Deprecate use of template directory relative to core

Warning now issued since skins have been updated.

Additional change:
Previously deprecations in release notes were in the wrong
section (Relating to ResourceLoaderSkinModule) these are
moved alongside the newly added deprecation note alongside
other skin deprecations.

Bug: T262067
Depends-On: I52bee67732cc72ec6857b6fc10cfbdd89ef9b8db
Depends-On:  I338198878e78cb5c6f47c53fdf18d3944655e965
Change-Id: Ic60524fe3c054706dbea15cc04235e979952e9f5

RELEASE-NOTES-1.37

@@ -675,6 +675,8 @@ because of Phabricator reports.
   BaseTemplateAfterPortlet hook, which were deprecated in 1.35,
   now emit deprecation warnings.
 * The LocalFile::getHistory() hook is deprecated.
+* Previously the Skin templateDirectory option inside skin.json had to be
+  relative to MediaWiki core. This should now be relative to the skin.
 * Calling WikiPage::prepareContentForEdit() without a UserIdentity is now
   deprecated.
 * User::getEditTokenObject(), ::getEditToken(), and ::matchEditToken() were each

includes/registration/ExtensionProcessor.php

@@ -638,8 +638,11 @@ class ExtensionProcessor implements Processor {
 					if ( is_dir( $correctedPath ) ) {
 						$data['args'][0]['templateDirectory'] = $correctedPath;
 					} else {
-						// TODO: deprecate directories relative to core.
 						$data['args'][0]['templateDirectory'] = $templateDirectory;
+						wfDeprecatedMsg(
+							'Template directory should be relative to skin or omitted.',
+							'1.37'
+						);
 					}
 				} elseif ( isset( $data['args'][0] ) ) {
 					// If not set, we set a sensible default.

tests/phpunit/includes/registration/ExtensionProcessorTest.php

@@ -63,6 +63,7 @@ class ExtensionProcessorTest extends MediaWikiIntegrationTestCase {
 	}
 
 	public function testExtractSkins() {
+		$this->expectDeprecation();
 		$processor = new ExtensionProcessor();
 		$processor->extractInfo( $this->dir, self::$default + [
 			'ValidSkinNames' => [