feat: Make the Evaluator customizable

[chrfwow]

This PR

Makes the evaluator configurable via the FlagdOptions

Related Issues

Fixes #1732

[gemini-code-assist]

Summary of Changes

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This pull request introduces the capability to customize the Evaluator used by the flagd provider when operating in in-process mode. This enhancement allows developers to inject their own evaluation logic through FlagdOptions, providing greater flexibility and control over flag resolution. The changes ensure that if no custom evaluator is supplied, the default FlagdCore implementation is used, maintaining existing functionality while enabling advanced customization.

Highlights

• Customizable Evaluator: The FlagdOptions now includes an Evaluator field, allowing users to provide a custom evaluation logic for in-process mode.
• Dependency Injection: The InProcessResolver constructor has been updated to accept and utilize the Evaluator specified in FlagdOptions, falling back to FlagdCore if no custom evaluator is provided.
• Test Coverage: New unit tests have been added to InProcessResolverTest to verify that both custom and default evaluators are correctly used and injected.

Changelog

• providers/flagd/src/main/java/dev/openfeature/contrib/providers/flagd/FlagdOptions.java
  • Imported Evaluator class.
  • Formatted a Javadoc link for better readability.
  • Added a new evaluator field with a default value, making the evaluator configurable.
• providers/flagd/src/main/java/dev/openfeature/contrib/providers/flagd/resolver/process/InProcessResolver.java
  • Modified the constructor to retrieve the Evaluator from FlagdOptions.
  • Implemented a fallback mechanism to use FlagdCore if no custom Evaluator is provided.
  • Updated the FlagStore initialization to use the resolved Evaluator.
  • Added a getEvaluator() method for testing purposes.
• providers/flagd/src/test/java/dev/openfeature/contrib/providers/flagd/resolver/process/InProcessResolverTest.java
  • Added necessary Mockito imports for mocking and verification.
  • Introduced usesSuppliedEvaluator test to confirm custom evaluator injection.
  • Added usesFlagdCoreEvaluatorWhenNotSupplied test to verify default evaluator behavior.

Activity

• The pull request was created by chrfwow.
• No human comments or reviews have been recorded yet.

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[gemini-code-assist]

Code Review

This pull request introduces a valuable enhancement by making the Evaluator customizable in FlagdOptions. This allows users to provide their own flag evaluation logic for the in-process resolver. The implementation is clean, and the new functionality is well-covered by unit tests.

My main feedback, which is included as a specific comment, is to improve the documentation for the new evaluator option to include thread-safety requirements, as custom implementations will be called from multiple threads concurrently. This will help prevent potential race conditions for users of this new feature.

[gemini-code-assist]

It's important to document the thread-safety requirements for custom Evaluator implementations. The setFlags method is called by an internal streamer thread, while the resolve*Value methods are called by application threads. Without this information in the Javadoc, users might provide a non-thread-safe implementation, leading to potential race conditions.

Suggested change

	/**
	* The evaluator to use for flag evaluations. Defaults to {@code new FlagdCore()}. Only applicable in the in-process
	* mode
	*/
	/**
	* The evaluator to use for flag evaluations. Defaults to {@code new FlagdCore()}.
	* Only applicable in the in-process mode.
	* <p>
	* <b>Note:</b> Custom implementations of {@link Evaluator} must be thread-safe, as
	* methods can be called concurrently from multiple threads.
	*/

[chrfwow]

This is not a concern of a builder method

[aepfli]

i think we should also add the SPI option, if a a evaluator is available, we use it via ServiceLoader, but the configuration via flagdOptions takes precedence over SPI.

[chrfwow]

@aepfli is SPI already setup for this project? I found no module.info file in the current state