Strangeness with packageOverrides

gistfile1.md

$ cat ~/.nixpkgs/config.nix

{
  packageOverrides = pkgs: {
    testEnv = pkgs.buildEnv {
      name = "test";
      paths = [];
    };
  };
}

$ cat test.nix

let pkgs = import ./. {}; in
{
  testEnv = pkgs.buildEnv {
    name = "test";
    paths = [];
  };
}

$ nix-build -A testEnv --dry-run

these derivations will be built:
  /nix/store/agsjh4w2d20fby9vxafv9sx7crzhqhp4-test.drv
  /nix/store/bg0bv4kz2cq959hfq52i4azjrzzdj0bl-perl-5.14.2.drv

$ nix-build -A testEnv test.nix --dry-run

these derivations will be built:
  /nix/store/9spn30n0shxnpyzsr8pf5b6ddbw395dm-test.drv

Try this patch:

Index: pkgs/top-level/all-packages.nix
===================================================================
--- pkgs/top-level/all-packages.nix     (revision 32455)
+++ pkgs/top-level/all-packages.nix     (working copy)
@@ -241,7 +241,7 @@
   };
 
   buildEnv = import ../build-support/buildenv {
-    inherit runCommand perl;
+    inherit (pkgs) runCommand perl;
   };
 
   dotnetenv = import ../build-support/dotnetenv {