What's the use case? If the option is not defined why would you like to check if it was passed?

@jakzal The issue is that you can't determine if an option was passed by the user when the value is optional (see #11572 and symfony/symfony-docs#4110).

@xabbuh do you like the hasParsedOption() method name?

I think the implementation should be actually different. There is no need to add another method with a weird name nobody will understand. I was more thinking about adding an additional argument to the existing getOption() method.

@fabpot I think the challenge with an additional argument to getOption is that wouldn't address getOptions, which I would also expect to support tri-state optionals:

command.php
$this->getOptions() => [ 'foo' => 'value when not given' ]

command.php --foo
$this->getOptions() => [ 'foo' => 'value when given but blank' ]

command.php --foo=bar
$this->getOptions() => [ 'foo' => 'bar' ];

Also, I just noticed changing getOption contradicts what @stof indicated on a related issue:

Changing getOption() is not possible as it would be a BC break (and would make many valid use cases harder to implement).
However, we could add a new method to check whether the option is present or no (still difficult in term of BC though as we cannot change the InputInterface itself for BC reasons)

While you guys are at it, it might also be useful to be able to determine if an argument has been set.