feat: nestjs async factory

[imranismail]

Adds forRootAsync() method to enable asynchronous configuration of the OpenFeature NestJS module using dependency injection. This allows OpenFeature to be configured with values from other providers (e.g., ConfigService) that are only available at runtime.

Changes

Implementation:

• Migrated to NestJS ConfigurableModuleBuilder pattern for standardized async module support
• Added forRootAsync() method that supports useFactory, useClass, and useExisting patterns
• Refactored forRoot() to use the same internal buildModule() method for consistency
• Changed provider initialization to use setProviderAndWait() instead of synchronous setProvider() for proper async handling
• Moved OpenFeature SDK initialization into a factory provider to ensure it runs after module bootstrap

New Features:

• forRootAsync() with full DI support (useFactory, inject, imports, etc.)
• domains configuration in extras for domain-scoped client injection, unfortunately this is required to be able to build the client token for domains, since dependency tree needs to be determined synchronously at "build" time.
• isGlobal configuration option (defaults to true)
• Async provider initialization with proper dependency ordering

Migration Guide

Before (still works):

OpenFeatureModule.forRoot({
  defaultProvider: myProvider,
  useGlobalInterceptor: true,
})

After (with async config):

OpenFeatureModule.forRootAsync({
  imports: [ConfigModule],
  useFactory: async (config: ConfigService) => ({
    defaultProvider: new Provider({
      apiKey: config.get<string>('PROVIDER_API_KEY'),
    }),
    providers: {
      'domain-scoped-client': new Provider({
        apiKey: config.get<string>('DOMAIN_A_API_KEY'),
      }),
    }
  }),
  inject: [ConfigService],
  isGlobal: true,
  useGlobalInterceptor: true,
  domains: ['domain-scoped-client'], // if using domain-scoped clients
})

Breaking Changes

Minor: The useGlobalInterceptor option moved from the main options to extras. However, this is backward compatible because the ConfigurableModuleBuilder merges extras into the options type.

[gemini-code-assist]

Summary of Changes

Hello @imranismail, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the OpenFeature NestJS module by introducing robust asynchronous configuration capabilities. It allows developers to dynamically configure OpenFeature providers and settings using NestJS's powerful dependency injection, making the module more flexible and adaptable to complex application setups where configuration values might not be immediately available at module registration time. The changes leverage NestJS's ConfigurableModuleBuilder for a more idiomatic and maintainable implementation.

Highlights

• Asynchronous Module Configuration: Introduced a forRootAsync() method, enabling the OpenFeature NestJS module to be configured asynchronously using NestJS's dependency injection system. This supports useFactory, useClass, and useExisting patterns, allowing configuration values to be sourced from other providers available at runtime.
• Standardized Module Building: Migrated the module implementation to use NestJS's ConfigurableModuleBuilder pattern, ensuring a standardized approach for module configuration and extensibility. The existing forRoot() method has been refactored to use a common buildModule() helper for consistency.
• Asynchronous Provider Initialization: Changed OpenFeature provider initialization to use OpenFeature.setProviderAndWait() instead of synchronous setProvider(). This ensures proper asynchronous handling and correct ordering, as the OpenFeature SDK initialization is now moved into a factory provider that runs after module bootstrap.
• New Configuration Options: Added domains configuration for injecting domain-scoped clients, and an isGlobal configuration option (defaulting to true) to control module globality. The useGlobalInterceptor option has been moved to extras but remains backward compatible.

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[gemini-code-assist]

Code Review

This pull request introduces a significant and valuable feature by adding asynchronous module configuration capabilities to the OpenFeature NestJS module. The implementation correctly leverages NestJS's ConfigurableModuleBuilder and properly handles asynchronous provider initialization. My review includes a few suggestions to enhance maintainability and test quality, such as using a constant for a repeated injection token, renaming a parameter for better clarity, and improving the robustness of a test case for the logger functionality.

[lukas-reining]

Hey @imranismail, thanks for the PR. This is a great addition.
I will try to review tomorrow!

[imranismail]

@lukas-reining I've changed the implementation slightly, also ensure existing test passes.

I'm a bit concerned about having to specify the domains again in the extras, happy to hear some ideas if you have.

[lukas-reining]

Sorry for the delay @imranismail!
Will review tomorrow finally!