Building renderer fails

[wvengen]

Trying to run ws-server, I find a build error. Manually building the renderer shows me:

Sending build context to Docker daemon   7.68kB
Step 1/12 : FROM debian:sid-slim
 ---> 6d7423739c45
Step 2/12 : RUN apt-get update && apt-get install --no-install-recommends -y ruby curl bzip2 git locales gsfonts ghostscript fonts-dejavu-extra psmisc emacs-intl-fonts xfonts-intl-.* fonts-ipafont-mincho xfonts-bolkhov-75dpi xfonts-cronyx-100dpi xfonts-cronyx-75dpi patch python2 python3 &&     localedef -i en_US -c -f UTF-8 -A /usr/share/locale/locale.alias en_US.UTF-8 &&     curl -L https://github.com/stedolan/jq/releases/download/jq-1.5/jq-linux64 > /usr/local/bin/jq &&     chmod +x /usr/local/bin/jq && echo 42 | jq .
 ---> Running in 1aa342bb8bed
Get:1 http://deb.debian.org/debian sid InRelease [198 kB]
Get:2 http://deb.debian.org/debian sid/main amd64 Packages [9759 kB]
Fetched 9957 kB in 2s (4822 kB/s)
Reading package lists...
Reading package lists...
Building dependency tree...
Reading state information...
Package python2 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'python2' has no installation candidate
The command '/bin/sh -c apt-get update && apt-get install --no-install-recommends -y ruby curl bzip2 git locales gsfonts ghostscript fonts-dejavu-extra psmisc emacs-intl-fonts xfonts-intl-.* fonts-ipafont-mincho xfonts-bolkhov-75dpi xfonts-cronyx-100dpi xfonts-cronyx-75dpi patch python2 python3 &&     localedef -i en_US -c -f UTF-8 -A /usr/share/locale/locale.alias en_US.UTF-8 &&     curl -L https://github.com/stedolan/jq/releases/download/jq-1.5/jq-linux64 > /usr/local/bin/jq &&     chmod +x /usr/local/bin/jq && echo 42 | jq .' returned a non-zero code: 100

so current Debian sid doesn't seem to have Python2 anymore, at least not in the repositories used here (main).
And indeed, searching for it in stable doesn't return anything, but oldstable has it.

A temporary fix would be to use an older Debian version as base image.
Why is Python 2 needed?

[wvengen]

Note that adduser isn't installed anymore by default, so needs to be added to the list of packages to be installed.