$ENV{"NIX_PREFETCH_GIT_CHECKOUT_HOOK"} = "git describe > .git-version";

	# Checked out code often wants to be able to run `git
	# describe', e.g., code that uses Gnulib's `git-version-gen'
	# script.  Thus, we leave `.git' in there.
	$ENV{"NIX_PREFETCH_GIT_LEAVE_DOT_GIT"} = "1";