On the cxx platform, every TurboModuleRegistry lookup answers a new C++ TurboModule instance, where Android and iOS keep one per name

Start from the reproducer test at packages/react-native/Libraries/TurboModule/__tests__/TurboModuleLookup-itest.js and run it with Fantom to confirm the identity failure. Trace the lookup through ReactCxxTurboModuleProvider::operator() into TurboModuleBinding::getModule, and compare with Android's TurboModuleManager per-name cache. Decide whether the cache belongs in the provider or the binding, then make repeated TurboModuleRegistry.get('SourceCode') calls return one instance without changing other platforms.

Description

On React Native's cxx platform (ReactCxxPlatform, which Fantom's tester runs), ReactCxxTurboModuleProvider::operator() returns a new std::shared_ptr<TurboModule> for every lookup: each provider is called again and each built-in module is std::make_shared again, with no cache by name. ReactHost installs that provider as TurboModuleBinding's module provider directly, and TurboModuleBinding::getModule caches only the module's jsRepresentation_, on the instance it was just handed, so two TurboModuleRegistry.get(name) calls answer two different objects. Android's TurboModuleManager (turboModuleCache_) and iOS's RCTTurboModuleManager keep one instance per name, and TurboModuleBinding::getModule itself says "TurboModules are cached by name in TurboModuleManagers".

A C++ TurboModule that keeps state, a subscription or a registered commit hook therefore behaves on cxx as it does on no device: its state lives only as long as JavaScript holds the one object it was set on, and each lookup can register another hook. I met it with a C++ module that installs a commit hook on its first use; in Fantom's tester the hook went away with the object one lookup returned.

Steps to reproduce

1. git clone https://github.com/YevheniiKotyrlo/react-native-fantom-reproducer && cd react-native-fantom-reproducer
2. ./fantom/reproduce.sh cxx-turbomodule-per-lookup (needs Docker). It clones react/react-native at main, builds Fantom's tester, and runs this test, its license and Flow header left out here, as packages/react-native/Libraries/TurboModule/__tests__/TurboModuleLookup-itest.js:

import '@react-native/fantom/src/setUpDefaultReactNativeEnvironment';

import * as TurboModuleRegistry from '../TurboModuleRegistry';

describe('TurboModuleRegistry', () => {
  it('answers the same module for every lookup of one name', () => {
    expect(TurboModuleRegistry.get('SourceCode')).not.toBeNull();
    const first = TurboModuleRegistry.get('SourceCode');
    const second = TurboModuleRegistry.get('SourceCode');
    expect(first === second).toBe(true);
  });
});

The same on a checkout of main: put that file in place, then yarn workspace @react-native/fantom build and yarn fantom packages/react-native/Libraries/TurboModule/__tests__/TurboModuleLookup-itest.js. The reproducer builds with Clang 23 and CXXFLAGS=-Wno-error=deprecated-literal-operator for #59667; the defect does not depend on the compiler.

React Native Version

0.88.0 (reproduced on main at 54905a2)

Affected Platforms

Build - Linux

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

System:
  OS: Linux 6.18 Ubuntu 22.04.5 LTS 22.04.5 LTS (Jammy Jellyfish)
  CPU: (24) x64 AMD Ryzen 9 9950X3D 16-Core Processor
  Memory: 116.43 GB / 125.63 GB
  Shell:
    version: 5.1.16
    path: /bin/bash
Binaries:
  Node:
    version: 22.14.0
    path: /usr/local/bin/node
  Yarn:
    version: 1.22.22
    path: /usr/local/bin/yarn
  npm:
    version: 10.9.2
    path: /usr/local/bin/npm
  Watchman: Not Found
SDKs:
  Android SDK:
    API Levels:
      - "37"
    Build Tools:
      - 37.0.0
    Android NDK: 28.2.13676358
IDEs:
  Android Studio: Not Found
Languages:
  Java:
    version: 17.0.20.1
    path: /usr/bin/javac
  Ruby:
    version: 3.0.2
    path: /usr/bin/ruby
npmPackages:
  "@react-native-community/cli": Not Found
  react: Not Found
  react-native: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: Not found
  newArchEnabled: Not found
iOS:
  hermesEnabled: Not found
  newArchEnabled: Not found

Stacktrace or Logs

FAIL fantom packages/react-native/Libraries/TurboModule/__tests__/TurboModuleLookup-itest.js (6.401 s)
  TurboModuleRegistry (hermes)
    ✕ answers the same module for every lookup of one name (1 ms)

  ● TurboModuleRegistry (hermes) › answers the same module for every lookup of one name

    Expected true but received false.
        at construct (native)
        at apply (native)

MANDATORY Reproducer

https://github.com/YevheniiKotyrlo/react-native-fantom-reproducer

Screenshots and Videos

No response