Add error handling for --clear-schema on Oracle.

core/command/db/converttype.php

@@ -120,6 +120,17 @@ class ConvertType extends Command {
 		$toDB = $this->getToDBConnection($input, $output);
 
 		if ($input->getOption('clear-schema')) {
+			if ($input->getArgument('type') === 'oci') {
+				// Doctrine unconditionally tries (at least in version 2.3)
+				// to drop sequence triggers when dropping a table, even though
+				// such triggers may not exist. This results in errors like
+				// "ORA-04080: trigger 'OC_STORAGES_AI_PK' does not exist".
+				$output->writeln(sprintf(
+					'<error>The --clear-schema option is not supported when converting to Oracle (oci).</error>',
+					$input->getArgument('type')
+				));
+				return 1;
+			}
 			$this->clearSchema($toDB->getSchemaManager(), $input, $output);
 		}