Setting Annotations from a shell-script

There are clear documented ways to set outputs, paths and environment variables from inside a shell script. Use the :: prefix.

But I can’t find any similar documentation for annotations. Is it possible or are you required to use the node based javascript API?

At least warnings and errors are possible in basically the same way: https://help.github.com/en/actions/reference/workflow-commands-for-github-actions#setting-a-warning-message