{
  unstableSource,
  attributeName ? "unstable",
}:

self: super:

let
  useUnstable = self.config.useUnstable or true;
  sanitizePlatform = platformConfig: self.lib.removeAttrs platformConfig [
    "emulator"
    "emulatorAvailable"
    "darwinSdkVersion"
    "darwinMinVersion"
    "parsed"
  ];

  unstablePkgs = import unstableSource {
    # localSystem -> pkgs.stdenv.buildPlatform
    localSystem = sanitizePlatform self.stdenv.buildPlatform;
    # crossSystem -> pkgs.stdenv.hostPlatform or pkgs.stdenv.targetPlatform ??
    # passing below
    # config -> pkgs.config
    config = self.config;
    # overlays -> partial of pkgs.overlays
    overlays = self.overlays;
    # crossOverlays -> partial of pkgs.overlays
    # crossOverlays are merged to overlays, not sure what issues that might raise.
    # ignoring.
  } // self.lib.optionalAttrs (
    self.lib.systems.equals self.stdenv.buildPlatform self.stdenv.hostPlatform
  ) {
    # workaround for some odd structured packages that changes behaviour
    # when crossSystem is passed.
    crossSystem = sanitizePlatform self.stdenv.hostPlatform;
  };
in
{
  "${attributeName}" = if useUnstable then unstablePkgs else self;
}