We at nixpkgs package python projects from GitHub by pulling their tarball, which is much quicker than doing a full or bare git checkout. Subsequently, we don't have a Git repo that setuptools-git-versioning could infer the version from.

With setuptools-scm there is an environment variable SETUPTOOLS_SCM_PRETEND_VERSION through which the version can be explicitly. Adding support for such an escape hatch would be appreciated.