flake: put nixpkgs in NIX_PATH and system registry for flake configs

Currently there are a bunch of really wacky hacks required to get
nixpkgs path correctly set up under flake configs such that `nix run
nixpkgs#hello` and `nix run -f '<nixpkgs>' hello` hit the nixpkgs that
the system was built with. In particular you have to use specialArgs or
an anonymous module, and everyone has to include this hack in their own
configs.

We can do this for users automatically.

NixOS/nixpkgs@e456032addae76701eb17e6c03fc515fd78ad74f

Co-authored-by: Antoine Cotten <hello@acotten.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/flake.nix b/flake.nix
index e25fe6a..0f79d77 100644
--- a/flake.nix
+++ b/flake.nix
@@ -27,6 +27,7 @@
             }
             ++ [ ({ lib, ... }: {
               nixpkgs.source = lib.mkDefault nixpkgs;
+              nixpkgs.flake.source = lib.mkDefault nixpkgs;
 
               system.checks.verifyNixPath = lib.mkDefault false;