[hamandcheese]

I think it only lazily copies files that are referenced by your nix expression.

I tested this branch, and a flake-based shell launched in 3 seconds inside a large monorepo (vs 30 seconds before). I don't think it is possible to copy this repo in 3 seconds.

[takeda]

I hope that helps with nixpkgs repo as this takes a lot of time whenever it is updated.

[hamandcheese]

I don't think it will. There isn't any good way to incrementally fetch remote nix files, so to use nixpkgs it all has to be downloaded and unpacked.

[hamandcheese]

Unless you mean when developing on the nixpkgs repo, in which case it could help.