Create ParserFetchTemplateData hook

This is moved from TemplateData, but the interface isn't quite right.
Filed T304899 to improve it in the future.

Bug: T304740
Change-Id: Iadd1ed70b72fc282bd5addfc1654aa73322ea470

autoload.php

@@ -967,6 +967,7 @@ $wgAutoloadLocalClasses = [
 	'MediaWiki\\Hook\\ParserCacheSaveCompleteHook' => __DIR__ . '/includes/parser/Hook/ParserCacheSaveCompleteHook.php',
 	'MediaWiki\\Hook\\ParserClearStateHook' => __DIR__ . '/includes/parser/Hook/ParserClearStateHook.php',
 	'MediaWiki\\Hook\\ParserClonedHook' => __DIR__ . '/includes/parser/Hook/ParserClonedHook.php',
+	'MediaWiki\\Hook\\ParserFetchTemplateDataHook' => __DIR__ . '/includes/parser/Hook/ParserFetchTemplateDataHook.php',
 	'MediaWiki\\Hook\\ParserFirstCallInitHook' => __DIR__ . '/includes/parser/Hook/ParserFirstCallInitHook.php',
 	'MediaWiki\\Hook\\ParserGetVariableValueSwitchHook' => __DIR__ . '/includes/parser/Hook/ParserGetVariableValueSwitchHook.php',
 	'MediaWiki\\Hook\\ParserGetVariableValueTsHook' => __DIR__ . '/includes/parser/Hook/ParserGetVariableValueTsHook.php',

includes/HookContainer/HookRunner.php

@@ -282,6 +282,7 @@ class HookRunner implements
 	\MediaWiki\Hook\ParserCacheSaveCompleteHook,
 	\MediaWiki\Hook\ParserClearStateHook,
 	\MediaWiki\Hook\ParserClonedHook,
+	\MediaWiki\Hook\ParserFetchTemplateDataHook,
 	\MediaWiki\Hook\ParserFirstCallInitHook,
 	\MediaWiki\Hook\ParserGetVariableValueSwitchHook,
 	\MediaWiki\Hook\ParserGetVariableValueTsHook,
@@ -2867,6 +2868,13 @@ class HookRunner implements
 		);
 	}
 
+	public function onParserFetchTemplateData( array $titles, array &$tplData ): bool {
+		return $this->container->run(
+			'ParserFetchTemplateData',
+			[ $titles, &$tplData ]
+		);
+	}
+
 	public function onParserFirstCallInit( $parser ) {
 		return $this->container->run(
 			'ParserFirstCallInit',

includes/parser/Hook/ParserFetchTemplateDataHook.php

@@ -0,0 +1,36 @@
+<?php
+
+namespace MediaWiki\Hook;
+
+/**
+ * This is a hook handler interface, see docs/Hooks.md.
+ * Use the hook name "ParserFetchTemplateData" to register handlers
+ * implementing this interface.
+ *
+ * @unstable
+ * @ingroup Hooks
+ */
+interface ParserFetchTemplateDataHook {
+	/**
+	 * This hook allows Parsoid to fetch additional serialization information
+	 * about a Template, including the type of its arguments, whether they
+	 * should be serialized as inline or block style wikitext, etc.
+	 * See [[Extension:TemplateData]] for more information.
+	 *
+	 * @param string[] $titles An array of template names
+	 * @param array<string,object> &$tplData The hook will create an
+	 *  associative array, mapping each given
+	 *  template name to an object representing the TemplateData for that
+	 *  template, or special objects if the title doesn't exist, is missing
+	 *  TemplateData, or has malformed TemplateData.
+	 * @return bool Typically returns true, to allow all registered hooks a
+	 *  chance to fill in template data.
+	 *
+	 * @unstable temporary hook; will be cleaned up before it is made stable
+	 * @since 1.39
+	 */
+	public function onParserFetchTemplateData(
+		array $titles,
+		array &$tplData
+	): bool;
+}

includes/parser/Parsoid/Config/DataAccess.php

@@ -408,9 +408,10 @@ class DataAccess extends IDataAccess {
 	/** @inheritDoc */
 	public function fetchTemplateData( IPageConfig $pageConfig, string $title ): ?array {
 		$ret = [];
-		// @todo: Document this hook in MediaWiki / Extension:TemplateData
-		$this->hookContainer->run(
-			'ParserFetchTemplateData', [ [ $title ], &$ret ]
+		// @todo: This hook needs some clean up: T304899
+		$this->hookRunner->onParserFetchTemplateData(
+			[ $title ],
+			$ret # value returned by reference
 		);
 
 		// Cast value to array since the hook returns this as a stdclass