nested declarations in a widget's parameters break the widget in wysiwyg editor

[ioweb-gr]

Preconditions (*)

1. 2.3.3

Steps to reproduce (*)

1. Create a module which creates a custom widget.
2. Add a parameter for an image chooser like this

<parameter name="photo" xsi:type="block" visible="true" sort_order="10">
    <label translate="true">Photo</label>
    <description translate="true">Contact photo</description>
    <block class="Vendor\Widget\Block\Adminhtml\Widget\ImageChooser">
        <data>
            <item name="button" xsi:type="array">
                <item name="open" xsi:type="string">Choose Image...</item>
            </item>
        </data>
    </block>
</parameter>

3. The image chooser class

use Magento\Framework\Data\Form\Element\AbstractElement as Element;
use Magento\Backend\Block\Template\Context as TemplateContext;
use Magento\Framework\Data\Form\Element\Factory as FormElementFactory;
use Magento\Backend\Block\Template;
class ImageChooser extends Template
{
    /**
     * @var \Magento\Framework\Data\Form\Element\Factory
     */
    protected $elementFactory;
    /**
     * @param TemplateContext $context
     * @param FormElementFactory $elementFactory
     * @param array $data
     */
    public function __construct(
        TemplateContext $context,
        FormElementFactory $elementFactory,
        $data = []
    ) {
        $this->elementFactory = $elementFactory;
        parent::__construct($context, $data);
    }
    /**
     * Prepare chooser element HTML
     *
     * @param Element $element
     * @return Element
     */
    public function prepareElementHtml(Element $element)
    {
        $config = $this->_getData('config');
        $sourceUrl = $this->getUrl('cms/wysiwyg_images/index',
            ['target_element_id' => $element->getId(), 'type' => 'file']);
        /** @var \Magento\Backend\Block\Widget\Button $chooser */
        $chooser = $this->getLayout()->createBlock('Magento\Backend\Block\Widget\Button')
            ->setType('button')
            ->setClass('btn-chooser')
            ->setLabel($config['button']['open'])
            ->setOnClick('MediabrowserUtility.openDialog(\''. $sourceUrl .'\')')
            ->setDisabled($element->getReadonly());
        /** @var \Magento\Framework\Data\Form\Element\Text $input */
        $input = $this->elementFactory->create("text", ['data' => $element->getData()]);
        $input->setId($element->getId());
        $input->setForm($element->getForm());
        $input->setClass("widget-option input-text admin__control-text");
        if ($element->getRequired()) {
            $input->addClass('required-entry');
        }
        $element->setData('after_element_html', $input->getElementHtml() . $chooser->toHtml());
        return $element;
    }
}

4. You end up with a string like this after trying to import the image
   {{widget type="Vendor\Widget\Block\TwinProductSlider" photo="https://example.com/admin/cms/wysiwyg/directive/___directive/e3ttZWRpYSB1cmw9InRlc3QvU2NyZWVuc2hvdF80LnBuZyJ9fQ,,/key/b2c5cfcfabd77525750beb97f9652a4690c523684f849a0a10b810baf9f2b39c/"}}

5. When you save the cms page for example that contains the widget you end up with this
   {{widget type="Vendor\Widget\Block\TwinProductSlider" photo="{{media url="test/Screenshot_4.png"}}"}}

6. This ends up breaking the widget because of nesting. In the backend it looks like this
   

Expected result (*)

1. The widget does not break

Actual result (*)

1. The widget is broken
   

In order to work around the issue we have to use static urls for media images or create a plugin to change the behaviour so that the parameter value is modified on save.

I've tracked lots of issues in various tutorials and gists and they all have to end up with some workaround like this to make it work. e.g.
https://gist.github.com/cedricblondeau/6174911fb4bba6cb4943#gistcomment-2056776

In my opinion this shouldn't happen out of the box and looks like a bug.
Also:
is there no predefined image upload block for widgets? Why so?

[m2-assistant]

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[m2-assistant]

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[magento-engcom-team]

✅ Confirmed by @engcom-Kilo
Thank you for verifying the issue. Based on the provided information internal tickets MC-31019 were created

Issue Available: @engcom-Kilo, You will be automatically unassigned. Contributors/Maintainers can claim this issue to continue. To reclaim and continue work, reassign the ticket to yourself.

[ioweb-gr]

Let me note that most developers in order to work around the issue encode the widgets in base64 encoding. That way they bypass the issue however, base64 encoding is not possible to fail-safe detect as there are many false positives in all detection mechanisms so nested widgets are very prone to break with this approach because you can never be 100% sure the string was encoded in the first place.

Hopefully a better way to handle such cases can be introduced instead of this approach.