add nixpkgs-unstable to standard template

I decided it is a common enough usecase, so it makes sense to include it

Co-authored-by: Will Forman <wf8581@gmail.com>

standard/flake.lock

@@ -37,10 +37,27 @@
         "type": "github"
       }
     },
+    "nixpkgs-unstable": {
+      "locked": {
+        "lastModified": 1672953546,
+        "narHash": "sha256-oz757DnJ1ITvwyTovuwG3l9cX6j9j6/DH9eH+cXFJmc=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "a518c77148585023ff56022f09c4b2c418a51ef5",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "root": {
       "inputs": {
         "home-manager": "home-manager",
-        "nixpkgs": "nixpkgs"
+        "nixpkgs": "nixpkgs",
+        "nixpkgs-unstable": "nixpkgs-unstable"
       }
     },
     "utils": {

standard/flake.nix

@@ -4,6 +4,10 @@
   inputs = {
     # Nixpkgs
     nixpkgs.url = "github:nixos/nixpkgs/nixos-22.11";
+    # You can access packages and modules from different nixpkgs revs
+    # at the same time. Here's an working example:
+    nixpkgs-unstable.url = "github:nixos/nixpkgs/nixos-unstable";
+    # Also see the 'unstable-packages' overlay at 'overlays/default.nix'.
 
     # Home manager
     home-manager.url = "github:nix-community/home-manager";
@@ -43,7 +47,7 @@
       );
 
       # Your custom packages and modifications, exported as overlays
-      overlays = import ./overlays;
+      overlays = import ./overlays { inherit inputs; };
       # Reusable nixos modules you might want to export
       # These are usually stuff you would upstream into nixpkgs
       nixosModules = import ./modules/nixos;

standard/home-manager/home.nix

@@ -18,6 +18,7 @@
     # You can add overlays here
     overlays = [
       # Add overlays your own flake exports (from overlays and pkgs dir):
+      outputs.overlays.unstable
       outputs.overlays.modifications
       outputs.overlays.additions
 

standard/nixos/configuration.nix

@@ -22,6 +22,7 @@
     # You can add overlays here
     overlays = [
       # Add overlays your own flake exports (from overlays and pkgs dir):
+      outputs.overlays.unstable
       outputs.overlays.modifications
       outputs.overlays.additions
 

standard/overlays/default.nix

@@ -1,4 +1,5 @@
 # This file defines overlays
+{ inputs, ... }:
 {
   # This one brings our custom packages from the 'pkgs' directory
   additions = final: _prev: import ../pkgs { pkgs = final; };
@@ -11,4 +12,13 @@
     # ...
     # });
   };
+
+  # When applied, the unstable nixpkgs set (declared in the flake inputs) will
+  # be accessible through 'pkgs.unstable'
+  unstable-packages = final: _prev: {
+    unstable = import inputs.nixpkgs-unstable {
+      system = final.system;
+      config.allowUnfree = true;
+    };
+  };
 }