Use `tools/default.nix` for tools.

docs/source/dev/README.rst

@@ -49,7 +49,7 @@ To update the version of NixOS we deploy with, run:
 
 .. code: shell
 
-   nix-shell --command 'tools/update-nixpkgs'
+   nix-shell --command 'update-nixpkgs'
 
 That will update ``nixpkgs-2015.json`` to the latest release on the nixos-21.05 channel.
 

shell.nix

@@ -3,25 +3,14 @@ let
 in
 { pkgs ? release2105, lib ? pkgs.lib, python ? pkgs.python3 }:
 let
-  # This is a python envionment that has the dependencies
-  # for the development python scripts we use, and the
-  # helper library.
-  python-env = python.buildEnv.override {
-    extraLibs = [ python.pkgs.httpx ];
-    # Add `.pth` file pointing at the directory containg our helper library.
-    # This will get added to `sys.path` by `site.py`.
-    # See https://docs.python.org/3/library/site.html
-    postBuild = ''
-      echo ${lib.escapeShellArg ./tools/pylib} > $out/${lib.escapeShellArg python.sitePackages}/tools.pth
-    '';
-  };
+  tools = pkgs.callPackage ./tools {};
 in
 pkgs.mkShell {
   shellHook = ''
     export NIX_PATH="nixpkgs=${pkgs.path}";
   '';
   buildInputs = [
-    python-env
+    tools
     pkgs.morph
     pkgs.jp
   ];

tools/default.nix

+{ pkgs, lib, makeWrapper, ... }:
+let
+  python = pkgs.python3;
+  # This is a python envionment that has the dependencies
+  # for the development python scripts we use, and the
+  # helper library.
+  python-env = python.buildEnv.override {
+    extraLibs = [ python.pkgs.httpx ];
+    # Add `.pth` file pointing at the directory containg our helper library.
+    # This will get added to `sys.path` by `site.py`.
+    # See https://docs.python.org/3/library/site.html
+    postBuild = ''
+      echo ${lib.escapeShellArg ./pylib} > $out/${lib.escapeShellArg python.sitePackages}/tools.pth
+    '';
+  };
+in
+# This derivation creates a package that wraps our tools to setup an environment
+# with there dependencies available.
+pkgs.runCommand "ps_tools" {
+  nativeBuildInputs = [ makeWrapper ];
+} ''
+  mkdir -p $out/bin
+  # makeWrapper <executable> <wrapperfile> <args>
+  # See https://nixos.org/manual/nixpkgs/stable/#fun-makeWrapper
+  makeWrapper ${python-env}/bin/python $out/bin/update-nixpkgs --add-flags ${toString ./update-nixpkgs}
+''