nix: replace manual system iteration by flake-utils

Let's not reinvent the wheel. This makes the flake more readable, and also would
detect typos in the system list.

flake.lock

@@ -2,11 +2,11 @@
   "nodes": {
     "flake-utils": {
       "locked": {
-        "lastModified": 1659877975,
-        "narHash": "sha256-zllb8aq3YO3h8B/U0/J1WBgAL8EX5yWf5pMj3G0NAmc=",
+        "lastModified": 1667395993,
+        "narHash": "sha256-nuEHfE/LcWyuSWnS8t12N1wc105Qtau+/OdUAjtQ0rA=",
         "owner": "numtide",
         "repo": "flake-utils",
-        "rev": "c0e246b9b83f637f4681389ecabcb2681b4f3af0",
+        "rev": "5aed5285a952e0b949eb3ba02c12fa4fcfef535f",
         "type": "github"
       },
       "original": {
@@ -31,13 +31,16 @@
     },
     "root": {
       "inputs": {
+        "flake-utils": "flake-utils",
         "nixpkgs": "nixpkgs",
         "rust-overlay": "rust-overlay"
       }
     },
     "rust-overlay": {
       "inputs": {
-        "flake-utils": "flake-utils",
+        "flake-utils": [
+          "flake-utils"
+        ],
         "nixpkgs": [
           "nixpkgs"
         ]

flake.nix

@@ -1,30 +1,32 @@
 {
-  description = "jujutsu";
+  description = "Jujutsu VCS, a Git-compatible DVCS that is both simple and powerful";
 
   inputs = {
+    # For listing and iterating nix systems
+    flake-utils.url = "github:numtide/flake-utils";
+
     # For installing non-standard rustc versions
     rust-overlay.url = "github:oxalica/rust-overlay";
     rust-overlay.inputs.nixpkgs.follows = "nixpkgs";
+    rust-overlay.inputs.flake-utils.follows = "flake-utils";
   };
 
-  outputs = { self, nixpkgs, rust-overlay, ... }:
+  outputs = { self, nixpkgs, flake-utils, rust-overlay }:
     let
-      lib = nixpkgs.lib;
-      systems = [
-        "aarch64-linux"
-        "aarch64-darwin"
-        "i686-linux"
-        "x86_64-darwin"
-        "x86_64-linux"
+      systems = with flake-utils.lib.system; [
+        aarch64-linux
+        aarch64-darwin
+        i686-linux
+        x86_64-darwin
+        x86_64-linux
       ];
-      foreachSystem = f: lib.foldl' (attrs: system: lib.recursiveUpdate attrs (f system)) { } systems;
     in
     {
       overlays.default = (final: prev: {
         jujutsu = self.packages.${final.system}.jujutsu;
       });
     } //
-    (foreachSystem (system:
+    (flake-utils.lib.eachSystem systems (system:
       let
         pkgs = import nixpkgs {
           inherit system;
@@ -34,7 +36,7 @@
         };
       in
       {
-        packages.${system} = {
+        packages = {
           jujutsu = pkgs.rustPlatform.buildRustPackage rec {
             pname = "jujutsu";
             version = "unstable-${self.shortRev or "dirty"}";
@@ -70,19 +72,19 @@
           };
           default = self.packages.${system}.jujutsu;
         };
-        apps.${system}.default = {
+        apps.default = {
           type = "app";
           program = "${self.packages.${system}.jujutsu}/bin/jj";
         };
-        checks.${system}.jujutsu = self.packages.${system}.jujutsu.overrideAttrs ({ ... }: {
+        checks.jujutsu = self.packages.${system}.jujutsu.overrideAttrs ({ ... }: {
           cargoBuildType = "debug";
           cargoCheckType = "debug";
           preCheck = ''
             export RUST_BACKTRACE=1
           '';
         });
-        formatter.${system} = pkgs.nixpkgs-fmt;
-        devShells.${system}.default = pkgs.mkShell {
+        formatter = pkgs.nixpkgs-fmt;
+        devShells.default = pkgs.mkShell {
           buildInputs = with pkgs; [
             # Using the minimal profile with explicit "clippy" extension to avoid
             # two versions of rustfmt