Sharescopes do not work

[itd-cba]

Describe the bug

Issue: Module Federation shareScopes Not Working as Expected

Description

We are currently migrating our large application to Module Federation and need to utilize the shareScopes feature because we cannot upgrade all microfrontends to new React versions simultaneously. Our approach is to have a shareScope for each React version currently in use and include all additional dependencies in the same React scope.

However, we are encountering an issue where sharing a scope that is not the "default" is not working. We can see the different scopes in the window.__FEDERATION variable, but two microfrontends using the react19 scope are not sharing their dependencies correctly and end up loading their own React instances.

Current Setup

We have a main app that integrates all remotes. The remotes define their shared dependencies via the rsbuild plugin. The main app registers the remotes at runtime with the following code:

import { registerPlugins, registerRemotes, init } from '@module-federation/enhanced/runtime';

export const registerMicroFrontends = async () => {
  try {
    const microfrontendUrls = await getAllMicrofrontends();

    const remotes = Object.entries(microfrontendUrls).map(([key, value]) => ({
      name: key,
      entry: `${value.baseUrl}/mf-manifest.json`,
    }));

    registerRemotes(remotes);
    registerPlugins([errorHandlingPlugin()]);
  } catch (e) {
    logger.warn('Failed to register (some) microfrontends.', e);
  }
};

The main app defines its shared dependencies at build time using the following configuration:

pluginModuleFederation({
  name: 'appaxolotl',
  dts: false,
  shared: [
    {
      react: { singleton: true, requiredVersion: packageJson.dependencies.react },
      'react-dom': { singleton: true, requiredVersion: packageJson.dependencies['react-dom'] },
    },
  ],
});

For microfrontends that use React 19, we use the following configuration and attempt to leverage the shareScope feature:

pluginModuleFederation({
  name: 'portfoliopenguin',
  dts: false,
  runtimePlugins: [],
  exposes: {
    './bootstrap': './src/bootstrap.tsx',
  },
  shared: [
    {
      react: { singleton: true, requiredVersion: packageJson.dependencies.react, shareScope: 'react19' },
      'react-dom': { singleton: true, requiredVersion: packageJson.dependencies['react-dom'], shareScope: 'react19' },
      '@mui/material': { singleton: false, requiredVersion: packageJson.dependencies['@mui/material'], shareScope: 'react19' },
    },
  ],
});

After the microfrondends got registered by the main app they will be loaded via loadRemote when they are actually needed. The "filterfalcon" gets loaded right after the remotes got registered and the second microfrontend is loaded when its route gets called.

Observed Behavior

At runtime, both React 19 microfrontends have the react19 shareScope, but they do not share dependencies correctly. Here is a snapshot of the window__FEDERATION__SHARE__.

And here the broken part:
Here we can see that both have the same scope but still both load their own dependencies.

Expected Behavior

Microfrontends using the same react19 scope should share the React instance instead of loading separate copies.

Questions

• Are we missing any additional runtime configuration required for shareScopes?

Any guidance or insights would be greatly appreciated!

Used Package Manager

pnpm

System Info

- Module Federation Version: 0.8.9
- React Versions: 18.3.1, 19.0.0
- Build Tool: `rsbuild`

Validations

• Read the docs.
• Read the common issues list.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Module federation issue and not a framework-specific issue.
• The provided reproduction is a minimal reproducible example of the bug.

[itd-cba]

@ScriptedAlchemy can you have a look? the feature is not very documented in detail

[ScriptedAlchemy]

@itd-cba provide a repo