$ git clone https://github.com/nix-community/nixpkgs-swh && cd nixpkgs-swh
$ ./scripts/generate.sh build/ unstable
...
substitution of path '/nix/store/r2jd6ygnmirm2g803mksqqjm4y39yi6i-git-2.33.1' succeeded
** Generate sources.json and README for release unstable
*** Query Hydra to get latest build commit
*** Generate sources-unstable.json for commit b7a6fde153d9470afdb6aa1da51c4117f03b84ed ...
warning: unknown setting 'experimental-features'
unpacking 'https://github.com/NixOS/nixpkgs/archive/b7a6fde153d9470afdb6aa1da51c4117f03b84ed.tar.gz'...
trace: lib.crossLists is deprecated, use lib.cartesianProductOfSets instead
trace: warning: literalExample is deprecated, use literalExpression instead, or use literalDocBook for a non-Nix description.
trace: warning: lib.mkFixStrictness has no effect and will be removed. It returns its argument unmodified, so you can just remove any calls.
trace: `lib.nixpkgsVersion` is deprecated, use `lib.version` instead!
trace: warning: lib.readPathsFromFile is deprecated, use a list instead
trace: Warning: `showVal` is deprecated and will be removed in the next release, please use `traceSeqN`
trace: lib.zip is deprecated, use lib.zipAttrsWith instead
error: undefined variable 'ocamlNativeNuildInputs' at /nix/store/1plbhwlwyr223l7cc0l08bzp064ar70l-b7a6fde153d9470afdb6aa1da51c4117f03b84ed.tar.gz/pkgs/applications/science/logic/coq/default.nix:86:15
(use '--show-trace' to show detailed location information)

real    2m48.312s
user    2m54.012s
sys     0m9.243s