Warn in development when a view reports its safe area insets in a loop - #58111
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`EventEmitter::experimental_flushSync` only *requests* a beat, which is processed at the next `EventBeat::induce`. On Android the induce happens within the frame, before drawing, so a synchronous request made during layout is processed in that frame. On iOS it is not: the run loop observer that induces the beat runs before Core Animation's commit observer, so a request made from `layoutSubviews` — inside CA's commit cycle — is only processed one frame later. `AppleEventBeat` now also schedules an induce in the display phase of the current commit cycle. Core Animation runs a commit as layout → display → commit, so a zero-sized layer marked as needing display during layout has its `display` called after the whole layout pass and before the transaction is committed. A layer is kept in every visible window of every foreground scene, since the request can come from any of them — a modal and the LogBox are windows of their own — and only a layer in the tree being committed is guaranteed a display this cycle. Requests within one cycle coalesce into a single induce, so mounting ten observing views is one beat rather than ten. Two related fixes in `EventBeat` itself: a synchronous request is no longer stranded behind an already-scheduled asynchronous beat (it would silently lose its this-frame guarantee, and the leftover flag would make an unrelated later beat blocking), and `induce` becomes public so platform beats can call it from a callback. `AppleEventBeat.cpp` becomes `.mm` for the Objective-C. Covered by new unit tests in `EventBeatTest.cpp`. This is the platform half of the safe area insets work: it is what makes an inset change reported from `layoutSubviews` render in the frame it happened in. `VirtualView` uses the same mechanism.
Reports the part of a view that is covered by the system UI, as a view prop:
```jsx
<View
experimental_onSafeAreaInsetsChange={({nativeEvent: {insets, frame}}) => {
// insets: {top, right, bottom, left}, frame: {x, y, width, height}
}}
/>
```
`SafeAreaView` is deprecated in favour of `react-native-safe-area-context`,
but core surfaces like LogBox and the element inspector cannot depend on the
library, so core keeps a private copy of the deprecated component alive. The
smallest primitive that lets both sides go away is native code reporting
inset values to JavaScript — today the library's own `RNCSafeAreaProvider`
component. This adds that primitive, with the payload the library already
uses, so `SafeAreaProvider` can swap its native component for a plain `View`.
Insets are relative to the view: one laid out inside the safe area reports
zeros. That is what makes the prop composable and stops nested providers
from double-padding.
**Cost when unused.** The prop is a `bool` in `BaseViewProps`, like
`onLayout`; native only observes the safe area when it is set. On iOS the
flag is read from the props the view already holds and the last-sent insets
live behind a single pointer ivar that stays nil unless the view observes;
the only unconditional cost is a branch in `layoutSubviews`,
`didMoveToWindow` and `safeAreaInsetsDidChange`.
**Cost when used.** Events fire only when the *insets* change — the frame is
in the payload but not in the trigger — so a view moving inside a scroll
view emits nothing, and 50 observing rows scroll at the same frame times as
zero. An observing view allocates nothing per frame on Android in the steady
state. Benchmarked with the "Scroll benchmark" section of the new RNTester
example.
**Synchronous dispatch.** The event goes out through
`EventEmitter::experimental_flushSync` as a `Discrete` event, so inset-driven
layout is mounted in the frame the insets changed in — first mount included,
and on rotation the padding animates with the transition instead of jumping
after it.
Edge cases covered: view flattening (the prop forms a stacking context so
the host view cannot be optimized away), view recycling on both platforms,
Android views fully clipped by an ancestor, and multi-window iPad.
`Dimensions.get('window').experimental_safeAreaInsets` (and
`useWindowDimensions`) reports the safe area insets of the window, using the
same native computation as the view prop applied to the window itself.
Unlike the prop, this is available synchronously at startup — no event has to
arrive first — and it updates through the existing `change` event. That is
what the safe area context library needs `initialWindowMetrics` for, its last
remaining native module, and it is what lets a component render padded on its
very first frame instead of correcting itself once the first inset event
lands.
The field is absent on platforms and versions that cannot report it, rather
than reported as zeros, so a consumer can tell "no insets" from "unknown".
The system UI does not move many times a second, so a sustained stream of inset events means the layout is feeding the insets back into the position of the observed view: it is offset by the insets it reports, which moves it out from under the system UI, which changes its insets. Every one of those events renders synchronously, so the loop is paid for in frames. `View` wraps the handler in development builds and warns once per view above ten events in a second. The check lives in the handler `View` passes down rather than in either platform's observer, so it covers iOS and Android with one implementation and surfaces in LogBox with a JavaScript stack. The production branch is the identity function, so the module stays out of the bundle, and the native prop is unaffected either way — function props are normalized to `true` before props are diffed, so wrapping does not produce an update. Counts are kept per view in a `WeakMap` keyed by the event target, so views that do not loop are never charged for it. RNTester grows the mistake it warns about, and a Fantom test with a mocked clock covers the rate, the once-per-view behaviour, per-view counting, and that the handler still receives its event.
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Summary:
The system UI does not move many times a second, so a sustained stream of inset events means the layout is feeding the insets back into the position of the observed view: it is offset by the insets it reports, which moves it out from under the system UI, which changes its insets. Every one of those events renders synchronously, so the loop is paid for in frames.
Viewwraps the handler in development builds and warns once per view above ten events in a second. The check lives in the handlerViewpasses down rather than in either platform's observer, so one implementation covers iOS and Android and the warning surfaces in LogBox with a JavaScript stack instead of in logcat. That placement has one gap worth naming: the prop is onBaseViewProps, soText,ImageandScrollViewaccept it too and are not checked.Viewis where it is used in practice.The production branch is the identity function, so the module stays out of the bundle. The native prop is unaffected either way — function props are normalized to
truebefore props are diffed (ReactNativeAttributePayload.js), so a fresh wrapper per render does not produce an update. Counts are kept per view in aWeakMapkeyed by the event target, so views that do not loop pay nothing.Stacked on #58110. This PR's diff includes the ones below it until they merge; review the top commit.
Changelog:
[GENERAL] [ADDED] - Warn in development when a view reports its safe area insets in a loop
Test Plan:
covering silence at a plausible rate (20 changes 200 ms apart), one warning per view under a loop, per-view counting, and that the handler still receives its event — all with a mocked clock.
On device: RNTester grows the mistake it warns about, a view offset by the insets it reports. On an iPhone 17 Pro simulator, starting the loop produced 2652 inset events and exactly one warning, reaching LogBox and the app log:
Stack — split out of #57967, which stays open as the prototype and design discussion. GitHub will not take a fork branch as a pull request base, so each of these targets
mainand its diff contains the ones below it until they merge.This PR's own change, without the ones below it: 4 files.
👉 4. #58111 — Warn in development when a view reports its safe area insets in a loop
5. #58112 — Render the internal SafeAreaView from the safe area insets prop
6. #58113 — Remove the native SafeAreaView and the deprecated public export