Default Nix installations don't include user channels in NIX_PATH, causing inconsistent tool behavior #2033

nixpkgs=/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs:nixos-config=/etc/nixos/configuration.nix:/nix/var/nix/profiles/per-user/root/channels

$ nix-channel --list             
nixpkgsunstable https://nixos.org/channels/nixpkgs-unstable

$ nix-env -iA nixpkgsunstable.git
installing 'git-minimal-2.16.2'

$ nix-shell -p nixpkgsunstable.git
error: undefined variable 'nixpkgsunstable' at (string):1:94
(use '--show-trace' to show detailed location information)

$ nix-shell '<nixpkgsunstable>' -p git
error: file 'nixpkgsunstable' was not found in the Nix search path (add it using $NIX_PATH or -I), at (string):1:94
(use '--show-trace' to show detailed location information)

$ nix-build '<nixpkgsunstable>' -A git
error: file 'nixpkgsunstable' was not found in the Nix search path (add it using $NIX_PATH or -I)

$ export NIX_PATH=$NIX_PATH:$HOME/.nix-defexpr/channels

$ nix-env -iA nixpkgsunstable.git    
replacing old 'git-minimal-2.16.2'
installing 'git-minimal-2.16.2'

$ nix-shell -p nixpkgsunstable.git    
error: undefined variable 'nixpkgsunstable' at (string):1:94
(use '--show-trace' to show detailed location information)

$ nix-shell '<nixpkgsunstable>' -p git

[nix-shell:~]$ exit

$ nix-build '<nixpkgsunstable>' -A git
/nix/store/jaani1kx4a4kvz11d0myfkjjiiklfl7w-git-2.16.2