Nix support & automated update (#130)

* Add a nix flake

* Update flake deps and nix package's version nightly

* nix-flake: Update vendorSha256 on each push

An extra commit will be pushed only if needed

* Move flake.* into root directory

Update flake.lock

* nix-flake: Support more systems, commit hash as version

* Don't automatically update flake.lock

flake.nix

@@ -0,0 +1,44 @@
+{
+  inputs.nixpkgs.url = "nixpkgs/nixos-unstable";
+
+  outputs = {
+    self,
+    nixpkgs,
+  }:
+    with nixpkgs.lib; let
+      # List of explicetely unsupported systems
+      explicitelyUnsupportedSystems = [];
+
+      # Packwiz should support all 64-bit systems supported by go, but nix only
+      # support strictly less, so all nix-supported systems are included
+      # (except ones in explicitelyUnsupportedSystems).
+      supportedSystems =
+        filter
+        # Filter out systems that are explicetely supported
+        (s: ! elem s explicitelyUnsupportedSystems)
+        # This lists all systems reasonably well-supported by nix
+        (import "${nixpkgs}/lib/systems/flake-systems.nix" {});
+
+      # Helper generating outputs for each supported system
+      forAllSystems = genAttrs supportedSystems;
+
+      # Import nixpkgs' package set for each system.
+      nixpkgsFor = forAllSystems (system: import nixpkgs {inherit system;});
+    in {
+      # Packwiz package
+      packages = forAllSystems (system: let
+        pkgs = nixpkgsFor.${system};
+      in rec {
+        packwiz = pkgs.callPackage ./nix {
+          version = substring 0 8 self.rev or "dirty";
+          vendorSha256 = readFile ./nix/vendor-sha256;
+          buildGoModule = pkgs.buildGo118Module;
+        };
+        # Build packwiz by default when no package name is specified
+        default = packwiz;
+      });
+
+      # This flake's nix code formatter
+      formatter = forAllSystems (system: nixpkgsFor.${system}.alejandra);
+    };
+}