@enumag Could you please first add a failing test case for this?

Something like:

$form =$this->factory->create('text','test');$form->submit(array());$this->assertSame('test',$form->getData());$this->assertFalse($form->isValid());

This listener sounds like a bad idea (also for performances), this should be checked inForm::submit() instead IMHO, like this is done for compound forms here

But since not compound forms can be submitted an array (like a multiple non expandedChoiceType as you pointed out), it means that we should use an internal option to define the behavior (accepting array or not), anyway I can't find a better solution right now.

@HeahDude Good suggestions although far from solving the issue. The problem with failing test is that checking if the form is not valid is NOT enough. It will still cause the error when rendering the invalid form. But I can't add a test for rendering because the form component itself has no templates.

I believe it's necessary to actually throw away the submitted value as it's not only invalid but also can't be used for rendering - the test should check that the value got trashed AND the form is invalid. Where do you think this should happen? (Probably based on the internal option.)

If my test above is green (which should not currently), then the issue should be solved, meaning we should preventarray() === $form->getData().

I've linked two places where I think we can handle this in theForm class. But others can have a better idea.

I guess that should be fixed in 2.7 base branch?

Note thatFileType uses themultiple attribute as well, it don't use data transformer and expect anarray() also.

@HeahDude We could introduce an option that can be used by form types to define the accepted types when the type is not compound. Before Symfony 4.0 the default value would benull which doesn't do anything, but we would already deprecate thenull value. In 4.0, we would then disallownull and makestring the new default value.

Related to#4102

Closing in favor of#29307