feat: add hook data support

[alexandraoberaigner]

This PR

this re-adds hook data support avoiding breaking changes in the binary (we introduced with v1.18.0)

Related Issues

#1472

###Notes

With v1.18.1 we reverted the hook data feature:

revert hook data to resolve bytecode incompatibility (#1613) (9845601)

[gemini-code-assist]

Summary of Changes

Hello @alexandraoberaigner, 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 reintroduces and refines the support for HookData within the OpenFeature SDK, allowing individual hooks to maintain state across their lifecycle stages during a flag evaluation. This feature was previously removed in v1.18.0 and is now brought back without introducing breaking changes to the binary. The implementation ensures that each hook instance receives its own isolated data store, enabling more complex and stateful hook logic.

Highlights

• Reintroduction of Hook Data Support: The pull request re-enables the ability for hooks to store and retrieve data across their various execution stages during a flag evaluation, a feature previously removed in v1.18.0.
• New HookData Interface and Implementation: A new HookData interface is introduced, along with a DefaultHookData implementation, providing a mechanism for hooks to maintain state isolated to a single flag evaluation.
• Enhanced HookContext: The HookContext class is updated to include a HookData field, allowing hooks to access their specific data store throughout the evaluation process.
• Updated Hook Lifecycle Management: The HookSupport class is refactored to manage HookData instances, ensuring they are created per hook and passed correctly through the before, after, error, and finallyAfter stages.
• Comprehensive Testing: New unit tests for HookData and HookContextWithData are added, and existing HookSupport tests are extended to validate the correct isolation and persistence of hook data across stages.

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[gemini-code-assist]

Code Review

This pull request re-introduces hook data support, which is a great addition for allowing hooks to maintain state across execution stages. The implementation is solid, with good test coverage for the new functionality. I've identified a few areas for improvement, mainly concerning code clarity, consistency, and a potential thread-safety issue in the HookData implementation. My detailed comments and suggestions are provided below.

[aepfli]

I do like the object based approach, but i have a hard time supporting the changes how hooksupport/hookexecutor is created for each execution. We are bound now for testing, and have no easy way to replace this implementation with a different one.

[codecov]

Codecov Report

❌ Patch coverage is 92.06349% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.20%. Comparing base (3ef41f5) to head (0e897f2).
⚠️ Report is 23 commits behind head on main.

Files with missing lines	Patch %	Lines
src/main/java/dev/openfeature/sdk/HookContext.java	79.16%	1 Missing and 4 partials ⚠️
src/main/java/dev/openfeature/sdk/HookSupport.java	95.74%	0 Missing and 2 partials ⚠️
...in/java/dev/openfeature/sdk/OpenFeatureClient.java	91.30%	0 Missing and 2 partials ⚠️
src/main/java/dev/openfeature/sdk/ObjectHook.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1620      +/-   ##
============================================
+ Coverage     92.06%   93.20%   +1.14%     
- Complexity      488      521      +33     
============================================
  Files            46       51       +5     
  Lines          1184     1265      +81     
  Branches        105      112       +7     
============================================
+ Hits           1090     1179      +89     
+ Misses           62       50      -12     
- Partials         32       36       +4     

Flag	Coverage Δ
unittests	93.20% <92.06%> (+1.14%)	⬆️

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[chrfwow]

Do we have plans for e2e tests?

[alexandraoberaigner]

Do we have plans for e2e tests?

as discussed: will be a follow up task to add a gherkin test

[aepfli]

/gemini review

[gemini-code-assist]

Code Review

This pull request re-introduces hook data support, which was previously reverted. The changes are quite extensive, refactoring the hook execution logic to be more structured and to support per-hook data stores for the duration of a flag evaluation. A key aspect of this PR is maintaining binary compatibility by deprecating old constructors and methods in HookContext rather than removing them.

My review focuses on improving code clarity, robustness, and removing redundancy. I've suggested simplifying the lazy initialization in DefaultHookData to make it thread-safe and easier to read. I've also pointed out a complex Optional handling in HookSupport that could be made more straightforward, and some redundant null checks in OpenFeatureClient. Overall, the changes are well-structured and achieve the goal of adding hook data support while being mindful of backward compatibility.

[sonarqubecloud]

Quality Gate passed

Issues
46 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[chrfwow]

lgtm, however, I would love to see a test that does a full flag evaluation using HookData

[chrfwow]

Can we use a setter here on the Pair to avoid to create Pairs twice for each Hook?