anchor.diff:          header "checking pkgs/top-level/all-packages.nix on $platform"
           nix-env --readonly-mode -f pkgs/top-level/all-packages.nix \
               --show-trace --argstr system "$platform" \
  -            -qa \* --drv-path --system-filter \* --system --meta --xml
  +            -qa \* --drv-path --system-filter \* --system --meta --xml > /dev/null
           stopNest
       done
   
  
positive.code: 
    configurePhase = ''
      eval "$preConfigure"
      releaseName=nixpkgs-$(cat $src/VERSION)$VERSION_SUFFIX
      echo "release name is $releaseName"
      echo $releaseName > relname
    '';
  
negative.code:    also builds the documentation and tests whether the Nix expressions
     evaluate correctly. */
  
  { nixpkgs ? { outPath = (import ./all-packages.nix {}).lib.cleanSource ../..; revCount = 1234; shortRev = "abcdef"; }
  , officialRelease ? false
  }:
  
  with import nixpkgs.outPath {};
  
  releaseTools.sourceTarball {
    name = "nixpkgs-tarball";
    src = nixpkgs;
    inherit officialRelease;
  
    version = builtins.readFile ../../VERSION;
    versionSuffix = if officialRelease then "" else "pre${toString nixpkgs.revCount}_${nixpkgs.shortRev}";
  
    buildInputs = [
      lzma
  