It's been fun, it feels like a new superpower to "quickly fix something and send a PR". It's also a super dangerous rabbit hole generator, because now that it's easy to fix stuff, it's very tempting to do so… 🐇
My prototype has some rough edges:
It clones the latest commit, which doesn't always compile using the #nixpkgs setup (but it seems reasonable to check whether the bug is still there).
And invoking the phases of the nixpkgs stdenv manually can be tricky. https://nixos.org/manual/nixpkgs/stable/#sec-building-stdenv-package-in-nix-shell