Add \OC::$APPSROOTS to mappings for findWebRoot

TemplateLayout.patch

Index: lib/private/TemplateLayout.php
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- lib/private/TemplateLayout.php	(revision 4f2837017c95f063d99a05b6cd6a5e73ac388d75)
+++ lib/private/TemplateLayout.php	(date 1574544614260)
@@ -48,6 +48,8 @@
 class TemplateLayout extends \OC_Template {
 
 	private static $versionHash = '';
+	/** @var null|array A list of additional mappings for findWebRoot. null means not initialized. */
+	private static $partyMap;
 
 	/**
 	 * @var \OCP\IConfig
@@ -298,7 +300,7 @@
 		$locator = new \OC\Template\CSSResourceLocator(
 			\OC::$server->getLogger(),
 			$theme,
-			array( \OC::$SERVERROOT => \OC::$WEBROOT ),
+			[\OC::$SERVERROOT => \OC::$WEBROOT] + self::partyMap(),
 			array( \OC::$SERVERROOT => \OC::$WEBROOT ),
 			$SCSSCacher
 		);
@@ -334,7 +336,7 @@
 		$locator = new \OC\Template\JSResourceLocator(
 			\OC::$server->getLogger(),
 			$theme,
-			array( \OC::$SERVERROOT => \OC::$WEBROOT ),
+			[\OC::$SERVERROOT => \OC::$WEBROOT] + self::partyMap(),
 			array( \OC::$SERVERROOT => \OC::$WEBROOT ),
 			\OC::$server->query(JSCombiner::class)
 			);
@@ -342,6 +344,27 @@
 		return $locator->getResources();
 	}
 
+	/**
+	 * Create a list of additional mappings for findWebRoot
+	 *
+	 * @return array
+	 */
+	private static function partyMap(): array {
+		if (is_array(self::$partyMap)) {
+			return self::$partyMap;
+		}
+
+		self::$partyMap = [];
+		foreach (\OC::$APPSROOTS as $appsRoot) {
+			$realPath = realpath($appsRoot['path']);
+			if (strpos($realPath, \OC::$SERVERROOT) === 0) {
+				continue;
+			}
+			self::$partyMap[$realPath] = $appsRoot['url'];
+		}
+		return self::$partyMap;
+	}
+
 	/**
 	 * Converts the absolute file path to a relative path from \OC::$SERVERROOT
 	 * @param string $filePath Absolute path