Add useTraitHiddenOnIOS feature flag#56655
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Mirrors useTraitHiddenOnAndroid (react#54112) on iOS so apps can opt out of the `Trait::Hidden` slice-skip optimization in sliceChildShadowNodeViewPairs. When the flag is `false`, Hidden subtrees remain in the mount slice and are hidden via `UIView.hidden = YES` through the existing UIView+ComponentViewProtocol path (D8460108, 2018) instead of being torn down via REMOVE + DELETE. Default `true` so iOS behaviour is unchanged for everyone who doesn't override it.
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This was referenced Apr 29, 2026
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The goal of feature flags is to control rollout of experimental changes, not to provide runtime configuration.
Fabric's solution to this is native state, which is stored on the ShadowNode and will persist even when the view is unmounted from the native tree. For specific components losing state, please send PR's to persist it this way. |
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Closes #56656.
Summary:
Adds
useTraitHiddenOnIOS, the iOS twin ofuseTraitHiddenOnAndroid. Defaults totrueso iOS behaviour is unchanged.Set it to
falseandTrait::Hiddensubtrees stay mounted and get hidden viaUIView.hidden = YESinstead of being torn down viaREMOVE + DELETE. That hide path has been in the codebase since 2018 — the 2020 slice-skip just makes it unreachable on iOS by default.Why does this matter?
Custom Fabric components that mutate native state via Commands (the same way
RCTTextInput.focus()andRCTScrollView.scrollTo()do) lose that state silently every time an ancestor togglesdisplay: none. Commands have no prop-shape, so React can't replay them onto the freshly-built instance. And<Suspense>flipsdisplay: noneevery time it suspends — so anything below a Suspense boundary that holds Command-set state is exposed today.10-second, 3-tap reproducer: https://github.com/SudoPlz/reproducer-react-native.
Why a flag instead of just flipping the default?
Same approach as #54112 — the existing platform behaviour stays the default, apps opt out if they need to. No surprises for anyone not actively reaching for it.
Changelog:
[IOS] [ADDED] -
useTraitHiddenOnIOSfeature flag (defaults totrue)Test Plan:
zIndexAndFlattenedNodesinStackingContextTest.cppalready exercisesdisplay: noneand asserts the iOS arm via#ifdef ANDROID / #else. With the flag at its defaulttruethat assertion still holds, so existing-behaviour coverage is free.displayNoneRespectsUseTraitHiddenOnIOSOptOutoverrides the flag tofalseand asserts the inverse: Hidden subtree stays mounted, mirroring what the Android arm already says. Skipped on Android viaGTEST_SKIPbecause the iOS gate is unreachable there.