Add Nix dev shell and direnv support

Author: ryze312

.envrc

@@ -0,0 +1 @@
+use flake

.gitignore

@@ -1 +1,2 @@
 /target
+/.direnv

flake.lock

@@ -0,0 +1,32 @@
+{
+  inputs = {
+    nixpkgs.url = "nixpkgs/nixpkgs-unstable";
+
+    fenix = {
+      url = "github:nix-community/fenix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+
+  outputs = { self, nixpkgs, fenix }:
+  let
+    overlays = [ fenix.overlays.default ];
+
+    getPkgsFor = (system: import nixpkgs {
+      inherit system overlays;
+    });
+
+    forEachSystem = func: nixpkgs.lib.genAttrs [
+      "x86_64-linux"
+      "aarch64-linux"
+
+      "aarch64-darwin"
+      "x86_64-darwin"
+    ] (system: func (getPkgsFor system));
+
+  in {
+    devShells = forEachSystem (pkgs: {
+      default = pkgs.callPackage ./shell.nix {};
+    });
+  };
+}

flake.nix

@@ -0,0 +1,4 @@
+[toolchain]
+channel = "stable"
+profile = "default"
+targets = ["x86_64-unknown-linux-gnu", "aarch64-unknown-linux-gnu"]

rust-toolchain.toml

@@ -0,0 +1,12 @@
+{ mkShell, fenix }:
+
+let
+  toolchain = fenix.fromToolchainFile {
+    file = ./rust-toolchain.toml;
+    sha256 = "opUgs6ckUQCyDxcB9Wy51pqhd0MPGHUVbwRKKPGiwZU=";
+  };
+in
+
+mkShell {
+  packages = [ toolchain ];
+}