refactor(flake): move some code out of flake.in.nix

packages/repl/repl.nix

@@ -0,0 +1,49 @@
+{
+  flakePath ? null,
+  hostnamePath ? "/etc/hostname",
+  registryPath ? /etc/nix/registry.json,
+}: let
+  inherit (builtins) getFlake head match currentSystem readFile pathExists filter fromJSON;
+
+  selfFlake =
+    if pathExists registryPath
+    then filter (it: it.from.id == "self") (fromJSON (readFile registryPath)).flakes
+    else [];
+
+  flakePath' =
+    toString
+    (
+      if flakePath != null
+      then flakePath
+      else if selfFlake != []
+      then (head selfFlake).to.path
+      else "/etc/nixos"
+    );
+
+  flake =
+    if pathExists flakePath'
+    then getFlake flakePath'
+    else {};
+  hostname =
+    if pathExists hostnamePath
+    then head (match "([a-zA-Z0-9\\-]+)\n" (readFile hostnamePath))
+    else "";
+
+  nixpkgsFromInputsPath = flake.inputs.nixpkgs.outPath or "";
+  nixpkgs =
+    flake.pkgs.${currentSystem}.nixpkgs
+    or (
+      if nixpkgsFromInputsPath != ""
+      then import nixpkgsFromInputsPath {}
+      else {}
+    );
+
+  nixpkgsOutput = removeAttrs (nixpkgs // nixpkgs.lib or {}) ["options" "config"];
+in
+  {inherit flake;}
+  // flake
+  // builtins
+  // (flake.nixosConfigurations or {})
+  // flake.nixosConfigurations.${hostname} or {}
+  // nixpkgsOutput
+  // {getFlake = path: getFlake (toString path);}