[jankeromnes]

I don't think VS/GH Codespaces are open-source, and they don't seem to support GitLab.

However, if you do need something based on open-source that works with GitLab, take a look at https://www.gitpod.io

You can even self-host it: https://www.gitpod.io/blog/gitpod-self-hosted-0.4.0/