anchor.diff:      optionals
       platforms;
   
  -  version = "4.19";
  +  version = "4.20";
   
     baseUrls = [
       "https://ftp.mozilla.org/pub/mozilla.org/nspr/releases/v${version}/src"
  
positive.code: 
    passthru = {
      srcVerification = fetchurl {
        inherit (src)
          outputHash
          outputHashAlgo
          urls;
        sha256Urls = map (n: "${n}/SHA256SUMS") baseUrls;
        failEarly = true;
      };
    };
  
  
negative.code:   src = fetchurl {
      urls = map (n: "${n}/nspr-${version}.tar.gz") baseUrls;
      hashOutput = false;
      sha256 = "2c8964913da89ffbaf464d49ce44d79e8804e1794ef9a8c52a7bff7224d1556e";
    };
  
    prePatch = ''
  