nix fmt and support aarch64-darwin

default.nix

@@ -1,12 +1,17 @@
-{ pkgs ? import <nixpkgs> {},
-  system ? builtins.currentSystem }:
-
-let
+{
+  pkgs ? import <nixpkgs> {},
+  system ? builtins.currentSystem,
+}: let
   inherit (pkgs) lib;
   sources = builtins.fromJSON (lib.strings.fileContents ./sources.json);
 
   # mkBinaryInstall makes a derivation that installs Zig from a binary.
-  mkBinaryInstall = { url, version, sha256 }: pkgs.stdenv.mkDerivation {
+  mkBinaryInstall = {
+    url,
+    version,
+    sha256,
+  }:
+    pkgs.stdenv.mkDerivation {
       inherit version;
 
       pname = "zig";
@@ -24,19 +29,28 @@ let
     };
 
   # The packages that are tagged releases
-  taggedPackages = lib.attrsets.mapAttrs
+  taggedPackages =
+    lib.attrsets.mapAttrs
     (k: v: mkBinaryInstall {inherit (v.${system}) version url sha256;})
     (lib.attrsets.filterAttrs
       (k: v: (builtins.hasAttr system v) && (v.${system}.url != null))
       (builtins.removeAttrs sources ["master"]));
 
   # The master packages
-  masterPackages = lib.attrsets.mapAttrs'
-    (k: v: lib.attrsets.nameValuePair
-      (if k == "latest" then "master" else ("master-" + k))
+  masterPackages =
+    lib.attrsets.mapAttrs' (
+      k: v:
+        lib.attrsets.nameValuePair
+        (
+          if k == "latest"
+          then "master"
+          else ("master-" + k)
+        )
         (mkBinaryInstall {inherit (v.${system}) version url sha256;})
     )
-    sources.master;
+    (lib.attrsets.filterAttrs
+      (k: v: (builtins.hasAttr system v) && (v.${system}.url != null))
+      sources.master);
 
   # This determines the latest /released/ version.
   latest = lib.lists.last (

flake.nix

@@ -6,12 +6,15 @@
     flake-utils.url = "github:numtide/flake-utils";
   };
 
-  outputs = { self, nixpkgs, flake-utils, ... }:
-    # List of systems where binaries are provided.
-    let
-      systems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" ];
-      outputs = flake-utils.lib.eachSystem systems (system:
-        let pkgs = nixpkgs.legacyPackages.${system};
+  outputs = {
+    self,
+    nixpkgs,
+    flake-utils,
+    ...
+  }: let
+    systems = ["x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin"];
+    outputs = flake-utils.lib.eachSystem systems (system: let
+      pkgs = nixpkgs.legacyPackages.${system};
     in rec {
       # The packages exported by the Flake:
       #  - default - latest /released/ version
@@ -26,8 +29,13 @@
         default = apps.zig;
         zig = flake-utils.lib.mkApp {drv = packages.default;};
       };
+
+      # nix fmt
+      formatter = pkgs.alejandra;
     });
-    in outputs // {
+  in
+    outputs
+    // {
       # Overlay that can be imported so you can access the packages
       # using zigpkgs.master.latest or whatever you'd like.
       overlays.default = final: prev: {