code: public function onSchemaIndexDefinition(SchemaIndexDefinitionEventArgs $event): void
      {
          // Skip for doctrine/dbal >= 2.9
          if (method_exists(AbstractPlatform::class, 'supportsColumnLengthIndexes')) {
              return;
          }
  
          $connection = $event->getConnection();
  
          if (!$connection->getDatabasePlatform() instanceof MySqlPlatform) {
              return;
          }
  
          $data = $event->getTableIndex();
  
          // Ignore primary keys
          if ('PRIMARY' === $data['name']) {
              return;
          }
  
          $columns = [];
          $query = sprintf("SHOW INDEX FROM %s WHERE Key_name='%s'", $event->getTable(), $data['name']);
          $result = $connection->executeQuery($query);
  
          while ($row = $result->fetch()) {
              if (null !== $row['Sub_part']) {
                  $columns[] = sprintf('%s(%s)', $row['Column_name'], $row['Sub_part']);
              } else {
                  $columns[] = $row['Column_name'];
              }
          }
  
          $event->setIndex(
              new Index(
                  $data['name'],
                  $columns,
                  $data['unique'],
                  $data['primary'],
                  $data['flags'],
                  $data['options']
              )
          );
  
          $event->preventDefault();
      }
docs: Adds the index length on MySQL platforms for Doctrine DBAL <2.9.