Following is one of reason I consider we should add Ubuntu code name into crystal build name.
I come from China, i have to use mirror because is a very low internet when connect to outside, so i add some code like this into Dockerfile.
FROM crystallang/crystal:1.7.2 RUN echo 'deb https://mirrors.bfsu.edu.cn/ubuntu/ focal main restricted universe multiverse\n \ deb https://mirrors.bfsu.edu.cn/ubuntu/ focal-updates main restricted universe multiverse\n \ deb https://mirrors.bfsu.edu.cn/ubuntu/ focal-backports main restricted universe multiverse\n \ deb http://security.ubuntu.com/ubuntu/ focal-security main restricted universe multiverse\n \ ' > /etc/apt/sources.list
Even, not use like this, let user know new Ubuntu stable release is used is useful.
So, i consider add a alias for include Ubuntu version number e.g. crystal:1.8.0-22.04 Or like golang(It use Debian code name),
bullseye is good.