Add a way to include plugin stylesheets optionally only if the file exists

plugins/archive/archive.php

@@ -25,11 +25,7 @@ class archive extends rcube_plugin
         if ($rcmail->task == 'mail' && ($rcmail->action == '' || $rcmail->action == 'show')
             && ($archive_folder = $rcmail->config->get('archive_mbox'))
         ) {
-            $skin_path = $this->local_skin_path();
-            if (is_file($this->home . "/$skin_path/archive.css")) {
-                $this->include_stylesheet("$skin_path/archive.css");
-            }
-
+            $this->include_stylesheet($this->local_skin_path() . '/archive.css', true);
             $this->include_script('archive.js');
             $this->add_texts('localization', true);
             $this->add_button(

plugins/help/help.php

@@ -55,10 +55,7 @@ class help extends rcube_plugin
         }
 
         // add style for taskbar button (must be here) and Help UI
-        $skin_path = $this->local_skin_path();
-        if (is_file($this->home . "/$skin_path/help.css")) {
-            $this->include_stylesheet("$skin_path/help.css");
-        }
+        $this->include_stylesheet($this->local_skin_path() . '/help.css', true);
     }
 
     function action()

plugins/markasjunk/markasjunk.php

@@ -21,14 +21,9 @@ class markasjunk extends rcube_plugin
         $this->add_hook('storage_init', array($this, 'storage_init'));
 
         if ($rcmail->action == '' || $rcmail->action == 'show') {
-            $skin_path = $this->local_skin_path();
-
             $this->add_texts('localization', true);
             $this->include_script('markasjunk.js');
-
-            if (is_file($this->home . "/$skin_path/markasjunk.css")) {
-                $this->include_stylesheet("$skin_path/markasjunk.css");
-            }
+            $this->include_stylesheet($this->local_skin_path() . '/markasjunk.css', true);
 
             $this->add_button(array(
                     'type'     => 'link',

plugins/zipdownload/zipdownload.php

@@ -86,7 +86,7 @@ class zipdownload extends rcube_plugin
                     break;
             }
 
-            $this->include_stylesheet($this->local_skin_path() . '/zipdownload.css');
+            $this->include_stylesheet($this->local_skin_path() . '/zipdownload.css', true);
         }
 
         return $p;

program/lib/Roundcube/rcube_plugin.php

@@ -354,11 +354,12 @@ abstract class rcube_plugin
     /**
      * Make this stylesheet available on the client
      *
-     * @param string $fn File path; absolute or relative to the plugin directory
+     * @param string $fn        File path; absolute or relative to the plugin directory
+     * @param bool   $if_exists Include the file only if exists
      */
-    public function include_stylesheet($fn)
+    public function include_stylesheet($fn, $if_exists = false)
     {
-        $this->api->include_stylesheet($this->resource_url($fn));
+        $this->api->include_stylesheet($this->resource_url($fn), $if_exists);
     }
 
     /**

program/lib/Roundcube/rcube_plugin_api.php

@@ -604,11 +604,21 @@ class rcube_plugin_api
     /**
      * Include a plugin stylesheet in the current HTML page
      *
-     * @param string $fn Path to stylesheet
+     * @param string $fn        Path to stylesheet
+     * @param bool   $if_exists Include stylesheet only if the file exists
      */
-    public function include_stylesheet($fn)
+    public function include_stylesheet($fn, $if_exists = false)
     {
         if (is_object($this->output) && $this->output->type == 'html') {
+            if ($if_exists && $fn[0] != '/' && !preg_match('|^https?://|i', $fn)) {
+                $rcube = rcube::get_instance();
+                $path  = unslashify($rcube->config->get('assets_dir') ?: RCUBE_INSTALL_PATH);
+
+                if (!is_file("$path/$fn")) {
+                    return;
+                }
+            }
+
             $src = $this->resource_url($fn);
             $this->output->include_css($src);
         }