Flake inputs should be able to do a sparse checkout of a Git repository

[virchau13]

Is your feature request related to a problem? Please describe.
Being able to get a subset of the files for very big repositories is often necessary. For example, I had to download the entire repository (~2.7GiB) of ryanoasis/nerd-fonts just to use the 53.7 KiB font-patcher script in the root. Similarly, using the same nerd-fonts repository, I may only want to download the patched-fonts/FantasqueSansMono/ directory and ignore the rest of the files.

Describe the solution you'd like
In flake inputs, it should be possible to specify a subset of files / directories from a Git repository, and the flake fetcher automatically tries something like a sparse checkout before falling back to simply cloning the full repository. This may be useful for more than just Git repositories, too.

Describe alternatives you've considered
For fetching single files from GitHub repositories, one can use fetchurl; but this doesn't fit with the entire model of flakes as a whole (nix flake update won't update it, etc.) Also, this doesn't work for directories.

[rehno-lindeque]

This is now implemented in lib.fetchgit, lib.fetchFromGitHub as of NixOS/nixpkgs#135881.

I would love to have this available in builtins.fetchTree as well in order to do work directly inside nixpkgs (instead of in private overlays).

{
  inputs = {
    pytorch = {
      url =  "github:me/nixpkgs";
      ref = "pytorch-1.11.0";
      subtree = "pkgs/development/python-modules/pytorch"; # or sparseCheckout
      flake = false;
    };
  };
  outputs = { self, ... }: {
    overlays.default = final: prev: {
      pytorch_1_11_0 = final.callPackage self.inputs.pytorch {}; 
      pytorch-bin_1_11_0 = final.callPackage "${self.inputs.pytorch}/bin.nix" {};
    };
  };
}

Related: #3785 #4097 #4414

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/nixpkgss-current-development-workflow-is-not-sustainable/18741/69

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/nix-2-9-0-released/19407/6

[michaelBelsanti]

This feature was merged some time ago and this issue should be closed.

[virchau13]

@quasigod-io I did some searching and can't find a PR or documentation for this feature. Can you point me to where this was implemented?

[michaelBelsanti]

Nevermind, I made a mistake reading this issue last night. My apologies.

[dzmitry-lahoda]

do we have example repo to look at? so we can be sure it works?