Add rust-toolchain and nix flake.

rust-toolchain will allow us to ensure that everyone developing on the
repository is using the same version of rust.

Nix flake will provide out-of-the-box development environment for nix
users with the right rust version.

.envrc

@@ -0,0 +1,11 @@
+# If nix is installed hook into it.
+if [ $(which nix) ]
+then
+    use flake
+fi
+
+# If nu is the current shell use toolkit.nu
+if [ $(echo $SHELL) == $(which nu) ]
+then    
+    nu -e "use toolkit.nu"
+fi

.gitignore

@@ -4,3 +4,4 @@
 
 .vscode/*
 .DS_Store
+.direnv

flake.nix

@@ -0,0 +1,37 @@
+{
+  description = "The New Nushell Parser";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+
+    rust-overlay = {
+      url = "github:oxalica/rust-overlay";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+
+  outputs =
+    {
+      nixpkgs,
+      rust-overlay,
+      flake-utils,
+      ...
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        overlays = [ (import rust-overlay) ];
+        pkgs = import nixpkgs { inherit system overlays; };
+        rustToolchain = pkgs.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml;
+      in
+      {
+        devShells.default = pkgs.mkShell {
+          nativeBuildInputs = [
+            rustToolchain
+            pkgs.rust-analyzer
+          ];
+        };
+      }
+    );
+}

rust-toolchain.toml

@@ -0,0 +1,3 @@
+[toolchain]
+profile = "default"
+channel = "1.81.0"