Add direnv config for work on nix systems.

Add flake.nix and .envrc inputs for use on nix as declarative nix is
best nix.

Autogenerate flake.lock based on flake.nix.

Add .direnv/ to .gitignore.

.envrc

@@ -0,0 +1 @@
+use_flake .

.gitignore

@@ -10,4 +10,5 @@ rls/
 *.ts
 *.js
 #*#
-.DS_Store
+.DS_Store
+.direnv/

flake.nix

@@ -0,0 +1,49 @@
+{
+  description = "Direnv environment for rust";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  inputs.flake-utils.url = "github:numtide/flake-utils";
+  inputs.fenix = {
+    url = "github:nix-community/fenix";
+    inputs.nixpkgs.follows = "nixpkgs";
+  };
+  outputs = { nixpkgs, flake-utils, fenix, ... }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs {
+          inherit system;
+          overlays = [ fenix.overlays.default ];
+        };
+      in
+      {
+        devShells.default = pkgs.mkShell {
+          packages = [
+            (pkgs.fenix.stable.withComponents [
+              "cargo"
+              "clippy"
+              "rust-src"
+              "rustc"
+              "rustfmt"
+              "rust-analyzer"
+            ])
+            pkgs.bacon
+            pkgs.pkg-config
+            pkgs.openssl
+          ];
+          shellHook = ''
+            export PKG_CONFIG_PATH=${
+              pkgs.lib.makeSearchPathOutput "dev" "lib/pkgconfig" [
+                pkgs.glib
+                pkgs.gtk3
+                pkgs.pango
+                pkgs.gdk-pixbuf
+                pkgs.cairo
+                pkgs.at-spi2-atk
+                pkgs.harfbuzz
+                pkgs.zlib
+                pkgs.gtk-layer-shell
+              ]
+            }
+          '';
+        };
+      });
+}