Real-time collaboration: Add more robust mergeCrdtBlocks() testing #74304

alecgeatches · 2025-12-31T20:26:50Z

As part of the work in add/flattened-rtc-blocks, we're making significant changes to the Y.Doc block data structure. This PR adds more complex and edge-case testing for mergeCrdtBlocks(), and also fixes a couple of bugs found during the process.

We will use these tests to reduce the risk that block data structure changes introduce merge errors.

Fixed bugs

The handles block type changes from non-rich-text to rich-text test was failing when an attribute transitioned from a raw string to rich-text (Y.Text) content when the string value was the same. The fix is the attributeHasTypeChange boolean which ensure both the data type and content must be the same to skip a merge.
Client Id deduplication was only running on a single level of blocks, which caused the removes duplicate clientIds across different nesting levels test. This meant a client ID could be freely duplicated as long as it was not in the same nesting level within the block structure. The code has been changed to:
1. Merge blocks, then
2. Check at the top level that all client IDs are unique.
This required making an internal mergeCrdtBlocksInternal() function that does the normal work of what mergeCrdtBlocks() did previously, then run the top level logic after. This ensures the whole block structure of client IDs are deduplicated and avoids recursively making that check.

Testing Instructions

To run the CRDT test suite:

npm run test:unit -- --testPathPattern=crdt-blocks

github-actions · 2025-12-31T20:27:04Z

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Co-authored-by: alecgeatches <[email protected]>
Co-authored-by: chriszarate <[email protected]>
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alecgeatches · 2025-12-31T20:27:31Z

@chriszarate Added a few new tests for mergeCrdtBlocks() and a couple of bug fixes. Please take a look when you have a chance.

chriszarate · 2025-12-31T20:38:48Z

packages/core-data/src/utils/crdt-blocks.ts

-		if ( ! clientId ) {
-			continue;
+		if ( clientId ) {


is this logic inverted for any particular reason?

This just allows the recursion on innerBlocks to run even if the current block is missing a client ID. I'm not clear on when a clientId will be missing from a block or if that's even a real possibility, but it was accounted for in the original code. Do you have any insight on when this happens? Should we also bail on innerBlocks in this unusual case?

No particular insight. IIRC it was copied over from Kevin's initial implementation.

This bit of code had to change to accommodate client ID deduping of the whole tree, and I think this change makes sense in that context. I can also remove this small overhaul if you want to keep it the same, but it made more sense to me to dedupe across more than one level at a time.

SirLouen

@alecgeatches this patch is not applying for me. It's rebased to the lastest trunk?

I cannot find a cursorPosition in crdt-blocks-ts

https://github.com/WordPress/gutenberg/blob/trunk/packages/core-data/src/utils/crdt-blocks.ts

alecgeatches · 2025-12-31T21:13:21Z

@SirLouen This PR is currently into our WordPress:wpvip/rtc-plugin branch, which we use to make changes upstream of actual Gutenberg trunk.

You can see cursorPosition in the branch: https://github.com/WordPress/gutenberg/blob/wpvip/rtc-plugin/packages/core-data/src/utils/crdt-blocks.ts#L195

SirLouen · 2025-12-31T22:23:55Z

@alecgeatches is this an unofficial fork or something? Isn't planned to be merged into trunk?

chriszarate · 2026-01-01T16:00:42Z

@alecgeatches is this an unofficial fork or something? Isn't planned to be merged into trunk?

This branch leads our trunk-based PRs to support our experimental plugin, which helps us validate our work against a different network transport and test in real-world scenarios. After this validation, we open PRs against trunk.

chriszarate · 2026-01-02T23:20:57Z

packages/core-data/src/utils/crdt-blocks.ts

+							const currentAttribute =
+								currentAttributes.get( attributeName );
+							const isRichText = isRichTextAttribute(
+								block.name,
+								attributeName
+							);


Could we conceivably have other attribute type transitions that we need to expect? Is there another more flexible approach that would allow us to add them in the future (and mark the location accordingly)?

Addressed in cdfe518, let me know what you think! This adds isExpectedAttributeType() which is a less brittle way of doing the same check, and modifies our block attribute cache to store all expected block types, not just those for rich text.

Actually, let me add one more change to do the same for the isRichText if statement.

Added some more changes in b283ed9 to move type-specific logic into another function.

…e function

…74304) * Add tests for mergeCrdtBlocks() edge cases * Fix potential bug if merged attribute has type change * Fix clientId deduping across block nesting levels * Move type checking in block attribute update to separate more-flexible function * Separate type-specific attribute logic into updateYBlockAttribute()

…sting (#74304) * Add tests for mergeCrdtBlocks() edge cases * Fix potential bug if merged attribute has type change * Fix clientId deduping across block nesting levels * Move type checking in block attribute update to separate more-flexible function * Separate type-specific attribute logic into updateYBlockAttribute()

…sting (WordPress#74304) * Add tests for mergeCrdtBlocks() edge cases * Fix potential bug if merged attribute has type change * Fix clientId deduping across block nesting levels * Move type checking in block attribute update to separate more-flexible function * Separate type-specific attribute logic into updateYBlockAttribute()

…sting (#74304) * Add tests for mergeCrdtBlocks() edge cases * Fix potential bug if merged attribute has type change * Fix clientId deduping across block nesting levels * Move type checking in block attribute update to separate more-flexible function * Separate type-specific attribute logic into updateYBlockAttribute()

alecgeatches added 3 commits December 31, 2025 12:53

Add tests for mergeCrdtBlocks() edge cases

1e9d100

Fix potential bug if merged attribute has type change

edb9b8e

Fix clientId deduping across block nesting levels

9a652b0

alecgeatches marked this pull request as ready for review December 31, 2025 20:26

alecgeatches requested a review from nerrad as a code owner December 31, 2025 20:26

github-actions bot added the [Package] Core data /packages/core-data label Dec 31, 2025

alecgeatches changed the title ~~Add more robust mergeCrdtBlocks() testing, fix edge cases~~ Real-time collaboration: Add more robust mergeCrdtBlocks() testing Dec 31, 2025

chriszarate reviewed Dec 31, 2025

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SirLouen reviewed Dec 31, 2025

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chriszarate added [Feature] Real-time Collaboration Phase 3 of the Gutenberg roadmap around real-time collaboration [Type] Experimental Experimental feature or API. labels Jan 1, 2026

chriszarate reviewed Jan 2, 2026

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alecgeatches added 2 commits January 5, 2026 13:17

Move type checking in block attribute update to separate more-flexibl…

cdfe518

…e function

Separate type-specific attribute logic into updateYBlockAttribute()

b283ed9

chriszarate approved these changes Jan 5, 2026

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chriszarate merged commit bacc977 into WordPress:wpvip/rtc-plugin Jan 5, 2026
32 of 36 checks passed

chriszarate deleted the add/more-merge-crdt-block-tests branch January 5, 2026 22:59

Real-time collaboration: Add more robust mergeCrdtBlocks() testing #74304

Real-time collaboration: Add more robust mergeCrdtBlocks() testing #74304

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alecgeatches commented Dec 31, 2025

Fixed bugs

Testing Instructions

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