anchor.diff:    #
     # The result is `pkgs' where all the derivations depending on `foo'
     # will use the new version.
  -  overridePackages = f:
  -    let
  -      newpkgs = pkgsFun newpkgs overrides;
  -      overrides = mkOverrides pkgs (f newpkgs pkgs);
  -    in newpkgs;
  +  overridePackages = f: lib.fix' (lib.extends f pkgs.__unfix__);
   
     # Override system. This is useful to build i686 packages on x86_64-linux.
     forceSystem = system: kernel: (import ./all-packages.nix) {
  
positive.code:       AppKit Carbon Cocoa IOKit OSAKit Quartz QuartzCore WebKit
        ImageCaptureCore GSS ImageIO;
    });
    emacs24Macport = self.emacs24Macport_24_5;
  
    emacs25pre = lowPrio (callPackage ../applications/editors/emacs-25 {
      # use override to enable additional features
  
negative.code:   platform = if platform_ != null then platform_
      else config.platform or platformAuto;
  
    # The complete set of packages, after applying the overrides
    pkgsFinal = lib.fix' (lib.extends configOverrides (lib.extends stdenvOverrides pkgsFun));
  
    stdenvOverrides =
      # We don't want stdenv overrides in the case of cross-building,
      # or otherwise the basic overrided packages will not be built
      # with the crossStdenv adapter.
      if crossSystem == null
        then self: super: lib.optionalAttrs (super.stdenv ? overrides) (super.stdenv.overrides super)
        else self: super: {};
  
    # Packages can be overriden globally via the `packageOverrides'
    # configuration option, which must be a function that takes `pkgs'
    # as an argument and returns a set of new or overriden packages.
    # The recommended usage follows this snippet:
    #   packageOverrides = super: let self = super.pkgs in ...
    # `super' is the *original* (un-overriden) set of packages,
    # while `self' refers to the final (overriden) set of packages.
    configOverrides =
        if config ? packageOverrides && bootStdenv == null # don't apply config overrides in stdenv boot
          then self: config.packageOverrides
          else self: super: {};
  
    # The package compositions.  Yes, this isn't properly indented.
    pkgsFun = pkgs:
      let defaultScope = pkgs // pkgs.xorg;
          helperFunctions = pkgs_.stdenvAdapters // pkgs_.trivial-builders;
          pkgsRet = helperFunctions // pkgs_;
          pkgs_ = with pkgs; {
    # Helper functions that are exported through `pkgs'.
    trivial-builders = import ../build-support/trivial-builders.nix { inherit lib; inherit stdenv; inherit (xorg) lndir; };
    stdenvAdapters = import ../stdenv/adapters.nix pkgs;
  
    # Make some arguments passed to all-packages.nix available
    inherit system platform;
  