Fix a few issues

01-devshell/flake.lock

@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1776169885,
+        "narHash": "sha256-l/iNYDZ4bGOAFQY2q8y5OAfBBtrDAaPuRQqWaFHVRXM=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "4bd9165a9165d7b5e33ae57f3eecbcb28fb231c9",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

01-devshell/flake.nix

@@ -10,11 +10,13 @@
 
   # Outputs: a function that receives all inputs and returns an attrset.
   # The attrset's structure is what `nix` CLI commands look for (e.g. `devShells.<system>.default`).
-  outputs = { self, nixpkgs, ... }:
+  outputs =
+    { nixpkgs, ... }:
     let
       system = "x86_64-linux";
       pkgs = import nixpkgs { inherit system; };
-    in {
+    in
+    {
       # `nix develop` picks this up by default.
       devShells.${system}.default = pkgs.mkShell {
         packages = with pkgs; [

02-package/flake.nix

@@ -8,11 +8,13 @@
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
   };
 
-  outputs = { self, nixpkgs, ... }:
+  outputs =
+    { self, nixpkgs, ... }:
     let
       system = "x86_64-linux";
       pkgs = import nixpkgs { inherit system; };
-    in {
+    in
+    {
       packages.${system}.default = pkgs.stdenv.mkDerivation {
         pname = "greet";
         version = "0.1.0";
@@ -42,6 +44,7 @@
       apps.${system}.default = {
         type = "app";
         program = "${self.packages.${system}.default}/bin/greet";
+        meta.description = "Run the packaged greet script.";
       };
     };
 }

03-multi-system/flake.nix

@@ -8,7 +8,8 @@
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
   };
 
-  outputs = { self, nixpkgs, ... }:
+  outputs =
+    { self, nixpkgs, ... }:
     let
       # List every system you want to support.
       supportedSystems = [
@@ -20,11 +21,10 @@
 
       # Helper: apply a function to each system and collect results into an attrset.
       # `nixpkgs.lib.genAttrs` turns a list of keys + a function into { key = f key; … }.
-      forAllSystems = f:
+      forAllSystems =
-        nixpkgs.lib.genAttrs supportedSystems (system:
+        f: nixpkgs.lib.genAttrs supportedSystems (system: f (import nixpkgs { inherit system; }));
-          f (import nixpkgs { inherit system; })
+    in
-        );
+    {
-    in {
       # Every output that varies per system goes through `forAllSystems`.
       packages = forAllSystems (pkgs: {
         default = pkgs.writeShellScriptBin "hello-multi" ''
@@ -34,7 +34,10 @@
 
       devShells = forAllSystems (pkgs: {
         default = pkgs.mkShell {
-          packages = with pkgs; [ jq ripgrep ];
+          packages = with pkgs; [
+            jq
+            ripgrep
+          ];
           shellHook = ''
             echo "dev shell on $(uname -s)/$(uname -m)"
           '';
@@ -44,8 +47,8 @@
       # `nix flake check` evaluates everything under `checks`.
       # Wrapping a simple test here shows the pattern.
       checks = forAllSystems (pkgs: {
-        runs = pkgs.runCommand "hello-multi-runs" {} ''
+        runs = pkgs.runCommand "hello-multi-runs" { } ''
-          ${self.packages.${pkgs.system}.default}/bin/hello-multi > $out
+          ${self.packages.${pkgs.stdenv.hostPlatform.system}.default}/bin/hello-multi > $out
         '';
       });
     };

Makefile

@@ -5,9 +5,9 @@ EXAMPLES := $(sort $(wildcard [0-9][0-9]-*))
 # Tools are invoked via `nix run` so nothing needs to be pre-installed beyond Nix itself.
 # Override any of these if you have the tools on $PATH and want faster startup.
 NIX        ?= nix
-NIXFMT     ?= $(NIX) run nixpkgs#nixfmt-rfc-style --
+NIXFMT     ?= $(NIX) run nixpkgs\#nixfmt --
-STATIX     ?= $(NIX) run nixpkgs#statix --
+STATIX     ?= $(NIX) run nixpkgs\#statix --
-DEADNIX    ?= $(NIX) run nixpkgs#deadnix --
+DEADNIX    ?= $(NIX) run nixpkgs\#deadnix --
 
 # Selector for single-example targets (dev, show, update-one).
 EXAMPLE    ?=