Use system helper to get free space

apps/files_trashbin/lib/Quota.php

@@ -55,14 +55,13 @@ public function calculateFreeSpace($trashbinSize, $user) {
 		if ($userObject === null) {
 			return 0;
 		}
-		$quota = $this->getUserQuota($userObject);
 
 		$userFolder = \OC::$server->getUserFolder($user);
 		if ($userFolder === null) {
 			return 0;
 		}
 
-		$free = $quota - $userFolder->getSize(); // remaining free space for user
+		$free = $this->getFreeSpace($userObject);
 		if ($free > 0) {
 			// does trashbin size hit purge limit with the current free space
 			$availableSpace = ($free * $this->getPurgeLimit() / 100) - $trashbinSize;
@@ -84,21 +83,30 @@ public function getPurgeLimit() {
 	}
 
 	/**
-	 * Get user quota or free space when there is no quota set
+	 * Get free space for the current user
+	 * or free disk space if the current user has no quota set
 	 *
 	 * @param IUser $user
-	 * @return int|mixed
+	 * @return int
 	 */
-	protected function getUserQuota(IUser $user) {
+	protected function getFreeSpace(IUser $user) {
 		$quota = \OC_Util::getUserQuota($user);
 		if ($quota === FileInfo::SPACE_UNLIMITED) {
-			$quota = Filesystem::free_space('/');
+			$free = Filesystem::free_space('/');
 			// inf or unknown free space
-			if ($quota < 0) {
-				$quota = PHP_INT_MAX;
+			if ($free < 0) {
+				$free = PHP_INT_MAX;
+			}
+		} else {
+			$rootInfo = \OC\Files\Filesystem::getFileInfo('/', false);
+			if ($rootInfo instanceof FileInfo) {
+				$storage = $rootInfo->getStorage();
+				$free = $storage->free_space('');
+			} else {
+				$free = 0;
 			}
 		}
 
-		return $quota;
+		return $free;
 	}
 }

changelog/unreleased/36494

@@ -0,0 +1,5 @@
+Bugfix: Files shared with user cause purge of the trashbin content
+
+Files_thrashbin app counted incoming shares on calculation of the occupied space. It caused purge of the trashbin content when trashbin_retention_obligation is auto, user has quota set and incoming shares exceed 50% of this quota.
+
+https://github.com/owncloud/core/pull/36494