Improve overlay lib functions some more.

distros/default.nix

@@ -2,7 +2,7 @@
 
 self: super: {
   rosPackages = rec {
-    lib = super.lib // import ../lib { inherit self; };
+    lib = super.lib // import ../lib { inherit lib self; };
 
     kinetic = import ./distro-overlay.nix {
       distro = "kinetic";

lib/default.nix

@@ -3,6 +3,12 @@
 , rosSelf ? null }:
 with lib;
 {
+  mergeOverlays = foldr composeExtensions (_: _: {});
+
+  mkOverlay = overlays: let
+    s = mergeOverlays overlays s {};
+  in s;
+
   patchVendorUrl = pkg: {
     url, sha256,
     originalUrl ? url,
@@ -52,4 +58,4 @@ with lib;
       sed -i '/find_package(Boost [^)]*/s/signals//g' CMakeLists.txt
     '' + postPatch;
   });
-} // (import ./mk-overlay.nix { inherit lib; })
+}

lib/mk-overlay.nix

@@ -1,9 +0,0 @@
-{ lib }:
-with lib;
-rec {
-  mergeOverlays = foldr composeExtensions (_: _: {});
-
-  mkOverlay = overlays: let
-    self = mergeOverlays overlays self {};
-  in self;
-}

overlay.nix

@@ -1,6 +1,5 @@
-self: super:
-with import ./lib/mk-overlay.nix { inherit (super) lib; };
-mergeOverlays [
+self: super: with super.lib;
+foldr composeExtensions (_: _: {}) [
   (import ./pkgs)
   (import ./distros)
 ] self super

pkgs/default.nix

@@ -3,7 +3,7 @@ self: super: with super.lib; let
   pythonOverridesFor = python: python.override (old: {
     packageOverrides = pySelf: pySuper: {
       bson = pySelf.callPackage ./bson { };
-    
+
       catkin-pkg = pySelf.callPackage ./catkin-pkg { };
 
       colcon-cmake = pySelf.callPackage ./colcon/cmake.nix { };