Motivation for this change

Even though fetchzip uses stdenv's unpackFile to unpack .{tar{,.*},zip} files, it doesn't expose any convenient way to extend it to handle anything other than that.

Additionally, fetchzip's stripRoot goes beyond ignoring archive metadata/algorithm non-determinism and affects actual archive contents.

This is an attempt at a more explicit API that only fetches, then unpacks with one of inputs. It uses SRI hashes added in Nix 2.2 to avoid code churn that happens to algorithm-specific arg attrs as hash algorithms change.

stripRoot is implemented a la carte as a function that takes a directory and returns its first child.

Short list of changes:

• add unpackCmd hook to dpkg
• add SRI hash support to fetchurl
• add fetchArchive + docs
• showcase fetchArchive on typora derivation
• add lib.stripRoot + docs

Fetch examples:

fetchArchive {
  url = https://github.com/NixOS/nix/archive/2.2.1.tar.gz;
  hash = "sha512-U8y9gVgvjowXZ/lTp7fxqRrWFbxZwrbS4LY95XduiM2plvhQ37rJ5TACo/PHStCILSvhzHG19UBZ1bWP62jEgQ==";
}

fetchArchive {
  url = https://github.com/NixOS/nix/archive/2.2.1.zip;
  hash = "sha512-U8y9gVgvjowXZ/lTp7fxqRrWFbxZwrbS4LY95XduiM2plvhQ37rJ5TACo/PHStCILSvhzHG19UBZ1bWP62jEgQ==";
  inputs = [ unzip ];
}

fetchArchive {
  url = https://deb.debian.org/debian/pool/main/a/apt/apt_1.4.8_arm64.deb;
  hash = "sha512-/6NY2ZhfJIKA6Qzg5vBxVaG9qfR7TqF/kK2ntzwMGXGpg2ycopjUAtxLqqRsM87OZQsYS7hklQhHcvx/NVz3dQ==";
  inputs = [ dpkg ];
}

Derivation override example:

nixUnstable.overrideAttrs (super: {
  src = lib.stripRoot (fetchArchive {
    url = https://github.com/NixOS/nix/archive/2.2.1.tar.gz;
    hash = "sha512-U8y9gVgvjowXZ/lTp7fxqRrWFbxZwrbS4LY95XduiM2plvhQ37rJ5TACo/PHStCILSvhzHG19UBZ1bWP62jEgQ==";
  });
})

Maybe this should better be called fetchThenUnpack. Also, instead of lib.stripRoot, stdenv can be tweaked into supporting non-stripped sources.

cc @grahamc, @LnL7, @oxij, @zimbatm

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.