Optimize is empty rendering

Closes #3492962

src/Element/ComponentElementAlter.php

@@ -124,12 +124,12 @@ class ComponentElementAlter implements TrustedCallbackInterface {
    * @return bool
    *   Returns true for empty.
    */
-  protected static function isSlotEmpty(array $slot, int $max_level = 1, int $level = 0): bool {
+  public static function isSlotEmpty(array $slot, int $max_level = 2, int $level = 0): bool {
     if (is_array($slot) && empty($slot)) {
       return TRUE;
     }
     if ($level < $max_level) {
-      foreach (Element::getVisibleChildren($slot) as $child) {
+      foreach (Element::children($slot) as $child) {
         if (self::isSlotEmpty($slot[$child], $max_level, $level + 1) === FALSE) {
           return FALSE;
         }
@@ -138,7 +138,29 @@ class ComponentElementAlter implements TrustedCallbackInterface {
         }
       }
     }
-    if (Element::isEmpty($slot)) {
+
+    return self::checkSlotEmpty($slot);
+  }
+
+  /**
+   * Advanced indicates whether the given element is empty.
+   *
+   * Before using Element::isEmpty($slot) the slot values are trimmed
+   * to catch more empty cases.
+   *
+   * @param array $slot
+   *   The slot.
+   *
+   * @return bool
+   *   Whether the given element is empty.
+   */
+  private static function checkSlotEmpty(array $slot):bool {
+    foreach (['#markup', '#plain_text'] as $key) {
+      if (array_key_exists($key, $slot) && empty($slot[$key])) {
+        unset($slot[$key]);
+      }
+    }
+    if (Element::isEmpty($slot) || Element::isVisibleElement($slot) === FALSE) {
       return TRUE;
     }
     return FALSE;