flake.nix: replace fenix with rust-overlay

flake.nix

@@ -1,36 +1,41 @@
 {
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
-    fenix.url = "github:nix-community/fenix";
-    fenix.inputs.nixpkgs.follows = "nixpkgs";
+
+    rust-overlay.url = "github:oxalica/rust-overlay";
+    rust-overlay.inputs.nixpkgs.follows = "nixpkgs";
   };
 
-
-  outputs = { self, nixpkgs, fenix }@inputs:
-  let 
+  outputs = { self, nixpkgs, rust-overlay }:
+  let
     systems = [
       "x86_64-linux"
       "aarch64-linux"
+      "x86_64-darwin"
       "aarch64-darwin"
+      "armv7l-linux"
     ];
     forAllSystems = f: nixpkgs.lib.genAttrs systems (system: let
-      toolchain = fenix.packages.${system}.complete;
       pkgs = import nixpkgs {
         inherit system;
         overlays = [
-          (_: super: let pkgs = fenix.inputs.nixpkgs.legacyPackages.${system}; in fenix.overlays.default pkgs pkgs)
+          (import rust-overlay)
         ];
       };
+
+      rust-bin = rust-overlay.lib.mkRustBin { } pkgs.buildPackages;
+      toolchain = rust-bin.stable.latest.default;
     in f system pkgs toolchain);
   in {
-    devShell = forAllSystems (system: pkgs: toolchain: pkgs.mkShell {
-      packages = [
-        (toolchain.withComponents [
-          "cargo" "rustc" "rustfmt" "clippy"
-        ])
-        pkgs.mpv
-      ];
-      RUST_SRC_PATH = "${toolchain.rust-src}/lib/rustlib/src/rust/";
+    devShells = forAllSystems (system: pkgs: toolchain: {
+      default = pkgs.mkShell {
+        nativeBuildInputs = [
+          toolchain
+          pkgs.mpv
+        ];
+
+        RUST_SRC_PATH = "${toolchain}/lib/rustlib/src/rust/library";
+      };
     });
   };
-}
+}