Issue #2987060 by Sut3kh, andypost, greggles, Anybody, lkacenja, jnrfred:...

Issue #2987060 by Sut3kh, andypost, greggles, Anybody, lkacenja, jnrfred: Commerce 2 Completion Registration checkout pane

src/Plugin/Commerce/CheckoutPane/EmailRegistrationCompletionRegistration.php

+<?php
+
+namespace Drupal\email_registration\Plugin\Commerce\CheckoutPane;
+
+use Drupal\commerce_checkout\Plugin\Commerce\CheckoutPane\CompletionRegister;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Provides the registration pane without username.
+ *
+ * Assumes email_registration is enabled.
+ *
+ * @CommerceCheckoutPane(
+ *   id = "email_registration_completion_registration",
+ *   label = @Translation("Email registration guest registration after checkout"),
+ * )
+ */
+class EmailRegistrationCompletionRegistration extends CompletionRegister {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildPaneForm(array $pane_form, FormStateInterface $form_state, array &$complete_form) {
+    $pane_form = parent::buildPaneForm($pane_form, $form_state, $complete_form);
+
+    // Set the name as per email_registration_form_user_register_form_alter().
+    $pane_form['name'] = [
+      '#type' => 'hidden',
+      '#value' => 'email_registration_' . user_password(),
+    ];
+
+    // Try and help password managers.
+    // https://www.chromium.org/developers/design-documents/form-styles-that-chromium-understands
+    $pane_form['email'] = [
+      '#type' => 'textfield',
+      '#value' => $this->order->getEmail(),
+      '#attributes' => [
+        'autocomplete' => 'username',
+      ],
+      '#wrapper_attributes' => [
+        'style' => 'display: none;',
+      ],
+    ];
+
+    return $pane_form;
+  }
+
+}