Load blocks from the secondary menu in the node preprocess hook

Fix missing secondary menu

web/themes/custom/agarica/agarica.theme

@@ -4,6 +4,64 @@ use Drupal\block\Entity\Block;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Url;
 
+/**
+* Implements hook_preprocess_node() for NODE document templates.
+*/
+function agarica_preprocess_node(&$variables) {
+  // Allowed view modes
+  $view_mode = $variables['view_mode']; // Retrieve view mode
+  $allowed_view_modes = ['full']; // Array of allowed view modes (for performance so as to not execute on unneeded nodes)
+
+  // If view mode is in allowed view modes list, pass to agarica_add_regions_to_node()
+  if(in_array($view_mode, $allowed_view_modes)) {
+    // Allowed regions (for performance so as to not execute for unneeded region)
+    $allowed_regions = ['secondary_menu'];
+    agarica_add_regions_to_node($allowed_regions, $variables);
+  }
+}
+
+/**
+* THEME_add_regions_to_node
+*/
+
+function agarica_add_regions_to_node($allowed_regions, &$variables) {
+  // Retrieve active theme
+  $theme = \Drupal::theme()->getActiveTheme()->getName();
+
+  // Retrieve theme regions
+  $available_regions = system_region_list($theme, 'REGIONS_ALL');
+
+  // Validate allowed regions with available regions
+  $regions = array_intersect(array_keys($available_regions), $allowed_regions);
+
+  // For each region
+  foreach ($regions as $key => $region) {
+
+    // Load region blocks
+    $blocks = Drupal::entityTypeManager()
+      ->getStorage('block')
+      ->loadByProperties(['theme' => $theme, 'region' => $region]);
+
+    // Sort ‘em
+    uasort($blocks, 'Drupal\block\Entity\Block::sort');
+
+    // Capture viewable blocks and their settings to $build
+    $build = [];
+    foreach ($blocks as $key => $block) {
+      if ($block->access('view')) {
+        $view_builder = \Drupal::entityTypeManager()
+          ->getViewBuilder($block
+          ->getEntityTypeId());
+        $build[$key] = $view_builder
+          ->view($block, 'block');
+      }
+    }
+
+    // Add build to region
+    $variables[$region] = $build;
+  }
+}
+
 /**
  * Implements hook_preprocess_region__footer().
  */