python.pkgs.bootstrapped-pip: upgrade pkg_resources, fixes #26392

pip 9.0.1 vendors a version of setuptools/pkg_resources which has been
fixed in setuptools/pkg_resources but not yet in pip. Because we're now
facing this issue with nox, we update pkg_resources to the version we
also have in setuptools. Let's cross our fingers this will work without
breaking other stuff.

pkgs/development/python-modules/bootstrapped-pip/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, python, fetchPypi, makeWrapper, unzip }:
+{ stdenv, python, fetchPypi, fetchurl, makeWrapper, unzip }:
 
 let
   wheel_source = fetchPypi {
@@ -13,6 +13,15 @@ let
     format = "wheel";
     sha256 = "f2900e560efc479938a219433c48f15a4ff4ecfe575a65de385eeb44f2425587";
   };
+
+  # TODO: Shouldn't be necessary anymore for pip > 9.0.1!
+  # https://github.com/NixOS/nixpkgs/issues/26392
+  # https://github.com/pypa/setuptools/issues/885
+  pkg_resources = fetchurl {
+    url = https://raw.githubusercontent.com/pypa/setuptools/v36.0.1/pkg_resources/__init__.py;
+    sha256 = "1wdnq3mammk75mifkdmmjx7yhnpydvnvi804na8ym4mj934l2jkv";
+  };
+
 in stdenv.mkDerivation rec {
   pname = "pip";
   version = "9.0.1";
@@ -29,6 +38,8 @@ in stdenv.mkDerivation rec {
     unzip -d $out/${python.sitePackages} $src
     unzip -d $out/${python.sitePackages} ${setuptools_source}
     unzip -d $out/${python.sitePackages} ${wheel_source}
+    # TODO: Shouldn't be necessary anymore for pip > 9.0.1!
+    cp ${pkg_resources} $out/${python.sitePackages}/pip/_vendor/pkg_resources/__init__.py
   '';
 
   patchPhase = ''