anchor.diff:  
     iproute2mac = callPackage ../os-specific/darwin/iproute2mac { };
   
  -  libobjc = apple-source-releases.objc4;
  +  libobjc = self.objc4;
   
     lsusb = callPackage ../os-specific/darwin/lsusb { };
   
  
positive.code: 
    rewrite-tbd = callPackage ../os-specific/darwin/rewrite-tbd { };
  
    checkReexportsHook = makeSetupHook {
      deps = [ pkgs.darwin.print-reexports ];
    } ../os-specific/darwin/print-reexports/setup-hook.sh;
  
  
negative.code: 
    # Must use pkgs.callPackage to avoid infinite recursion.
  
    # Open source packages that are built from source
    appleSourcePackages = pkgs.callPackage ../os-specific/darwin/apple-source-releases { } self;
  
    impure-cmds = pkgs.callPackage ../os-specific/darwin/impure-cmds { };
  
    # macOS 10.12 SDK
    apple_sdk_10_12 = pkgs.callPackage ../os-specific/darwin/apple-sdk {
      inherit (buildPackages.darwin) print-reexports;
      inherit (self) darwin-stubs;
    };
  
    # macOS 11.0 SDK
    apple_sdk_11_0 = pkgs.callPackage ../os-specific/darwin/apple-sdk-11.0 { };
  
    # Pick an SDK
    apple_sdk = if stdenv.hostPlatform.isAarch64 then apple_sdk_11_0 else apple_sdk_10_12;
  
    # Pick the source of libraries: either Apple's open source releases, or the
    # SDK.
    useAppleSDKLibs = stdenv.hostPlatform.isAarch64;
  
    chooseLibs = {
      inherit (
        if useAppleSDKLibs
          then apple_sdk
          else appleSourcePackages
      ) Libsystem LibsystemCross libcharset libunwind objc4 configd IOKit;
  
      inherit (
        if useAppleSDKLibs
          then apple_sdk.frameworks
          else appleSourcePackages
      ) Security;
    };
  in
  
  impure-cmds // appleSourcePackages // chooseLibs // {
  
    inherit apple_sdk;
  
  