Works for me (with NixOS channel).

I'm very hesitant about this. I'm pretty sure there was a reason for using the nixpkgs symlink but I don't remember what it was.

@edolstra Maybe you would prefer the original, #39682? I didn't like having it in the top tree, but that was before I realized that the channels already have the nixpkgs symlink.

Maybe this commit (2cd7c1f) which actually creates the symlink in question has an explanation?

commit 2cd7c1f19888ae73bf7ef0f41a45680cfb86334a
Author: Eelco Dolstra <eelco.dolstra@logicblox.com>
Date:   Wed Aug 5 17:29:08 2015 +0200

    Unify NixOS and Nixpkgs channel structure
    
    This is primarily to ensure that
    
      -I nixpkgs=https://nixos.org/channels/nixos-unstable/nixexprs.tar.xz
    
    and
    
      -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-unstable.tar.gz
    
    and
    
      -I nixpkgs=https://nixos.org/channels/nixpkgs-unstable/nixexprs.tar.xz
    
    behave consistently.
    
    It also allows installing packages via "nix-env -iA nixos.<pkg>"
    rather than "nixos.pkgs.<pkg>". It would be even better to allow
    "nixpkgs.<pkg>", but that requires a change to nix-channel.

Locations that do have nixpkgs -> . symlink:

• https://nixos.org/channels/nixos-unstable/nixexprs.tar.xz

Locations that don't (currently broken for nix-channel, fixed by this patch):

• https://github.com/NixOS/nixpkgs-channels/archive/nixos-unstable.tar.gz
• https://nixos.org/channels/nixpkgs-unstable/nixexprs.tar.xz
• https://github.com/NixOS/nixpkgs/archive/master.tar.gz

This seems to be a safe change to me, because it only normalizes the first case. For this change to cause breakage, there should be a nixpkgs channel that has nixpkgs/ directory that it is something other than nixpkgs -> . symlink.

I agree with that analysis, this change seems safe. I'm guessing it used to be needed for pre-15.09 channels but those seem to be garbage-collected already so I can't check.

Superseded by #40892.

Sorry I missed this, but thanks for all the discussion!