anchor.diff:  }:
   
   let
  -  version = "4.17.1";
  +  version = "4.19";
   
     tarballUrls = [
       "mirror://kernel/linux/kernel/people/kdave/btrfs-progs/btrfs-progs-v${version}.tar"
  
positive.code:   src = fetchurl {
      urls = map (n: "${n}.xz") tarballUrls;
      hashOutput = false;
      sha256 = "bf0b34f1538c0b6e88f959937b0419678cadbf2ba7044336dcbfb2bcdc28cd74";
    };
  
    nativeBuildInputs = [
  
negative.code:   passthru = {
      srcVerification = fetchurl rec {
        failEarly = true;
        inherit (src)
          urls
          outputHash
          outputHashAlgo;
        fullOpts = {
          pgpDecompress = true;
          pgpsigUrls = map (n: "${n}.sign") tarballUrls;
          pgpKeyFingerprint = "F2B4 1200 C54E FB30 380C  1756 C565 D5F9 D76D 583B";
        };
      };
    };
  
  