Add custom packages

overlays/default.nix

@@ -0,0 +1,35 @@
+final: prev:
+
+/*
+  Generate an overlay from `pkgs` by handling the `callPackage` behaviour
+  ourselves, making exceptions for namespaced package sets. We cannot reuse
+  the definitions from `self.legacyPackages.${prev.system}`, as that would
+  evaluate nixpkgs twice here (prev.system does not exist then).
+*/
+
+let
+  lib = prev.lib;
+
+  pkgs = lib.packagesFromDirectoryRecursive {
+    callPackage = path: overrides: path;
+    directory = ../pkgs;
+  };
+in
+  lib.mapAttrs
+    (name: value:
+      if lib.isAttrs value then
+        if lib.hasAttrByPath [ name "overrideScope" ] prev then
+          # Namespaced package sets created with `lib.makeScope pkgs.newScope`.
+          prev.${name}.overrideScope (final': prev':
+            lib.mapAttrs (name': value': final'.callPackage value' { }) value)
+        else if lib.hasAttrByPath [ name "extend" ] prev then
+          # Namespaced package sets created with `lib.makeExtensible`.
+          prev.${name}.extend (final': prev':
+            lib.mapAttrs (name': value': final.callPackage value' { }) value)
+        else
+          # Namespaced package sets in regular attrsets.
+          prev.${name} // value
+      else
+        final.callPackage value { })
+    pkgs
+