Issue #3260668 by phenaproxima: UpdateReady should have "cancel" button

src/Form/UpdateReady.php

@@ -139,6 +139,11 @@ class UpdateReady extends FormBase {
     ];
 
     $form['actions'] = ['#type' => 'actions'];
+    $form['actions']['cancel'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Cancel update'),
+      '#submit' => ['::cancel'],
+    ];
     $form['actions']['submit'] = [
       '#type' => 'submit',
       '#value' => $this->t('Continue'),
@@ -184,4 +189,13 @@ class UpdateReady extends FormBase {
     batch_set($batch);
   }
 
+  /**
+   * Cancels the in-progress update.
+   */
+  public function cancel(array &$form, FormStateInterface $form_state): void {
+    $this->updater->destroy();
+    $this->messenger()->addStatus($this->t('The update was successfully cancelled.'));
+    $form_state->setRedirect('automatic_updates.report_update');
+  }
+
 }

tests/src/Functional/UpdaterFormTest.php

@@ -263,6 +263,7 @@ class UpdaterFormTest extends AutomaticUpdatesFunctionalTestBase {
 
     // Delete the existing update.
     $page->pressButton('Delete existing update');
+    $assert_session->pageTextContains('Staged update deleted');
     $assert_session->pageTextNotContains('Cannot begin an update because another Composer operation is currently in progress.');
 
     // Ensure we can start another update after deleting the existing one.
@@ -273,6 +274,12 @@ class UpdaterFormTest extends AutomaticUpdatesFunctionalTestBase {
     $this->assertUpdateReady();
     $this->assertUpdateStagedTimes(2);
     $assert_session->buttonExists('Continue');
+    // Cancel the update, then ensure that we are bounced back to the start
+    // page, and that it will allow us to begin the update anew.
+    $page->pressButton('Cancel update');
+    $assert_session->addressEquals('/admin/reports/updates/automatic-update');
+    $assert_session->pageTextContains('The update was successfully cancelled.');
+    $assert_session->buttonExists('Update');
   }
 
   /**