Use a better error message and point the users to the support channels

Signed-off-by: Joas Schilling <coding@schilljs.com>

lib/private/Installer.php

@@ -41,6 +41,7 @@
 
 namespace OC;
 
+use Doctrine\DBAL\Exception\TableExistsException;
 use OC\App\AppStore\Fetcher\AppFetcher;
 use OC\App\CodeChecker\CodeChecker;
 use OC\App\CodeChecker\EmptyCheck;
@@ -457,7 +458,14 @@ class Installer {
 		//install the database
 		$appPath = OC_App::getAppPath($app);
 		if(is_file("$appPath/appinfo/database.xml")) {
-			OC_DB::createDbFromStructure("$appPath/appinfo/database.xml");
+			try {
+				OC_DB::createDbFromStructure("$appPath/appinfo/database.xml");
+			} catch (TableExistsException $e) {
+				throw new HintException(
+					'Failed to enable app ' . $app,
+					'Please ask for help via one of our <a href="https://nextcloud.com/support/" target="_blank" rel="noreferrer">support channels</a>.'
+				);
+			}
 		}
 
 		//run appinfo/install.php

lib/private/Updater.php

@@ -121,6 +121,10 @@ class Updater extends BasicEmitter {
 		$success = true;
 		try {
 			$this->doUpgrade($currentVersion, $installedVersion);
+		} catch (HintException $exception) {
+			$this->log->logException($exception, ['app' => 'core']);
+			$this->emit('\OC\Updater', 'failure', array($exception->getMessage() . ': ' .$exception->getHint()));
+			$success = false;
 		} catch (\Exception $exception) {
 			$this->log->logException($exception, ['app' => 'core']);
 			$this->emit('\OC\Updater', 'failure', array(get_class($exception) . ': ' .$exception->getMessage()));