Use fenix

flake.nix

@@ -3,19 +3,27 @@
   inputs = {
     nixpkgs.url = "nixpkgs/nixos-unstable";
     flake-utils.url = "github:numtide/flake-utils";
+    fenix = {
+      url = "github:nix-community/fenix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
     naersk = {
       url = "github:nmattia/naersk";
       inputs.nixpkgs.follows = "nixpkgs";
     };
   };
 
-  outputs = { self, nixpkgs, flake-utils, naersk }:
+  outputs = { self, nixpkgs, flake-utils, fenix, naersk }:
     flake-utils.lib.eachDefaultSystem (
       system: let
         pkgs = import nixpkgs {
           inherit system;
         };
-        naersk-lib = naersk.lib."${system}";
+        rustToolchain = fenix.packages."${system}".stable.defaultToolchain;
+        naersk-lib = naersk.lib.${system}.override {
+          cargo = rustToolchain;
+          rustc = rustToolchain;
+        };
       in
         rec {
           packages.azirevpn = naersk-lib.buildPackage {
@@ -30,11 +38,8 @@
           devShell = pkgs.mkShell {
             name = "azirevpn-env";
             buildInputs = [
-              pkgs.cargo
-              pkgs.clippy
+              rustToolchain
               pkgs.rust-analyzer
-              pkgs.rustc
-              pkgs.rustfmt
             ];
           };
         }