Issue #3248928: Redirect or provide link to apply form for user who started update if accessing start form

src/Form/UpdaterForm.php

@@ -14,6 +14,7 @@ use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Link;
 use Drupal\Core\State\StateInterface;
 use Drupal\Core\Url;
+use Drupal\package_manager\Exception\StageException;
 use Drupal\system\SystemManager;
 use Drupal\update\UpdateManagerInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -113,6 +114,31 @@ class UpdaterForm extends FormBase {
   public function buildForm(array $form, FormStateInterface $form_state) {
     $this->messenger()->addWarning($this->t('This is an experimental Automatic Updater using Composer. Use at your own risk.'));
 
+    $stage_exists = FALSE;
+    if (!$this->updater->isAvailable()) {
+      // If there's a stage ID stored in the session, try to claim the stage
+      // with it. If we succeed, then an update is already in progress, and the
+      // current session started it, so redirect them to the confirmation form.
+      $stage_id = $this->session->get('_automatic_updates_stage_id');
+      if ($stage_id) {
+        try {
+          $this->updater->claim($stage_id);
+          return $this->redirect('automatic_updates.confirmation_page', [
+            'stage_id' => $stage_id,
+          ]);
+        }
+        catch (StageException $e) {
+          // If the form has been submitted do not display this error message
+          // because ::deleteExistingUpdate() may run on submit. The message
+          // will still be displayed on form build if needed.
+          if (!$form_state->getUserInput()) {
+            $this->messenger()->addError($this->t('Cannot begin an update because another Composer operation is currently in progress.'));
+          }
+          $stage_exists = TRUE;
+        }
+      }
+    }
+
     $form['last_check'] = [
       '#theme' => 'update_last_check',
       '#last' => $this->state->get('update.last_check', 0),
@@ -224,43 +250,21 @@ class UpdaterForm extends FormBase {
 
     // If there were no errors, allow the user to proceed with the update.
     if ($this->getOverallSeverity($results) !== SystemManager::REQUIREMENT_ERROR) {
-      $form['actions'] = $this->actions($form_state);
-    }
-    return $form;
-  }
-
-  /**
-   * Builds the form actions.
-   *
-   * @param \Drupal\Core\Form\FormStateInterface $form_state
-   *   The form state.
-   *
-   * @return mixed[][]
-   *   The form's actions elements.
-   */
-  protected function actions(FormStateInterface $form_state): array {
-    $actions = ['#type' => 'actions'];
-
-    if (!$this->updater->isAvailable()) {
-      // If the form has been submitted do not display this error message
-      // because ::deleteExistingUpdate() may run on submit. The message will
-      // still be displayed on form build if needed.
-      if (!$form_state->getUserInput()) {
-        $this->messenger()->addError($this->t('Cannot begin an update because another Composer operation is currently in progress.'));
-      }
-      $actions['delete'] = [
-        '#type' => 'submit',
-        '#value' => $this->t('Delete existing update'),
-        '#submit' => ['::deleteExistingUpdate'],
-      ];
-    }
-    else {
-      $actions['submit'] = [
-        '#type' => 'submit',
-        '#value' => $this->t('Update'),
+      $form['actions'] = [
+        'submit' => [
+          '#type' => 'submit',
+          '#value' => $this->t('Update'),
+        ],
+        'delete' => [
+          '#type' => 'submit',
+          '#value' => $this->t('Delete existing update'),
+          '#submit' => ['::deleteExistingUpdate'],
+          '#access' => $stage_exists,
+        ],
+        '#type' => 'actions',
       ];
     }
-    return $actions;
+    return $form;
   }
 
   /**