anchor.diff:  
   { doCoverageAnalysis ? false
   , lcovFilter ? []
  +, lcovExtraTraceFiles ? []
   , src, stdenv
   , name ? if doCoverageAnalysis then "nix-coverage" else "nix-build"
   , ... } @ args:
  
positive.code:       ${args.lcov}/bin/lcov --remove app.info $lcovFilter > app2.info
        set +o noglob
        mv app2.info app.info
        mkdir $out/coverage
        ${args.lcov}/bin/genhtml app.info -o $out/coverage > log
  
        # Grab the overall coverage percentage for use in release overviews.
        grep "Overall coverage rate" log | sed 's/^.*(\(.*\)%).*$/\1/' > $out/nix-support/coverage-rate
  
negative.code: 
      lcovFilter = ["/nix/store/*"] ++ lcovFilter;
  
      inherit lcovExtraTraceFiles;
  
      meta = (if args ? meta then args.meta else {}) // {
        description = if doCoverageAnalysis then "Coverage analysis" else "Native Nix build on ${stdenv.system}";
  