build fails with Extension error

[tristan-k]

I tried to build the iso from arch linux but it fails with a extension error.

  CC      sound/usb/usx2y/snd-usb-usx2y.mod.o
  LD [M]  sound/usb/usx2y/snd-usb-usx2y.ko
  CC      sound/x86/snd-hdmi-lpe-audio.mod.o
  LD [M]  sound/x86/snd-hdmi-lpe-audio.ko
  CC      sound/xen/snd_xen_front.mod.o
  LD [M]  sound/xen/snd_xen_front.ko
  CC      virt/lib/irqbypass.mod.o
  LD [M]  virt/lib/irqbypass.ko
  SPHINX  htmldocs --> file:///home/pve/Downloads/archiso-bcachefs/packages/linux-bcachefs-git/src/bcachefs/Documentation/output
  PARSE   include/uapi/linux/dvb/audio.h
  PARSE   include/uapi/linux/dvb/ca.h
  PARSE   include/uapi/linux/dvb/dmx.h
  PARSE   include/uapi/linux/dvb/frontend.h
  PARSE   include/uapi/linux/dvb/net.h
  PARSE   include/uapi/linux/dvb/video.h
  PARSE   include/uapi/linux/videodev2.h
  PARSE   include/uapi/linux/media.h
  PARSE   include/uapi/linux/cec.h
  PARSE   include/uapi/linux/lirc.h
Sphinx v3.0.2 in Verwendung

Extension error:
Could not import extension cdomain (exception: cannot import name 'c_funcptr_sig_re' from 'sphinx.domains.c' (/usr/lib/python3.8/site-packages/sphinx/domains/c.py))
make[1]: *** [Documentation/Makefile:81: htmldocs] Fehler 2
make: *** [Makefile:1579: htmldocs] Fehler 2
==> FEHLER: Ein Fehler geschah in build().
    Breche ab...

[vale981]

Sorry, this issue somehow escaped me.
That looks like a bug in sphinx.

Check out https://github.com/abelian424/archiso-bcachefs-mainline

It seems to work around the issue.