[Android] Missing native component crashes Fabric instead of rendering UnimplementedNativeView

Inizia da ComponentDescriptorRegistry::at() e segui il percorso di mount di Android attraverso SurfaceMountingManager e ViewManagerRegistry.get(). Confronta il comportamento di Android con il controllo di supporto e il percorso di fallback di RCTComponentViewFactory su iOS. Usa il reproducer obbligatorio per verificare che un componente nativo mancante esegua il rendering di UnimplementedNativeView, mantenga la surface in esecuzione e registri il nome del componente mancante.

Description

On Android, mounting a Fabric component whose native ViewManager is missing from the binary throws IllegalViewOperationException and tears down the surface. On iOS the same app renders the UnimplementedNativeView placeholder and keeps running. Reproduced on RN 0.86.0 with the New Architecture on both platforms.

The cause is in ComponentDescriptorRegistry::at(): an unknown component name is assumed to be a legacy view and gets an UnstableLegacyViewManagerAutomaticComponentDescriptor. Since useFabricInterop() defaults to true, the UnimplementedNativeViewComponentDescriptor branch never runs. Nothing checks the assumption, so the failure lands at mount in SurfaceMountingManager → ViewManagerRegistry.get(), which throws. Android does install the fallback, and the crash message itself lists UnimplementedNativeView among the registered ViewManagers. It's wired up and simply unreachable. iOS doesn't have this problem because RCTComponentViewFactory checks isSupported: before taking the interop path and otherwise falls through to the placeholder.

JS can't catch it earlier: under bridgeless, view configs come from static Codegen definitions and the native side is never consulted.

Any app with a library's JS installed but its native code absent hits this: a dependency added without rebuilding, or a build that predates it.

Expected: Android behaves like iOS, rendering the placeholder plus a log naming the missing component. The name matters, since today's crash at least identifies the component and a silent placeholder would hide the problem entirely.

Steps to reproduce

1. Clone https://github.com/TaduJR/rn-repro-fabric-interop-viewmanager the entire reproducer is App.tsx, which registers a Fabric component (via NativeComponentRegistry.get, the same registration Codegen emits) under a name no native code provides. Node 24+ required (the config files are TypeScript).
2. npm install
3. npx react-native run-android
4. The screen shows Fabric = true, bridgeless = true and hasViewManagerConfig(ThisNativeComponentIsNotInTheBinary) = false, confirming the component exists in no native registry.
5. Press Mount the component.
6. The surface crashes with IllegalViewOperationException instead of rendering the UnimplementedNativeView placeholder.

React Native Version

0.86.0

Affected Platforms

Runtime - Android, Build - MacOS

Areas

Fabric - The New Renderer, Codegen

Output of npx @react-native-community/cli info

System:
  OS: macOS 26.5.2
  CPU: (14) arm64 Apple M4 Pro
  Memory: 194.66 MB / 24.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 24.13.0
    path: /Users/natu/.nvm/versions/node/v24.13.0/bin/node
  Yarn:
    version: 1.22.22
    path: /Users/natu/.nvm/versions/node/v24.13.0/bin/yarn
  npm:
    version: 11.6.2
    path: /Users/natu/.nvm/versions/node/v24.13.0/bin/npm
  Watchman:
    version: 2026.03.16.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.16.2
    path: /Users/natu/.rbenv/shims/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 25.5
      - iOS 26.5
      - macOS 26.5
      - tvOS 26.5
      - visionOS 26.5
      - watchOS 26.5
  Android SDK:
    API Levels:
      - "33"
      - "34"
      - "36"
      - "36"
      - "37"
    Build Tools:
      - 35.0.0
      - 36.0.0
      - 36.1.0
      - 37.0.0
    System Images:
      - android-35 | Google Play Tablet ARM 64 v8a
      - android-36.1 | Google Play ARM 64 v8a
      - android-36 | Google Play ARM 64 v8a
      - android-36 | Pre-Release 16 KB Page Size Google Play ARM 64 v8a
      - android-37.0 | 16 KB Page Size Google Play ARM 64 v8a
      - android-37.0 | 16 KB Page Size Google APIs ARM 64 v8a
    Android NDK: Not Found
IDEs:
  Android Studio: 2026.1 AI-261.23567.138.2611.15646644
  Xcode:
    version: 26.6/17F113
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 25.0.3
    path: /usr/bin/javac
  Ruby:
    version: 3.3.4
    path: /Users/natu/.rbenv/shims/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 20.1.0
    wanted: 20.1.0
  react:
    installed: 19.2.3
    wanted: 19.2.3
  react-native:
    installed: 0.86.0
    wanted: 0.86.0
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: true
  newArchEnabled: true

Stacktrace or Logs

com.facebook.react.uimanager.IllegalViewOperationException: Can't find ViewManager 'ThisNativeComponentIsNotInTheBinary' nor 'RCTThisNativeComponentIsNotInTheBinary' in ViewManagerRegistry, existing names are: [DebuggingOverlay, RCTSafeAreaView, RCTModalHostView, AndroidProgressBar, AndroidHorizontalScrollView, RCTImageView, RCTText, AndroidHorizontalScrollContentView, UnimplementedNativeView, RCTScrollView, RCTView, AndroidDrawerLayout, AndroidSwitch, AndroidSwipeRefreshLayout, AndroidTextInput, RCTSelectableText, VirtualView]
	at com.facebook.react.uimanager.ViewManagerRegistry.get(ViewManagerRegistry.kt:72)
	at com.facebook.react.fabric.mounting.SurfaceMountingManager.createViewUnsafe(SurfaceMountingManager.kt:610)
	at com.facebook.react.fabric.mounting.SurfaceMountingManager.preallocateView(SurfaceMountingManager.kt:1104)
	at com.facebook.react.fabric.mounting.mountitems.PreAllocateViewMountItem.execute(PreAllocateViewMountItem.kt:39)
	at com.facebook.react.fabric.mounting.MountItemDispatcher.executeOrEnqueue(MountItemDispatcher.kt:379)
	at com.facebook.react.fabric.mounting.MountItemDispatcher.dispatchPreMountItemsImpl(MountItemDispatcher.kt:331)
	at com.facebook.react.fabric.mounting.MountItemDispatcher.dispatchPreMountItems(MountItemDispatcher.kt:325)
	at com.facebook.react.fabric.FabricUIManager$DispatchUIFrameCallback.doFrameGuarded(FabricUIManager.java:1623)
	at com.facebook.react.uimanager.GuardedFrameCallback.doFrame(GuardedFrameCallback.kt:42)
	at com.facebook.react.modules.core.ReactChoreographer.frameCallback$lambda$1(ReactChoreographer.kt:58)
	at android.view.Choreographer.doCallbacks(Choreographer.java:1252)
	at android.view.Choreographer.doFrame(Choreographer.java:1205)
	at android.os.Looper.loop(Looper.java:397)
	at android.app.ActivityThread.main(ActivityThread.java:9523)

MANDATORY Reproducer

https://github.com/TaduJR/rn-repro-fabric-interop-viewmanager

Screenshots and Videos

Android:

iOS: