If there is a stack.yaml extra-deps entry which is a git repo with multiple subdirs (e.g. cardano-wallet/stack.yaml), then the entire git repo is fetched for each subdirs entry.

It still functions correctly, but is quite slow when you have a big repo like cardano-sl (bloated by stack2nix code) and 14 or so subdirs.

I'm not sure why the fetches aren't cached. Within the stack2nix output it has the fetchgit output, which shows exactly the same store path for each dependency.