Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/lib/Drupal/Core/Display/Annotation/DisplayVariant.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Display\Annotation\DisplayVariant.
+ */
+
+namespace Drupal\Core\Display\Annotation;
+
+use Drupal\Component\Annotation\Plugin;
+
+/**
+ * Defines a display variant annotation object.
+ *
+ * Display variants are used to dictate the output of a given Display, which
+ * can be used to control the output of many parts of Drupal.
+ *
+ * Variants are usually chosen by some selection criteria, and are instantiated
+ * directly. Each variant must define its own approach to rendering, and can
+ * either load its own data or be injected with data from another Display
+ * object.
+ *
+ * @todo: Revise description when/if Displays are added to core:
+ *   https://www.drupal.org/node/2292733
+ *
+ * Plugin namespace: Plugin\DisplayVariant
+ *
+ * For working examples, see
+ * - \Drupal\Core\Render\Plugin\DisplayVariant\SimplePageVariant
+ * - \Drupal\block\Plugin\DisplayVariant\BlockPageVariant
+ *
+ * @see \Drupal\Core\Display\VariantInterface
+ * @see \Drupal\Core\Display\VariantBase
+ * @see \Drupal\Core\Display\VariantManager
+ * @see \Drupal\Core\Display\PageVariantInterface
+ * @see plugin_api
+ *
+ * @Annotation
+ */
+class DisplayVariant extends Plugin {
+
+  /**
+   * The plugin ID.
+   *
+   * @var string
+   */
+  public $id;
+
+  /**
+   * The administrative label.
+   *
+   * @var \Drupal\Core\Annotation\Translation
+   *
+   * @ingroup plugin_translatable
+   */
+  public $admin_label = '';
+
+}

core/lib/Drupal/Core/Display/Annotation/PageDisplayVariant.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Display\Annotation\PageDisplayVariant.
+ */
+
+namespace Drupal\Core\Display\Annotation;
+
+/**
+ * Defines a page display variant annotation object.
+ *
+ * Page display variants are a specific type of display variant, intended to
+ * render entire pages. They must render the crucial parts of a page, which are:
+ * - the title
+ * - the main content
+ * - any messages (#type => status_messages)
+ *
+ * @see \Drupal\Core\Display\VariantInterface
+ * @see \Drupal\Core\Display\PageVariantInterface
+ * @see \Drupal\Core\Display\VariantBase
+ * @see \Drupal\Core\Display\VariantManager
+ * @see plugin_api
+ *
+ * @Annotation
+ */
+class PageDisplayVariant extends DisplayVariant {
+
+}

core/lib/Drupal/Core/Display/PageVariantInterface.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Display\PageVariantInterface.
+ */
+
+namespace Drupal\Core\Display;
+
+/**
+ * Provides an interface for PageDisplayVariant plugins.
+ *
+ * Page display variants are a specific type of DisplayVariant, intended for
+ * "pages", which always have some main content to be rendered. Hence page
+ * display variants may choose to render that main content in a certain way:
+ * decorated in a certain way, laid out in a certain way, et cetera.
+ *
+ * For example, the \Drupal\block\Plugin\DisplayVariant\FullPageVariant page
+ * display variant is used by the Block module to control regions and output
+ * blocks placed in those regions.
+ *
+ * @see \Drupal\Core\Display\Annotation\DisplayVariant
+ * @see \Drupal\Core\Display\VariantBase
+ * @see \Drupal\Core\Display\VariantManager
+ * @see plugin_api
+ */
+interface PageVariantInterface extends VariantInterface {
+
+  /**
+   * Sets the main content for the page being rendered.
+   *
+   * @param array $main_content
+   *   The render array representing the main content.
+   *
+   * @return $this
+   */
+  public function setMainContent(array $main_content);
+
+}

core/lib/Drupal/Core/Display/VariantBase.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Display\VariantBase.
+ */
+
+namespace Drupal\Core\Display;
+
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Plugin\PluginBase;
+use Drupal\Core\Plugin\PluginDependencyTrait;
+use Drupal\Core\Session\AccountInterface;
+
+/**
+ * Provides a base class for DisplayVariant plugins.
+ *
+ * @see \Drupal\Core\Display\Annotation\DisplayVariant
+ * @see \Drupal\Core\Display\VariantInterface
+ * @see \Drupal\Core\Display\VariantManager
+ * @see plugin_api
+ */
+abstract class VariantBase extends PluginBase implements VariantInterface {
+
+  use PluginDependencyTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+
+    $this->setConfiguration($configuration);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function label() {
+    return $this->configuration['label'];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function adminLabel() {
+    return $this->pluginDefinition['admin_label'];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function id() {
+    return $this->configuration['uuid'];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getWeight() {
+    return (int) $this->configuration['weight'];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setWeight($weight) {
+    $this->configuration['weight'] = (int) $weight;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getConfiguration() {
+    return array(
+      'id' => $this->getPluginId(),
+    ) + $this->configuration;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setConfiguration(array $configuration) {
+    $this->configuration = $configuration + $this->defaultConfiguration();
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function defaultConfiguration() {
+    return array(
+      'label' => '',
+      'uuid' => '',
+      'weight' => 0,
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function calculateDependencies() {
+    return $this->dependencies;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
+    $form['label'] = array(
+      '#type' => 'textfield',
+      '#title' => $this->t('Label'),
+      '#description' => $this->t('The label for this display variant.'),
+      '#default_value' => $this->label(),
+      '#maxlength' => '255',
+    );
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateConfigurationForm(array &$form, FormStateInterface $form_state) {
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
+    $this->configuration['label'] = $form_state->getValue('label');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function access(AccountInterface $account = NULL) {
+    return TRUE;
+  }
+
+}

core/lib/Drupal/Core/Display/VariantInterface.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Display\VariantInterface.
+ */
+
+namespace Drupal\Core\Display;
+
+use Drupal\Component\Plugin\ConfigurablePluginInterface;
+use Drupal\Component\Plugin\PluginInspectionInterface;
+use Drupal\Core\Plugin\PluginFormInterface;
+use Drupal\Core\Session\AccountInterface;
+
+/**
+ * Provides an interface for DisplayVariant plugins.
+ *
+ * @see \Drupal\Core\Display\Annotation\DisplayVariant
+ * @see \Drupal\Core\Display\VariantBase
+ * @see \Drupal\Core\Display\VariantManager
+ * @see plugin_api
+ */
+interface VariantInterface extends PluginInspectionInterface, ConfigurablePluginInterface, PluginFormInterface {
+
+  /**
+   * Returns the user-facing display variant label.
+   *
+   * @return string
+   *   The display variant label.
+   */
+  public function label();
+
+  /**
+   * Returns the admin-facing display variant label.
+   *
+   * This is for the type of display variant, not the configured variant itself.
+   *
+   * @return string
+   *   The display variant administrative label.
+   */
+  public function adminLabel();
+
+  /**
+   * Returns the unique ID for the display variant.
+   *
+   * @return string
+   *   The display variant ID.
+   */
+  public function id();
+
+  /**
+   * Returns the weight of the display variant.
+   *
+   * @return int
+   *   The display variant weight.
+   */
+  public function getWeight();
+
+  /**
+   * Sets the weight of the display variant.
+   *
+   * @param int $weight
+   *   The weight to set.
+   */
+  public function setWeight($weight);
+
+  /**
+   * Determines if this display variant is accessible.
+   *
+   * @param \Drupal\Core\Session\AccountInterface $account
+   *   (optional) The user for which to check access, or NULL to check access
+   *   for the current user. Defaults to NULL.
+   *
+   * @return bool
+   *   TRUE if this display variant is accessible, FALSE otherwise.
+   */
+  public function access(AccountInterface $account = NULL);
+
+  /**
+   * Builds and returns the renderable array for the display variant.
+   *
+   * @return array
+   *   A render array for the display variant.
+   */
+  public function build();
+
+}

core/lib/Drupal/Core/Display/VariantManager.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Display\VariantManager.
+ */
+
+namespace Drupal\Core\Display;
+
+use Drupal\Core\Cache\CacheBackendInterface;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Plugin\DefaultPluginManager;
+
+/**
+ * Manages discovery of display variant plugins.
+ *
+ * @see \Drupal\Core\Display\Annotation\DisplayVariant
+ * @see \Drupal\Core\Display\VariantInterface
+ * @see \Drupal\Core\Display\VariantBase
+ * @see plugin_api
+ */
+class VariantManager extends DefaultPluginManager {
+
+  /**
+   * Constructs a new VariantManager.
+   *
+   * @param \Traversable $namespaces
+   *   An object that implements \Traversable which contains the root paths
+   *   keyed by the corresponding namespace to look for plugin implementations.
+   * @param \Drupal\Core\Cache\CacheBackendInterface $cache_backend
+   *   Cache backend instance to use.
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   *   The module handler to invoke the alter hook with.
+   */
+  public function __construct(\Traversable $namespaces, CacheBackendInterface $cache_backend, ModuleHandlerInterface $module_handler) {
+    parent::__construct('Plugin/DisplayVariant', $namespaces, $module_handler, 'Drupal\Core\Display\VariantInterface', 'Drupal\Core\Display\Annotation\DisplayVariant');
+
+    $this->setCacheBackend($cache_backend, 'variant_plugins');
+    $this->alterInfo('display_variant_plugin');
+  }
+
+}