Issue #2906028 by mglaman: Add theme suggestions for the checkout order summary and completion message templates

Author: mglaman

modules/checkout/commerce_checkout.module

@@ -52,9 +52,13 @@ function commerce_checkout_theme_suggestions_commerce_checkout_form(array $varia
   $original = $variables['theme_hook_original'];
   $suggestions = [];
   $suggestions[] = $original;
+  $suggestions[] = $original . '__' . $variables['form']['#plugin_id'];
+  $suggestions[] = $original . '__' . $variables['form']['#entity_id'];
   // If the checkout form has a sidebar, suggest the enhanced layout.
   if (isset($variables['form']['sidebar']) && Element::isVisibleElement($variables['form']['sidebar'])) {
     $suggestions[] = $original . '__with_sidebar';
+    $suggestions[] = $original . '__' . $variables['form']['#plugin_id'] . '__with_sidebar';
+    $suggestions[] = $original . '__' . $variables['form']['#entity_id'] . '__with_sidebar';
   }
 
   return $suggestions;

modules/checkout/src/Plugin/Commerce/CheckoutFlow/CheckoutFlowBase.php

@@ -257,6 +257,8 @@ public function buildForm(array $form, FormStateInterface $form_state, $step_id
 
     $steps = $this->getVisibleSteps();
     $form['#tree'] = TRUE;
+    $form['#entity_id'] = $this->entityId;
+    $form['#plugin_id'] = $this->pluginId;
     $form['#step_id'] = $step_id;
     $form['#title'] = $steps[$step_id]['label'];
     $form['#theme'] = ['commerce_checkout_form'];