Issue #3096676 by quietone, Wim Leers, mikelutz, heddn, gabesullice, alexpott:...

Issue #3096676 by quietone, Wim Leers, mikelutz, heddn, gabesullice, alexpott: system_maintenance migrations uses incorrect maintenance mode variable in Drupal 7 migrations

(cherry picked from commit c494a61e)

core/modules/migrate_drupal/tests/fixtures/drupal7.php

@@ -58608,10 +58608,6 @@
   'name' => 'site_name',
   'value' => 's:13:"The Site Name";',
 ))
-->values(array(
-  'name' => 'site_offline_message',
-  'value' => 's:42:"This is a custom maintenance mode message.";',
-))
 ->values(array(
   'name' => 'site_slogan',
   'value' => 's:10:"The Slogan";',

core/modules/system/migrations/system_maintenance.yml

@@ -7,10 +7,20 @@ migration_tags:
 source:
   plugin: variable
   variables:
+    - maintenance_mode_message
     - site_offline_message
   source_module: system
 process:
-  message: site_offline_message
+  message:
+  -
+    plugin: callback
+    callable: array_filter
+    source:
+      - maintenance_mode_message
+      - site_offline_message
+  -
+    plugin: callback
+    callable: current
 destination:
   plugin: config
   config_name: system.maintenance

core/modules/system/tests/src/Kernel/Migrate/d7/MigrateSystemConfigurationTest.php

@@ -128,6 +128,18 @@ class MigrateSystemConfigurationTest extends MigrateDrupal7TestBase {
   protected function setUp(): void {
     parent::setUp();
 
+    // The system_maintenance migration gets both the Drupal 6 and Drupal 7
+    // site maintenance message. Add a row with the Drupal 6 version of the
+    // maintenance message to confirm that the Drupal 7 variable is selected in
+    // the migration.
+    // See https://www.drupal.org/project/drupal/issues/3096676
+    $this->sourceDatabase->insert('variable')
+      ->fields([
+        'name' => 'site_offline_message',
+        'value' => 's:16:"Drupal 6 message";',
+      ])
+      ->execute();
+
     $migrations = [
       'd7_system_authorize',
       'd7_system_cron',