anchor.diff:             (pkgs.lib.composeExtensions
                 (self.packageSourceOverrides source-overrides)
                 overrides))
  -        .callCabal2nix (builtins.baseNameOf root) root {};
  +        .callCabal2nix name root {};
         in if returnShellEnv then (modifier drv).env else modifier drv;
   
       ghcWithPackages = selectFrom: withPackages (selectFrom self);
  
positive.code:     callCabal2nix = name: src: args: self.callCabal2nixWithOptions name src "" args;
  
      # : { root : Path
      #   , source-overrides : Defaulted (Either Path VersionNumber)
      #   , overrides : Defaulted (HaskellPackageOverrideSet)
      #   , modifier : Defaulted
  
negative.code:     # for nix-build or nix-shell to build that package.
      developPackage =
        { root
        , name ? builtins.baseNameOf root
        , source-overrides ? {}
        , overrides ? self: super: {}
        , modifier ? drv: drv
  