nixos/direnv: add enable{Bash,Fish,Zsh}Integrations

use shorthand function for enabled by default options

nixos/modules/programs/direnv.nix

@@ -6,6 +6,13 @@
 }:
 let
   cfg = config.programs.direnv;
+  enabledOption =
+    x:
+    lib.mkEnableOption x
+    // {
+      default = true;
+      example = false;
+    };
 in
 {
   options.programs.direnv = {
@@ -18,6 +25,16 @@ in
 
     package = lib.mkPackageOption pkgs "direnv" { };
 
+    enableBashIntegration = enabledOption ''
+      Bash integration
+    '';
+    enableZshIntegration = enabledOption ''
+      Zsh integration
+    '';
+    enableFishIntegration = enabledOption ''
+      Fish integration
+    '';
+
     direnvrcExtra = lib.mkOption {
       type = lib.types.lines;
       default = "";
@@ -34,22 +51,14 @@ in
       the hiding of direnv logging
     '';
 
-    loadInNixShell =
-      lib.mkEnableOption ''
-        loading direnv in `nix-shell` `nix shell` or `nix develop`
-      ''
-      // {
-        default = true;
-      };
+    loadInNixShell = enabledOption ''
+      loading direnv in `nix-shell` `nix shell` or `nix develop`
+    '';
 
     nix-direnv = {
-      enable =
-        (lib.mkEnableOption ''
-          a faster, persistent implementation of use_nix and use_flake, to replace the built-in one
-        '')
-        // {
-          default = true;
-        };
+      enable = enabledOption ''
+        a faster, persistent implementation of use_nix and use_flake, to replace the builtin one
+      '';
 
       package = lib.mkOption {
         default = pkgs.nix-direnv.override { nix = config.nix.package; };
@@ -65,7 +74,7 @@ in
   config = lib.mkIf cfg.enable {
 
     programs = {
-      zsh.interactiveShellInit = ''
+      zsh.interactiveShellInit = lib.mkIf cfg.enableZshIntegration ''
         if ${lib.boolToString cfg.loadInNixShell} || printenv PATH | grep -vqc '/nix/store'; then
          eval "$(${lib.getExe cfg.package} hook zsh)"
         fi
@@ -73,13 +82,13 @@ in
 
       #$NIX_GCROOT for "nix develop" https://github.com/NixOS/nix/blob/6db66ebfc55769edd0c6bc70fcbd76246d4d26e0/src/nix/develop.cc#L530
       #$IN_NIX_SHELL for "nix-shell"
-      bash.interactiveShellInit = ''
+      bash.interactiveShellInit = lib.mkIf cfg.enableBashIntegration ''
         if ${lib.boolToString cfg.loadInNixShell} || [ -z "$IN_NIX_SHELL$NIX_GCROOT$(printenv PATH | grep '/nix/store')" ] ; then
          eval "$(${lib.getExe cfg.package} hook bash)"
         fi
       '';
 
-      fish.interactiveShellInit = ''
+      fish.interactiveShellInit = lib.mkIf cfg.enableFishIntegration ''
         if ${lib.boolToString cfg.loadInNixShell};
         or printenv PATH | grep -vqc '/nix/store';
          ${lib.getExe cfg.package} hook fish | source
@@ -88,20 +97,17 @@ in
     };
 
     environment = {
-      systemPackages =
-        if cfg.loadInNixShell then
-          [ cfg.package ]
-        else
-          [
-            #direnv has a fish library which sources direnv for some reason
-            (pkgs.symlinkJoin {
-              inherit (cfg.package) name;
-              paths = [ cfg.package ];
-              postBuild = ''
-                rm -rf $out/share/fish
-              '';
-            })
-          ];
+      systemPackages = [
+        # direnv has a fish library which automatically sources direnv for some reason
+        # I don't see any harm in doing this if we're sourcing it with fish.interactiveShellInit
+        (pkgs.symlinkJoin {
+          inherit (cfg.package) name;
+          paths = [ cfg.package ];
+          postBuild = ''
+            rm -rf $out/share/fish
+          '';
+        })
+      ];
 
       variables = {
         DIRENV_CONFIG = "/etc/direnv";