programs.zsh.zplug: add zplugHome option

Add an option to set custom `$ZPLUG_HOME`. Changing it with
`home.sessionVariables` doesnt work, since it has to be exported
before Zplug is initialised

modules/programs/zplug.nix

@@ -31,6 +31,14 @@ in {
       type = types.listOf pluginModule;
       description = "List of zplug plugins.";
     };
+
+    zplugHome = mkOption {
+      type = types.path;
+      default = "${config.home.homeDirectory}/.zplug";
+      defaultText = "~/.zplug";
+      apply = toString;
+      description = "Path to zplug home directory.";
+    };
   };
 
   config = mkIf cfg.enable {
@@ -39,6 +47,8 @@ in {
     programs.zsh.initExtraBeforeCompInit = ''
       source ${pkgs.zplug}/init.zsh
 
+      export ZPLUG_HOME=${cfg.zplugHome}
+
       ${optionalString (cfg.plugins != [ ]) ''
         ${concatStrings (map (plugin: ''
           zplug "${plugin.name}"${

tests/modules/programs/zplug/modules.nix

@@ -8,6 +8,7 @@ with lib;
       enable = true;
       zplug = {
         enable = true;
+        zplugHome = ~/.customZplugHome;
         plugins = [
           {
             name = "plugins/git";
@@ -43,6 +44,9 @@ with lib;
 
       assertFileRegex home-files/.zshrc \
         '^zplug load$'
+
+      assertFileContains home-files/.zshrc \
+        'export ZPLUG_HOME=${config.programs.zsh.zplug.zplugHome}'
     '';
   };
 }