[RFC] Improve type inference for `getData()` about laminas-form HOT 3 CLOSED

<?php

/**
 * @template TValues
 */
interface Filter {
    /** @return TValues */
    public function getValues(): array;
}

/**
 * @psalm-type MyPayload = array{
 *    foo: non-empty-string,
 * }
 * @implements Filter<MyPayload>
 */
class MyFilter implements Filter {
    
    public function getValues(): array
    {
        return ['foo' => 'bar'];
    }
}

/** @template TFilterShape */
interface Form
{
    /** @return TFilterShape */
    public function getData(): array;
    
    /** @param Filter<TFilterShape> $filter **/
    public function setFilter(Filter $filter): void;
}

/**
 * @template TFilterShape
 * @implements Form<TFilterShape>
 */
abstract class BaseForm implements Form
{
    /** @var Filter<TFilterShape> */
    private Filter|null $filter = null;
    
    /** @return TFilterShape */
    public function getData(): array
    {
        if (! $this->filter) { throw new Exception('Bad News'); }
        
        return $this->filter->getValues();
    }
    
    /** @param Filter<TFilterShape> $filter **/
    public function setFilter(Filter $filter): void
    {
        $this->filter = $filter;
    }
}

/**
 * @psalm-import-type MyPayload from MyFilter
 * @extends BaseForm<MyPayload>
 */
class MyForm extends BaseForm
{
}

$form = new MyForm();
$form->setFilter(new MyFilter());

$foo = $form->getData()['foo'];

/** @psalm-trace $foo */