overlays.default: Only set nix

We should keep users' pkgs tidy.

Author: roberth

flake.nix

@@ -305,9 +305,20 @@
 
     in
     {
-      # A Nixpkgs overlay that overrides the 'nix' and
-      # 'nix-perl-bindings' packages.
-      overlays.default = overlayFor (p: p.stdenv);
+      overlays.internal = overlayFor (p: p.stdenv);
+
+      /**
+        A Nixpkgs overlay that sets `nix` to something like `packages.<system>.nix-everything`,
+        except dependencies aren't taken from (flake) `nix.inputs.nixpkgs`, but from the Nixpkgs packages
+        where the overlay is used.
+       */
+      overlays.default = final: prev:
+      let
+        packageSets = packageSetsFor { pkgs = final; };
+      in
+      {
+        nix = packageSets.nixComponents.nix-everything;
+      };
 
       hydraJobs = import ./packaging/hydra.nix {
         inherit