Skins: Support useskin=json

This allows rendering of the data passed to the skin rendering
layer, to allow developers to debug the information used to render
a skin.

Bug: T364696
Change-Id: I32aaa6a85d24df4f4689269f6a455823bb08196b

includes/Output/OutputPage.php

@@ -2907,7 +2907,8 @@ class OutputPage extends ContextSource {
 			return $return ? '' : null;
 		}
 
-		$response = $this->getRequest()->response();
+		$request = $this->getRequest();
+		$response = $request->response();
 		$config = $this->getConfig();
 
 		if ( $this->mRedirect != '' ) {
@@ -2957,7 +2958,6 @@ class OutputPage extends ContextSource {
 		# Buffer output; final headers may depend on later processing
 		ob_start();
 
-		$response->header( 'Content-type: ' . $config->get( MainConfigNames::MimeType ) . '; charset=UTF-8' );
 		$response->header( 'Content-language: ' .
 			MediaWikiServices::getInstance()->getContentLanguage()->getHtmlCode() );
 
@@ -2990,6 +2990,7 @@ class OutputPage extends ContextSource {
 		}
 
 		if ( $this->mArticleBodyOnly ) {
+			$response->header( 'Content-type: ' . $config->get( MainConfigNames::MimeType ) . '; charset=UTF-8' );
 			if ( $this->cspOutputMode === self::CSP_HEADERS ) {
 				$this->CSP->sendHeaders();
 			}
@@ -3001,6 +3002,15 @@ class OutputPage extends ContextSource {
 			}
 
 			$sk = $this->getSkin();
+			$skinOptions = $sk->getOptions();
+
+			if ( $skinOptions['format'] === 'json' ) {
+				$response->header( 'Content-type: application/json; charset=UTF-8' );
+				return json_encode( [
+					$this->msg( 'skin-json-warning' )->escaped() => $this->msg( 'skin-json-warning-message' )->escaped()
+				] + $sk->getTemplateData() );
+			}
+			$response->header( 'Content-type: ' . $config->get( MainConfigNames::MimeType ) . '; charset=UTF-8' );
 			$this->loadSkinModules( $sk );
 
 			MWDebug::addModules( $this );

includes/ServiceWiring.php

@@ -2161,6 +2161,19 @@ return [
 				]
 			]
 		], true );
+		// Register a hidden skin for outputting skin json
+		$factory->register( 'json', 'SkinJSON', [
+			'class' => SkinApi::class,
+			'args' => [
+				[
+					'name' => 'json',
+					'styles' => [],
+					'supportsMwHeading' => true,
+					'format' => 'json',
+					'templateDirectory' => __DIR__ . '/skins/templates/apioutput',
+				]
+			]
+		] );
 
 		return $factory;
 	},

includes/skins/Skin.php

@@ -272,6 +272,11 @@ abstract class Skin extends ContextSource {
 	 *  - `name`: Required. Internal skin name, generally in lowercase to comply with conventions
 	 *     for interface message keys and CSS class names which embed this value.
 	 *
+	 *  - `format`: Enable rendering of skin as json or html.
+	 *
+	 *     Since: MW 1.43
+	 *     Default: `html`
+	 *
 	 *  - `styles`: ResourceLoader style modules to load on all pages. Default: `[]`
 	 *
 	 *  - `scripts`: ResourceLoader script modules to load on all pages. Default: `[]`
@@ -2411,6 +2416,7 @@ abstract class Skin extends ContextSource {
 			'styles' => [],
 			'scripts' => [],
 			'toc' => true,
+			'format' => 'html',
 			'bodyClasses' => [],
 			'bodyOnly' => false,
 			'clientPrefEnabled' => false,

includes/skins/SkinApi.php

@@ -29,7 +29,6 @@
  * @since 1.25
  */
 class SkinApi extends SkinMustache {
-	public $skinname = 'apioutput';
 	/**
 	 * Extension of class methods is discouraged.
 	 * Developers are encouraged to improve the flexibility of SkinMustache

languages/i18n/en.json

@@ -4414,6 +4414,8 @@
 	"skin-action-undelete": "Undelete",
 	"skin-action-delete": "Delete",
 	"skin-action-move": "Move",
+	"skin-json-warning": "@WARNING",
+	"skin-json-warning-message": "This is not an API, it is only for debugging! Do not use in gadgets or production code.",
 	"copyupload-allowed-domains": "",
 	"parsoid-stash-rate-limit-error": "Stashing failed because rate limit was exceeded. Please try again later.",
 	"parsoid-resource-limit-exceeded": "Parsoid resources limit exceeded: $1",

languages/i18n/qqq.json

@@ -4676,6 +4676,8 @@
 	"skin-action-undelete": "Tab at top of page, in vector skin.\n{{Identical|Undelete}}",
 	"skin-action-delete": "Used in the Vector skin, as the name of a tab at the top of the page. See for example {{canonicalurl:Translating:MediaWiki|useskin=vector}}\n\n{{Identical|Delete}}",
 	"skin-action-move": "The \"Move\" action renames pages.\n\nUsed in the Vector skin, on the tabs at the top of the page. See for example {{canonicalurl:Talk:Main_Page|useskin=vector}}\n\n{{Identical|Move}}",
+	"skin-json-warning": "Should be prefixed with '@' character. Shown in useskin=json response.",
+	"skin-json-warning-message": "Shown in useskin=json response. Warns user that this is only intended for debugging.",
 	"copyupload-allowed-domains": "{{notranslate}}",
 	"parsoid-stash-rate-limit-error": "Error message returned by parsoid REST endpoints when the rate limit for stashing has been exceeded.",
 	"parsoid-resource-limit-exceeded": "Error message indicating that Parsoid exceeded resource limits.  Parameters:\n* $1 - a non-translatable internal error message specifying the problem.",