Show the paragraph and field label of fields that fail validation

And we definitively want to test cover this improvement.
If i remember right, we also already have some tests that cover validation and should be easy to extend.

For now, promoting for better prioritization as such validation errors are really annoying when you hit them as a user.

After applying this patch, I get an error when the address module tries to validate a field:

Error: Call to a member function getEntity() on string in Drupal\paragraphs\Plugin\Field\FieldWidget\ParagraphsWidget->massageFormValues() (line 2248 of modules/contrib/paragraphs/src/Plugin/Field/FieldWidget/ParagraphsWidget.php).

The property on which "getEntity()" is executed, is indeed a string which contains the invalid postal code of my address field.

So this is a new patch which does some extra checks... seems to work for me. Don't know if the approach is fool proof though...

Made a little woopsie :)

Patch doesn't apply.

Trying to move this forward.

Earlier patches seem to no longer be relevant since we are not including error messages directly in the widget anymore, we are now relying on the form display form validation helper. Because of this there's no interdiff, it's a totally different patch.

I tried to think different approaches for this, and ended up with the idea that it might just be easier/safer to post-process the error messages and prefix labels when appropriate. Admittedly not the cleanest/most efficient approach possible, but it seemed a good compromise to not having to deal with all different possible ways violation messages are added to the form.

I updated one test but there might be others that need updating too, let's see what the testbot says.

Some minor test tweaks and wording improvement.

I have rerolled this patch with the latest version.

Updated the patch.

I created a patch that handles errors only for collapsed paragraphs, because I found the previous patch to be buggy handling all $form_state errors.

Labels structure/logic is the same as the patch above, I just replaced default basic collapsed error.

A little bit adjusted patch from #16.
Now it also tries to display the actual field name from nested paragraph.

Marked NR to initiate testing on #17.

#17 works fine here when a required field inside a collapsed paragraph have a null value

• Encountered an error when validation fails on a field without a label property. Fixed by using the getLabel() method.
• Update test to check for the improved error message contents.

Tested on Drupal 10.3.0-dev and Paragraphs 8.x-1.17

Paragraph label is displayed in the error message. Collapsing a required paragraph also triggers validation. We can confirm that the error message is triggered at both the node level and paragraph level.

RTBC

Converted to a MR, did manual testing, fixed a fatal error that could happen if the target type is no longer allowed by loading the paragraph type directly to get its label.

There's still room for improvement, specifically when you have multiple nested paragraphs, then the delta is not unique, but it's obviously a big improvement. Merged.

Just as a note for anyone looking into that change: By adding a sixth parameter to the widget class, this breaks functionality for modules extending Paragraphs, for example "Default Paragraphs".

That's unfortunate, missed that, I'd accept a patch to make it conditional with fallback in a new issue.