doctrine/migrations — pull request #160 by c960657 (2014-03-08 15:36:00+00:00)
Title: Do not generate file if there are no changes

The following code in DiffCommand.php is never run because of the "Migration can only be executed safely on XXX"-warning that is always added:

```
if ( ! $up && ! $down) {
$output->writeln('No changes detected in your mapping information.', 'ERROR');

return;
}
```

This regression was introduced in February 2011: 14f6389c99e3a4c60085ce27fe608317db962e13

With this patch, the warning is only added when there are actual changes to migrate.