--- /dev/null
+<?php
+
+namespace Drupal\Core\Render;
+
+/**
+ * Defines an interface for turning a render array into a string.
+ */
+interface RendererInterface {
+
+ /**
+ * Renders final HTML given a structured array tree.
+ *
+ * Calls ::render() in such a way that placeholders are replaced.
+ *
+ * Should therefore only be used in occasions where the final rendering is
+ * happening, just before sending a Response:
+ * - system internals that are responsible for rendering the final HTML
+ * - render arrays for non-HTML responses, such as feeds
+ *
+ * (Cannot be executed within another render context.)
+ *
+ * @param array $elements
+ * The structured array describing the data to be rendered.
+ *
+ * @return \Drupal\Component\Render\MarkupInterface
+ * The rendered HTML.
+ *
+ * @throws \LogicException
+ * When called from inside another renderRoot() call.
+ *
+ * @see \Drupal\Core\Render\RendererInterface::render()
+ */
+ public function renderRoot(&$elements);
+
+ /**
+ * Renders final HTML in situations where no assets are needed.
+ *
+ * Calls ::render() in such a way that placeholders are replaced.
+ *
+ * Useful for instance when rendering the values of tokens or emails, which
+ * need a render array being turned into a string, but do not need any of the
+ * bubbleable metadata (the attached assets and cache tags).
+ *
+ * Some of these are a relatively common use case and happen *within* a
+ * ::renderRoot() call, but that is generally highly problematic (and hence an
+ * exception is thrown when a ::renderRoot() call happens within another
+ * ::renderRoot() call). However, in this case, we only care about the output,
+ * not about the bubbling. Hence this uses a separate render context, to not
+ * affect the parent ::renderRoot() call.
+ *
+ * (Can be executed within another render context: it runs in isolation.)
+ *
+ * @param array $elements
+ * The structured array describing the data to be rendered.
+ *
+ * @return \Drupal\Component\Render\MarkupInterface
+ * The rendered HTML.
+ *
+ * @see \Drupal\Core\Render\RendererInterface::renderRoot()
+ * @see \Drupal\Core\Render\RendererInterface::render()
+ */
+ public function renderPlain(&$elements);
+
+ /**
+ * Renders final HTML for a placeholder.
+ *
+ * Renders the placeholder in isolation.
+ *
+ * @param string $placeholder
+ * An attached placeholder to render. (This must be a key of one of the
+ * values of $elements['#attached']['placeholders'].)
+ * @param array $elements
+ * The structured array describing the data to be rendered.
+ *
+ * @return array
+ * The updated $elements.
+ *
+ * @see \Drupal\Core\Render\RendererInterface::render()
+ */
+ public function renderPlaceholder($placeholder, array $elements);
+
+ /**
+ * Renders HTML given a structured array tree.
+ *
+ * Renderable arrays have two kinds of key/value pairs: properties and
+ * children. Properties have keys starting with '#' and their values influence
+ * how the array will be rendered. Children are all elements whose keys do not
+ * start with a '#'. Their values should be renderable arrays themselves,
+ * which will be rendered during the rendering of the parent array. The markup
+ * provided by the children is typically inserted into the markup generated by
+ * the parent array.
+ *
+ * An important aspect of rendering is caching the result, when appropriate.
+ * Because the HTML of a rendered item includes all of the HTML of the
+ * rendered children, caching it requires certain information to bubble up
+ * from child elements to their parents:
+ * - Cache contexts, so that the render cache is varied by every context that
+ * affects the rendered HTML. Because cache contexts affect the cache ID,
+ * and therefore must be resolved for cache hits as well as misses, it is
+ * up to the implementation of this interface to decide how to implement
+ * the caching of items whose children specify cache contexts not directly
+ * specified by the parent. \Drupal\Core\Render\Renderer implements this
+ * with a lazy two-tier caching strategy. Alternate strategies could be to
+ * not cache such parents at all or to cache them with the child elements
+ * replaced by placeholder tokens that are dynamically rendered after cache
+ * retrieval.
+ * - Cache tags, so that cached renderings are invalidated when site content
+ * or configuration that can affect that rendering changes.
+ * - Placeholders, with associated self-contained placeholder render arrays,
+ * for executing code to handle dynamic requirements that cannot be cached.
+ * A render context (\Drupal\Core\Render\RenderContext) can be used to perform
+ * bubbling; it is a stack of \Drupal\Core\Render\BubbleableMetadata objects.
+ *
+ * Additionally, whether retrieving from cache or not, it is important to
+ * know all of the assets (CSS and JavaScript) required by the rendered HTML,
+ * and this must also bubble from child to parent. Therefore,
+ * \Drupal\Core\Render\BubbleableMetadata includes that data as well.
+ *
+ * The process of rendering an element is recursive unless the element defines
+ * an implemented theme hook in #theme. During each call to
+ * Renderer::render(), the outermost renderable array (also known as an
+ * "element") is processed using the following steps:
+ * - If this element has already been printed (#printed = TRUE) or the user
+ * does not have access to it (#access = FALSE), then an empty string is
+ * returned.
+ * - If no render context is set yet, an exception is thrown. Otherwise,
+ * an empty \Drupal\Core\Render\BubbleableMetadata is pushed onto the
+ * render context.
+ * - If this element has #cache defined then the cached markup for this
+ * element will be returned if it exists in Renderer::render()'s cache. To
+ * use Renderer::render() caching, set the element's #cache property to an
+ * associative array with one or several of the following keys:
+ * - 'keys': An array of one or more keys that identify the element. If
+ * 'keys' is set, the cache ID is created automatically from these keys.
+ * - 'contexts': An array of one or more cache context IDs. These are
+ * converted to a final value depending on the request. (For instance,
+ * 'user' is mapped to the current user's ID.)
+ * - 'max-age': A time in seconds. Zero seconds means it is not cacheable.
+ * \Drupal\Core\Cache\Cache::PERMANENT means it is cacheable forever.
+ * - 'bin': Specify a cache bin to cache the element in. Default is
+ * 'default'.
+ * When there is a render cache hit, there is no rendering work left to be
+ * done, so the stack must be updated. The empty (and topmost) frame that
+ * was just pushed onto the stack is updated with all bubbleable rendering
+ * metadata from the element retrieved from render cache. Then, this stack
+ * frame is bubbled: the two topmost frames are popped from the stack,
+ * they are merged, and the result is pushed back onto the stack.
+ * However, also in case of a cache miss we have to do something. Note
+ * that a Renderer renders top-down, which means that we try to render a
+ * parent first, and we try to avoid the work of rendering the children by
+ * using the render cache. Though in this case, we are dealing with a
+ * cache miss. So a Renderer traverses down the tree, rendering all
+ * children. In doing so, the render stack is updated with the bubbleable
+ * metadata of the children. That means that once the children are
+ * rendered, we can render cache this element. But the cache ID may have
+ * *changed* at that point, because the children's cache contexts have
+ * been bubbled!
+ * It is for that case that we must store the current (pre-bubbling) cache
+ * ID, so that we can compare it with the new (post-bubbling) cache ID
+ * when writing to the cache. We store the current cache ID in
+ * $pre_bubbling_cid.
+ * - If this element has #type defined and the default attributes for this
+ * element have not already been merged in (#defaults_loaded = TRUE) then
+ * the defaults for this type of element, defined by an element plugin,
+ * are merged into the array. #defaults_loaded is set by functions that
+ * process render arrays and call the element info service before passing
+ * the array to Renderer::render(), such as form_builder() in the Form
+ * API.
+ * - If this element has #create_placeholder set to TRUE, and it has a
+ * #lazy_builder callback, then the element is replaced with another
+ * element that has only two properties: #markup and #attached. #markup
+ * will contain placeholder markup, and #attached contains the placeholder
+ * metadata, that will be used for replacing this placeholder. That
+ * metadata contains a very compact render array (containing only
+ * #lazy_builder and #cache) that will be rendered to replace the
+ * placeholder with its final markup. This means that when the
+ * #lazy_builder callback is called, it received a render array to add to
+ * that only contains #cache.
+ * - If this element has a #lazy_builder or an array of #pre_render
+ * functions defined, they are called sequentially to modify the element
+ * before rendering. #lazy_builder is preferred, since it allows for
+ * placeholdering (see previous step), but #pre_render is still supported.
+ * Both have their use case: #lazy_builder is for building a render array,
+ * #pre_render is for decorating an existing render array.
+ * After the #lazy_builder function is called, #lazy_builder is removed,
+ * and #built is set to TRUE.
+ * After the #lazy_builder and all #pre_render functions have been called,
+ * #printed is checked a second time in case a #lazy_builder or
+ * #pre_render function flags the element as printed. If #printed is set,
+ * we return early and hence no rendering work is left to be done,
+ * similarly to a render cache hit. Once again, the empty (and topmost)
+ * frame that was just pushed onto the stack is updated with all
+ * bubbleable rendering metadata from the element whose #printed = TRUE.
+ * Then, this stack frame is bubbled: the two topmost frames are popped
+ * from the stack, they are merged, and the result is pushed back onto the
+ * stack.
+ * - The child elements of this element are sorted by weight using uasort()
+ * in \Drupal\Core\Render\Element::children(). Since this is expensive,
+ * when passing already sorted elements to Renderer::render(), for example
+ * from a database query, set $elements['#sorted'] = TRUE to avoid sorting
+ * them a second time.
+ * - The main render phase to produce #children for this element takes
+ * place:
+ * - If this element has #theme defined and #theme is an implemented theme
+ * hook/suggestion then ThemeManagerInterface::render() is called and
+ * must render both the element and its children. If #render_children is
+ * set, ThemeManagerInterface::render() will not be called.
+ * #render_children is usually only set internally by
+ * ThemeManagerInterface::render() so that we can avoid the situation
+ * where Renderer::render() called from within a theme preprocess
+ * function creates an infinite loop.
+ * - If this element does not have a defined #theme, or the defined #theme
+ * hook is not implemented, or #render_children is set, then
+ * Renderer::render() is called recursively on each of the child
+ * elements of this element, and the result of each is concatenated onto
+ * #children. This is skipped if #children is not empty at this point.
+ * - Once #children has been rendered for this element, if #theme is not
+ * implemented and #markup is set for this element, #markup will be
+ * prepended to #children.
+ * - If this element has #states defined then JavaScript state information
+ * is added to this element's #attached attribute by
+ * drupal_process_states().
+ * - If this element has #attached defined then any required libraries,
+ * JavaScript, CSS, or other custom data are added to the current page by
+ * \Drupal\Core\Render\AttachmentsResponseProcessorInterface::processAttachments().
+ * - If this element has an array of #theme_wrappers defined and
+ * #render_children is not set, #children is then re-rendered by passing
+ * the element in its current state to ThemeManagerInterface::render()
+ * successively for each item in #theme_wrappers. Since #theme and
+ * #theme_wrappers hooks often define variables with the same names it is
+ * possible to explicitly override each attribute passed to each
+ * #theme_wrappers hook by setting the hook name as the key and an array
+ * of overrides as the value in #theme_wrappers array.
+ * For example, if we have a render element as follows:
+ * @code
+ * array(
+ * '#theme' => 'image',
+ * '#attributes' => array('class' => array('foo')),
+ * '#theme_wrappers' => array('container'),
+ * );
+ * @endcode
+ * and we need to pass the class 'bar' as an attribute for 'container', we
+ * can rewrite our element thus:
+ * @code
+ * array(
+ * '#theme' => 'image',
+ * '#attributes' => array('class' => array('foo')),
+ * '#theme_wrappers' => array(
+ * 'container' => array(
+ * '#attributes' => array('class' => array('bar')),
+ * ),
+ * ),
+ * );
+ * @endcode
+ * - If this element has an array of #post_render functions defined, they
+ * are called sequentially to modify the rendered #children. Unlike
+ * #pre_render functions, #post_render functions are passed both the
+ * rendered #children attribute as a string and the element itself.
+ * - If this element has #prefix and/or #suffix defined, they are
+ * concatenated to #children.
+ * - The rendering of this element is now complete. The next step will be
+ * render caching. So this is the perfect time to update the stack. At
+ * this point, children of this element (if any), have been rendered also,
+ * and if there were any, their bubbleable rendering metadata will have
+ * been bubbled up into the stack frame for the element that is currently
+ * being rendered. The render cache item for this element must contain the
+ * bubbleable rendering metadata for this element and all of its children.
+ * However, right now, the topmost stack frame (the one for this element)
+ * currently only contains the metadata for the children. Therefore, the
+ * topmost stack frame is updated with this element's metadata, and then
+ * the element's metadata is replaced with the metadata in the topmost
+ * stack frame. This element now contains all bubbleable rendering
+ * metadata for this element and all its children, so it's now ready for
+ * render caching.
+ * - If this element has #cache defined, the rendered output of this element
+ * is saved to Renderer::render()'s internal cache. This includes the
+ * changes made by #post_render.
+ * At the same time, if $pre_bubbling_cid is set, it is compared to the
+ * calculated cache ID. If they are different, then a redirecting cache
+ * item is created, containing the #cache metadata of the current element,
+ * and written to cache using the value of $pre_bubbling_cid as the cache
+ * ID. This ensures the pre-bubbling ("wrong") cache ID redirects to the
+ * post-bubbling ("right") cache ID.
+ * - If this element also has #cache_properties defined, all the array items
+ * matching the specified property names will be cached along with the
+ * element markup. If properties include children names, the system
+ * assumes only children's individual markup is relevant and ignores the
+ * parent markup. This approach is normally not needed and should be
+ * adopted only when dealing with very advanced use cases.
+ * - If this element has attached placeholders ([#attached][placeholders]),
+ * or any of its children has (which we would know thanks to the stack
+ * having been updated just before the render caching step), its
+ * placeholder element containing a #lazy_builder function is rendered in
+ * isolation. The resulting markup is used to replace the placeholder, and
+ * any bubbleable metadata is merged.
+ * Placeholders must be unique, to guarantee that for instance, samples of
+ * placeholders are not replaced as well.
+ * - Just before finishing the rendering of this element, this element's
+ * stack frame (the topmost one) is bubbled: the two topmost frames are
+ * popped from the stack, they are merged and the result is pushed back
+ * onto the stack.
+ * So if for instance this element was a child element, then a new frame
+ * was pushed onto the stack element at the beginning of rendering this
+ * element, it was updated when the rendering was completed, and now we
+ * merge it with the frame for the parent, so that the parent now has the
+ * bubbleable rendering metadata for its child.
+ * - #printed is set to TRUE for this element to ensure that it is only
+ * rendered once.
+ * - The final value of #children for this element is returned as the
+ * rendered output.
+ *
+ * @param array $elements
+ * The structured array describing the data to be rendered.
+ * @param bool $is_root_call
+ * (Internal use only.) Whether this is a recursive call or not. See
+ * ::renderRoot().
+ *
+ * @return \Drupal\Component\Render\MarkupInterface
+ * The rendered HTML.
+ *
+ * @throws \LogicException
+ * When called outside of a render context (i.e. outside of a renderRoot(),
+ * renderPlain() or executeInRenderContext() call).
+ * @throws \Exception
+ * If a #pre_render callback throws an exception, it is caught to mark the
+ * renderer as no longer being in a root render call, if any. Then the
+ * exception is rethrown.
+ *
+ * @see \Drupal\Core\Render\ElementInfoManagerInterface::getInfo()
+ * @see \Drupal\Core\Theme\ThemeManagerInterface::render()
+ * @see drupal_process_states()
+ * @see \Drupal\Core\Render\AttachmentsResponseProcessorInterface::processAttachments()
+ * @see \Drupal\Core\Render\RendererInterface::renderRoot()
+ */
+ public function render(&$elements, $is_root_call = FALSE);
+
+ /**
+ * Checks whether a render context is active.
+ *
+ * This is useful only in very specific situations to determine whether the
+ * system is already capable of collecting bubbleable metadata. Normally it
+ * should not be necessary to be concerned about this.
+ *
+ * @return bool
+ * TRUE if the renderer has a render context active, FALSE otherwise.
+ */
+ public function hasRenderContext();
+
+ /**
+ * Executes a callable within a render context.
+ *
+ * Only for very advanced use cases. Prefer using ::renderRoot() and
+ * ::renderPlain() instead.
+ *
+ * All rendering must happen within a render context. Within a render context,
+ * all bubbleable metadata is bubbled and hence tracked. Outside of a render
+ * context, it would be lost. This could lead to missing assets, incorrect
+ * cache variations (and thus security issues), insufficient cache
+ * invalidations, and so on.
+ *
+ * Any and all rendering must therefore happen within a render context, and it
+ * is this method that provides that.
+ *
+ * @param \Drupal\Core\Render\RenderContext $context
+ * The render context to execute the callable within.
+ * @param callable $callable
+ * The callable to execute.
+ *
+ * @return mixed
+ * The callable's return value.
+ *
+ * @throws \LogicException
+ * In case bubbling has failed, can only happen in case of broken code.
+ *
+ * @see \Drupal\Core\Render\RenderContext
+ * @see \Drupal\Core\Render\BubbleableMetadata
+ */
+ public function executeInRenderContext(RenderContext $context, callable $callable);
+
+ /**
+ * Merges the bubbleable rendering metadata o/t 2nd render array with the 1st.
+ *
+ * @param array $a
+ * A render array.
+ * @param array $b
+ * A render array.
+ *
+ * @return array
+ * The first render array, modified to also contain the bubbleable rendering
+ * metadata of the second render array.
+ *
+ * @see \Drupal\Core\Render\BubbleableMetadata
+ */
+ public function mergeBubbleableMetadata(array $a, array $b);
+
+ /**
+ * Adds a dependency on an object: merges its cacheability metadata.
+ *
+ * For instance, when a render array depends on some configuration, an entity,
+ * or an access result, we must make sure their cacheability metadata is
+ * present on the render array. This method makes doing that simple.
+ *
+ * @param array &$elements
+ * The render array to update.
+ * @param \Drupal\Core\Cache\CacheableDependencyInterface|mixed $dependency
+ * The dependency. If the object implements CacheableDependencyInterface,
+ * then its cacheability metadata will be used. Otherwise, the passed in
+ * object must be assumed to be uncacheable, so max-age 0 is set.
+ *
+ * @see \Drupal\Core\Cache\CacheableMetadata::createFromObject()
+ */
+ public function addCacheableDependency(array &$elements, $dependency);
+
+}
projects / yaffs-website / blobdiff