This script generates an entry in a text file for each time a
derivation is referred to by another in nixpkgs.
For initial testing, this output can be turned into group-layers
compatible JSON with this *trivial* invocation:
cat output | awk '{ print "{\"" $2 "\":" $1 "}"}' | jq -s '. | add | with_entries(.key |= sub("/nix/store/[a-z0-9]+-";""))' > test-data.json
