anchor.diff:  
     passthru = {
       srcVerification = fetchurl {
  +      failEarly = true;
         inherit (src)
           outputHash
           outputHashAlgo
           urls;
  -      sha256Urls = map (n: "${n}/SHA256SUMS") baseUrls;
  -      failEarly = true;
  +      fullOpts = {
  +        sha256Urls = map (n: "${n}/SHA256SUMS") baseUrls;
  +      };
       };
     };
   
  
positive.code:     optionals
      platforms;
  
    version = "4.19";
  
    baseUrls = [
      "https://ftp.mozilla.org/pub/mozilla.org/nspr/releases/v${version}/src"
  
negative.code:   src = fetchurl {
      urls = map (n: "${n}/nspr-${version}.tar.gz") baseUrls;
      hashOutput = false;
      sha256 = "2c8964913da89ffbaf464d49ce44d79e8804e1794ef9a8c52a7bff7224d1556e";
    };
  
    prePatch = ''
  