anchor.diff:  
     tools = buildFromGitHub {
       version = 2;
  -    rev = "dd796641777bce15ee87fb6bea64943b648bdcf3";
  -    date = "2016-12-14";
  +    rev = "908849c3379245f71612058fbf92cf6bf58c3c75";
  +    date = "2016-12-20";
       owner = "golang";
       repo = "tools";
  -    sha256 = "1hc211absrwj54wkczw57d19s2zmp262pxrrndg59k5cpk6xiynv";
  +    sha256 = "16r0v2f4fq64i0xh1g80bf4qnvv398ypsw7v48zqz7ibxlj5ayab";
       goPackagePath = "golang.org/x/tools";
       goPackageAliases = [ "code.google.com/p/go.tools" ];
   
  
positive.code: 
    crypto = buildFromGitHub {
      version = 2;
      rev = "2b786ab9e9649dc660afa3bd580fd05a05e20d95";
      date = "2016-12-19";
      owner    = "golang";
      repo     = "crypto";
      sha256 = "17aqinhp9g0515jvxxpm29villnvp0fxmlzdfvhg41rjivp864h9";
      goPackagePath = "golang.org/x/crypto";
      goPackageAliases = [
        "code.google.com/p/go.crypto"
  
negative.code: 
    utp = buildFromGitHub {
      version = 2;
      rev = "cb02a8a1ac94501fb8421531cd94d874360d35b1";
      owner  = "anacrolix";
      repo   = "utp";
      sha256 = "0cx70k83bccd1kxrwf3v957hhc3pr0dxzdym15bxdkylkrmg6jwk";
      date = "2016-12-20";
      propagatedBuildInputs = [
        envpprof
        missinggo
  