resourceloader: Fix debug mode for RL-to-RL cross-wiki module loads

The native "foreign module source" feature, as used by the GlobalCssJs
extension, did not work correctly in debug mode as the urls returned
by the remote wiki were formatted as "/w/load.php...", which would
be interpreted by the browser relative to the host document, instead
of relative to the parent script.

For example:

1. Page view on en.wikipedia.org.

2. Script call to
   meta.wikimedia.org/w/load.php?debug=true&modules=ext.globalCssJs.user&user

   This URL is formatted by getScriptURLsForDebug on en.wikipedia.org,
   when building the article HTML. It knows the modules is on Meta, and
   formats it as such.

   So far so good.

3. meta.wikimedia.org responds with an array of urls for sub resources.
   That array contained URLs like "/w/load.php...only=scripts".

   These were formatted by getScriptURLsForDebug running on Meta,
   no longer with a reason to make it a Meta-Wiki URL as it isn't
   perceived as cross-wiki. It is indistinguishable from debugging
   a Meta-Wiki page view from its perspective.

This patch affects scenario 3 by always expanding it relative to the
current-request's wgServer. We still only do this in debug mode. There
is not yet a need to do this in non-debug mode, and if there was we'd
likely want to find a way to avoid it in the common case to keep
embedded URLs short.

The ResourceLoader::expandUrl() method is similar to the one in
Wikimedia\Minify\CSSMin.

Test Plan:

* view-source:http://mw.localhost:8080/w/load.php?debug=1&modules=site
  For Module base class.
  Before, the array entries were relative. After, they are full.
* view-source:http://mw.localhost:8080/w/load.php?debug=1&modules=jquery
  For FileModule.
  Before, the array entries were relative. After, they are full.
* view-source:http://mw.localhost:8080/wiki/Main_Page?debug=true
  Unchanged.
* view-source:http://mw.localhost:8080/wiki/Main_Page
  Unchanged.

Bug: T255367
Change-Id: I83919744b2677c7fb52b84089ecc60b89957d32a

1 files changed, 22 insertions, 0 deletions

diff --git a/tests/phpunit/includes/resourceloader/ResourceLoaderFileModuleTest.php b/tests/phpunit/includes/resourceloader/ResourceLoaderFileModuleTest.php
index bc01ce49053f..7959742b10cc 100644
--- a/tests/phpunit/includes/resourceloader/ResourceLoaderFileModuleTest.php
+++ b/tests/phpunit/includes/resourceloader/ResourceLoaderFileModuleTest.php
@@ -168,6 +168,28 @@ class ResourceLoaderFileModuleTest extends ResourceLoaderTestCase {
 	}
 
 	/**
+	 * @covers ResourceLoader::expandUrl
+	 * @covers ResourceLoaderFileModule
+	 */
+	public function testGetScriptURLsForDebug() {
+		$ctx = $this->getResourceLoaderContext();
+		$module = new ResourceLoaderFileModule( [
+			'localBasePath' => __DIR__ . '/../../data/resourceloader',
+			'remoteBasePath' => '/w/something',
+			'scripts' => [ 'script-comment.js' ],
+		] );
+		$module->setName( 'testing' );
+		$module->setConfig( $ctx->getResourceLoader()->getConfig() );
+
+		$this->assertEquals(
+			[
+				'https://example.org/w/something/script-comment.js'
+			],
+			$module->getScriptURLsForDebug( $ctx )
+		);
+	}
+
+	/**
 	 * @covers ResourceLoaderFileModule
 	 */
 	public function testGetAllSkinStyleFiles() {