wikimedia/mediawiki-core

View on GitHub
includes/content/ContentHandler.php

Summary

Maintainability
F
5 days
Test Coverage
<?php

/**
 * Base class for content handling.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @since 1.21
 *
 * @file
 * @ingroup Content
 *
 * @author Daniel Kinzler
 */

use MediaWiki\CommentStore\CommentStore;
use MediaWiki\Content\Renderer\ContentParseParams;
use MediaWiki\Content\Transform\PreloadTransformParams;
use MediaWiki\Content\Transform\PreSaveTransformParams;
use MediaWiki\Content\ValidationParams;
use MediaWiki\Context\IContextSource;
use MediaWiki\Context\RequestContext;
use MediaWiki\Deferred\DeferrableUpdate;
use MediaWiki\Diff\TextDiffer\ManifoldTextDiffer;
use MediaWiki\HookContainer\HookRunner;
use MediaWiki\HookContainer\ProtectedHookAccessorTrait;
use MediaWiki\Logger\LoggerFactory;
use MediaWiki\MainConfigNames;
use MediaWiki\MediaWikiServices;
use MediaWiki\Page\ParserOutputAccess;
use MediaWiki\Parser\ParserOutput;
use MediaWiki\Revision\RevisionRecord;
use MediaWiki\Revision\SlotRecord;
use MediaWiki\Revision\SlotRenderingProvider;
use MediaWiki\Search\ParserOutputSearchDataExtractor;
use MediaWiki\Title\Title;
use Wikimedia\Assert\Assert;
use Wikimedia\ScopedCallback;

/**
 * A content handler knows how do deal with a specific type of content on a wiki
 * page. Content is stored in the database in a serialized form (using a
 * serialization format a.k.a. MIME type) and is unserialized into its native
 * PHP representation (the content model), which is wrapped in an instance of
 * the appropriate subclass of Content.
 *
 * ContentHandler instances are stateless singletons that serve, among other
 * things, as a factory for Content objects. Generally, there is one subclass
 * of ContentHandler and one subclass of Content for every type of content model.
 *
 * Some content types have a flat model, that is, their native representation
 * is the same as their serialized form. Examples would be JavaScript and CSS
 * code. As of now, this also applies to wikitext (MediaWiki's default content
 * type), but wikitext content may be represented by a DOM or AST structure in
 * the future.
 *
 * @stable to extend
 *
 * @ingroup Content
 */
abstract class ContentHandler {
    use ProtectedHookAccessorTrait;

    /**
     * Convenience function for getting flat text from a Content object. This
     * should only be used in the context of backwards compatibility with code
     * that is not yet able to handle Content objects!
     *
     * If $content is null, this method returns the empty string.
     *
     * If $content is an instance of TextContent, this method returns the flat
     * text as returned by $content->getText().
     *
     * If $content is not a TextContent object, this method returns null.
     *
     * @since 1.21
     *
     * @deprecated since 1.37, use Content::getText() for TextContent instances
     * instead. Hard deprecated since 1.43.
     *
     * @param Content|null $content
     * @return string|null Textual form of the content, if available.
     */
    public static function getContentText( Content $content = null ) {
        wfDeprecated( __METHOD__, '1.37' );
        if ( $content === null ) {
            return '';
        }

        if ( $content instanceof TextContent ) {
            return $content->getText();
        }

        wfDebugLog( 'ContentHandler', 'Accessing ' . $content->getModel() . ' content as text!' );
        return null;
    }

    /**
     * Convenience function for creating a Content object from a given textual
     * representation.
     *
     * $text will be deserialized into a Content object of the model specified
     * by $modelId (or, if that is not given, $title->getContentModel()) using
     * the given format.
     *
     * @since 1.21
     *
     * @param string $text The textual representation, will be
     *    unserialized to create the Content object
     * @param Title|null $title The title of the page this text belongs to.
     *    Required if $modelId is not provided.
     * @param string|null $modelId The model to deserialize to. If not provided,
     *    $title->getContentModel() is used.
     * @param string|null $format The format to use for deserialization. If not
     *    given, the model's default format is used.
     *
     * @throws MWContentSerializationException
     * @throws MWUnknownContentModelException
     * @return Content A Content object representing the text.
     */
    public static function makeContent( $text, Title $title = null,
        $modelId = null, $format = null ) {
        if ( !$title && !$modelId ) {
            throw new InvalidArgumentException( "Must provide a Title object or a content model ID." );
        }

        return MediaWikiServices::getInstance()
            ->getContentHandlerFactory()
            ->getContentHandler( $modelId ?? $title->getContentModel() )
            ->unserializeContent( $text, $format );
    }

    /**
     * Returns the name of the default content model to be used for the page
     * with the given title.
     *
     * Note: There should rarely be need to call this method directly.
     * To determine the actual content model for a given page, use
     * Title::getContentModel().
     *
     * Which model is to be used by default for the page is determined based
     * on several factors:
     * - The global setting $wgNamespaceContentModels specifies a content model
     *   per namespace.
     * - The hook ContentHandlerDefaultModelFor may be used to override the page's default
     *   model.
     * - Pages in NS_MEDIAWIKI and NS_USER default to the CSS or JavaScript
     *   model if they end in .js or .css, respectively.
     * - Pages in NS_MEDIAWIKI default to the wikitext model otherwise.
     * - The hook TitleIsCssOrJsPage may be used to force a page to use the CSS
     *   or JavaScript model. This is a compatibility feature. The ContentHandlerDefaultModelFor
     *   hook should be used instead if possible.
     * - The hook TitleIsWikitextPage may be used to force a page to use the
     *   wikitext model. This is a compatibility feature. The ContentHandlerDefaultModelFor
     *   hook should be used instead if possible.
     *
     * If none of the above applies, the wikitext model is used.
     *
     * @since 1.21
     * @deprecated since 1.33, use SlotRoleHandler::getDefaultModel() together with
     *   SlotRoleRegistry::getRoleHandler(). Hard deprecated since 1.43.
     *
     * @param Title $title
     *
     * @return string Default model name for the page given by $title
     */
    public static function getDefaultModelFor( Title $title ) {
        wfDeprecated( __METHOD__, '1.33' );
        $slotRoleregistry = MediaWikiServices::getInstance()->getSlotRoleRegistry();
        $mainSlotHandler = $slotRoleregistry->getRoleHandler( 'main' );
        return $mainSlotHandler->getDefaultModel( $title );
    }

    /**
     * Returns the appropriate ContentHandler singleton for the given Content
     * object.
     *
     * @deprecated since 1.35, instead use
     *   ContentHandlerFactory::getContentHandler( $content->getModel() ).
     *   Hard deprecated since 1.43.
     *
     * @since 1.21
     *
     * @param Content $content
     *
     * @return ContentHandler
     * @throws MWUnknownContentModelException
     */
    public static function getForContent( Content $content ) {
        wfDeprecated( __METHOD__, '1.35' );
        return MediaWikiServices::getInstance()
            ->getContentHandlerFactory()
            ->getContentHandler( $content->getModel() );
    }

    /**
     * Returns the ContentHandler singleton for the given model ID. Use the
     * CONTENT_MODEL_XXX constants to identify the desired content model.
     *
     * ContentHandler singletons are taken from the global $wgContentHandlers
     * array. Keys in that array are model names, the values are either
     * ContentHandler singleton objects, or strings specifying the appropriate
     * subclass of ContentHandler.
     *
     * If a class name is encountered when looking up the singleton for a given
     * model name, the class is instantiated and the class name is replaced by
     * the resulting singleton in $wgContentHandlers.
     *
     * If no ContentHandler is defined for the desired $modelId, the
     * ContentHandler may be provided by the ContentHandlerForModelID hook.
     * If no ContentHandler can be determined, an MWUnknownContentModelException is raised.
     *
     * @since 1.21
     *
     * @deprecated since 1.35, use ContentHandlerFactory::getContentHandler
     *   Hard deprecated since 1.43.
     * @see  ContentHandlerFactory::getContentHandler()
     *
     * @param string $modelId The ID of the content model for which to get a
     *    handler. Use CONTENT_MODEL_XXX constants.
     *
     * @throws MWUnknownContentModelException If no handler is known for the model ID.
     * @return ContentHandler The ContentHandler singleton for handling the model given by the ID.
     */
    public static function getForModelID( $modelId ) {
        wfDeprecated( __METHOD__, '1.35' );
        return MediaWikiServices::getInstance()
            ->getContentHandlerFactory()
            ->getContentHandler( $modelId );
    }

    /**
     * Returns the localized name for a given content model.
     *
     * Model names are localized using system messages. Message keys
     * have the form content-model-$name, where $name is getContentModelName( $id ).
     *
     * @param string $name The content model ID, as given by a CONTENT_MODEL_XXX
     *    constant or returned by Content::getModel() or SlotRecord::getModel().
     * @param Language|null $lang The language to parse the message in (since 1.26)
     *
     * @return string The content model's localized name.
     */
    public static function getLocalizedName( $name, Language $lang = null ) {
        // Messages: content-model-wikitext, content-model-text,
        // content-model-javascript, content-model-css
        // Lowercase the name as message keys need to be in lowercase, T358341
        $key = "content-model-" . strtolower( $name ?? '' );

        $msg = wfMessage( $key );
        if ( $lang ) {
            $msg->inLanguage( $lang );
        }

        return $msg->exists() ? $msg->plain() : $name;
    }

    /**
     * @deprecated since 1.35, use ContentHandlerFactory::getContentModels
     *   Hard deprecated since 1.43.
     * @see ContentHandlerFactory::getContentModels
     *
     * @return string[]
     */
    public static function getContentModels() {
        wfDeprecated( __METHOD__, '1.35' );
        return MediaWikiServices::getInstance()->getContentHandlerFactory()->getContentModels();
    }

    /**
     * @return string[]
     *
     * @deprecated since 1.35, use ContentHandlerFactory::getAllContentFormats
     *   Hard deprecated since 1.43.
     * @see ContentHandlerFactory::getAllContentFormats
     */
    public static function getAllContentFormats() {
        wfDeprecated( __METHOD__, '1.35' );
        return MediaWikiServices::getInstance()->getContentHandlerFactory()->getAllContentFormats();
    }

    // ------------------------------------------------------------------------

    /**
     * @var string
     */
    protected $mModelID;

    /**
     * @var string[]
     */
    protected $mSupportedFormats;

    /**
     * Constructor, initializing the ContentHandler instance with its model ID
     * and a list of supported formats. Values for the parameters are typically
     * provided as literals by subclass's constructors.
     *
     * @stable to call
     *
     * @param string $modelId (use CONTENT_MODEL_XXX constants).
     * @param string[] $formats List for supported serialization formats
     *    (typically as MIME types)
     */
    public function __construct( $modelId, $formats ) {
        $this->mModelID = $modelId;
        $this->mSupportedFormats = $formats;
    }

    /**
     * Serializes a Content object of the type supported by this ContentHandler.
     *
     * @stable to override
     *
     * @since 1.21
     *
     * @param Content $content The Content object to serialize
     * @param string|null $format The desired serialization format
     *
     * @return string Serialized form of the content
     */
    abstract public function serializeContent( Content $content, $format = null );

    /**
     * Applies transformations on export (returns the blob unchanged by default).
     * Subclasses may override this to perform transformations such as conversion
     * of legacy formats or filtering of internal meta-data.
     *
     * @stable to override
     *
     * @param string $blob The blob to be exported
     * @param string|null $format The blob's serialization format
     *
     * @return string
     */
    public function exportTransform( $blob, $format = null ) {
        return $blob;
    }

    /**
     * Unserializes a Content object of the type supported by this ContentHandler.
     *
     * @stable to override
     * @since 1.21
     *
     * @param string $blob Serialized form of the content
     * @param string|null $format The format used for serialization
     *
     * @return Content The Content object created by deserializing $blob
     * @throws MWContentSerializationException
     */
    abstract public function unserializeContent( $blob, $format = null );

    /**
     * Apply import transformation (by default, returns $blob unchanged).
     * This gives subclasses an opportunity to transform data blobs on import.
     *
     * @stable to override
     * @since 1.24
     *
     * @param string $blob
     * @param string|null $format
     *
     * @return string
     */
    public function importTransform( $blob, $format = null ) {
        return $blob;
    }

    /**
     * Creates an empty Content object of the type supported by this
     * ContentHandler.
     *
     * @stable to override
     * @since 1.21
     *
     * @return Content
     */
    abstract public function makeEmptyContent();

    /**
     * Creates a new Content object that acts as a redirect to the given page,
     * or null if redirects are not supported by this content model.
     *
     * This default implementation always returns null. Subclasses supporting redirects
     * must override this method.
     *
     * Note that subclasses that override this method to return a Content object
     * should also override supportsRedirects() to return true.
     *
     * @stable to override
     * @since 1.21
     *
     * @param Title $destination The page to redirect to.
     * @param string $text Text to include in the redirect, if possible.
     *
     * @return Content|null Always null.
     */
    public function makeRedirectContent( Title $destination, $text = '' ) {
        return null;
    }

    /**
     * Returns the model id that identifies the content model this
     * ContentHandler can handle. Use with the CONTENT_MODEL_XXX constants.
     *
     * @since 1.21
     *
     * @return string The model ID
     */
    public function getModelID() {
        return $this->mModelID;
    }

    /**
     * @since 1.21
     *
     * @param string $model_id The model to check
     *
     * @throws MWException If the model ID is not the ID of the content model supported by this
     * ContentHandler.
     */
    protected function checkModelID( $model_id ) {
        if ( $model_id !== $this->mModelID ) {
            throw new MWException( "Bad content model: " .
                "expected {$this->mModelID} " .
                "but got $model_id." );
        }
    }

    /**
     * Returns a list of serialization formats supported by the
     * serializeContent() and unserializeContent() methods of this
     * ContentHandler.
     *
     * @stable to override
     * @since 1.21
     *
     * @return string[] List of serialization formats as MIME type like strings
     */
    public function getSupportedFormats() {
        return $this->mSupportedFormats;
    }

    /**
     * The format used for serialization/deserialization by default by this
     * ContentHandler.
     *
     * This default implementation will return the first element of the array
     * of formats that was passed to the constructor.
     *
     * @stable to override
     * @since 1.21
     *
     * @return string The name of the default serialization format as a MIME type
     */
    public function getDefaultFormat() {
        return $this->mSupportedFormats[0];
    }

    /**
     * Returns true if $format is a serialization format supported by this
     * ContentHandler, and false otherwise.
     *
     * Note that if $format is null, this method always returns true, because
     * null means "use the default format".
     *
     * @stable to override
     * @since 1.21
     *
     * @param string $format The serialization format to check
     *
     * @return bool
     */
    public function isSupportedFormat( $format ) {
        if ( !$format ) {
            return true; // this means "use the default"
        }

        return in_array( $format, $this->mSupportedFormats );
    }

    /**
     * Convenient for checking whether a format provided as a parameter is actually supported.
     *
     * @param string $format The serialization format to check
     *
     * @throws MWException If the format is not supported by this content handler.
     */
    protected function checkFormat( $format ) {
        if ( !$this->isSupportedFormat( $format ) ) {
            throw new MWException(
                "Format $format is not supported for content model "
                . $this->getModelID()
            );
        }
    }

    /**
     * Returns overrides for action handlers.
     * Classes listed here will be used instead of the default one when
     * (and only when) $wgActions[$action] === true. This allows subclasses
     * to override the default action handlers.
     *
     * @stable to override
     * @since 1.21
     *
     * @return array<string,class-string|callable|false|Action|array> An array mapping action names
     *  (typically "view", "edit", "history" etc.) to a specification according to
     *  {@see ActionFactory::getActionSpec}. Can be the full qualified class name of an Action
     *  class, a callable taking ( Article $article, IContextSource $context ) as parameters and
     *  returning an Action object, false to disable an action, an actual Action object,
     *  or an ObjectFactory specification array (can have 'class', 'services', etc.).
     *  An empty array in this default implementation.
     *
     * @see Action::factory
     */
    public function getActionOverrides() {
        return [];
    }

    /**
     * Factory for creating an appropriate DifferenceEngine for this content model.
     * Since 1.32, this is only used for page-level diffs; to diff two content objects,
     * use getSlotDiffRenderer.
     *
     * The DifferenceEngine subclass to use is selected in getDiffEngineClass(). The
     * GetDifferenceEngine hook will receive the DifferenceEngine object and can replace or
     * wrap it.
     * (Note that in older versions of MediaWiki the hook documentation instructed extensions
     * to return false from the hook; you should not rely on always being able to decorate
     * the DifferenceEngine instance from the hook. If the owner of the content type wants to
     * decorate the instance, overriding this method is a safer approach.)
     *
     * @todo This is page-level functionality so it should not belong to ContentHandler.
     *   Move it to a better place once one exists (e.g. PageTypeHandler).
     *
     * @since 1.21
     *
     * @param IContextSource $context Context to use, anything else will be ignored.
     * @param int $old Revision ID we want to show and diff with.
     * @param int|string $new Either a revision ID or one of the strings 'cur', 'prev' or 'next'.
     * @param int $rcid FIXME: Deprecated, no longer used. Defaults to 0.
     * @param bool $refreshCache If set, refreshes the diff cache. Defaults to false.
     * @param bool $unhide If set, allow viewing deleted revs. Defaults to false.
     *
     * @return DifferenceEngine
     */
    public function createDifferenceEngine( IContextSource $context, $old = 0, $new = 0,
        $rcid = 0, // FIXME: Deprecated, no longer used
        $refreshCache = false, $unhide = false
    ) {
        $diffEngineClass = $this->getDiffEngineClass();
        $differenceEngine = new $diffEngineClass( $context, $old, $new, $rcid, $refreshCache, $unhide );
        $this->getHookRunner()->onGetDifferenceEngine(
            $context, $old, $new, $refreshCache, $unhide, $differenceEngine );
        return $differenceEngine;
    }

    /**
     * Get an appropriate SlotDiffRenderer for this content model.
     *
     * @stable to override
     * @since 1.32
     *
     * @param IContextSource $context
     * @param array $options An associative array of options passed to the SlotDiffRenderer:
     *   - diff-type: (string) The text diff format
     *   - contentLanguage: (string) The language code of the content language,
     *     to be passed to the TextDiffer constructor. This is ignored if a
     *     TextDiffer object is provided.
     *   - textDiffer: (TextDiffer) A TextDiffer object to use for text
     *     comparison.
     * @return SlotDiffRenderer
     */
    final public function getSlotDiffRenderer( IContextSource $context, array $options = [] ) {
        $slotDiffRenderer = $this->getSlotDiffRendererWithOptions( $context, $options );
        if ( get_class( $slotDiffRenderer ) === TextSlotDiffRenderer::class ) {
            // To keep B/C, when SlotDiffRenderer is not overridden for a given content type
            // but DifferenceEngine is, use that instead.
            $differenceEngine = $this->createDifferenceEngine( $context );
            if ( get_class( $differenceEngine ) !== DifferenceEngine::class ) {
                // TODO turn this into a deprecation warning in a later release
                LoggerFactory::getInstance( 'diff' )->info(
                    'Falling back to DifferenceEngineSlotDiffRenderer', [
                        'modelID' => $this->getModelID(),
                        'DifferenceEngine' => get_class( $differenceEngine ),
                    ] );
                $slotDiffRenderer = new DifferenceEngineSlotDiffRenderer( $differenceEngine );
            }
        }
        $this->getHookRunner()->onGetSlotDiffRenderer( $this, $slotDiffRenderer, $context );
        return $slotDiffRenderer;
    }

    /**
     * Return the SlotDiffRenderer appropriate for this content handler.
     * @deprecated since 1.35; use getSlotDiffRendererWithOptions instead
     *   Emitting deprecation warnings since 1.41.
     * @param IContextSource $context
     * @return SlotDiffRenderer|null
     */
    protected function getSlotDiffRendererInternal( IContextSource $context ) {
        return null;
    }

    /**
     * Return the SlotDiffRenderer appropriate for this content handler.
     * @stable to override
     *
     * @param IContextSource $context
     * @param array $options See getSlotDiffRenderer()
     *
     * @return SlotDiffRenderer
     */
    protected function getSlotDiffRendererWithOptions( IContextSource $context, $options = [] ) {
        $internalRenderer = $this->getSlotDiffRendererInternal( $context );
        // `getSlotDiffRendererInternal` has been overridden by a class using the deprecated method.
        // Options will not work so exit early!
        if ( $internalRenderer !== null ) {
            wfDeprecated( 'ContentHandler::getSlotDiffRendererInternal', '1.35' );
            return $internalRenderer;
        }
        return $this->createTextSlotDiffRenderer( $options );
    }

    /**
     * Create a TextSlotDiffRenderer and inject dependencies
     *
     * @since 1.41
     *
     * @param array $options See getSlotDiffRenderer()
     * @return TextSlotDiffRenderer
     */
    final protected function createTextSlotDiffRenderer( array $options = [] ): TextSlotDiffRenderer {
        $slotDiffRenderer = new TextSlotDiffRenderer();

        $services = MediaWikiServices::getInstance();
        $statsdDataFactory = $services->getStatsdDataFactory();
        $slotDiffRenderer->setStatsdDataFactory( $statsdDataFactory );
        $slotDiffRenderer->setHookContainer( $services->getHookContainer() );
        $slotDiffRenderer->setContentModel( $this->getModelID() );

        if ( isset( $options['textDiffer'] ) ) {
            $textDiffer = $options['textDiffer'];
        } else {
            if ( isset( $options['contentLanguage'] ) ) {
                $language = $services->getLanguageFactory()->getLanguage( $options['contentLanguage'] );
            } else {
                $language = $services->getContentLanguage();
            }
            $config = $services->getMainConfig();
            $textDiffer = new ManifoldTextDiffer(
                RequestContext::getMain(),
                $language,
                $config->get( MainConfigNames::DiffEngine ),
                $config->get( MainConfigNames::ExternalDiffEngine ),
                $config->get( MainConfigNames::Wikidiff2Options )
            );
        }
        $format = $options['diff-type'] ?? 'table';
        if ( !$textDiffer->hasFormat( $format ) ) {
            // Maybe it would be better to throw an exception here, but at
            // present, the value comes straight from user input without
            // validation, so we have to fall back.
            $format = 'table';
        }
        $slotDiffRenderer->setFormat( $format );
        $slotDiffRenderer->setTextDiffer( $textDiffer );
        if ( $options['inline-toggle'] ?? false ) {
            $slotDiffRenderer->setInlineToggleEnabled();
        }

        return $slotDiffRenderer;
    }

    /**
     * Get the language in which the content of the given page is written.
     *
     * This default implementation just returns the content language (except for pages
     * in the MediaWiki namespace)
     *
     * Note that the page's language is not cacheable, since it may in some
     * cases depend on user settings.
     *
     * Also note that the page language may or may not depend on the actual content of the page,
     * that is, this method may load the content in order to determine the language.
     *
     * @stable to override
     * @since 1.21
     *
     * @param Title $title The page to determine the language for.
     * @param Content|null $content The page's content, if you have it handy, to avoid reloading it.
     *
     * @return Language
     */
    public function getPageLanguage( Title $title, Content $content = null ) {
        $services = MediaWikiServices::getInstance();
        $pageLang = $services->getContentLanguage();

        if ( $title->inNamespace( NS_MEDIAWIKI ) ) {
            // Parse mediawiki messages with correct target language
            [ /* $unused */, $lang ] = $services->getMessageCache()->figureMessage( $title->getText() );
            $pageLang = $services->getLanguageFactory()->getLanguage( $lang );
        }

        // Unused, T299369
        $userLang = null;
        $this->getHookRunner()->onPageContentLanguage( $title, $pageLang, $userLang );

        if ( !$pageLang instanceof Language ) {
            throw new UnexpectedValueException( 'onPageContentLanguage() hook provided an invalid $pageLang object.' );
        }

        return $pageLang;
    }

    /**
     * Get the language in which the content of this page is written when
     * viewed by user. Defaults to $this->getPageLanguage(), but if the user
     * specified a preferred variant, the variant will be used.
     *
     * This default implementation just returns $this->getPageLanguage( $title, $content ) unless
     * the user specified a preferred variant.
     *
     * Note that the pages view language is not cacheable, since it depends on user settings.
     *
     * Also note that the page language may or may not depend on the actual content of the page,
     * that is, this method may load the content in order to determine the language.
     *
     * @stable to override
     * @deprecated since 1.42 Use ParserOutput::getLanguage instead. See also OutputPage::getContLangForJS.
     * @since 1.21
     * @param Title $title The page to determine the language for.
     * @param Content|null $content The page's content, if you have it handy, to avoid reloading it.
     * @return Language The page's language for viewing
     */
    public function getPageViewLanguage( Title $title, Content $content = null ) {
        $pageLang = $this->getPageLanguage( $title, $content );

        if ( $title->getNamespace() !== NS_MEDIAWIKI ) {
            // If the user chooses a variant, the content is actually
            // in a language whose code is the variant code.
            $variant = $this->getLanguageConverter( $pageLang )->getPreferredVariant();
            if ( $pageLang->getCode() !== $variant ) {
                $pageLang = MediaWikiServices::getInstance()->getLanguageFactory()
                    ->getLanguage( $variant );
            }
        }

        return $pageLang;
    }

    /**
     * Determines whether the content type handled by this ContentHandler
     * can be used for the main slot of the given page.
     *
     * This default implementation always returns true.
     * Subclasses may override this to restrict the use of this content model to specific locations,
     * typically based on the namespace or some other aspect of the title, such as a special suffix
     * (e.g. ".svg" for SVG content).
     *
     * @note this calls the ContentHandlerCanBeUsedOn hook which may be used to override which
     * content model can be used where.
     *
     * @stable to override
     *
     * @see SlotRoleHandler::isAllowedModel
     *
     * @param Title $title The page's title.
     *
     * @return bool True if content of this kind can be used on the given page, false otherwise.
     */
    public function canBeUsedOn( Title $title ) {
        $ok = true;

        $this->getHookRunner()->onContentModelCanBeUsedOn( $this->getModelID(), $title, $ok );

        return $ok;
    }

    /**
     * Returns the name of the diff engine to use.
     *
     * @stable to override
     * @since 1.21
     *
     * @return class-string<DifferenceEngine>
     */
    protected function getDiffEngineClass() {
        return DifferenceEngine::class;
    }

    /**
     * Attempts to merge differences between three versions. Returns a new
     * Content object for a clean merge and false for failure or a conflict.
     *
     * This default implementation always returns false.
     *
     * @stable to override
     * @since 1.21
     *
     * @param Content $oldContent The page's previous content.
     * @param Content $myContent One of the page's conflicting contents.
     * @param Content $yourContent One of the page's conflicting contents.
     *
     * @return Content|false Always false.
     */
    public function merge3( Content $oldContent, Content $myContent, Content $yourContent ) {
        return false;
    }

    /**
     * Shorthand for getting a Language Converter for specific language
     * @param Language $language Language of converter
     * @return ILanguageConverter
     */
    private function getLanguageConverter( $language ): ILanguageConverter {
        return MediaWikiServices::getInstance()->getLanguageConverterFactory()
            ->getLanguageConverter( $language );
    }

    /**
     * Return type of change if one exists for the given edit.
     *
     * @stable to override
     * @since 1.31
     *
     * @param Content|null $oldContent The previous text of the page.
     * @param Content|null $newContent The submitted text of the page.
     * @param int $flags Bit mask: a bit mask of flags submitted for the edit.
     *
     * @return string|null String key representing type of change, or null.
     */
    private function getChangeType(
        Content $oldContent = null,
        Content $newContent = null,
        $flags = 0
    ) {
        $oldTarget = $oldContent !== null ? $oldContent->getRedirectTarget() : null;
        $newTarget = $newContent !== null ? $newContent->getRedirectTarget() : null;

        // We check for the type of change in the given edit, and return string key accordingly

        // Blanking of a page
        if ( $oldContent && $oldContent->getSize() > 0 &&
            $newContent && $newContent->getSize() === 0
        ) {
            return 'blank';
        }

        // Redirects
        if ( $newTarget ) {
            if ( !$oldTarget ) {
                // New redirect page (by creating new page or by changing content page)
                return 'new-redirect';
            } elseif ( !$newTarget->equals( $oldTarget ) ||
                $oldTarget->getFragment() !== $newTarget->getFragment()
            ) {
                // Redirect target changed
                return 'changed-redirect-target';
            }
        } elseif ( $oldTarget ) {
            // Changing an existing redirect into a non-redirect
            return 'removed-redirect';
        }

        // New page created
        if ( $flags & EDIT_NEW && $newContent ) {
            if ( $newContent->getSize() === 0 ) {
                // New blank page
                return 'newblank';
            } else {
                return 'newpage';
            }
        }

        // Removing more than 90% of the page
        if ( $oldContent && $newContent && $oldContent->getSize() > 10 * $newContent->getSize() ) {
            return 'replace';
        }

        // Content model changed
        if ( $oldContent && $newContent && $oldContent->getModel() !== $newContent->getModel() ) {
            return 'contentmodelchange';
        }

        return null;
    }

    /**
     * Return an applicable auto-summary if one exists for the given edit.
     *
     * @stable to override
     * @since 1.21
     *
     * @param Content|null $oldContent The previous text of the page.
     * @param Content|null $newContent The submitted text of the page.
     * @param int $flags Bit mask: a bit mask of flags submitted for the edit.
     *
     * @return string An appropriate auto-summary, or an empty string.
     */
    public function getAutosummary(
        Content $oldContent = null,
        Content $newContent = null,
        $flags = 0
    ) {
        $changeType = $this->getChangeType( $oldContent, $newContent, $flags );

        // There's no applicable auto-summary for our case, so our auto-summary is empty.
        if ( !$changeType ) {
            return '';
        }

        // Set the maximum auto-summary length to the general maximum summary length
        // T221617
        $summaryLimit = CommentStore::COMMENT_CHARACTER_LIMIT;

        // Decide what kind of auto-summary is needed.
        switch ( $changeType ) {
            case 'new-redirect':
                $newTarget = $newContent->getRedirectTarget();
                $truncatedtext = $newContent->getTextForSummary(
                    $summaryLimit
                    - strlen( wfMessage( 'autoredircomment' )->inContentLanguage()->text() )
                    - strlen( $newTarget->getFullText() )
                );

                return wfMessage( 'autoredircomment', $newTarget->getFullText() )
                    ->plaintextParams( $truncatedtext )->inContentLanguage()->text();
            case 'changed-redirect-target':
                $oldTarget = $oldContent->getRedirectTarget();
                $newTarget = $newContent->getRedirectTarget();

                $truncatedtext = $newContent->getTextForSummary(
                    $summaryLimit
                    - strlen( wfMessage( 'autosumm-changed-redirect-target' )
                        ->inContentLanguage()->text() )
                    - strlen( $oldTarget->getFullText() )
                    - strlen( $newTarget->getFullText() )
                );

                return wfMessage( 'autosumm-changed-redirect-target',
                        $oldTarget->getFullText(),
                        $newTarget->getFullText() )
                    ->rawParams( $truncatedtext )->inContentLanguage()->text();
            case 'removed-redirect':
                $oldTarget = $oldContent->getRedirectTarget();
                $truncatedtext = $newContent->getTextForSummary(
                    $summaryLimit
                    - strlen( wfMessage( 'autosumm-removed-redirect' )
                        ->inContentLanguage()->text() )
                    - strlen( $oldTarget->getFullText() ) );

                return wfMessage( 'autosumm-removed-redirect', $oldTarget->getFullText() )
                    ->rawParams( $truncatedtext )->inContentLanguage()->text();
            case 'newpage':
                // If they're making a new article, give its text, truncated, in the summary.
                $truncatedtext = $newContent->getTextForSummary(
                    $summaryLimit - strlen( wfMessage( 'autosumm-new' )->inContentLanguage()->text() ) );

                return wfMessage( 'autosumm-new' )->rawParams( $truncatedtext )
                    ->inContentLanguage()->text();
            case 'blank':
                return wfMessage( 'autosumm-blank' )->inContentLanguage()->text();
            case 'replace':
                $truncatedtext = $newContent->getTextForSummary(
                    $summaryLimit - strlen( wfMessage( 'autosumm-replace' )->inContentLanguage()->text() ) );

                return wfMessage( 'autosumm-replace' )->rawParams( $truncatedtext )
                    ->inContentLanguage()->text();
            case 'newblank':
                return wfMessage( 'autosumm-newblank' )->inContentLanguage()->text();
            default:
                return '';
        }
    }

    /**
     * Return an applicable tag if one exists for the given edit or return null.
     *
     * @stable to override
     * @since 1.31
     *
     * @param Content|null $oldContent The previous text of the page.
     * @param Content|null $newContent The submitted text of the page.
     * @param int $flags Bit mask: a bit mask of flags submitted for the edit.
     *
     * @return string|null An appropriate tag, or null.
     */
    public function getChangeTag(
        Content $oldContent = null,
        Content $newContent = null,
        $flags = 0
    ) {
        $changeType = $this->getChangeType( $oldContent, $newContent, $flags );

        // There's no applicable tag for this change.
        if ( !$changeType ) {
            return null;
        }

        // Core tags use the same keys as ones returned from $this->getChangeType()
        // but prefixed with pseudo namespace 'mw-', so we add the prefix before checking
        // if this type of change should be tagged
        $tag = 'mw-' . $changeType;

        // Not all change types are tagged, so we check against the list of defined tags.
        if ( in_array( $tag, ChangeTags::getSoftwareTags() ) ) {
            return $tag;
        }

        return null;
    }

    /**
     * Auto-generates a deletion reason
     *
     * @stable to override
     * @since 1.21
     *
     * @param Title $title The page's title
     * @param bool &$hasHistory Whether the page has a history
     *
     * @return string|false String containing deletion reason or empty string, or
     *    boolean false if no revision occurred
     */
    public function getAutoDeleteReason( Title $title, &$hasHistory = false ) {
        if ( func_num_args() === 2 ) {
            wfDeprecated( __METHOD__ . ': $hasHistory parameter', '1.38' );
        }
        $dbr = MediaWikiServices::getInstance()->getConnectionProvider()->getReplicaDatabase();
        $revStore = MediaWikiServices::getInstance()->getRevisionStore();

        // Get the last revision
        $revRecord = $revStore->getRevisionByTitle( $title );

        if ( $revRecord === null ) {
            return false;
        }

        // Get the article's contents
        $content = $revRecord->getContent( SlotRecord::MAIN );
        $blank = false;

        // If the page is blank, use the text from the previous revision,
        // which can only be blank if there's a move/import/protect dummy
        // revision involved
        if ( !$content || $content->isEmpty() ) {
            $prev = $revStore->getPreviousRevision( $revRecord );

            if ( $prev ) {
                $revRecord = $prev;
                $content = $prev->getContent( SlotRecord::MAIN );
                $blank = true;
            }
        }

        $this->checkModelID( $revRecord->getSlot( SlotRecord::MAIN )->getModel() );

        // Find out if there was only one contributor
        // Only scan the last 20 revisions
        $queryBuilder = $revStore->newSelectQueryBuilder( $dbr )
            ->where( [
                'rev_page' => $title->getArticleID(),
                $dbr->bitAnd( 'rev_deleted', RevisionRecord::DELETED_USER ) . ' = 0'
            ] )
            ->limit( 20 );
        $res = $queryBuilder->caller( __METHOD__ )->fetchResultSet();

        if ( !$res->numRows() ) {
            // This page has no revisions, which is very weird
            return false;
        }

        $hasHistory = ( $res->numRows() > 1 );
        $row = $res->fetchObject();

        if ( $row ) { // $row is false if the only contributor is hidden
            $onlyAuthor = $row->rev_user_text;
            // Try to find a second contributor
            foreach ( $res as $row ) {
                if ( $row->rev_user_text != $onlyAuthor ) { // T24999
                    $onlyAuthor = false;
                    break;
                }
            }
        } else {
            $onlyAuthor = false;
        }

        // Generate the summary with a '$1' placeholder
        if ( $blank ) {
            // The current revision is blank and the one before is also
            // blank. It's just not our lucky day
            $reason = wfMessage( 'exbeforeblank', '$1' )->inContentLanguage()->text();
        } else {
            if ( $onlyAuthor ) {
                $reason = wfMessage(
                    'excontentauthor',
                    '$1',
                    $onlyAuthor
                )->inContentLanguage()->text();
            } else {
                $reason = wfMessage( 'excontent', '$1' )->inContentLanguage()->text();
            }
        }

        if ( $reason == '-' ) {
            // Allow these UI messages to be blanked out cleanly
            return '';
        }

        // Max content length = max comment length - length of the comment (excl. $1)
        $maxLength = CommentStore::COMMENT_CHARACTER_LIMIT - ( strlen( $reason ) - 2 );
        $text = $content ? $content->getTextForSummary( $maxLength ) : '';

        // Now replace the '$1' placeholder
        $reason = str_replace( '$1', $text, $reason );

        return $reason;
    }

    /**
     * Get the Content object that needs to be saved in order to undo all changes
     * between $undo and $undoafter.
     *
     * @stable to override
     * @since 1.21
     * @since 1.32 accepts Content objects for all parameters instead of Revision objects.
     *  Passing Revision objects is deprecated.
     * @since 1.37 only accepts Content objects
     *
     * @param Content $currentContent The current text
     * @param Content $undoContent The content of the revision to undo
     * @param Content $undoAfterContent Must be from an earlier revision than $undo
     * @param bool $undoIsLatest Set true if $undo is from the current revision (since 1.32)
     *
     * @return Content|false Content on success, false on failure
     */
    public function getUndoContent(
        Content $currentContent,
        Content $undoContent,
        Content $undoAfterContent,
        $undoIsLatest = false
    ) {
        try {
            $this->checkModelID( $currentContent->getModel() );
            $this->checkModelID( $undoContent->getModel() );
            if ( !$undoIsLatest ) {
                // If we are undoing the most recent revision,
                // its ok to revert content model changes. However
                // if we are undoing a revision in the middle, then
                // doing that will be confusing.
                $this->checkModelID( $undoAfterContent->getModel() );
            }
        } catch ( MWException $e ) {
            // If the revisions have different content models
            // just return false
            return false;
        }

        if ( $currentContent->equals( $undoContent ) ) {
            // No use doing a merge if it's just a straight revert.
            return $undoAfterContent;
        }

        $undone_content = $this->merge3( $undoContent, $undoAfterContent, $currentContent );

        return $undone_content;
    }

    /**
     * Returns true for content models that support caching using the
     * ParserCache mechanism. See WikiPage::shouldCheckParserCache().
     *
     * @stable to override
     * @since 1.21
     *
     * @return bool Always false.
     */
    public function isParserCacheSupported() {
        return false;
    }

    /**
     * Returns true if this content model supports sections.
     * This default implementation returns false.
     *
     * Content models that return true here should also implement
     * Content::getSection, Content::replaceSection, etc. to handle sections.
     *
     * @stable to override
     *
     * @return bool Always false.
     */
    public function supportsSections() {
        return false;
    }

    /**
     * Returns true if this content model supports categories.
     * The default implementation returns true.
     *
     * @stable to override
     *
     * @return bool Always true.
     */
    public function supportsCategories() {
        return true;
    }

    /**
     * Returns true if this content model supports redirects.
     * This default implementation returns false.
     *
     * Content models that return true here should also implement
     * ContentHandler::makeRedirectContent to return a Content object.
     *
     * @stable to override
     *
     * @return bool Always false.
     */
    public function supportsRedirects() {
        return false;
    }

    /**
     * Return true if this content model supports direct editing, such as via EditPage.
     * This should return true for TextContent and its derivatives, and return false
     * for structured data content.
     *
     * @stable to override
     *
     * @return bool Default is false.
     */
    public function supportsDirectEditing() {
        return false;
    }

    /**
     * If a non-existing page can be created with the contents from another (arbitrary) page being
     * preloaded in the editor, see {@see EditPage::getContentObject}. Only makes sense together
     * with {@see supportsDirectEditing}.
     *
     * @stable to override
     * @since 1.39
     *
     * @return bool
     */
    public function supportsPreloadContent(): bool {
        return false;
    }

    /**
     * Whether an edit on the content should trigger an HTML render and ParserCache entry.
     *
     * @stable to override
     * @since 1.37
     *
     * @return bool true if edit should trigger an HTML render false otherwise
     */
    public function generateHTMLOnEdit(): bool {
        return true;
    }

    /**
     * Whether or not this content model supports direct editing via ApiEditPage
     *
     * @stable to override
     *
     * @return bool Default is false, and true for TextContent and derivatives.
     */
    public function supportsDirectApiEditing() {
        return $this->supportsDirectEditing();
    }

    /**
     * Get fields definition for search index
     *
     * @todo Expose title, redirect, namespace, text, source_text, text_bytes
     *       field mappings here. (see T142670 and T143409)
     *
     * @stable to override
     *
     * @param SearchEngine $engine
     * @return SearchIndexField[] List of fields this content handler can provide.
     * @since 1.28
     */
    public function getFieldsForSearchIndex( SearchEngine $engine ) {
        $fields = [];
        $fields['category'] = $engine->makeSearchFieldMapping(
            'category',
            SearchIndexField::INDEX_TYPE_TEXT
        );
        $fields['category']->setFlag( SearchIndexField::FLAG_CASEFOLD );

        $fields['external_link'] = $engine->makeSearchFieldMapping(
            'external_link',
            SearchIndexField::INDEX_TYPE_KEYWORD
        );

        $fields['outgoing_link'] = $engine->makeSearchFieldMapping(
            'outgoing_link',
            SearchIndexField::INDEX_TYPE_KEYWORD
        );

        $fields['template'] = $engine->makeSearchFieldMapping(
            'template',
            SearchIndexField::INDEX_TYPE_KEYWORD
        );
        $fields['template']->setFlag( SearchIndexField::FLAG_CASEFOLD );

        $fields['content_model'] = $engine->makeSearchFieldMapping(
            'content_model',
            SearchIndexField::INDEX_TYPE_KEYWORD
        );

        return $fields;
    }

    /**
     * Add new field definition to array.
     * @param SearchIndexField[] &$fields
     * @param SearchEngine $engine
     * @param string $name
     * @param string $type
     * @return SearchIndexField[] new field defs
     * @since 1.28
     */
    protected function addSearchField( &$fields, SearchEngine $engine, $name, $type ) {
        $fields[$name] = $engine->makeSearchFieldMapping( $name, $type );
        return $fields;
    }

    /**
     * Return fields to be indexed by search engine
     * as representation of this document.
     * Overriding class should call parent function or take care of calling
     * the SearchDataForIndex hook.
     *
     * The $output must be the result of a call to {@link getParserOutputForIndexing()}
     * on the same content handler. That method may return ParserOutput
     * {@link ParserOutput::hasText() without HTML}; this base implementation
     * does not rely on the HTML being present, so it is safe to call
     * even by subclasses that override {@link getParserOutputForIndexing()}
     * to skip HTML generation. On the other hand,
     * since the default implementation of {@link getParserOutputForIndexing()}
     * does generate HTML, subclasses are free to rely on the HTML here
     * if they do not override {@link getParserOutputForIndexing()}.
     *
     * @stable to override
     * @param WikiPage $page Page to index
     * @param ParserOutput $output
     * @param SearchEngine $engine Search engine for which we are indexing
     * @param RevisionRecord|null $revision Revision content to fetch if provided or use the latest revision
     *                                      from WikiPage::getRevisionRecord() if not
     * @return array Map of name=>value for fields, an empty array is returned if the latest
     *               revision cannot be retrieved.
     * @since 1.28
     */
    public function getDataForSearchIndex(
        WikiPage $page,
        ParserOutput $output,
        SearchEngine $engine,
        RevisionRecord $revision = null
    ) {
        $revision ??= $page->getRevisionRecord();
        if ( $revision === null ) {
            LoggerFactory::getInstance( 'search' )->warning(
                "Called getDataForSearchIndex on the page {page_id} for which the " .
                "latest revision cannot be loaded.",
                [ "page_id" => $page->getId() ]
            );
            return [];
        }
        Assert::invariant( $revision->getPageId() === $page->getId(),
            '$revision and $page must target the same page_id' );

        $fieldData = [];
        $content = $revision->getContent( SlotRecord::MAIN );

        if ( $content ) {
            $searchDataExtractor = new ParserOutputSearchDataExtractor();

            $fieldData['category'] = $searchDataExtractor->getCategories( $output );
            $fieldData['external_link'] = $searchDataExtractor->getExternalLinks( $output );
            $fieldData['outgoing_link'] = $searchDataExtractor->getOutgoingLinks( $output );
            $fieldData['template'] = $searchDataExtractor->getTemplates( $output );

            $text = $content->getTextForSearchIndex();

            $fieldData['text'] = $text;
            $fieldData['source_text'] = $text;
            $fieldData['text_bytes'] = $content->getSize();
            $fieldData['content_model'] = $content->getModel();
        }

        $this->getHookRunner()->onSearchDataForIndex( $fieldData, $this, $page, $output, $engine );
        $this->getHookRunner()->onSearchDataForIndex2( $fieldData, $this, $page, $output, $engine, $revision );

        return $fieldData;
    }

    /**
     * Produce page output suitable for indexing.
     * Typically used with {@link getDataForSearchIndex()}.
     *
     * Specific content handlers may override it if they need different content handling.
     *
     * The default implementation returns output {@link ParserOutput::hasText() with HTML},
     * but callers should not rely on this, and subclasses may override this method
     * and skip HTML generation if it is not needed for indexing.
     * (In that case, they should not attempt to store the output in the $cache.)
     *
     * @stable to override
     *
     * @param WikiPage $page
     * @param ParserCache|null $cache deprecated since 1.38 and won't have any effect
     * @param RevisionRecord|null $revision
     * @return ParserOutput|null null when the ParserOutput cannot be obtained
     * @see ParserOutputAccess::getParserOutput() for failure modes
     */
    public function getParserOutputForIndexing(
        WikiPage $page,
        ParserCache $cache = null,
        RevisionRecord $revision = null
    ) {
        // TODO: MCR: ContentHandler should be called per slot, not for the whole page.
        // See T190066.
        $parserOptions = $page->makeParserOptions( 'canonical' );
        $parserOptions->setRenderReason( 'ParserOutputForIndexing' );
        $parserOutputAccess = MediaWikiServices::getInstance()->getParserOutputAccess();
        return $parserOutputAccess->getParserOutput(
            $page,
            $parserOptions,
            $revision,
            ParserOutputAccess::OPT_NO_UPDATE_CACHE
        )->getValue();
    }

    /**
     * Get the latest revision of the given $page,
     * fetching it from the primary if necessary.
     *
     * @param WikiPage $page
     * @return RevisionRecord
     * @since 1.36 (previously private)
     */
    protected function latestRevision( WikiPage $page ): RevisionRecord {
        $revRecord = $page->getRevisionRecord();
        if ( $revRecord == null ) {
            // If the content represents a brand new page it's possible
            // we need to fetch it from the primary.
            $page->loadPageData( IDBAccessObject::READ_LATEST );
            $revRecord = $page->getRevisionRecord();
            if ( $revRecord == null ) {
                $text = $page->getTitle()->getPrefixedText();
                throw new MWException(
                    "No revision could be loaded for page: $text" );
            }
        }

        return $revRecord;
    }

    /**
     * Returns a list of DeferrableUpdate objects for recording information about the
     * given Content in some secondary data store.
     *
     * Application logic should not call this method directly. Instead, it should call
     * DerivedPageDataUpdater::getSecondaryDataUpdates().
     *
     * @note Implementations must not return a LinksUpdate instance. Instead, a LinksUpdate
     * is created by the calling code in DerivedPageDataUpdater, on the combined ParserOutput
     * of all slots, not for each slot individually. This is in contrast to the old
     * getSecondaryDataUpdates method defined by AbstractContent, which returned a LinksUpdate.
     *
     * @note Implementations should not call $content->getParserOutput, they should call
     * $slotOutput->getSlotRendering( $role, false ) instead if they need to access a ParserOutput
     * of $content. This allows existing ParserOutput objects to be re-used, while avoiding
     * creating a ParserOutput when none is needed.
     *
     * @stable to override
     *
     * @param Title $title The title of the page to supply the updates for
     * @param Content $content The content to generate data updates for.
     * @param string $role The role (slot) in which the content is being used. Which updates
     *        are performed should generally not depend on the role the content has, but the
     *        DeferrableUpdates themselves may need to know the role, to track to which slot the
     *        data refers, and to avoid overwriting data of the same kind from another slot.
     * @param SlotRenderingProvider $slotOutput A provider that can be used to gain access to
     *        a ParserOutput of $content by calling $slotOutput->getSlotParserOutput( $role, false ).
     * @return DeferrableUpdate[] A list of DeferrableUpdate objects for putting information
     *        about this content object somewhere. The default implementation returns an empty
     *        array.
     * @since 1.32
     */
    public function getSecondaryDataUpdates(
        Title $title,
        Content $content,
        $role,
        SlotRenderingProvider $slotOutput
    ) {
        return [];
    }

    /**
     * Returns a list of DeferrableUpdate objects for removing information about content
     * in some secondary data store. This is used when a page is deleted, and also when
     * a slot is removed from a page.
     *
     * Application logic should not call this method directly. Instead, it should call
     * WikiPage::getSecondaryDataUpdates().
     *
     * @note Implementations must not return a LinksDeletionUpdate instance. Instead, a
     * LinksDeletionUpdate is created by the calling code in WikiPage.
     * This is in contrast to the old getDeletionUpdates method defined by AbstractContent,
     * which returned a LinksUpdate.
     *
     * @note Implementations should not rely on the page's current content, but rather the current
     * state of the secondary data store.
     *
     * @stable to override
     *
     * @param Title $title The title of the page to supply the updates for
     * @param string $role The role (slot) in which the content is being used. Which updates
     *        are performed should generally not depend on the role the content has, but the
     *        DeferrableUpdates themselves may need to know the role, to track to which slot the
     *        data refers, and to avoid overwriting data of the same kind from another slot.
     *
     * @return DeferrableUpdate[] A list of DeferrableUpdate objects for putting information
     *        about this content object somewhere. The default implementation returns an empty
     *        array.
     *
     * @since 1.32
     */
    public function getDeletionUpdates( Title $title, $role ) {
        return [];
    }

    /**
     * Returns a $content object with pre-save transformations applied (or the same
     * object if no transformations apply).
     *
     * @note Not stable to call other then from ContentHandler hierarchy.
     * Callers need to use ContentTransformer::preSaveTransform.
     * @stable to override
     * @since 1.37
     *
     * @param Content $content
     * @param PreSaveTransformParams $pstParams
     *
     * @return Content
     */
    public function preSaveTransform(
        Content $content,
        PreSaveTransformParams $pstParams
    ): Content {
        return $content;
    }

    /**
     * Returns a $content object with preload transformations applied (or the same
     * object if no transformations apply).
     *
     * @note Not stable to call other then from ContentHandler hierarchy.
     * Callers need to use ContentTransformer::preLoadTransform.
     * @stable to override
     * @since 1.37
     *
     * @param Content $content
     * @param PreloadTransformParams $pltParams
     *
     * @return Content
     */
    public function preloadTransform(
        Content $content,
        PreloadTransformParams $pltParams
    ): Content {
        return $content;
    }

    /**
     * Validate content for saving it.
     *
     * This may be used to check the content's consistency with global state. This function should
     * NOT write any information to the database.
     *
     * Note that this method will usually be called inside the same transaction
     * bracket that will be used to save the new revision, so the revision passed
     * in is probably unsaved (has no id) and might belong to unsaved page.
     *
     * @since 1.38
     * @stable to override
     *
     * @param Content $content
     * @param ValidationParams $validationParams
     *
     * @return StatusValue A status object indicating if content can be saved in the given revision.
     */
    public function validateSave(
        Content $content,
        ValidationParams $validationParams
    ) {
        if ( $content->isValid() ) {
            return StatusValue::newGood();
        } else {
            return StatusValue::newFatal( "invalid-content-data" );
        }
    }

    /**
     * Returns a ParserOutput object containing information derived from this content.
     * Most importantly, unless $cpoParams->getGenerateHtml was false, the return value contains an
     * HTML representation of the content.
     *
     * Subclasses that want to control the parser output may override
     * fillParserOutput() instead.
     *
     *
     *
     * @since 1.38
     *
     * @param Content $content
     * @param ContentParseParams $cpoParams
     * @return ParserOutput Containing information derived from this content.
     */
    public function getParserOutput(
        Content $content,
        ContentParseParams $cpoParams
    ) {
        $services = MediaWikiServices::getInstance();
        $title = $services->getTitleFactory()->newFromPageReference( $cpoParams->getPage() );
        $parserOptions = $cpoParams->getParserOptions();

        if ( $parserOptions->getIsPreview() ) {
            $scopedCallback = $parserOptions->setupFakeRevision( $title, $content, $parserOptions->getUserIdentity() );
        }

        $hookRunner = new HookRunner( $services->getHookContainer() );

        $po = new ParserOutput();

        // Initialize to the page language
        $po->setLanguage( $title->getPageLanguage() );

        $parserOptions->registerWatcher( [ &$po, 'recordOption' ] );
        if ( $hookRunner->onContentGetParserOutput(
            // FIXME $cpoParams->getRevId() may be null here?
            // @phan-suppress-next-line PhanTypeMismatchArgumentNullable
            $content, $title, $cpoParams->getRevId(), $parserOptions, $cpoParams->getGenerateHtml(), $po )
        ) {
            // Save and restore the old value, just in case something is reusing
            // the ParserOptions object in some weird way.
            $oldRedir = $parserOptions->getRedirectTarget();
            $parserOptions->setRedirectTarget( $content->getRedirectTarget() );

            $po->resetParseStartTime();
            $this->fillParserOutput(
                $content,
                $cpoParams,
                $po
            );
            $po->recordTimeProfile();

            MediaWikiServices::getInstance()->get( '_ParserObserver' )->notifyParse(
                $title,
                $cpoParams->getRevId(),
                $parserOptions,
                $content,
                $po
            );
            $parserOptions->setRedirectTarget( $oldRedir );
        }

        $hookRunner->onContentAlterParserOutput( $content, $title, $po );
        $parserOptions->registerWatcher( null );
        if ( isset( $scopedCallback ) ) {
            ScopedCallback::consume( $scopedCallback );
        }

        return $po;
    }

    /**
     * A temporary layer to move AbstractContent::fillParserOutput to ContentHandler::fillParserOutput
     *
     * @internal only core AbstractContent::fillParserOutput implementations need to call this.
     * @since 1.38
     * @param Content $content
     * @param ContentParseParams $cpoParams
     * @param ParserOutput &$output The output object to fill (reference).
     */
    public function fillParserOutputInternal(
        Content $content,
        ContentParseParams $cpoParams,
        ParserOutput &$output
    ) {
        $this->fillParserOutput( $content, $cpoParams, $output );
    }

    /**
     * Fills the provided ParserOutput with information derived from the content.
     * Unless $cpoParams->getGenerateHtml() was false,
     * this includes an HTML representation of the content.
     *
     * If $cpoParams->getGenerateHtml() is false, and you chose not to generate
     * html, the ParserOutput must have a text of null. If the
     * text of the ParserOutput object is anything other than null (even if ''),
     * it is assumed that you don't support not generating html, and that it is
     * safe to reuse the parser output for calls expecting that html was generated.
     *
     * Subclasses are expected to override this method.
     *
     * This placeholder implementation always throws an exception.
     *
     * @stable to override
     *
     * @since 1.38
     * @param Content $content
     * @param ContentParseParams $cpoParams
     * @param ParserOutput &$output The output object to fill (reference).
     */
    protected function fillParserOutput(
        Content $content,
        ContentParseParams $cpoParams,
        ParserOutput &$output
    ) {
        // Subclasses must override fillParserOutput() to directly don't fail.
        throw new LogicException( 'Subclasses of ContentHandler must override fillParserOutput!' );
    }

}