Fix iOS TextInput IME composition issues for CJK languages#56082
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kdwkr wants to merge 1 commit intofacebook:mainfrom
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Fix iOS TextInput IME composition issues for CJK languages#56082kdwkr wants to merge 1 commit intofacebook:mainfrom
kdwkr wants to merge 1 commit intofacebook:mainfrom
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CJK (Chinese/Japanese/Korean) IME composition on Fabric was broken in multiple ways - the composition underline disappeared and composition state was destroyed. This was caused by four independent issues: 1. `updateEventEmitter:` reapplied `defaultTextAttributes` every render, which destroyed the composition underline. Now deferred during active `markedTextRange` and applied after composition ends. 2. `_setAttributedString:` overwrote `attributedText` during state round-trips, resetting `markedTextRange`. Now skipped when `markedTextRange` is active. 3. `textInputShouldChangeText:inRange:` enforced `maxLength` during composition, blocking or truncating intermediate IME input. Now deferred until composition commits, with post-composition truncation. 4. `textInputDidChangeSelection` used `isEqual:` on attributed strings, which always failed during composition due to system underline attributes. Changed to bare text comparison via `isEqualToString:`. These issues only affected the New Architecture (Fabric); Paper was unaffected due to its asynchronous bridge timing. Fixes: facebook#48497 Fixes: facebook#55257 Fixes: facebook#55059
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Summary:
CJK (Chinese/Japanese/Korean) IME composition on Fabric is broken — the composition underline disappears and composition state is destroyed during input. This affects Japanese, Chinese, and Korean users on the New Architecture and has been reported as a market-blocking issue.
Root causes and fixes:
updateEventEmitter:reappliesdefaultTextAttributesevery render —RCTWrapEventEmittercreates a newNSDataeach time, failingisEqualToDictionary:, which triggers[super setDefaultTextAttributes:]and destroys the composition underline. Fix: defer during activemarkedTextRange, apply after composition ends intextInputDidChange._setAttributedString:overwrites text during state round-trips —updateState:round-trips call_setAttributedString:which replacesattributedText, resettingmarkedTextRange. Fix: skip whenmarkedTextRangeis active; text syncs viatextInputDidChange→_updateStateafter composition.maxLengthenforcement blocks IME mid-composition —textInputShouldChangeText:inRange:enforcesmaxLengthwithout checkingmarkedTextRange, truncating intermediate CJK input (e.g., Korean ㅎ→하→한). Fix: defermaxLengthduring composition, enforce via post-composition truncation intextInputDidChange.textInputDidChangeSelectiontriggers spurious updates in multiline —isEqual:onNSAttributedStringfails during composition due to system underline attributes, causing unnecessarytextInputDidChangecalls. Fix: use.string isEqualToString:for bare text comparison.Paper (old architecture) is unaffected; these issues are Fabric-only due to synchronous
updateEventEmitter:/updateState:calls.Fixes #48497
Fixes #55257
Fixes #55059
Changelog:
[IOS] [FIXED] - Fix CJK IME composition underline disappearing and composition state being destroyed in Fabric TextInput
Test Plan:
RCTTextInputComponentViewIMETests.mmcovering all 4 fixesclang -fsyntax-onlycompilation<TextInput>on Fabric — composition underline should remain visible and composition should not be interruptedmaxLengthprop works correctly after CJK composition commits<TextInput>does not fire spuriousonChangeevents during CJK composition