Add initial (very basic) add to cart form.

modules/product/commerce_product.info.yml

@@ -15,6 +15,7 @@ config_devel:
   - commerce_product.commerce_product_variation_type.default
   - commerce_order.commerce_line_item_type.product_variation
   - core.entity_form_display.commerce_product.default.default
+  - core.entity_view_display.commerce_product.default.default
   - core.entity_form_display.commerce_product_variation.default.default
   - core.entity_form_display.commerce_line_item.product_variation.default
   - core.entity_view_display.commerce_line_item.product_variation.default

modules/product/config/install/core.entity_view_display.commerce_product.default.default.yml

+langcode: en
+status: true
+dependencies:
+  config:
+    - commerce_product.commerce_product_type.default
+    - field.field.commerce_product.default.body
+    - field.field.commerce_product.default.stores
+    - field.field.commerce_product.default.variations
+  module:
+    - commerce_product
+    - text
+    - user
+id: commerce_product.default.default
+targetEntityType: commerce_product
+bundle: default
+mode: default
+content:
+  body:
+    type: text_default
+    weight: 0
+    label: hidden
+    settings: {  }
+    third_party_settings: {  }
+  variations:
+    type: add_to_cart
+    weight: 1
+    label: hidden
+    settings:
+      default_quantity: '1'
+      combine: true
+      show_quantity: false
+    third_party_settings: {  }
+hidden:
+  stores: true

modules/product/config/schema/commerce_product.schema.yml

@@ -43,6 +43,19 @@ field.field.*.*.*.third_party.commerce_product:
         type: label
         label: 'The title of the attribute for the Add to Cart form'
 
+field.formatter.settings.add_to_cart:
+  type: mapping
+  mapping:
+    show_quantity:
+      type: boolean
+      label: 'Whether to display a quantity input field on the add to cart form.'
+    default_quantity:
+      type: string
+      label: 'Default quantity'
+    combine:
+      type: boolean
+      label: 'Whether to attempt to combine line items containing the same product variation'
+
 action.configuration.publish_product_action:
   type: action_configuration_default
   label: 'Configuration for the Publish product action'

modules/product/src/Form/AddToCartForm.php

+<?php
+
+/**
+ * @file
+ * Contains \Drupal\commerce_product\Form\AddToCartForm.
+ */
+
+namespace Drupal\commerce_product\Form;
+
+use Drupal\commerce_cart\CartManagerInterface;
+use Drupal\commerce_cart\CartProviderInterface;
+use Drupal\commerce_store\StoreContextInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Link;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides the add to cart form for product variations.
+ */
+class AddToCartForm extends FormBase {
+
+  /**
+   * The cart manager.
+   *
+   * @var \Drupal\commerce_cart\CartManagerInterface
+   */
+  protected $cartManager;
+
+  /**
+   * The cart provider.
+   *
+   * @var \Drupal\commerce_cart\CartProviderInterface
+   */
+  protected $cartProvider;
+
+  /**
+   * The variation storage.
+   *
+   * @var \Drupal\Core\Entity\EntityStorageInterface
+   */
+  protected $variationStorage;
+
+  /**
+   * The store context.
+   *
+   * @var \Drupal\commerce_store\StoreContextInterface
+   */
+  protected $storeContext;
+
+  /**
+   * Constructs a new AddToCartForm object.
+   *
+   * @param \Drupal\commerce_cart\CartManagerInterface $cart_manager
+   *   The cart manager.
+   * @param \Drupal\commerce_cart\CartProviderInterface $cart_provider
+   *   The cart provider.
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+  49   The entity type manager.
+   * @param \Drupal\commerce_store\StoreContextInterface $store_context
+   *   The store context.
+   */
+  public function __construct(CartManagerInterface $cart_manager, CartProviderInterface $cart_provider, EntityTypeManagerInterface $entity_type_manager, StoreContextInterface $store_context) {
+    $this->cartManager = $cart_manager;
+    $this->cartProvider = $cart_provider;
+    $this->variationStorage = $entity_type_manager->getStorage('commerce_product_variation');
+    $this->storeContext = $store_context;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('commerce_cart.cart_manager'),
+      $container->get('commerce_cart.cart_provider'),
+      $container->get('entity_type.manager'),
+      $container->get('commerce_store.store_context')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'commerce_product_add_to_cart_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state, $product = NULL, array $settings = NULL) {
+    $variations = [];
+    foreach ($product->variations->referencedEntities() as $variation) {
+      $variations[$variation->id()] = $variation->label();
+    }
+
+    $form['#settings'] = $settings;
+    $form['variation'] = [
+      '#type' => 'select',
+      '#title' => $this->t('Select variation:'),
+      '#options' => $variations,
+    ];
+    if (!empty($settings['show_quantity'])) {
+      $form['quantity'] = [
+        '#type' => 'number',
+        '#title' => $this->t('Quantity'),
+        '#min' => 1,
+        '#max' => 9999,
+        '#step' => 1,
+      ];
+    }
+    else {
+      $form['quantity'] = [
+        '#type' => 'value',
+        '#value' => $settings['default_quantity'],
+      ];
+    }
+    $form['submit'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Add to cart'),
+    ];
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  function submitForm(array &$form, FormStateInterface $form_state) {
+    $variation = $this->variationStorage->load($form_state->getValue('variation'));
+    $available_stores = $variation->getProduct()->getStores();
+    if (count($available_stores) === 1) {
+      $store = reset($available_stores);
+    }
+    else {
+      $store = $this->storeContext->getStore();
+      if (!in_array($store, $available_stores)) {
+        // Throw an exception.
+      }
+    }
+    // @todo The order type should not be hardcoded.
+    $cart = $this->cartProvider->getCart('default', $store);
+    if (!$cart) {
+      $cart = $this->cartProvider->createCart('default', $store);
+    }
+    $quantity = $form_state->getValue('quantity');
+    $combine = $form['#settings']['combine'];
+    $this->cartManager->addEntity($cart, $variation, $quantity, $combine);
+    drupal_set_message(t('@variation added to @cart-link.', [
+      '@variation' => $variation->label(),
+      '@cart-link' => Link::createFromRoute('your cart', 'commerce_cart.page')->toString(),
+    ]));
+  }
+
+}

modules/product/src/Plugin/Field/FieldFormatter/AddToCartFormatter.php

+<?php
+
+/**
+ * @file
+ * Contains \Drupal\commerce_product\Plugin\Field\FieldFormatter\AddToCartFormatter.
+ */
+
+namespace Drupal\commerce_product\Plugin\Field\FieldFormatter;
+
+use Drupal\Core\Field\FormatterBase;
+use Drupal\Core\Field\FieldDefinitionInterface;
+use Drupal\Core\Field\FieldItemListInterface;
+use Drupal\Core\Form\FormBuilderInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\Core\Render\Element;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Plugin implementation of the 'add_to_cart' formatter.
+ *
+ * @FieldFormatter(
+ *   id = "add_to_cart",
+ *   label = @Translation("Add to cart form"),
+ *   field_types = {
+ *     "entity_reference",
+ *   },
+ * )
+ */
+class AddToCartFormatter extends FormatterBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * The form builder.
+   *
+   * @var \Drupal\Core\Form\FormBuilderInterface
+   */
+  protected $formBuilder;
+
+  /**
+   * Constructs an AddToCartFormatter object.
+   *
+   * @param string $plugin_id
+   *   The plugin_id for the formatter.
+   * @param mixed $plugin_definition
+   *   The plugin implementation definition.
+   * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
+   *   The definition of the field to which the formatter is associated.
+   * @param array $settings
+   *   The formatter settings.
+   * @param string $label
+   *   The formatter label display setting.
+   * @param string $view_mode
+   *   The view mode.
+   * @param array $third_party_settings
+   *   Any third party settings.
+   * @param \Drupal\Core\Form\FormBuilderInterface $form_builder
+   *   The form builder.
+   */
+  public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, FormBuilderInterface $form_builder) {
+    parent::__construct($plugin_id, $plugin_definition, $field_definition, $settings, $label, $view_mode, $third_party_settings);
+
+    $this->formBuilder = $form_builder;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function defaultSettings() {
+    return array(
+      'show_quantity' => FALSE,
+      'default_quantity' => 1,
+      'combine' => TRUE,
+    ) + parent::defaultSettings();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function settingsForm(array $form, FormStateInterface $form_state) {
+    $form = parent::settingsForm($form, $form_state);
+
+    $form['show_quantity'] = [
+      '#type' => 'checkbox',
+      '#title' => t('Display a quantity input field on the add to cart form.'),
+      '#default_value' => $this->getSetting('show_quantity'),
+    ];
+    $form['default_quantity'] = [
+      '#type' => 'number',
+      '#title' => t('Default quantity'),
+      '#default_value' => $this->getSetting('default_quantity'),
+      '#min' => 1,
+      '#max' => 9999,
+    ];
+    $form['combine'] = [
+      '#type' => 'checkbox',
+      '#title' => t('Attempt to combine line items containing the same product variation.'),
+      '#description' => t('The line item type, referenced product variation, and data from fields exposed on the Add to Cart form must all match to combine.'),
+      '#default_value' => $this->getSetting('combine'),
+    ];
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function settingsSummary() {
+    // @todo.
+    return [];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    // @see \Drupal\Core\Field\FormatterPluginManager::createInstance().
+    return new static(
+      $plugin_id,
+      $plugin_definition,
+      $configuration['field_definition'],
+      $configuration['settings'],
+      $configuration['label'],
+      $configuration['view_mode'],
+      $configuration['third_party_settings'],
+      $container->get('form_builder')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function viewElements(FieldItemListInterface $items, $langcode) {
+    // @todo Use a lazy_builder.
+    $product = $items->getEntity();
+    $settings = $this->getSettings();
+    return $this->formBuilder->getForm('\Drupal\commerce_product\Form\AddToCartForm', $product, $settings);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function isApplicable(FieldDefinitionInterface $field_definition) {
+    return \Drupal::moduleHandler()->moduleExists('commerce_cart');
+  }
+}