Update flake.nix

flake.nix

@@ -1,37 +1,37 @@
 {
   description = "A massively parallel functional runtime.";
-  
+
   inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
     flake-utils.url = "github:numtide/flake-utils";
-    rust-overlay.url = "github:oxalica/rust-overlay";
+    nix-cargo-integration.url = "github:yusdacra/nix-cargo-integration";
+    nix-filter.url = "github:numtide/nix-filter";
   };
 
-  outputs = { self, nixpkgs, flake-utils, rust-overlay }: 
+  outputs = { self, nixpkgs, flake-utils, nix-cargo-integration, nix-filter }:
     flake-utils.lib.eachDefaultSystem (system:
       let
         pkgs = import nixpkgs {
           inherit system;
-          overlays = [ rust-overlay.overlay ];
+          overlays = [ nix-cargo-integration.overlay ];
         };
 
-        src = builtins.filterSource
-          (name: type: builtins.elem (baseNameOf name) [
+        filteredSrc = nix-filter.lib.filterSource {
+          src = ./.;
+          filter = name: type: builtins.elem (baseNameOf name) [
             "src" "Cargo.lock" "Cargo.toml" "rust-toolchain.toml"
-          ])
-          ./.;
-
+          ] || (type == "directory" && builtins.elem (baseNameOf name) [
+            "src"
+          ]);
+        };
+
       in {
-        packages = {
-          hvm = pkgs.stdenv.mkDerivation {
-            pname = "hvm";
-            version = "0.1.0";
-            src = pkgs.lib.cleanSource src;
-            buildInputs = [ pkgs.openssl pkgs.pkg-config ];
-          };
+        defaultPackage = pkgs.nci.buildPackage {
+          name = "hvm";
+          src = filteredSrc;
+          cargoToml = "Cargo.toml";
+          buildInputs = with pkgs; [ openssl pkg-config ];
         };
-
-        defaultPackage = self.packages.${system}.hvm;
       }
     );
 }