Fix uncontrolled multiline TextInput not resizing when children change

[janicduplessis]

Summary:

When a multiline TextInput is uncontrolled (no value prop) and uses children for styled text, changing the children does not cause the TextInput to resize. For example, if the children go from multiline content to empty, the input stays at its expanded height.

Root cause

During a layout pass, YGNodeCalculateLayout calls measureContent() which uses attributedStringBoxToMeasure() to decide what text to measure. For uncontrolled TextInputs with Text children, attributedStringBox in state holds the native text from the last _updateState() call — but by the time the React tree children have changed (e.g. cleared), attributedStringBox still contains the old native text.

updateStateIfNeeded() would normally sync the state, but it runs in layout() which is called after YGNodeCalculateLayout has already computed sizes. So Yoga measures with stale text and the height doesn't update.

Fix

In attributedStringBoxToMeasure(), for uncontrolled TextInputs (props.text is empty), check if the React tree attributed string has diverged from what's stored in state. If so, use the React tree version for measurement instead of the stale attributedStringBox.

The check is guarded by props.text.empty() so controlled TextInputs (which are the common case and don't have this issue) skip it entirely with zero overhead.

Changelog:

[IOS][FIXED] - Fix uncontrolled multiline TextInput not resizing when children change

Test Plan:

1. Create an uncontrolled multiline TextInput with children:

const [text, setText] = useState('');
<TextInput multiline onChangeText={setText}>
  <Text>{text}</Text>
</TextInput>
<Button title="Clear" onPress={() => setText('')} />

2. Type enough text to make the input expand to multiple lines
3. Press "Clear" to empty the text
4. Before fix: Input stays at its expanded height
5. After fix: Input shrinks back to single-line height

[terrysahaidak]

Can confirm the fix is working for us on 0.83.2

[github-actions]

Warning

JavaScript API change detected

This PR commits an update to ReactNativeApi.d.ts, indicating a change to React Native's public JavaScript API.

• Please include a clear changelog message.
• This change will be subject to additional review.

This change was flagged as: POTENTIALLY_BREAKING

[victoriomolina]

LGTM