anchor.diff:  , fetchFromGitHub
   , flex
   , libffi
  -, pkgconfig
  +, pkg-config
   , protobuf
   , python3
   , readline
   , tcl
   , verilog
   , zlib
  +, plugins ? []
   }:
   
   # NOTE: as of late 2020, yosys has switched to an automation robot that
  
positive.code:   # add a symlink to fake things so that both variants work the same way. this
    # is also needed at build time for the test suite.
    postBuild   = "ln -sfv ${abc-verifier}/bin/abc ./yosys-abc";
    postInstall = "ln -sfv ${abc-verifier}/bin/abc $out/bin/yosys-abc";
  
    meta = with stdenv.lib; {
      description = "Open RTL synthesis framework and tools";
  
negative.code:       exit 1
      fi
  
      if ! grep -q "YOSYS_VER := $version" Makefile; then
        echo "ERROR: yosys version in Makefile isn't equivalent to version of the nix package ($version), failing."
        exit 1
      fi
    '';
  