Gate printMountItem in error handlers behind enableFabricLogs

[JakobFelixJulius]

Summary:

Two printMountItem() call sites in MountItemDispatcher.kt error handlers are not gated behind ReactNativeFeatureFlags.enableFabricLogs(), while every other printMountItem call site in the same file is.

When a Fabric mount operation fails under memory pressure, the unguarded error handler calls toString() on every mount item in the batch — each using String.format() — which triggers a fatal OutOfMemoryError (Android 256MB heap limit). The device is already low on memory when the original mount error occurs, so allocating diagnostic strings for the entire batch is the killing blow.

Impact: 67 affected users in production, 87% Android 16, all Samsung devices.

Production stacktrace (67 occurrences)

java.lang.OutOfMemoryError: Failed to allocate a 48 byte allocation with 2222800 free bytes and 2170KB until OOM, target footprint 268435456, growth limit 268435456; giving up on allocation because <1% of heap free after GC.
at java.util.Formatter.parse(Formatter.java:2737)
at java.util.Formatter.format(Formatter.java:2686)
at java.util.Formatter.format(Formatter.java:2640)
at java.lang.String.format(String.java:4489)
at com.facebook.react.fabric.mounting.mountitems.IntBufferBatchMountItem.toString(IntBufferBatchMountItem.kt:220)
at com.facebook.react.fabric.mounting.MountItemDispatcher$Companion.printMountItem(MountItemDispatcher.kt:358)
at com.facebook.react.fabric.mounting.MountItemDispatcher$Companion.access$printMountItem(MountItemDispatcher.kt:337)
at com.facebook.react.fabric.mounting.MountItemDispatcher.dispatchMountItems(MountItemDispatcher.kt:230)
at com.facebook.react.fabric.mounting.MountItemDispatcher.tryDispatchMountItems(MountItemDispatcher.kt:88)
at com.facebook.react.fabric.FabricUIManager$DispatchUIFrameCallback.doFrameGuarded(FabricUIManager.java:1484)
at com.facebook.react.uimanager.GuardedFrameCallback.doFrame(GuardedFrameCallback.kt:25)
at com.facebook.react.modules.core.ReactChoreographer.frameCallback$lambda$1(ReactChoreographer.kt:59)

Device: Samsung SM-S938B (Galaxy S25 Ultra), Android 16, 12GB RAM
Heap limit: 256MB, <1% free after GC

Fix:
Gate the two remaining printMountItem call sites behind enableFabricLogs(), matching the existing pattern used at all other call sites in the same file.

Changelog:

[ANDROID] [FIXED] - Gate diagnostic printMountItem calls in MountItemDispatcher error handlers behind enableFabricLogs() to prevent OOM crash

Test Plan:

Applied as a patch to a production app. OOM crash from the unguarded error handler path no longer occurs — confirmed over several weeks with 67 previously affected users.

The change is strictly additive gating — no logic changes. All other printMountItem call sites in the same file already use the same enableFabricLogs() guard, so this just makes the two error-handler sites consistent.

[Satttoshi]

This would be huge, I have the same OOM crashes with my Android users and it all points down to this.

[meta-codesync]

@alanleedev has imported this pull request. If you are a Meta employee, you can view this in D97414011.

[react-native-bot]

This pull request was successfully merged by @JakobFelixJulius in 7a546f9

^{When will my fix make it into a release? | How to file a pick request?}

[meta-codesync]

@alanleedev merged this pull request in 7a546f9.