GitLab is a open-core Git forge developed broadly by GitLab Inc.. It comes in both community & commericial editions (which can be self-hosted). There is also a U.S.-based gratis instance at https://gitlab.com/users/ (terms apply).

How to pin a GitLab repository with Nix + Nixtamal

Let’s show the way using the highlight repository. When you write this, you will substitute the owner & project slugs. In most cases, you will want to prefer fetching the archive (GitLab supports bzip) over the Git input kind. git ls-remote is preferred by us for being more generic.

Latest revision 

// manifest.kdl
inputs {
	highlight {
		archive {
			url "https://gitlab.com/saalen/highlight/-/archive/{{fresh-value}}/highlight-{{fresh-value}}.tar.bz2"
		}
	}
	fresh-cmd {
		$ git ls-remote --branches master "https://gitlab.com/saalen/highlight.git"
		| cut -f1
	}
}

Latest stable tagged version 

// manifest.kdl
inputs {
	highlight {
		archive {
			url "https://gitlab.com/saalen/highlight/-/archive/{{fresh-value}}/highlight-{{fresh-value}}.tar.bz2"
		}
	}
	// Looks for tag starting with v[0-9] since some tags didn’t take on
	// this version structure but also must end in [0-9] to remove alpha,
	// beta, release tags
	fresh-cmd {
		$ git ls-remote --tags --sort=v:refname "https://gitlab.com/saalen/highlight.git"
		| grep -E "'refs/tags/v([0-9]+\\.)+[0-9]+$'"
		| tail -n1
		| sed "'s|.*refs/tags/||'"
	}
}