st’s FAQ stipulates that libXft is fixed in libXft 2.3.5; however my system shows that I don’t have that version yet. One option would have been to install 2.3.5 I suppose.

$ apt list libXft*
Listing... Done
libxft-dev/aramo,now 2.3.4-1 amd64 [installed]
libxft2/aramo,now 2.3.4-1 amd64 [installed,automatic]

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