Undoing content inserted within a paragraph results in an error caused by a bad position path during the undo transformation

[aStewartDesign]

📝 Provide detailed reproduction steps (if any)

1. Use model.change(() => model.insertContent(...)) to insert two document fragments in the middle of a paragraph
2. Execute the undo command twice
3. On the second undo command, an error is thrown: CKEditorError: model-position-path-incorrect-format {"path":[]}

See my test case here which throws this error.

✔️ Expected result

No error is thrown and both changes are undone successfully.

❌ Actual result

An error is thrown: CKEditorError: model-position-path-incorrect-format {"path":[]}

❓ Possible solution

In my debugging, it seems like a bad path is getting created during the undo operation transformation. Even though the editor model only has one paragraph in it, an operation position is getting transformed into a position with the path [26]. I traced the bad path back to this transformation function which calls Position._getTransformedByMove, with the bad path ultimately getting created in Position._getCombined. After playing around with this a bit, I'm not exactly sure how to fix this so the positions get transformed correctly however this seems to be the location where the bad path is originally coming from.

📃 Other details

• Browser: Chrome v130
• OS: MacOS
• First affected CKEditor version: unknown
• Installed CKEditor plugins: ckeditor5-undo

---

If you'd like to see this fixed sooner, add a 👍 reaction to this post.

[scofalik]

@aStewartDesign, thank you for bringing this to our attention and attaching steps to reproduce as a test case, this was very helpful.

Just letting you know that we have a PR with a fix for this bug: #17427

[aStewartDesign]

Thank you, much appreciated! 🙏🏻

[scofalik]

Closed by #17427.