fix(View): pass fallbackKey to renderItem in default children branch

[cricrimessina]

Summary

Fix for React key warning. In View's renderItem, the default branch (used when a child doesn't match the Hidden or multi-child Fragment cases) never passes a fallbackKey, unlike the other two branches. So when a View/View.Item child has no explicit key, the wrapping Fragment ends up keyed with undefined — hence the "Each child in a list should have a unique key prop" warning.

Fix: pass usedIndex as fallbackKey, same as the other branches already do.

Related Issue

None — found while debugging a React key warning in a consuming app.

Screenshots / Recordings

No visual change, just a fix for a console warning.

Notes for Reviewers

Single line change:

return renderItem({ child, index: usedIndex, fallbackKey: usedIndex });

Example that triggers the warning before this fix — plain text and a <br /> as direct children, none with an explicit key:

<View as="p" justify="center" textAlign="center">
  {__("Some descriptive text explaining a concept to the user.")}
  <br />
  {__("A second sentence continuing the explanation, on its own line.")}
</View>

[blvdmitry]

@cricrimessina Hey, thanks for the PR, is this happening for you in React 18 or 19? I tried running fable against the PR trying to better understand the edge cases and it suggested that it shouldn't be happening in React 19 today already

[cricrimessina]

@blvdmitry Hi, thanks for looking into it! I reproduced this on React 19 (specifically 19.2.8).