Want to see the dirty innards of more Valve code? Well you're in luck as they now have a lot of work involved in the Steam Runtime on GitLab including the Pressure Vessel container.
Valve has for some time now had their own GitHub account, which is where they listed many different open source projects like GameNetworkingSockets, Proton and more. However, they've now added a bunch of other projects to their own hosted GitLab.
You can now find the steamrt group on their GitLab, which contains projects for various parts of the Steam Linux Runtime, including the source for the much newer Pressure Vessel container system which according to Valve contractor Timothee Besset on Twitter was previously "only available as a tarball release" from their download servers.
What is Pressure Vessel? It's kinda of like a simple version of Flatpak made for Steam games. Within the Linux Steam client, you can select "Steam Linux Runtime" under the right click -> properties menu of games at the bottom like so:
This then puts those Linux game builds into a game-specific container. There's many reasons for it, like allowing developers to test against a contained environment, and have it run across any Linux distribution and allow old games to continue working long into the future. Learn more about it here, where Collabora engineer Simon McVittie gave a run-down of their work. Valve are also now using the latest generation of the Linux Steam Runtime for the Proton 5.13-1 compatibility layer too.
When we queried on why Valve are now putting more up in the open on GitLab, instead of the GitHub that was being used originally, Besset mentioned to us "The projects you see on GitHub are often mirrored from an internal repo. It's awkward and creates friction for community contributions. The projects on gitlab is where we will do our work in the open.", which is awesome.