From d1f528277c4f8f5cf986d32a1c637b2a78715ed8 Mon Sep 17 00:00:00 2001
From: Chi <Chi@556138.no-reply.drupal.org>
Date: Wed, 16 Dec 2020 04:04:50 +0000
Subject: [PATCH] Issue #3173946 by Charlie ChX Negyesi, Chi: drupal_region()
 overcaches empty

---
 src/View/RegionViewBuilder.php             |  7 +++++--
 tests/src/Kernel/RegionViewBuilderTest.php | 10 +++++++++-
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/src/View/RegionViewBuilder.php b/src/View/RegionViewBuilder.php
index 0c0c5ad..78edb8e 100644
--- a/src/View/RegionViewBuilder.php
+++ b/src/View/RegionViewBuilder.php
@@ -81,7 +81,10 @@ class RegionViewBuilder {
 
     $build = [];
 
-    $cache_metadata = new CacheableMetadata();
+    $entity_type = $this->entityTypeManager->getDefinition('block');
+    $cache_metadata = (new CacheableMetadata())
+      ->addCacheTags($entity_type->getListCacheTags())
+      ->addCacheContexts($entity_type->getListCacheContexts());
 
     /** @var \Drupal\block\BlockInterface[] $blocks */
     foreach ($blocks as $id => $block) {
@@ -102,8 +105,8 @@ class RegionViewBuilder {
     if ($build) {
       $build['#region'] = $region;
       $build['#theme_wrappers'] = ['region'];
-      $cache_metadata->applyTo($build);
     }
+    $cache_metadata->applyTo($build);
 
     return $build;
   }
diff --git a/tests/src/Kernel/RegionViewBuilderTest.php b/tests/src/Kernel/RegionViewBuilderTest.php
index 1c8f5e8..a0d4ff6 100644
--- a/tests/src/Kernel/RegionViewBuilderTest.php
+++ b/tests/src/Kernel/RegionViewBuilderTest.php
@@ -63,7 +63,14 @@ final class RegionViewBuilderTest extends KernelTestBase {
 
     $build = $view_builder->build('sidebar_first');
     // The build should be empty because 'stable' is not a default theme.
-    self::assertSame([], $build);
+    $expected_build = [
+      '#cache' => [
+        'contexts' => [],
+        'tags' => ['config:block_list'],
+        'max-age' => Cache::PERMANENT,
+      ],
+    ];
+    self::assertSame($expected_build, $build);
 
     // Specify the theme name explicitly.
     $build = $view_builder->build('sidebar_first', 'stable');
@@ -103,6 +110,7 @@ final class RegionViewBuilderTest extends KernelTestBase {
         'contexts' => ['user'],
         'tags' => [
           'config:block.block.public_block',
+          'config:block_list',
           'tag_for_private_block',
           'tag_for_public_block',
         ],