Hi @seferov, this is the equivalent of the phpstan dynamic return type phpstan/phpstan-symfony#228

Any idea was could be wrong with my code @orklah ?

When I add dump inside the return type provider, it's executed and returning

return new Type\Union([
 new Type\Atomic\TGenericObject(FormErrorIterator::class, [
 new Type\Union([new TNamedObject(FormError::class)]),
 ]),
 ]);

Can you give me more details please? What are you trying to do, what is the issue you encounter? Note: I don't use symfony a lot so don't assume I know what those classes do :)

Can you give me more details please? What are you trying to do, what is the issue you encounter? Note: I don't use symfony a lot so don't assume I know what those classes do :)

Sure,

The method FormInterface::getErrors is returning a FormErrorIterator which is an Iterator of FormError|FormErrorIterator.

When you call getErrors(true, false) you really get a FormErrorIterator<FormError|FormErrorIterator>.
But in every other case, getErrors is returning a FormErrorIterator<FormError>., so you should be able to iterator on the FormErrorIterator and call getMessage (which is a method of a FormError) on every item.

So I tried to introduce a dynamic return type provider, which seems to return the correct value according to my dumps. I even added a stub for FormErrorIterator to be sure it's a generic for the items it iterate over. And still,

 foreach ($form->getErrors() as $error1) {
 $messages[] = $error1->getMessage();
 }

is reported as an error.

I can't see your Trace in the CI, but the fact Psalm emits a MixedAssignment is not a good sign. It may be because of the recursion on @template T of FormError|FormErrorIterator

Can you tell me what the Trace is returning on your side?

With

 foreach ($form->getErrors() as $error1) {
 /** @psalm-trace $error1 */
 $messages[] = $error1->getMessage();
 }

I had $error1: FormError|FormErrorIterator

I didn't try to trace $foo = $form->getErrors(), but I will.

yeah, please do. $error1 should definitely not be FormError|FormErrorIterator

$errors = $form->getErrors();
/** @psalm-trace $errors */
foreach ($errors as $error6) {
 /** @psalm-trace $error6 */
 $messages[] = $error6->getMessage();
}

gives

$errors: Symfony\Component\Form\FormErrorIterator<Symfony\Component\Form\FormError>
$error6: Symfony\Component\Form\FormError|Symfony\Component\Form\FormErrorIterator<Symfony\Component\Form\FormError|Symfony\Component\Form\FormErrorIterator<Symfony\Component\Form\FormError|Symfony\Component\Form\FormErrorIterator>> 

I discovered I think it was related to the definition of the current method

 /**
 * Returns the current element of the iterator.
 *
 * @return FormError|self An error or an iterator containing nested errors
 */
 public function current()
 {
 return current($this->errors);
 }

So I overrade the phpdoc in the stub to

 /**
 * @return T
 */
 public function current();

I'd like the confirmation by @orklah I did the right fix but I think this is ready to be merged @seferov :)

That's what I would have done too at least :)