anchor.diff:  
     configurePhase = ''
       eval "$preConfigure"
  -    releaseName=nixpkgs-$(cat $src/VERSION)$VERSION_SUFFIX
  +    releaseName=nixpkgs-$VERSION$VERSION_SUFFIX
       echo "release name is $releaseName"
       echo $releaseName > relname
     '';
  
positive.code:    also builds the documentation and tests whether the Nix expressions
     evaluate correctly. */
  
  { nixpkgs ? {outPath = (import ./all-packages.nix {}).lib.cleanSource ../..; rev = 1234;}
  , officialRelease ? false
  }:
  
  with import nixpkgs.outPath {};
  
  releaseTools.makeSourceTarball {
    name = "nixpkgs-tarball";
    src = nixpkgs;
    inherit officialRelease;
  
    buildInputs = [
      lzma
  
negative.code:         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 > /dev/null
          stopNest
      done
  
  