/**
* Builds the theme registry cache.
*
* Theme hook definitions are collected in the following order:
* - Modules
* - Base theme engines
* - Base themes
* - Theme engine
* - Theme
*
* All theme hook definitions are essentially just collated and merged in the
* above order. However, various extension-specific default values and
* customizations are required; e.g., to record the effective file path for
* theme template. Therefore, this method first collects all extensions per
* type, and then dispatches the processing for each extension to
* processExtension().
*
* After completing the collection, modules are allowed to alter it. Lastly,
* any derived and incomplete theme hook definitions that are hook suggestions
* for base hooks (e.g., 'block__node' for the base hook 'block') need to be
* determined based on the full registry and classified as 'base hook'.
*
* See the @link themeable Default theme implementations topic @endlink for
* details.
*
* @return \Drupal\Core\Utility\ThemeRegistry
* The build theme registry.
*
* @see hook_theme_registry_alter()
*/
protected function build()
{
$cache = array();
// First, preprocess the theme hooks advertised by modules. This will
// serve as the basic registry. Since the list of enabled modules is the
// same regardless of the theme used, this is cached in its own entry to
// save building it for every theme.
if ($cached = $this->cache->get('theme_registry:build:modules')) {
$cache = $cached->data;
} else {
foreach ($this->moduleHandler->getImplementations('theme') as $module) {
$this->processExtension($cache, $module, 'module', $module, $this->getPath($module));
}
// Only cache this registry if all modules are loaded.
if ($this->moduleHandler->isLoaded()) {
$this->cache->set("theme_registry:build:modules", $cache, Cache::PERMANENT, array('theme_registry'));
}
}
// Process each base theme.
// Ensure that we start with the root of the parents, so that both CSS files
// and preprocess functions comes first.
foreach (array_reverse($this->theme->getBaseThemes()) as $base) {
// If the base theme uses a theme engine, process its hooks.
$base_path = $base->getPath();
if ($this->theme->getEngine()) {
$this->processExtension($cache, $this->theme->getEngine(), 'base_theme_engine', $base->getName(), $base_path);
}
$this->processExtension($cache, $base->getName(), 'base_theme', $base->getName(), $base_path);
}
// And then the same thing, but for the theme.
if ($this->theme->getEngine()) {
$this->processExtension($cache, $this->theme->getEngine(), 'theme_engine', $this->theme->getName(), $this->theme->getPath());
}
// Hooks provided by the theme itself.
$this->processExtension($cache, $this->theme->getName(), 'theme', $this->theme->getName(), $this->theme->getPath());
// Discover and add all preprocess functions for theme hook suggestions.
$this->postProcessExtension($cache, $this->theme);
// Let modules and themes alter the registry.
$this->moduleHandler->alter('theme_registry', $cache);
$this->themeManager->alterForTheme($this->theme, 'theme_registry', $cache);
// @todo Implement more reduction of the theme registry entry.
// Optimize the registry to not have empty arrays for functions.
foreach ($cache as $hook => $info) {
if (empty($info['preprocess functions'])) {
unset($cache[$hook]['preprocess functions']);
}
}
$this->registry[$this->theme->getName()] = $cache;
return $this->registry[$this->theme->getName()];
}