Re-write Rust SDK

[sheepduke]

This PR

Re-writes the OpenFeature Rust SDK based on the spec.

This PR brings the following major improvements compared to existing code:

• A singleton of OpenFeature is implemented as per spec 1.1.1. The application author should call get_client to get an instance. No more manual creation.

• EvaluationDetails and ResolutionsDetails has been refined to use enum to store the reason and error code, per spec.

• Evaluation functions is now strongly typed. Meaning the user should call get_int_value to get an i64 value. This is required by the spec 1.3.1.

• Evaluation functions get_xx_value becomes async as suggested by the spec 1.4.11.

• Meaningful doc strings for public types and traits. Content selectively copied from the spec.

See Follow-up tasks for what has not been done.

Related Issues

Fixes:

• [SDK] Implement API singleton #6
• Adding more constraints for FeatureProvider trait? #12
• Refine the type of ResolutionDetails #13

Notes

Why re-writing?

I tried to patch existing code but ended up re-writing it. The main reason was that too much code needed to be changed to make both spec and Rust compiler happy.

For example, the old resolution function takes a type parameter T: Clone that makes it non object safe, which breaks the requirements of singleton (lazy_static), async and more. The provider author can never put this T value in a cache because it has Clone constraint that implies Sized etc etc.

There are some other pain points and I cannot recall now. Still, the existing code inspired me in a lot of ways. Just I was a bit lazy to patch everything and re-writing would be easier.

Follow-up Tasks

• Implement more evaluation functions get_xx_details.
• Implement hooks as per [SDK] implement hooks #5.
• Re-scan the spec and ensure everything is compliant.
• Use Clippy to guarantee the code quality (by running some selective rules).
• Address other issues in Rust SDK #9.

[beeme1mr]

Hey @sheepduke, could you please sign off your commits? It's a requirement from the CNCNF before we can merge.

To add your Signed-off-by line to every commit in this branch:

1. Ensure you have a local copy of your branch by checking out the pull request locally via command line.
2. In your local branch, run: git rebase HEAD~12 --signoff
3. Force push your changes to overwrite the branch: git push --force-with-lease origin main

[beeme1mr]

Looks good! As a follow-up, please update the readme to match the new package name and structure.

[beeme1mr]

Why did you remove the renovate config?

[justinabrahms]

Noting that this needs to be fixed before merge.

[sheepduke]

Could you please kindly explain to me what does this file do? I googled it but did not see anywhere related. Plus no usage in the code...

[justinabrahms]

I'm biased b/c I wrote this code, but you might like the pattern we used in the java-sdk where each test is annotated with a specification that it covers. It helps uncover which areas we're not covering yet.

https://github.com/open-feature/java-sdk/blob/main/src/test/java/dev/openfeature/sdk/FlagEvaluationSpecTest.java#L69

[justinabrahms]

Noting that this needs to be fixed before merge.

[sheepduke]

I'm biased b/c I wrote this code, but you might like the pattern we used in the java-sdk where each test is annotated with a specification that it covers. It helps uncover which areas we're not covering yet.

https://github.com/open-feature/java-sdk/blob/main/src/test/java/dev/openfeature/sdk/FlagEvaluationSpecTest.java#L69

@justinabrahms My apologies. Your request changes have been overwritten by my force-update to resolve the signing issue. :-(

Could you please kindly re-request it, or let me know what have you changed?

I am rather curious that how did you add the specification to the tests.

[justinabrahms]

The main thing we need to change is the renovate file being deleted.

As for spec tests, there's a python script in the repo which parses them and validates. Something for later, but you could probably make your life easier by commenting the relevant spec until we get something statically verifiable.

[sheepduke]

The main thing we need to change is the renovate file being deleted.

As for spec tests, there's a python script in the repo which parses them and validates. Something for later, but you could probably make your life easier by commenting the relevant spec until we get something statically verifiable.

Thanks for sharing the info. I have added this JSON file back and created an issue to track it:
#16

I have re-requested your review. :-)

[justinabrahms]

Ahh. Bit of confusion. I'll update the ticket. Renovate keeps our dependencies up to date. The json thing I mentioned was something else.