5 * Hooks and documentation related to the theme and render system.
9 * @defgroup themeable Theme system overview
11 * Functions and templates for the user interface that themes can override.
13 * Drupal's theme system allows a theme to have nearly complete control over
14 * the appearance of the site, which includes both the markup and the CSS used
15 * to style the markup. For this system to work, modules, instead of writing
16 * HTML markup directly, need to return "render arrays", which are structured
17 * hierarchical arrays that include the data to be rendered into HTML (or XML or
18 * another output format), and options that affect the markup. Render arrays
19 * are ultimately rendered into HTML or other output formats by recursive calls
20 * to drupal_render(), traversing the depth of the render array hierarchy. At
21 * each level, the theme system is invoked to do the actual rendering. See the
22 * documentation of drupal_render() and the
23 * @link theme_render Theme system and Render API topic @endlink for more
24 * information about render arrays and rendering.
26 * @section sec_twig_theme Twig Templating Engine
27 * Drupal 8 uses the templating engine Twig. Twig offers developers a fast,
28 * secure, and flexible method for building templates for Drupal 8 sites. Twig
29 * also offers substantial usability improvements over PHPTemplate, and does
30 * not require front-end developers to know PHP to build and manipulate Drupal
33 * For further information on theming in Drupal 8 see
34 * https://www.drupal.org/docs/8/theming
36 * For further Twig documentation see
37 * http://twig.sensiolabs.org/doc/templates.html
39 * @section sec_theme_hooks Theme Hooks
40 * The theme system is invoked in \Drupal\Core\Render\Renderer::doRender() by
41 * calling the \Drupal\Core\Theme\ThemeManagerInterface::render() function,
42 * which operates on the concept of "theme hooks". Theme hooks define how a
43 * particular type of data should be rendered. They are registered by modules by
44 * implementing hook_theme(), which specifies the name of the hook, the input
45 * "variables" used to provide data and options, and other information. Modules
46 * implementing hook_theme() also need to provide a default implementation for
47 * each of their theme hooks, normally in a Twig file, and they may also provide
48 * preprocessing functions. For example, the core Search module defines a theme
49 * hook for a search result item in search_theme():
52 * 'search_result' => array(
53 * 'variables' => array(
55 * 'plugin_id' => NULL,
57 * 'file' => 'search.pages.inc',
61 * Given this definition, the template file with the default implementation is
62 * search-result.html.twig, which can be found in the
63 * core/modules/search/templates directory, and the variables for rendering are
64 * the search result and the plugin ID. In addition, there is a function
65 * template_preprocess_search_result(), located in file search.pages.inc, which
66 * preprocesses the information from the input variables so that it can be
67 * rendered by the Twig template; the processed variables that the Twig template
68 * receives are documented in the header of the default Twig template file.
70 * hook_theme() implementations can also specify that a theme hook
71 * implementation is a theme function, but that is uncommon and not recommended.
72 * Note that while Twig templates will auto-escape variables, theme functions
73 * must explicitly escape any variables by using theme_render_and_autoescape().
74 * Failure to do so is likely to result in security vulnerabilities. Theme
75 * functions are deprecated in Drupal 8.0.x and will be removed before
76 * Drupal 9.0.x. Use Twig templates instead.
78 * @section sec_overriding_theme_hooks Overriding Theme Hooks
79 * Themes may register new theme hooks within a hook_theme() implementation, but
80 * it is more common for themes to override default implementations provided by
81 * modules than to register entirely new theme hooks. Themes can override a
82 * default implementation by creating a template file with the same name as the
83 * default implementation; for example, to override the display of search
84 * results, a theme would add a file called search-result.html.twig to its
85 * templates directory. A good starting point for doing this is normally to
86 * copy the default implementation template, and then modifying it as desired.
88 * In the uncommon case that a theme hook uses a theme function instead of a
89 * template file, a module would provide a default implementation function
90 * called theme_HOOK, where HOOK is the name of the theme hook (for example,
91 * theme_search_result() would be the name of the function for search result
92 * theming). In this case, a theme can override the default implementation by
93 * defining a function called THEME_HOOK() in its THEME.theme file, where THEME
94 * is the machine name of the theme (for example, 'bartik' is the machine name
95 * of the core Bartik theme, and it would define a function called
96 * bartik_search_result() in the bartik.theme file, if the search_result hook
97 * implementation was a function instead of a template). Normally, copying the
98 * default function is again a good starting point for overriding its behavior.
99 * Again, note that theme functions (unlike templates) must explicitly escape
100 * variables using theme_render_and_autoescape() or risk security
101 * vulnerabilities. Theme functions are deprecated in Drupal 8.0.x and will be
102 * removed before Drupal 9.0.x. Use Twig templates instead.
104 * @section sec_preprocess_templates Preprocessing for Template Files
105 * If the theme implementation is a template file, several functions are called
106 * before the template file is invoked to modify the variables that are passed
107 * to the template. These make up the "preprocessing" phase, and are executed
108 * (if they exist), in the following order (note that in the following list,
109 * HOOK indicates the hook being called or a less specific hook. For example, if
110 * '#theme' => 'node__article' is called, hook is node__article and node. MODULE
111 * indicates a module name, THEME indicates a theme name, and ENGINE indicates a
112 * theme engine name). Modules, themes, and theme engines can provide these
113 * functions to modify how the data is preprocessed, before it is passed to the
115 * - template_preprocess(&$variables, $hook): Creates a default set of variables
116 * for all theme hooks with template implementations. Provided by Drupal Core.
117 * - template_preprocess_HOOK(&$variables): Should be implemented by the module
118 * that registers the theme hook, to set up default variables.
119 * - MODULE_preprocess(&$variables, $hook): hook_preprocess() is invoked on all
120 * implementing modules.
121 * - MODULE_preprocess_HOOK(&$variables): hook_preprocess_HOOK() is invoked on
122 * all implementing modules, so that modules that didn't define the theme hook
123 * can alter the variables.
124 * - ENGINE_engine_preprocess(&$variables, $hook): Allows the theme engine to
125 * set necessary variables for all theme hooks with template implementations.
126 * - ENGINE_engine_preprocess_HOOK(&$variables): Allows the theme engine to set
127 * necessary variables for the particular theme hook.
128 * - THEME_preprocess(&$variables, $hook): Allows the theme to set necessary
129 * variables for all theme hooks with template implementations.
130 * - THEME_preprocess_HOOK(&$variables): Allows the theme to set necessary
131 * variables specific to the particular theme hook.
133 * @section sec_preprocess_functions Preprocessing for Theme Functions
134 * If the theming implementation is a function, only the theme-hook-specific
135 * preprocess functions (the ones ending in _HOOK) are called from the list
136 * above. This is because theme hooks with function implementations need to be
137 * fast, and calling the non-theme-hook-specific preprocess functions for them
138 * would incur a noticeable performance penalty.
140 * @section sec_suggestions Theme hook suggestions
141 * In some cases, instead of calling the base theme hook implementation (either
142 * the default provided by the module that defined the hook, or the override
143 * provided by the theme), the theme system will instead look for "suggestions"
144 * of other hook names to look for. Suggestions can be specified in several
146 * - In a render array, the '#theme' property (which gives the name of the hook
147 * to use) can be an array of theme hook names instead of a single hook name.
148 * In this case, the render system will look first for the highest-priority
149 * hook name, and if no implementation is found, look for the second, and so
150 * on. Note that the highest-priority suggestion is at the end of the array.
151 * - In a render array, the '#theme' property can be set to the name of a hook
152 * with a '__SUGGESTION' suffix. For example, in search results theming, the
153 * hook 'item_list__search_results' is given. In this case, the render system
154 * will look for theme templates called item-list--search-results.html.twig,
155 * which would only be used for rendering item lists containing search
156 * results, and if this template is not found, it will fall back to using the
157 * base item-list.html.twig template. This type of suggestion can also be
158 * combined with providing an array of theme hook names as described above.
159 * - A module can implement hook_theme_suggestions_HOOK(). This allows the
160 * module that defines the theme template to dynamically return an array
161 * containing specific theme hook names (presumably with '__' suffixes as
162 * defined above) to use as suggestions. For example, the Search module
163 * does this in search_theme_suggestions_search_result() to suggest
164 * search_result__PLUGIN as the theme hook for search result items, where
165 * PLUGIN is the machine name of the particular search plugin type that was
166 * used for the search (such as node_search or user_search).
168 * For further information on overriding theme hooks see
169 * https://www.drupal.org/node/2186401
171 * @section sec_alternate_suggestions Altering theme hook suggestions
172 * Modules can also alter the theme suggestions provided using the mechanisms
173 * of the previous section. There are two hooks for this: the
174 * theme-hook-specific hook_theme_suggestions_HOOK_alter() and the generic
175 * hook_theme_suggestions_alter(). These hooks get the current list of
176 * suggestions as input, and can change this array (adding suggestions and
179 * @section assets Assets
180 * We can distinguish between three types of assets:
181 * - Unconditional page-level assets (loaded on all pages where the theme is in
182 * use): these are defined in the theme's *.info.yml file.
183 * - Conditional page-level assets (loaded on all pages where the theme is in
184 * use and a certain condition is met): these are attached in
185 * hook_page_attachments_alter(), e.g.:
187 * function THEME_page_attachments_alter(array &$page) {
188 * if ($some_condition) {
189 * $page['#attached']['library'][] = 'mytheme/something';
193 * - Template-specific assets (loaded on all pages where a specific template is
194 * in use): these can be added by in preprocessing functions, using @code
195 * $variables['#attached'] @endcode, e.g.:
197 * function THEME_preprocess_menu_local_action(array &$variables) {
198 * // We require Modernizr's touch test for button styling.
199 * $variables['#attached']['library'][] = 'core/modernizr';
211 * @defgroup theme_render Render API overview
213 * Overview of the Theme system and Render API.
215 * The main purpose of Drupal's Theme system is to give themes complete control
216 * over the appearance of the site, which includes the markup returned from HTTP
217 * requests and the CSS files used to style that markup. In order to ensure that
218 * a theme can completely customize the markup, module developers should avoid
219 * directly writing HTML markup for pages, blocks, and other user-visible output
220 * in their modules, and instead return structured "render arrays" (see
221 * @ref arrays below). Doing this also increases usability, by ensuring that the
222 * markup used for similar functionality on different areas of the site is the
223 * same, which gives users fewer user interface patterns to learn.
225 * For further information on the Theme and Render APIs, see:
226 * - https://www.drupal.org/docs/8/theming
227 * - https://www.drupal.org/developing/api/8/render
228 * - @link themeable Theme system overview @endlink.
230 * @section arrays Render arrays
231 * The core structure of the Render API is the render array, which is a
232 * hierarchical associative array containing data to be rendered and properties
233 * describing how the data should be rendered. A render array that is returned
234 * by a function to specify markup to be sent to the web browser or other
235 * services will eventually be rendered by a call to drupal_render(), which will
236 * recurse through the render array hierarchy if appropriate, making calls into
237 * the theme system to do the actual rendering. If a function or method actually
238 * needs to return rendered output rather than a render array, the best practice
239 * would be to create a render array, render it by calling drupal_render(), and
240 * return that result, rather than writing the markup directly. See the
241 * documentation of drupal_render() for more details of the rendering process.
243 * Each level in the hierarchy of a render array (including the outermost array)
244 * has one or more array elements. Array elements whose names start with '#' are
245 * known as "properties", and the array elements with other names are "children"
246 * (constituting the next level of the hierarchy); the names of children are
247 * flexible, while property names are specific to the Render API and the
248 * particular type of data being rendered. A special case of render arrays is a
249 * form array, which specifies the form elements for an HTML form; see the
250 * @link form_api Form generation topic @endlink for more information on forms.
252 * Render arrays (at any level of the hierarchy) will usually have one of the
253 * following properties defined:
254 * - #type: Specifies that the array contains data and options for a particular
255 * type of "render element" (for example, 'form', for an HTML form;
256 * 'textfield', 'submit', for HTML form element types; 'table', for a table
257 * with rows, columns, and headers). See @ref elements below for more on
258 * render element types.
259 * - #theme: Specifies that the array contains data to be themed by a particular
260 * theme hook. Modules define theme hooks by implementing hook_theme(), which
261 * specifies the input "variables" used to provide data and options; if a
262 * hook_theme() implementation specifies variable 'foo', then in a render
263 * array, you would provide this data using property '#foo'. Modules
264 * implementing hook_theme() also need to provide a default implementation for
265 * each of their theme hooks, normally in a Twig file. For more information
266 * and to discover available theme hooks, see the documentation of
267 * hook_theme() and the
268 * @link themeable Default theme implementations topic. @endlink
269 * - #markup: Specifies that the array provides HTML markup directly. Unless
270 * the markup is very simple, such as an explanation in a paragraph tag, it
271 * is normally preferable to use #theme or #type instead, so that the theme
272 * can customize the markup. Note that the value is passed through
273 * \Drupal\Component\Utility\Xss::filterAdmin(), which strips known XSS
274 * vectors while allowing a permissive list of HTML tags that are not XSS
275 * vectors. (For example, <script> and <style> are not allowed.) See
276 * \Drupal\Component\Utility\Xss::$adminTags for the list of allowed tags. If
277 * your markup needs any of the tags not in this whitelist, then you can
278 * implement a theme hook and/or an asset library. Alternatively, you can use
279 * the key #allowed_tags to alter which tags are filtered.
280 * - #plain_text: Specifies that the array provides text that needs to be
281 * escaped. This value takes precedence over #markup.
282 * - #allowed_tags: If #markup is supplied, this can be used to change which
283 * tags are allowed in the markup. The value is an array of tags that
284 * Xss::filter() would accept. If #plain_text is set, this value is ignored.
288 * $output['admin_filtered_string'] = [
289 * '#markup' => '<em>This is filtered using the admin tag list</em>',
291 * $output['filtered_string'] = [
292 * '#markup' => '<video><source src="v.webm" type="video/webm"></video>',
293 * '#allowed_tags' => ['video', 'source'],
295 * $output['escaped_string'] = [
296 * '#plain_text' => '<em>This is escaped</em>',
300 * @see core.libraries.yml
303 * JavaScript and CSS assets are specified in the render array using the
304 * #attached property (see @ref sec_attached).
306 * @section elements Render elements
307 * Render elements are defined by Drupal core and modules. The primary way to
308 * define a render element is to create a render element plugin. There are
309 * two types of render element plugins:
310 * - Generic elements: Generic render element plugins implement
311 * \Drupal\Core\Render\Element\ElementInterface, are annotated with
312 * \Drupal\Core\Render\Annotation\RenderElement annotation, go in plugin
313 * namespace Element, and generally extend the
314 * \Drupal\Core\Render\Element\RenderElement base class.
315 * - Form input elements: Render elements representing form input elements
316 * implement \Drupal\Core\Render\Element\FormElementInterface, are annotated
317 * with \Drupal\Core\Render\Annotation\FormElement annotation, go in plugin
318 * namespace Element, and generally extend the
319 * \Drupal\Core\Render\Element\FormElement base class.
320 * See the @link plugin_api Plugin API topic @endlink for general information
321 * on plugins. You can search for classes with the RenderElement or FormElement
322 * annotation to discover what render elements are available. API reference
323 * sites (such as https://api.drupal.org) generate lists of all existing
324 * elements from these classes. Look for the Elements link in the API Navigation
327 * Modules can define render elements by defining an element plugin.
329 * @section sec_caching Caching
330 * The Drupal rendering process has the ability to cache rendered output at any
331 * level in a render array hierarchy. This allows expensive calculations to be
332 * done infrequently, and speeds up page loading. See the
333 * @link cache Cache API topic @endlink for general information about the cache
336 * In order to make caching possible, the following information needs to be
338 * - Cache keys: Identifiers for cacheable portions of render arrays. These
339 * should be created and added for portions of a render array that
340 * involve expensive calculations in the rendering process.
341 * - Cache contexts: Contexts that may affect rendering, such as user role and
342 * language. When no context is specified, it means that the render array
343 * does not vary by any context.
344 * - Cache tags: Tags for data that rendering depends on, such as for
345 * individual nodes or user accounts, so that when these change the cache
346 * can be automatically invalidated. If the data consists of entities, you
347 * can use \Drupal\Core\Entity\EntityInterface::getCacheTags() to generate
348 * appropriate tags; configuration objects have a similar method.
349 * - Cache max-age: The maximum duration for which a render array may be cached.
350 * Defaults to \Drupal\Core\Cache\Cache::PERMANENT (permanently cacheable).
352 * Cache information is provided in the #cache property in a render array. In
353 * this property, always supply the cache contexts, tags, and max-age if a
354 * render array varies by context, depends on some modifiable data, or depends
355 * on information that's only valid for a limited time, respectively. Cache keys
356 * should only be set on the portions of a render array that should be cached.
357 * Contexts are automatically replaced with the value for the current request
358 * (e.g. the current language) and combined with the keys to form a cache ID.
359 * The cache contexts, tags, and max-age will be propagated up the render array
360 * hierarchy to determine cacheability for containing render array sections.
362 * Here's an example of what a #cache property might contain:
365 * 'keys' => ['entity_view', 'node', $node->id()],
366 * 'contexts' => ['languages'],
367 * 'tags' => ['node:' . $node->id()],
368 * 'max-age' => Cache::PERMANENT,
372 * At the response level, you'll see X-Drupal-Cache-Contexts and
373 * X-Drupal-Cache-Tags headers.
375 * See https://www.drupal.org/developing/api/8/render/arrays/cacheability for
378 * @section sec_attached Attaching libraries in render arrays
379 * Libraries, JavaScript settings, feeds, HTML <head> tags and HTML <head> links
380 * are attached to elements using the #attached property. The #attached property
381 * is an associative array, where the keys are the attachment types and the
382 * values are the attached data.
384 * The #attached property can also be used to specify HTTP headers and the
385 * response status code.
387 * The #attached property allows loading of asset libraries (which may contain
388 * CSS assets, JavaScript assets, and JavaScript setting assets), JavaScript
389 * settings, feeds, HTML <head> tags and HTML <head> links. Specify an array of
390 * type => value pairs, where the type (most often 'library' — for libraries, or
391 * 'drupalSettings' — for JavaScript settings) to attach these response-level
394 * $build['#attached']['library'][] = 'core/jquery';
395 * $build['#attached']['drupalSettings']['foo'] = 'bar';
396 * $build['#attached']['feed'][] = [$url, $this->t('Feed title')];
399 * See \Drupal\Core\Render\AttachmentsResponseProcessorInterface for additional
402 * See \Drupal\Core\Asset\LibraryDiscoveryParser::parseLibraryInfo() for more
403 * information on how to define libraries.
405 * @section sec_placeholders Placeholders in render arrays
406 * Render arrays have a placeholder mechanism, which can be used to add data
407 * into the render array late in the rendering process. This works in a similar
408 * manner to \Drupal\Component\Render\FormattableMarkup::placeholderFormat(),
409 * with the text that ends up in the #markup property of the element at the
410 * end of the rendering process getting substitutions from placeholders that
411 * are stored in the 'placeholders' element of the #attached property.
413 * For example, after the rest of the rendering process was done, if your
414 * render array contained:
416 * $build['my_element'] = [
417 * '#attached' => ['placeholders' => ['@foo' => 'replacement']],
418 * '#markup' => ['Something about @foo'],
421 * then #markup would end up containing 'Something about replacement'.
423 * Note that each placeholder value can itself be a render array, which will be
424 * rendered, and any cache tags generated during rendering will be added to the
425 * cache tags for the markup.
427 * @section render_pipeline The render pipeline
428 * The term "render pipeline" refers to the process Drupal uses to take
429 * information provided by modules and render it into a response. See
430 * https://www.drupal.org/developing/api/8/render for more details on this
431 * process. For background on routing concepts, see
432 * @link routing Routing API. @endlink
434 * There are in fact multiple render pipelines:
435 * - Drupal always uses the Symfony render pipeline. See
436 * http://symfony.com/doc/2.7/components/http_kernel/introduction.html
437 * - Within the Symfony render pipeline, there is a Drupal render pipeline,
438 * which handles controllers that return render arrays. (Symfony's render
439 * pipeline only knows how to deal with Response objects; this pipeline
440 * converts render arrays into Response objects.) These render arrays are
441 * considered the main content, and can be rendered into multiple formats:
442 * HTML, Ajax, dialog, and modal. Modules can add support for more formats, by
443 * implementing a main content renderer, which is a service tagged with
444 * 'render.main_content_renderer'.
445 * - Finally, within the HTML main content renderer, there is another pipeline,
446 * to allow for rendering the page containing the main content in multiple
447 * ways: no decoration at all (just a page showing the main content) or blocks
448 * (a page with regions, with blocks positioned in regions around the main
449 * content). Modules can provide additional options, by implementing a page
450 * variant, which is a plugin annotated with
451 * \Drupal\Core\Display\Annotation\PageDisplayVariant.
453 * Routes whose controllers return a \Symfony\Component\HttpFoundation\Response
454 * object are fully handled by the Symfony render pipeline.
456 * Routes whose controllers return the "main content" as a render array can be
457 * requested in multiple formats (HTML, JSON, etc.) and/or in a "decorated"
458 * manner, as described above.
461 * @see \Symfony\Component\HttpKernel\KernelEvents::VIEW
462 * @see \Drupal\Core\EventSubscriber\MainContentViewSubscriber
463 * @see \Drupal\Core\Render\MainContent\MainContentRendererInterface
464 * @see \Drupal\Core\Render\MainContent\HtmlRenderer
465 * @see \Drupal\Core\Render\RenderEvents::SELECT_PAGE_DISPLAY_VARIANT
466 * @see \Drupal\Core\Render\Plugin\DisplayVariant\SimplePageVariant
467 * @see \Drupal\block\Plugin\DisplayVariant\BlockPageVariant
468 * @see \Drupal\Core\Render\BareHtmlPageRenderer
474 * @defgroup listing_page_element Page header for Elements page
476 * Introduction to form and render elements
478 * Render elements are referenced in render arrays. Render arrays contain data
479 * to be rendered, along with meta-data and attributes that specify how to
480 * render the data into markup; see the
481 * @link theme_render Render API topic @endlink for an overview of render
482 * arrays and render elements. Form arrays are a subset of render arrays,
483 * representing HTML forms; form elements are a subset of render elements,
484 * representing HTML elements for forms. See the
485 * @link form_api Form API topic @endlink for an overview of forms, form
486 * processing, and form arrays.
488 * Each form and render element type corresponds to an element plugin class;
489 * each of them either extends \Drupal\Core\Render\Element\RenderElement
490 * (render elements) or \Drupal\Core\Render\Element\FormElement (form
491 * elements). Usage and properties are documented on the individual classes,
492 * and the two base classes list common properties shared by all render
493 * elements and the form element subset, respectively.
497 * @see \Drupal\Core\Render\Element\RenderElement
498 * @see \Drupal\Core\Render\Element\FormElement
509 * Allow themes to alter the theme-specific settings form.
511 * With this hook, themes can alter the theme-specific settings form in any way
512 * allowable by Drupal's Form API, such as adding form elements, changing
513 * default values and removing form elements. See the Form API documentation on
514 * api.drupal.org for detailed information.
516 * Note that the base theme's form alterations will be run before any sub-theme
520 * Nested array of form elements that comprise the form.
522 * The current state of the form.
524 function hook_form_system_theme_settings_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state) {
525 // Add a checkbox to toggle the breadcrumb trail.
526 $form['toggle_breadcrumb'] = [
527 '#type' => 'checkbox',
528 '#title' => t('Display the breadcrumb'),
529 '#default_value' => theme_get_setting('features.breadcrumb'),
530 '#description' => t('Show a trail of links from the homepage to the current page.'),
535 * Preprocess theme variables for templates.
537 * This hook allows modules to preprocess theme variables for theme templates.
538 * It is called for all theme hooks implemented as templates, but not for theme
539 * hooks implemented as functions. hook_preprocess_HOOK() can be used to
540 * preprocess variables for a specific theme hook, whether implemented as a
541 * template or function.
543 * For more detailed information, see the
544 * @link themeable Theme system overview topic @endlink.
547 * The variables array (modify in place).
549 * The name of the theme hook.
551 function hook_preprocess(&$variables, $hook) {
554 // Add contextual links to the variables, if the user has permission.
556 if (!\Drupal::currentUser()->hasPermission('access contextual links')) {
560 if (!isset($hooks)) {
561 $hooks = theme_get_registry();
564 // Determine the primary theme function argument.
565 if (isset($hooks[$hook]['variables'])) {
566 $keys = array_keys($hooks[$hook]['variables']);
570 $key = $hooks[$hook]['render element'];
573 if (isset($variables[$key])) {
574 $element = $variables[$key];
577 if (isset($element) && is_array($element) && !empty($element['#contextual_links'])) {
578 $variables['title_suffix']['contextual_links'] = contextual_links_view($element);
579 if (!empty($variables['title_suffix']['contextual_links'])) {
580 $variables['attributes']['class'][] = 'contextual-links-region';
586 * Preprocess theme variables for a specific theme hook.
588 * This hook allows modules to preprocess theme variables for a specific theme
589 * hook. It should only be used if a module needs to override or add to the
590 * theme preprocessing for a theme hook it didn't define.
592 * For more detailed information, see the
593 * @link themeable Theme system overview topic @endlink.
596 * The variables array (modify in place).
598 function hook_preprocess_HOOK(&$variables) {
599 // This example is from rdf_preprocess_image(). It adds an RDF attribute
600 // to the image hook's variables.
601 $variables['attributes']['typeof'] = ['foaf:Image'];
605 * Provides alternate named suggestions for a specific theme hook.
607 * This hook allows modules to provide alternative theme function or template
610 * HOOK is the least-specific version of the hook being called. For example, if
611 * '#theme' => 'node__article' is called, then hook_theme_suggestions_node()
612 * will be invoked, not hook_theme_suggestions_node__article(). The specific
613 * hook called (in this case 'node__article') is available in
614 * $variables['theme_hook_original'].
616 * @todo Add @code sample.
618 * @param array $variables
619 * An array of variables passed to the theme hook. Note that this hook is
620 * invoked before any preprocessing.
623 * An array of theme suggestions.
625 * @see hook_theme_suggestions_HOOK_alter()
627 function hook_theme_suggestions_HOOK(array $variables) {
630 $suggestions[] = 'node__' . $variables['elements']['#langcode'];
636 * Alters named suggestions for all theme hooks.
638 * This hook is invoked for all theme hooks, if you are targeting a specific
639 * theme hook it's best to use hook_theme_suggestions_HOOK_alter().
641 * The call order is as follows: all existing suggestion alter functions are
642 * called for module A, then all for module B, etc., followed by all for any
643 * base theme(s), and finally for the active theme. The order is
644 * determined by system weight, then by extension (module or theme) name.
646 * Within each module or theme, suggestion alter hooks are called in the
647 * following order: first, hook_theme_suggestions_alter(); second,
648 * hook_theme_suggestions_HOOK_alter(). So, for each module or theme, the more
649 * general hooks are called first followed by the more specific.
651 * In the following example, we provide an alternative template suggestion to
652 * node and taxonomy term templates based on the user being logged in.
654 * function MYMODULE_theme_suggestions_alter(array &$suggestions, array $variables, $hook) {
655 * if (\Drupal::currentUser()->isAuthenticated() && in_array($hook, array('node', 'taxonomy_term'))) {
656 * $suggestions[] = $hook . '__' . 'logged_in';
662 * @param array $suggestions
663 * An array of alternate, more specific names for template files or theme
665 * @param array $variables
666 * An array of variables passed to the theme hook. Note that this hook is
667 * invoked before any variable preprocessing.
668 * @param string $hook
669 * The base hook name. For example, if '#theme' => 'node__article' is called,
670 * then $hook will be 'node', not 'node__article'. The specific hook called
671 * (in this case 'node__article') is available in
672 * $variables['theme_hook_original'].
675 * An array of theme suggestions.
677 * @see hook_theme_suggestions_HOOK_alter()
679 function hook_theme_suggestions_alter(array &$suggestions, array $variables, $hook) {
680 // Add an interface-language specific suggestion to all theme hooks.
681 $suggestions[] = $hook . '__' . \Drupal::languageManager()->getCurrentLanguage()->getId();
685 * Alters named suggestions for a specific theme hook.
687 * This hook allows any module or theme to provide alternative theme function or
688 * template name suggestions and reorder or remove suggestions provided by
689 * hook_theme_suggestions_HOOK() or by earlier invocations of this hook.
691 * HOOK is the least-specific version of the hook being called. For example, if
692 * '#theme' => 'node__article' is called, then node_theme_suggestions_node()
693 * will be invoked, not node_theme_suggestions_node__article(). The specific
694 * hook called (in this case 'node__article') is available in
695 * $variables['theme_hook_original'].
697 * @todo Add @code sample.
699 * @param array $suggestions
700 * An array of theme suggestions.
701 * @param array $variables
702 * An array of variables passed to the theme hook. Note that this hook is
703 * invoked before any preprocessing.
705 * @see hook_theme_suggestions_alter()
706 * @see hook_theme_suggestions_HOOK()
708 function hook_theme_suggestions_HOOK_alter(array &$suggestions, array $variables) {
709 if (empty($variables['header'])) {
710 $suggestions[] = 'hookname__' . 'no_header';
715 * Respond to themes being installed.
717 * @param array $theme_list
718 * Array containing the names of the themes being installed.
720 * @see \Drupal\Core\Extension\ThemeHandler::install()
722 function hook_themes_installed($theme_list) {
723 foreach ($theme_list as $theme) {
724 block_theme_initialize($theme);
729 * Respond to themes being uninstalled.
731 * @param array $theme_list
732 * Array containing the names of the themes being uninstalled.
734 * @see \Drupal\Core\Extension\ThemeHandler::uninstall()
736 function hook_themes_uninstalled(array $themes) {
737 // Remove some state entries depending on the theme.
738 foreach ($themes as $theme) {
739 \Drupal::state()->delete('example.' . $theme);
744 * Declare a template file extension to be used with a theme engine.
746 * This hook is used in a theme engine implementation in the format of
747 * ENGINE_extension().
750 * The file extension the theme engine will recognize.
752 function hook_extension() {
753 // Extension for template base names in Twig.
758 * Render a template using the theme engine.
760 * @param string $template_file
761 * The path (relative to the Drupal root directory) to the template to be
762 * rendered including its extension in the format 'path/to/TEMPLATE_NAME.EXT'.
763 * @param array $variables
764 * A keyed array of variables that are available for composing the output. The
765 * theme engine is responsible for passing all the variables to the template.
766 * Depending on the code in the template, all or just a subset of the
767 * variables might be used in the template.
770 * The output generated from the template. In most cases this will be a string
771 * containing HTML markup.
773 function hook_render_template($template_file, $variables) {
774 $twig_service = \Drupal::service('twig');
776 return $twig_service->loadTemplate($template_file)->render($variables);
780 * Alter the element type information returned from modules.
782 * A module may implement this hook in order to alter the element type defaults
783 * defined by a module.
786 * An associative array with structure identical to that of the return value
787 * of \Drupal\Core\Render\ElementInfoManagerInterface::getInfo().
789 * @see \Drupal\Core\Render\ElementInfoManager
790 * @see \Drupal\Core\Render\Element\ElementInterface
792 function hook_element_info_alter(array &$info) {
793 // Decrease the default size of textfields.
794 if (isset($info['textfield']['#size'])) {
795 $info['textfield']['#size'] = 40;
800 * Perform necessary alterations to the JavaScript before it is presented on
804 * An array of all JavaScript being presented on the page.
805 * @param \Drupal\Core\Asset\AttachedAssetsInterface $assets
806 * The assets attached to the current response.
808 * @see drupal_js_defaults()
809 * @see \Drupal\Core\Asset\AssetResolver
811 function hook_js_alter(&$javascript, \Drupal\Core\Asset\AttachedAssetsInterface $assets) {
812 // Swap out jQuery to use an updated version of the library.
813 $javascript['core/assets/vendor/jquery/jquery.min.js']['data'] = drupal_get_path('module', 'jquery_update') . '/jquery.js';
817 * Add dynamic library definitions.
819 * Modules may implement this hook to add dynamic library definitions. Static
820 * libraries, which do not depend on any runtime information, should be declared
821 * in a modulename.libraries.yml file instead.
824 * An array of library definitions to register, keyed by library ID. The
825 * library ID will be prefixed with the module name automatically.
827 * @see core.libraries.yml
828 * @see hook_library_info_alter()
830 function hook_library_info_build() {
832 // Add a library whose information changes depending on certain conditions.
833 $libraries['mymodule.zombie'] = [
838 if (Drupal::moduleHandler()->moduleExists('minifyzombies')) {
839 $libraries['mymodule.zombie'] += [
841 'mymodule.zombie.min.js' => [],
845 'mymodule.zombie.min.css' => [],
851 $libraries['mymodule.zombie'] += [
853 'mymodule.zombie.js' => [],
857 'mymodule.zombie.css' => [],
863 // Add a library only if a certain condition is met. If code wants to
864 // integrate with this library it is safe to (try to) load it unconditionally
865 // without reproducing this check. If the library definition does not exist
866 // the library (of course) not be loaded but no notices or errors will be
868 if (Drupal::moduleHandler()->moduleExists('vampirize')) {
869 $libraries['mymodule.vampire'] = [
871 'js/vampire.js' => [],
887 * Modify the JavaScript settings (drupalSettings).
889 * @param array &$settings
890 * An array of all JavaScript settings (drupalSettings) being presented on the
892 * @param \Drupal\Core\Asset\AttachedAssetsInterface $assets
893 * The assets attached to the current response.
895 * @see \Drupal\Core\Asset\AssetResolver
897 * The results of this hook are cached, however modules may use
898 * hook_js_settings_alter() to dynamically alter settings.
900 function hook_js_settings_build(array &$settings, \Drupal\Core\Asset\AttachedAssetsInterface $assets) {
901 // Manipulate settings.
902 if (isset($settings['dialog'])) {
903 $settings['dialog']['autoResize'] = FALSE;
908 * Perform necessary alterations to the JavaScript settings (drupalSettings).
910 * @param array &$settings
911 * An array of all JavaScript settings (drupalSettings) being presented on the
913 * @param \Drupal\Core\Asset\AttachedAssetsInterface $assets
914 * The assets attached to the current response.
916 * @see \Drupal\Core\Asset\AssetResolver
918 function hook_js_settings_alter(array &$settings, \Drupal\Core\Asset\AttachedAssetsInterface $assets) {
920 $settings['user']['uid'] = \Drupal::currentUser();
922 // Manipulate settings.
923 if (isset($settings['dialog'])) {
924 $settings['dialog']['autoResize'] = FALSE;
929 * Alter libraries provided by an extension.
931 * Allows modules and themes to change libraries' definitions; mostly used to
932 * update a library to a newer version, while ensuring backward compatibility.
933 * In general, such manipulations should only be done to extend the library's
934 * functionality in a backward-compatible way, to avoid breaking other modules
935 * and themes that may be using the library.
937 * @param array $libraries
938 * An associative array of libraries registered by $extension. Keyed by
939 * internal library name and passed by reference.
940 * @param string $extension
941 * Can either be 'core' or the machine name of the extension that registered
944 * @see \Drupal\Core\Asset\LibraryDiscoveryParser::parseLibraryInfo()
946 function hook_library_info_alter(&$libraries, $extension) {
947 // Update Farbtastic to version 2.0.
948 if ($extension == 'core' && isset($libraries['jquery.farbtastic'])) {
949 // Verify existing version is older than the one we are updating to.
950 if (version_compare($libraries['jquery.farbtastic']['version'], '2.0', '<')) {
951 // Update the existing Farbtastic to version 2.0.
952 $libraries['jquery.farbtastic']['version'] = '2.0';
953 // To accurately replace library files, the order of files and the options
954 // of each file have to be retained; e.g., like this:
955 $old_path = 'assets/vendor/farbtastic';
956 // Since the replaced library files are no longer located in a directory
957 // relative to the original extension, specify an absolute path (relative
958 // to DRUPAL_ROOT / base_path()) to the new location.
959 $new_path = '/' . drupal_get_path('module', 'farbtastic_update') . '/js';
962 $old_path . '/farbtastic.js' => $new_path . '/farbtastic-2.0.js',
964 foreach ($libraries['jquery.farbtastic']['js'] as $source => $options) {
965 if (isset($replacements[$source])) {
966 $new_js[$replacements[$source]] = $options;
969 $new_js[$source] = $options;
972 $libraries['jquery.farbtastic']['js'] = $new_js;
978 * Alter CSS files before they are output on the page.
981 * An array of all CSS items (files and inline CSS) being requested on the page.
982 * @param \Drupal\Core\Asset\AttachedAssetsInterface $assets
983 * The assets attached to the current response.
985 * @see Drupal\Core\Asset\LibraryResolverInterface::getCssAssets()
987 function hook_css_alter(&$css, \Drupal\Core\Asset\AttachedAssetsInterface $assets) {
988 // Remove defaults.css file.
989 unset($css[drupal_get_path('module', 'system') . '/defaults.css']);
993 * Add attachments (typically assets) to a page before it is rendered.
995 * Use this hook when you want to conditionally add attachments to a page.
997 * If you want to alter the attachments added by other modules or if your module
998 * depends on the elements of other modules, use hook_page_attachments_alter()
999 * instead, which runs after this hook.
1001 * If you try to add anything but #attached and #cache to the array, an
1002 * exception is thrown.
1004 * @param array &$attachments
1005 * An array that you can add attachments to.
1007 * @see hook_page_attachments_alter()
1009 function hook_page_attachments(array &$attachments) {
1010 // Unconditionally attach an asset to the page.
1011 $attachments['#attached']['library'][] = 'core/domready';
1013 // Conditionally attach an asset to the page.
1014 if (!\Drupal::currentUser()->hasPermission('may pet kittens')) {
1015 $attachments['#attached']['library'][] = 'core/jquery';
1020 * Alter attachments (typically assets) to a page before it is rendered.
1022 * Use this hook when you want to remove or alter attachments on the page, or
1023 * add attachments to the page that depend on another module's attachments (this
1024 * hook runs after hook_page_attachments().
1026 * If you try to add anything but #attached and #cache to the array, an
1027 * exception is thrown.
1029 * @param array &$attachments
1030 * Array of all attachments provided by hook_page_attachments() implementations.
1032 * @see hook_page_attachments()
1034 function hook_page_attachments_alter(array &$attachments) {
1035 // Conditionally remove an asset.
1036 if (in_array('core/jquery', $attachments['#attached']['library'])) {
1037 $index = array_search('core/jquery', $attachments['#attached']['library']);
1038 unset($attachments['#attached']['library'][$index]);
1043 * Add a renderable array to the top of the page.
1045 * @param array $page_top
1046 * A renderable array representing the top of the page.
1048 function hook_page_top(array &$page_top) {
1049 $page_top['mymodule'] = ['#markup' => 'This is the top.'];
1053 * Add a renderable array to the bottom of the page.
1055 * @param array $page_bottom
1056 * A renderable array representing the bottom of the page.
1058 function hook_page_bottom(array &$page_bottom) {
1059 $page_bottom['mymodule'] = ['#markup' => 'This is the bottom.'];
1063 * Register a module or theme's theme implementations.
1065 * The implementations declared by this hook specify how a particular render
1066 * array is to be rendered as HTML.
1068 * @param array $existing
1069 * An array of existing implementations that may be used for override
1070 * purposes. This is primarily useful for themes that may wish to examine
1071 * existing implementations to extract data (such as arguments) so that
1072 * it may properly register its own, higher priority implementations.
1074 * Whether a theme, module, etc. is being processed. This is primarily useful
1075 * so that themes tell if they are the actual theme being called or a parent
1076 * theme. May be one of:
1077 * - 'module': A module is being checked for theme implementations.
1078 * - 'base_theme_engine': A theme engine is being checked for a theme that is
1079 * a parent of the actual theme being used.
1080 * - 'theme_engine': A theme engine is being checked for the actual theme
1082 * - 'base_theme': A base theme is being checked for theme implementations.
1083 * - 'theme': The actual theme in use is being checked.
1085 * The actual name of theme, module, etc. that is being being processed.
1087 * The directory path of the theme or module, so that it doesn't need to be
1091 * An associative array of information about theme implementations. The keys
1092 * on the outer array are known as "theme hooks". For theme suggestions,
1093 * instead of the array key being the base theme hook, the key is a theme
1094 * suggestion name with the format 'base_hook_name__sub_hook_name'.
1095 * For render elements, the key is the machine name of the render element.
1096 * The array values are themselves arrays containing information about the
1097 * theme hook and its implementation. Each information array must contain
1098 * either a 'variables' element (for using a #theme element) or a
1099 * 'render element' element (for render elements), but not both.
1100 * The following elements may be part of each information array:
1101 * - variables: Only used for #theme in render array: an array of variables,
1102 * where the array keys are the names of the variables, and the array
1103 * values are the default values if they are not given in the render array.
1104 * Template implementations receive each array key as a variable in the
1105 * template file (so they must be legal PHP/Twig variable names). Function
1106 * implementations are passed the variables in a single $variables function
1107 * argument. If you are using these variables in a render array, prefix the
1108 * variable names defined here with a #.
1109 * - render element: Used for render element items only: the name of the
1110 * renderable element or element tree to pass to the theme function. This
1111 * name is used as the name of the variable that holds the renderable
1112 * element or tree in preprocess and process functions.
1113 * - file: The file the implementation resides in. This file will be included
1114 * prior to the theme being rendered, to make sure that the function or
1115 * preprocess function (as needed) is actually loaded.
1116 * - path: Override the path of the file to be used. Ordinarily the module or
1117 * theme path will be used, but if the file will not be in the default
1118 * path, include it here. This path should be relative to the Drupal root
1120 * - template: If specified, the theme implementation is a template file, and
1121 * this is the template name. Do not add 'html.twig' on the end of the
1122 * template name. The extension will be added automatically by the default
1123 * rendering engine (which is Twig.) If 'path' is specified, 'template'
1124 * should also be specified. If neither 'template' nor 'function' are
1125 * specified, a default template name will be assumed. For example, if a
1126 * module registers the 'search_result' theme hook, 'search-result' will be
1127 * assigned as its template name.
1128 * - function: (deprecated in Drupal 8.0.x, will be removed in Drupal 9.0.x)
1129 * If specified, this will be the function name to invoke for this
1130 * implementation. If neither 'template' nor 'function' are specified, a
1131 * default template name will be assumed. See above for more details.
1132 * - base hook: Used for theme suggestions only: the base theme hook name.
1133 * Instead of this suggestion's implementation being used directly, the base
1134 * hook will be invoked with this implementation as its first suggestion.
1135 * The base hook's files will be included and the base hook's preprocess
1136 * functions will be called in addition to any suggestion's preprocess
1137 * functions. If an implementation of hook_theme_suggestions_HOOK() (where
1138 * HOOK is the base hook) changes the suggestion order, a different
1139 * suggestion may be used in place of this suggestion. If after
1140 * hook_theme_suggestions_HOOK() this suggestion remains the first
1141 * suggestion, then this suggestion's function or template will be used to
1142 * generate the rendered output.
1143 * - pattern: A regular expression pattern to be used to allow this theme
1144 * implementation to have a dynamic name. The convention is to use __ to
1145 * differentiate the dynamic portion of the theme. For example, to allow
1146 * forums to be themed individually, the pattern might be: 'forum__'. Then,
1147 * when the forum is rendered, following render array can be used:
1149 * $render_array = array(
1150 * '#theme' => array('forum__' . $tid, 'forum'),
1151 * '#forum' => $forum,
1154 * - preprocess functions: A list of functions used to preprocess this data.
1155 * Ordinarily this won't be used; it's automatically filled in. By default,
1156 * for a module this will be filled in as template_preprocess_HOOK. For
1157 * a theme this will be filled in as twig_preprocess and
1158 * twig_preprocess_HOOK as well as themename_preprocess and
1159 * themename_preprocess_HOOK.
1160 * - override preprocess functions: Set to TRUE when a theme does NOT want
1161 * the standard preprocess functions to run. This can be used to give a
1162 * theme FULL control over how variables are set. For example, if a theme
1163 * wants total control over how certain variables in the page.html.twig are
1164 * set, this can be set to true. Please keep in mind that when this is used
1165 * by a theme, that theme becomes responsible for making sure necessary
1166 * variables are set.
1167 * - type: (automatically derived) Where the theme hook is defined:
1168 * 'module', 'theme_engine', or 'theme'.
1169 * - theme path: (automatically derived) The directory path of the theme or
1170 * module, so that it doesn't need to be looked up.
1173 * @see hook_theme_registry_alter()
1175 function hook_theme($existing, $type, $theme, $path) {
1177 'forum_display' => [
1178 'variables' => ['forums' => NULL, 'topics' => NULL, 'parents' => NULL, 'tid' => NULL, 'sortby' => NULL, 'forum_per_page' => NULL],
1181 'variables' => ['forums' => NULL, 'parents' => NULL, 'tid' => NULL],
1184 'variables' => ['new_posts' => NULL, 'num_posts' => 0, 'comment_mode' => 0, 'sticky' => 0],
1186 'status_report' => [
1187 'render element' => 'requirements',
1188 'file' => 'system.admin.inc',
1194 * Alter the theme registry information returned from hook_theme().
1196 * The theme registry stores information about all available theme hooks,
1197 * including which callback functions those hooks will call when triggered,
1198 * what template files are exposed by these hooks, and so on.
1200 * Note that this hook is only executed as the theme cache is re-built.
1201 * Changes here will not be visible until the next cache clear.
1203 * The $theme_registry array is keyed by theme hook name, and contains the
1204 * information returned from hook_theme(), as well as additional properties
1205 * added by \Drupal\Core\Theme\Registry::processExtension().
1209 * $theme_registry['block_content_add_list'] = array (
1210 * 'template' => 'block-content-add-list',
1211 * 'path' => 'core/themes/seven/templates',
1212 * 'type' => 'theme_engine',
1213 * 'theme path' => 'core/themes/seven',
1214 * 'includes' => array (
1215 * 0 => 'core/modules/block_content/block_content.pages.inc',
1217 * 'variables' => array (
1218 * 'content' => NULL,
1220 * 'preprocess functions' => array (
1221 * 0 => 'template_preprocess',
1222 * 1 => 'template_preprocess_block_content_add_list',
1223 * 2 => 'contextual_preprocess',
1224 * 3 => 'seven_preprocess_block_content_add_list',
1229 * @param $theme_registry
1230 * The entire cache of theme registry information, post-processing.
1233 * @see \Drupal\Core\Theme\Registry::processExtension()
1235 function hook_theme_registry_alter(&$theme_registry) {
1236 // Kill the next/previous forum topic navigation links.
1237 foreach ($theme_registry['forum_topic_navigation']['preprocess functions'] as $key => $value) {
1238 if ($value == 'template_preprocess_forum_topic_navigation') {
1239 unset($theme_registry['forum_topic_navigation']['preprocess functions'][$key]);
1245 * Alter the default, hook-independent variables for all templates.
1247 * Allows modules to provide additional default template variables or manipulate
1248 * existing. This hook is invoked from template_preprocess() after basic default
1249 * template variables have been set up and before the next template preprocess
1250 * function is invoked.
1252 * Note that the default template variables are statically cached within a
1253 * request. When adding a template variable that depends on other context, it is
1254 * your responsibility to appropriately reset the static cache in
1255 * template_preprocess() when needed:
1257 * drupal_static_reset('template_preprocess');
1260 * See user_template_preprocess_default_variables_alter() for an example.
1262 * @param array $variables
1263 * An associative array of default template variables, as set up by
1264 * _template_preprocess_default_variables(). Passed by reference.
1266 * @see template_preprocess()
1267 * @see _template_preprocess_default_variables()
1269 function hook_template_preprocess_default_variables_alter(&$variables) {
1270 $variables['is_admin'] = \Drupal::currentUser()->hasPermission('access administration pages');
1274 * @} End of "addtogroup hooks".