RTC: Fix syncing of emoji / surrogate pairs#76049
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chriszarate merged 2 commits intotrunkfrom Mar 2, 2026
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alecgeatches
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Confirmed that the trunk implementation caused syncing issues with emojis (�), and that this fix addresses them.
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| page, | ||
| } ); | ||
| await utils.setCollaboration( true ); | ||
| // Clean up any leftover users from previous runs before creating. |
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I've run into this bug once before, thanks for the fix!
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Size Change: +32 B (0%) Total Size: 6.87 MB
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maxschmeling
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* Fix syncing of emoji / surrogate pairs * Fix type errors
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I just cherry-picked this PR to the wp/7.0 branch to get it included in the next release: f23578a |
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* Fix syncing of emoji / surrogate pairs * Fix type errors
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* Fix syncing of emoji / surrogate pairs * Fix type errors
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What?
When two users are collaboratively editing a post via RTC, correctly sync emoji characters and other multi-code-unit Unicode characters.
Closes #76044
Why?
The Quill Delta diff engine in
@wordpress/syncusesdiffCharsfrom thedifflibrary (v8.0.3). Indiffv7+,diffCharsusesIntl.Segmenter(when available) to tokenize by grapheme cluster, so an emoji like 😀 counts as1token. However, theDelta Op.length()andOpIteratoruse JavaScript’s.length, which counts UTF-16 code units — where the same emoji counts as2.This mismatch occurs in
convertChangesToDelta()(packages/sync/src/quill-delta/Delta.ts), wherecomponent.countfromdiffCharsis used to advance theOpIterator. Since the iterator measures in UTF-16 code units but count is in grapheme clusters,.substr()calls inOpIterator.next()split surrogate pairs, producing lone surrogates that render as � or result in data corruption.The same mismatch affects cursor position arithmetic in
diffWithCursor(), wherelastDiffPositionis tracked in grapheme clusters butcursorAfterChangeis in UTF-16 code units.How?
Add a single normalization step after each call to
diffCharsthat replacescount(grapheme clusters) withvalue.length(UTF-16 code units).Testing Instructions
Screenshots or screencast
Before
before.mov
After
after.mov