Help: stuck with an infinite recursion after update

I’ve recently updated my single-user install of nix as per the manual

nix-channel --update; nix-env -iA nixpkgs.nix nixpkgs.cacert

Now when I try to perform any nix-env related action I encounter an infinite recursion:

% nix-env -qc                                                                                                                                                                                      
error: infinite recursion encountered, at /nix/store/chns71imikmxpfjgf6zwvirilagclijp-nixpkgs-21.05pre281594.6fc2b7ecc2a/nixpkgs/pkgs/top-level/aliases.nix:178:23
(use '--show-trace' to show detailed location information)

 % nix-env -iA nixpkgs.myPackages                                                                         
replacing old 'my-packages'
installing 'my-packages'
error: infinite recursion encountered, at /nix/store/chns71imikmxpfjgf6zwvirilagclijp-nixpkgs-21.05pre281594.6fc2b7ecc2a/nixpkgs/pkgs/top-level/aliases.nix:178:23
(use '--show-trace' to show detailed location information)

Adding --show-trace shows the following trace:

 % nix-env -qc --show-trace                                                                                              
error: while evaluating the attribute 'version' at /nix/store/chns71imikmxpfjgf6zwvirilagclijp-nixpkgs-21.05pre281594.6fc2b7ecc2a/nixpkgs/pkgs/development/tools/cask/default.nix:6:48:
while evaluating anonymous function at /nix/store/chns71imikmxpfjgf6zwvirilagclijp-nixpkgs-21.05pre281594.6fc2b7ecc2a/nixpkgs/pkgs/top-level/aliases.nix:27:22, called from undefined position:
while evaluating 'removeDistribute' at /nix/store/chns71imikmxpfjgf6zwvirilagclijp-nixpkgs-21.05pre281594.6fc2b7ecc2a/nixpkgs/pkgs/top-level/aliases.nix:15:22, called from /nix/store/chns71imikmxpfjgf6zwvirilagclijp-nixpkgs-21.05pre281594.6fc2b7ecc2a/nixpkgs/pkgs/top-level/aliases.nix:27:29:
while evaluating 'isDerivation' at /nix/store/chns71imikmxpfjgf6zwvirilagclijp-nixpkgs-21.05pre281594.6fc2b7ecc2a/nixpkgs/lib/attrsets.nix:323:18, called from /nix/store/chns71imikmxpfjgf6zwvirilagclijp-nixpkgs-21.05pre281594.6fc2b7ecc2a/nixpkgs/pkgs/top-level/aliases.nix:16:8:
while evaluating 'removeRecurseForDerivations' at /nix/store/chns71imikmxpfjgf6zwvirilagclijp-nixpkgs-21.05pre281594.6fc2b7ecc2a/nixpkgs/pkgs/top-level/aliases.nix:8:33, called from /nix/store/chns71imikmxpfjgf6zwvirilagclijp-nixpkgs-21.05pre281594.6fc2b7ecc2a/nixpkgs/pkgs/top-level/aliases.nix:28:31:
while evaluating 'checkInPkgs' at /nix/store/chns71imikmxpfjgf6zwvirilagclijp-nixpkgs-21.05pre281594.6fc2b7ecc2a/nixpkgs/pkgs/top-level/aliases.nix:22:20, called from /nix/store/chns71imikmxpfjgf6zwvirilagclijp-nixpkgs-21.05pre281594.6fc2b7ecc2a/nixpkgs/pkgs/top-level/aliases.nix:29:32:
infinite recursion encountered, at /nix/store/chns71imikmxpfjgf6zwvirilagclijp-nixpkgs-21.05pre281594.6fc2b7ecc2a/nixpkgs/pkgs/top-level/aliases.nix:178:23

If it’s helpful here’s info about my install:

% nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-darwin"`
 - host os: `Darwin 20.3.0, macOS 10.16`
 - multi-user?: `no`
 - sandbox: `no`
 - version: `nix-env (Nix) 2.3.10`
 - channels(ldeck): `"nixpkgs-21.05pre281594.6fc2b7ecc2a"`
 - nixpkgs: `/Users/ldeck/.nix-defexpr/channels/nixpkgs`

Is nixpkgs broken in recent unstable updates?
Any suggestions?

Okay, figured it out following the stack trace.

The issue was that my old ~/.config/nixpkgs/config.nix included this:

  myPackages = buildEnv {
    paths = [
      ...
      emacs
    ];
    ...
  };

  emacs = emacsWithPackages (epkgs: ...);

There seems to be a namespace conflict with more recent nixpkgs. So renaming to this works fine:

  myPackages = buildEnv {
    paths = [
      ...
      myEmacs
    ];
    ...
  };

  myEmacs = ...