Issue #3275335 by AdamPS: Inform the admin if config import is needed

src/Form/TestEmailForm.php

@@ -63,10 +63,6 @@ class TestEmailForm extends FormBase {
   public function buildForm(array $form, FormStateInterface $form_state) {
     $form['#tree'] = TRUE;
 
-    $form['description'] = [
-      '#markup' => '<p>' . $this->t('This page allows you to send a test email to a recipient of your choice.') . '</p>',
-    ];
-
     $form['recipient'] = [
       '#title' => $this->t('Recipient'),
       '#type' => 'textfield',

src/Processor/EmailBuilderManager.php

@@ -115,6 +115,21 @@ class EmailBuilderManager extends DefaultPluginManager implements EmailBuilderMa
     return $info ?? [];
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function importRequired() {
+    $state_all = $this->keyValue->get('import', []);
+
+    foreach ($this->getDefinitions() as $id => $definition) {
+      if ($definition['import'] && (($state_all[$id] ?? self::IMPORT_READY) == self::IMPORT_READY)) {
+        return TRUE;
+      }
+    }
+
+    return FALSE;
+  }
+
   /**
    * {@inheritdoc}
    */

src/Processor/EmailBuilderManagerInterface.php

@@ -36,6 +36,14 @@ interface EmailBuilderManagerInterface extends PluginManagerInterface {
    */
   public function getImportInfo();
 
+  /**
+   * Checks if config importing is required.
+   *
+   * @return bool
+   *   TRUE if import is required.
+   */
+  public function importRequired();
+
   /**
    * Imports config for the specified id.
    *

symfony_mailer.module

@@ -5,6 +5,9 @@
  * Allows sending emails with Symfony Mailer.
  */
 
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\Core\Url;
+
 /**
  * Implements hook_theme().
  */
@@ -40,3 +43,29 @@ function template_preprocess_email(array &$variables) {
   $variables['body'] = $email->getBody();
   $variables = array_merge($variables, $email->getVariables());
 }
+
+/**
+ * Implements hook_help().
+ */
+function symfony_mailer_help($route_name, RouteMatchInterface $route_match) {
+  // Remind site administrators if there are pending import operations. We
+  // don't need to issue the message on the import pages.
+  if ((substr($route_name, 0, strlen('symfony_mailer.import.')) != 'symfony_mailer.import.') && \Drupal::currentUser()->hasPermission('administer mailer') && \Drupal::service('plugin.manager.email_builder')->importRequired()) {
+    $params = [':import_config' => Url::fromRoute('symfony_mailer.import.status')->toString()];
+    \Drupal::messenger()->addError(t('There are Mailer configuration import operations pending: <a href=":import_config">import</a>.', $params));
+  }
+
+  switch ($route_name) {
+    case 'entity.mailer_policy.collection':
+      return '<p>' . t('Configure Mailer Policy to customise outgoing emails in many different ways. There are many possible policies to apply including: subject; body; addresses (from, to, ...); theme; transport; convert to plain text. Each policy can be set globally or for emails of a specific type.') . '</p>';
+
+    case 'symfony_mailer.import.status':
+      $params = [':mailer_policy' => Url::fromRoute('entity.mailer_policy.collection')->toString()];
+      $output = '<p>' . t('You can import configuration from existing modules to create an equivalent <a href=":mailer_policy">Mailer Policy</a>. It is recommended to run the import at the beginning, before you start editing policy.') . '</p>';
+      $output .= '<p>' . t('<b>Warning</b> importing overwrites existing policy. If you have already created working policy then you should skip the import.', $params);
+      return $output;
+
+    case 'symfony_mailer.test':
+      return '<p>' . t('Verify your Mailer configuration by sending a test email.') . '</p>';
+  }
+}