build: replace shell.nix with flake.nix for dev shell

.envrc

@@ -1 +1 @@
-use nix
+use flake

flake.lock

@@ -0,0 +1,44 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1720954236,
+        "narHash": "sha256-1mEKHp4m9brvfQ0rjCca8P1WHpymK3TOr3v34ydv9bs=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "53e81e790209e41f0c1efa9ff26ff2fd7ab35e27",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-24.05",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-unstable": {
+      "locked": {
+        "lastModified": 1720957393,
+        "narHash": "sha256-oedh2RwpjEa+TNxhg5Je9Ch6d3W1NKi7DbRO1ziHemA=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "693bc46d169f5af9c992095736e82c3488bf7dbb",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs",
+        "nixpkgs-unstable": "nixpkgs-unstable"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,35 @@
+{
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-24.05";
+    nixpkgs-unstable.url = "github:nixos/nixpkgs/nixos-unstable";
+  };
+
+  outputs = { self, nixpkgs, nixpkgs-unstable }: let
+    pkgs = nixpkgs.legacyPackages.x86_64-linux;
+    pkgs-unstable = nixpkgs-unstable.legacyPackages.x86_64-linux;
+  in {
+    devShells.x86_64-linux.default = pkgs.mkShell {
+      nativeBuildInputs = with pkgs; [
+          pkgs-unstable.rustup
+          pkgs-unstable.rustfmt
+          pkgs-unstable.clippy
+
+          gcc
+          cmake
+          pkg-config
+
+          xdelta
+          libwebp
+      ];
+
+      buildInputs = with pkgs; [
+          gtk4
+          glib
+          gdk-pixbuf
+          gobject-introspection
+
+          libadwaita
+      ];
+    };
+  };
+}

shell.nix

@@ -1,39 +0,0 @@
-let
-    nixpkgs = builtins.fetchGit {
-        name = "nixos-24.05";
-        url = "https://github.com/nixos/nixpkgs";
-        ref = "refs/heads/nixos-24.05";
-    };
-
-    nixpkgs-unstable = builtins.fetchGit {
-        name = "nixos-unstable";
-        url = "https://github.com/nixos/nixpkgs";
-        ref = "refs/heads/nixos-unstable";
-    };
-
-    pkgs = import nixpkgs {};
-    pkgs-unstable = import nixpkgs-unstable {};
-
-in pkgs.mkShell {
-    nativeBuildInputs = with pkgs; [
-        pkgs-unstable.rustup
-        pkgs-unstable.rustfmt
-        pkgs-unstable.clippy
-
-        gcc
-        cmake
-        pkg-config
-
-        xdelta
-        libwebp
-    ];
-
-    buildInputs = with pkgs; [
-        gtk4
-        glib
-        gdk-pixbuf
-        gobject-introspection
-
-        libadwaita
-    ];
-}