Description

Steps to reproduce:

1. clean 5.6.11 install
2. create a matrix Matrix field with an entry type (matrixEt) - it doesn’t have to have any fields in it, just the native title
3. create a blog section with an article entry type containing the matrix field
4. create an entry in the blog section (title: “root”), add one entry to the matrix (title: “test 1”) field; fully save each slideout and root entry;
5. open the edit page for entry from step 4;
6. change the title to “root 2”
7. edit “test 1” (dbl-click)
8. change the title to “test 1 edit”
9. close the “test 1” slideout without saving
10. reload the “root 2” page
11. edit “test 1” (dbl-click)
12. change the title again and notice that the autosave returns an error about the existing provisional draft.

Issue:
In step 8, the newly created provisional draft has its owner set to the canonical version of the root entry, not the provisional draft.

After ensuring that the nested element draft is owned by the owner provisional draft, the NestedElementManager->deleteNestedElements() needs to account for when we’re deleting an owner that’s a provisional draft. In that case, the nested elements that are also provisional drafts and only belong to the owner provisional draft also have to be deleted.

Huge thanks to @tommysvr for providing a video that made compiling the above steps so much easier.

Related issues

#16778