anchor summary error to field for nested matrix "blocks"

[i-just]

Description

For a matrix in a matrix where the view mode is set to inline-editable blocks, we need to continue to rewrite the errors all the way up to the element that contains the first inline matrix field. However, when adding a prefix to errors in the summary, we need to ensure only the immediate owner prefix is added. That way, we’re able to reliably anchor from the error summary to the affected field.

Related issues

#15797

[brandonkelly]

It’s expected that recursively-nested fields will get error attribute prefixes that reveal the full path to the element.

For example, locally I have a required Entries field that is nested in two parent Matrix entries, and when I save it without a value, the top-level entry gets an error with the following key:

navigation[fe6c1060-e895-4a44-9e15-b0341e6a58f8].elements[7872abb1-22ae-4523-9dde-95b51b239ac8].entry

• navigation is the first Matrix field
• fe6c1060-e895-4a44-9e15-b0341e6a58f8 is the navigation Matrix field’s entry UUID
• elements is the nested Matrix field
• 7872abb1-22ae-4523-9dde-95b51b239ac8 is the elements Matrix field’s entry UUID
• entry is the required Entries field

With this PR, the error’s key is only:

elements[7872abb1-22ae-4523-9dde-95b51b239ac8].entry

Which leaves out critical information, as the top-level entry doesn’t know anything about an elements field.

[i-just]

Thanks for the chat on this one, @brandonkelly! I reverted the previous change and used a different approach.