Duplicate streamfield block duplicates UUID

[fabienheureux]

Issue Summary

I noticed streamfield's blocks uuid can be not unique.

It can be an issue, in my case in a headless setup, I cache blocks based on their UUIDs.

Steps to Reproduce

For example, let's consider a streamfield, containing a structblock, containing a streamblock.
Duplicating an instance of this structblock, with existing streamblocks, cause the nested streamblock UUIDs to remain identical to the original ones

I created an example repo here https://github.com/fabienheureux/wagtail-duplicate-streamfield-uuid

1. git clone https://github.com/fabienheureux/wagtail-duplicate-streamfield-uuid
2. ./manage.py runserver
3. ./manage.py shell
4. from home.models import HomePage
5. print(HomePage.objects.first().blocks.raw_data)

[
   {
      "type":"simple_question",
      "value":{
         "extended_answer":{
            "body":[
               {
                  "type":"text",
                  "value":"<p data-block-key=\"a7uom\">Test 1 2 1 2</p>",
                  "id":"ff7f1a7a-42a6-46c9-915c-5ca453b23698" 
               }
            ]
         }
      },
      "id":"520971d8-3d49-4779-b833-46222fdd48e1"
   },
   {
      "type":"simple_question",
      "value":{
         "extended_answer":{
            "body":[
               {
                  "type":"text",
                  "value":"<p data-block-key=\"a7uom\">Coucou</p>",
                  "id":"ff7f1a7a-42a6-46c9-915c-5ca453b23698"
               }
            ]
         }
      },
      "id":"ec72605c-b58a-4d57-9ead-2af3196575b4"
   }
]

➡️ The body's UUIDs are the same

How to reproduce from Wagtail admin

1. Create a Streamfield block
2. Fill some data for the StreamBlock inside this block
3. Duplicate the Streamfield block

Technical details

• Python version: any version
• Django version: 3.2.9
• Wagtail version: 2.15.1

[fabienheureux]

To add to this, I tried to debug a bit and I placed a console.log in this file: https://github.com/wagtail/wagtail/blob/main/client/src/components/StreamField/blocks/StreamBlock.js#L294
Just after line 294

It appears that the id of a block is removed when duplicating but not its nested blocks' ids

// console.log(childState)
{
  "type": "simple_question",
  "value": {
    "extended_answer": {
      "body": [
        {
          "type": "text",
          "value": "{\"blocks\":[{\"key\":\"kpdv3\",\"text\":\"coucou\",\"type\":\"unstyled\",\"depth\":0,\"inlineStyleRanges\":[],\"entityRanges\":[],\"data\":{}}],\"entityMap\":{}}",
          "id": "f076404d-f25a-4199-9aab-a668151fae31"
        }
      ]
    }
  },
  "id": null
}

[fabienheureux]

I tried to fix this @gasman but I am very new to StreamField JavaScript's architecture.
https://github.com/wagtail/wagtail/pull/7713/files

From my point of view, it seems to work (ids are properly removed, and then added server side).
However, I might lack some knowledge to know where exactly do this change.

Let me know if you are happy with these changes, I will cleanup the PR and write a few tests.
Thanks !

[kbayliss]

Just a note that this is still an issue in wagtail==3.0.1