Suppress validation errors being shown in the preview

Moving this to the 2.0.x branch. Also, I think we need to figure out how to suppress these errors instead of just hiding them via CSS.

I know that the preview is built from the form state, which itself has methods available related to validation, namely:

setValidationEnforced()
setLimitValidationErrors()
setValidationComplete()

I tried using those within a copy of the form state in this module's compilePreview() function and then sending that to the tempstore $store_private->set() call at the end of the function, but it didn't seem to work. If we can get it working, however, I think this approach would be much better.

I believe this is also addressed in 2.1.x - marking as fixed.

Tested this in 2.1.0 and it still exhibits the same behavior.

Whoops my bad. On initial load in Gin with the preview open by default I don't see the validation error, but I do see it if I refresh the preview.

The error that I find most disruptive to the user experience is the error thrown when using an image field, such as when creating an article with a standard install of Drupal. You see the preview and everything thing looks great, but once you upload an image the only thing you see is the error about missing alt text.

IIRC I also tried this with Inline Form Errors installed, but it still didn't work, though that was with an older version.

I started a new MR targeting 2.1.x, removing all status messages.

Before the patch, an image field breaks the preview when an image is uploaded, showing only the validation error:

After the patch, the validation error isn't shown, but the preview is not show either. The result is even more confusing to the user, since it is effectively a black preview:

We need to actually suppress the errors, not just hide them.

I was able to successfully suppress all validation errors by decorating and adding preview form-specific logic to the form_error_handler service.

This is great, and works exactly the way I had hoped.

Back in action, reviewing...

I just found out this suppresses all errors on node forms.

Fixed!

I'll have to manually test this.