Duplicated paragraphs have wrong values

I'll test this a bit on some production environment while working with content.

+++ b/src/Plugin/Field/FieldWidget/ParagraphsWidget.php
@@ -1196,7 +1196,13 @@ class ParagraphsWidget extends WidgetBase {
+
+    $user_input = $form_state->getUserInput();
+    $duplicate_input = $user_input[$field_name][$delta];
+    array_splice($user_input[$field_name], $delta + 1, 0, [$duplicate_input]);
+    $form_state->setUserInput($user_input);
+

@@ -1204,7 +1210,7 @@ class ParagraphsWidget extends WidgetBase {
 
-    array_splice($widget_state['paragraphs'], $delta + 1, 0, $paragraph);
+    array_splice($widget_state['paragraphs'], $delta +1 , 0, $paragraph);
 

this might conflict with other things that we've also soon.

the way this works for new paragraphs, no matter where they are placed exactly is to append them and then use original deltas to position them.

We might want to consider doing the same here..

We also noticed similar bugs when duplicating a paragraph and then moving it before save, we ended up with some paragraphs lost and others duplicated.

Also marking as critical due to that. It's just the experimental widget, sure, but we are using that in production and so might others. API stability is one thing, data stability another.

Uh, this was a ride :)

Had to change the test a bit to work with this approach, bu it is working quite well now.

Tried moving items around before and after duplicating (and both) and it seems to be quite stable.

We need a test that does something like this:

Create a node with 3 paragraphs, A, B, C. Then move C first, then duplicate C, so youhave CCAB, then move B to second, then save. then make sure you have CBCA.

Expanded the test to cover that reorder stuff as well as deletions.