all: refactor to follow RFC140

pkgs/top-level/stage.nix

@@ -0,0 +1,24 @@
+# Composes a single bootstrapping of the package collection. The result is a set
+# of all the packages for some particular platform.
+
+{ lib
+, pkgs
+}:
+let
+
+  # An overlay to auto-call packages in .../by-name.
+  autoCalledPackages =
+    import ./by-name-overlay.nix { inherit pkgs lib; } ../by-name;
+
+  allPackages = _self: _super:
+    import ./all-packages.nix { inherit pkgs; };
+
+  toFix = (lib.flip lib.composeManyExtensions) (_self: { }) [
+    autoCalledPackages
+    allPackages
+  ];
+
+in
+
+# Return the complete set of packages.
+lib.fix toFix