anchor.diff:    src = fetchurl {
       urls = map (n: "${n}.xz") tarballUrls;
       hashOutput = false;
  -    sha256 = "bf0b34f1538c0b6e88f959937b0419678cadbf2ba7044336dcbfb2bcdc28cd74";
  +    sha256 = "d591fbe586cf83741fcf9df51859f8e9058ef5187c002b50d6fe84309e5ea349";
     };
   
     nativeBuildInputs = [
  
positive.code:   passthru = {
      srcVerification = fetchurl rec {
        failEarly = true;
        pgpDecompress = true;
        pgpsigUrls = map (n: "${n}.sign") tarballUrls;
        pgpKeyFingerprint = "F2B4 1200 C54E FB30 380C  1756 C565 D5F9 D76D 583B";
        inherit (src) urls outputHash outputHashAlgo;
      };
    };
  
  
negative.code: }:
  
  let
    version = "4.19";
  
    tarballUrls = [
      "mirror://kernel/linux/kernel/people/kdave/btrfs-progs/btrfs-progs-v${version}.tar"
  