How to disable automatic unpacking of nix flake inputs?

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1

Is it possible to disable the automatic unpacking of Nix Flake inputs?

For example, say we have the following flake.nix which depends on a non-flake tarball:

{
  inputs = {
    tarball = {
      url = "https://some.tar.zst";
      flake = false;
    };
  };
  outputs = { self, tarball }: {
    # I would like tarball to remain how it was downloaded, so no unpacking.
  }
}
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2

This sounds like @pwaller’s recent issue: Flake inputs fetched and unpacked despite outputs being a cache hit · Issue #9570 · NixOS/nix · GitHub

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3

Thanks, it’s similar to that issue but what I’m specifically looking for is something like:

{
  inputs = {
    tarball = {
      url = "https://some.tar.zst";
      flake = false;
      unpack = false;       # <--- disables the automatic unpacking of inputs
      name = "some.tar.zst" # <--- uses a proper name instead of /nix/store/...-source
    };
  };
  outputs = { self, tarball }: {
    # tarball now refers to the downloaded tarball in the nix store with the specified name like:
    # /nix/store/...-some.tar.zst
  }
}
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4

https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-flake

  • file: Plain files or directory tarballs, either over http(s) or from the local disk.In URL form, the schema must be file+http://, file+https:// or file+file://. If the extension doesn’t correspond to a known archive format (as defined by the tarball fetcher), then the file+ prefix can be dropped.

So in this case you want to avoid dropping the file+ before https:

inputs.tarball.url = "file+https://some.tar.zst";
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5

Ah yes, I have this exact complaint also; it would be very helpful to see in the output which flake sources are being fetched. I’m half tempted to make the change as a part of Builtin fetching should be representable by derivations · Issue #9077 · NixOS/nix · GitHub

This would name the derivations according to the flake input name in your case it would be (-tarball-source) because your input is .input.tarball.

I think the underlying reason for the existing behaviour is that this fetchTree call isn’t passed a name attribute.

The downside is that a nix upgrade making this change would cause all existing flake builds (relying on a flake input) to become subsitution misses, since it changes the source inputs in the derivation.

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