Trying to turn on theme debug, but getting an error: Drush command terminated abnormally due to an unrecoverable error

Question

I'm new to Drupal and Drush and so am hoping someone can shed some light on this.

I tried to turn on Theme Debug with Drush:

drush vset theme_debug 1

But I keep getting an error I don't entirely understand:

Drush command terminated abnormally due to an unrecoverable error.                                             
Error: Declaration of Drush\Command\DrushInputAdapter::hasParameterOption() must be compatible with
Symfony\Component\Console\Input\InputInterface::hasParameterOption($values, $onlyParams = false) in
phar:///usr/local/bin/drush/lib/Drush/Command/DrushInputAdapter.php, line 27

I tried drush status too and got the same issue, so I think drush is probably broken across the board.

I tried deleting and reinstalling drush and reprovisioning my virtual box to no affect.

Would anyone know what could've gone wrong here?

(I am running Drush 8.1.7. on Drupal 7.5)

Answer 1

Update drush

composer require drush/drush:9.0.0-alpha1