On the cxx platform, every TurboModuleRegistry lookup answers a new C++ TurboModule instance, where Android and iOS keep one per name #59672

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