direnv: add module

modules/programs/direnv.nix

@@ -0,0 +1,50 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  cfg = config.programs.direnv;
+
+in
+
+{
+  meta.maintainers = [ maintainers.rycee ];
+
+  options.programs.direnv = {
+    enable = mkEnableOption "direnv, the environment switcher";
+
+    enableBashIntegration = mkOption {
+      default = true;
+      type = types.bool;
+      description = ''
+        Whether to enable Bash integration.
+      '';
+    };
+
+    enableZshIntegration = mkOption {
+      default = true;
+      type = types.bool;
+      description = ''
+        Whether to enable Zsh integration.
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    home.packages = [ pkgs.direnv ];
+
+    programs.bash.initExtra =
+      mkIf cfg.enableBashIntegration (
+        # Using mkAfter to make it more likely to appear after other
+        # manipulations of the prompt.
+        mkAfter ''
+          eval "$(${pkgs.direnv}/bin/direnv hook bash)"
+        ''
+      );
+
+    programs.zsh.initExtra = mkIf cfg.enableZshIntegration ''
+      eval "$(${pkgs.direnv}/bin/direnv hook zsh)"
+    '';
+  };
+}