While we're at it, could we try to use the same user inside a docker container as the host uses?

bin/spc-alpine-docker build bcmath --build-cli
rm -rf source buildroot -> error, needs sudo, because we're not the owner of the files

Like --user "$(id -u):$(id -g)"?

Yep

Unfortunately there are no simple solution to use $(whoami) current user as mount dir for all docker engines. It depends on docker engine platform and version. Using --user will make docker inside full of permission denied error.

The only perfect option for linux is to restart docker CE as rootless mode. But luckily macOS docker always create mount dir as current user permission.

Restarting docker-ce in a different mode is not a solution, as it may be running on a host and linux could be a VM without docker installed.

If Docker can't handle it natively, there's a chown at the end, but that would prompt a password and only work if the user has sudo...