Issue #3385934 by phthlaap, joegraduate, useernamee, alexpott: The...

Issue #3385934 by phthlaap, joegraduate, useernamee, alexpott: The configuration synchronization page encounters errors when core.extension.yml is missing in the config/sync directory

(cherry picked from commit 96a211c7)

core/modules/field/field.module

@@ -314,11 +314,11 @@ function field_config_import_steps_alter(&$sync_steps, ConfigImporter $config_im
  * @see \Drupal\field\ConfigImporterFieldPurger
  */
 function field_form_config_admin_import_form_alter(&$form, FormStateInterface $form_state) {
-  // Only display the message when there is a storage comparer available and the
-  // form is not submitted.
+  // Only display the message when core.extension is available in the source
+  // storage and the form is not submitted.
   $user_input = $form_state->getUserInput();
   $storage_comparer = $form_state->get('storage_comparer');
-  if ($storage_comparer && empty($user_input)) {
+  if ($storage_comparer?->getSourceStorage()->exists('core.extension') && empty($user_input)) {
     $field_storages = ConfigImporterFieldPurger::getFieldStoragesToPurge(
       $storage_comparer->getSourceStorage()->read('core.extension'),
       $storage_comparer->getChangelist('delete')

core/modules/field/tests/src/Functional/FieldImportDeleteUninstallUiTest.php

@@ -130,4 +130,18 @@ public function testImportDeleteUninstall() {
     $this->assertFalse(isset($deleted_storages[$field_storage->uuid()]), 'Text field has been completed removed from the system.');
   }
 
+  /**
+   * Tests if the synchronization form is available when the core.extension.yml is missing.
+   */
+  public function testSynchronizeForm(): void {
+    $sync = $this->container->get('config.storage.sync');
+    $this->copyConfig($this->container->get('config.storage'), $sync);
+
+    $sync->delete('core.extension');
+    $this->drupalGet('admin/config/development/configuration');
+    $assertSession = $this->assertSession();
+    $this->assertSession()->elementExists('css', 'input[value="Import all"]')->click();
+    $assertSession->pageTextContains('The core.extension configuration does not exist.');
+  }
+
 }