[Nix-dev] version, branch, configuration of /var/run/{current, booted}-system ?

[Marc Weber]

Does nixos-rebuild .. already store

rev number (git / svn)
branch (git / svn)
configuration file contents of /etc/nixos/configuration.nix ?

Sometimes I wonder which system I'm running currently.
So I'd like to do a 
cat /var/run/current-system/version
to find out about the properties listed above.

Does this already exist? If not I'd like to add it.

Because you may include many additionaly files to
/etc/nixos/configuration.nix there must be an option
filesToBeIncludedinInfo = [ list of files included by configuration.nix ];

How would you call it?
Maybe even /etc/NIXOS is the right place to put this information in?

What do you think?

Marc Weber