nix: Allow changing to a fork in nixpkgs-version.nix

default.nix

@@ -22,10 +22,10 @@ let
 
   # Nix files that describe the Nixpkgs repository. We evaluate the expression
   # using `import` below.
-  nixpkgs =
+  nixpkgs = with nixpkgsVersion;
     builtins.fetchTarball {
-      url = "https://github.com/nixos/nixpkgs/archive/${nixpkgsVersion.rev}.tar.gz";
+      url = "https://github.com/${owner}/${repo}/archive/${rev}.tar.gz";
-      sha256 = nixpkgsVersion.tarballHash;
+      sha256 = tarballHash;
     };
 
   nixpkgs-patched = (import nixpkgs { inherit overlays system; }).applyPatches {

nix/nixpkgs-version.nix

@@ -1,5 +1,7 @@
 # Pinned version of Nixpkgs, generated with postgrest-nixpkgs-upgrade.
 {
+  owner = "NixOS";
+  repo = "nixpkgs";
   date = "2024-01-06";
   rev = "4bbf5a2eb6046c54f7a29a0964c642ebfe912cbc";
   tarballHash = "03p45qdcxqxc41mmzmmyzbkff29vv95vv643z0kd3mf1s2nnsy5b";

nix/tools/nixpkgsTools.nix

@@ -40,6 +40,8 @@ let
         cat > nix/nixpkgs-version.nix << EOF
         # Pinned version of Nixpkgs, generated with ${name}.
         {
+          owner = "NixOS";
+          repo = "nixpkgs";
           date = "$currentDate";
           rev = "$commitHash";
           tarballHash = "$tarballHash";