fix: flagd not throwing parse error when target key is not a primitive

[kylejuliandev]

This PR

JsonLogic returns the whole key even when the targeting hasn't been matched. For example, invalid is the key but the targeting is not valid so the whole json string gets returned. This causes the provider to return a Flag not found response (although the flag has been found, the targeting is just invalid). I found this while adding support in the flagd e2e tests for the targeting.feature and found the provider not returning the correct response.

{
    "flags": {
        "error-targeting-flag": {
            "defaultVariant": "two",
            "state": "ENABLED",
            "targeting": {
                "invalid": [
                    "this is not valid targeting"
                ]
            },
            "variants": {
                "one": 1,
                "two": 2
            }
        }
    }
}

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[gemini-code-assist]

Summary of Changes

Hello @kylejuliandev, 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 refines the flag evaluation logic within the flagd provider to accurately detect and report invalid targeting configurations. By introducing explicit checks for primitive JsonLogic evaluation results and robust exception handling, it ensures that flags with malformed targeting rules, such as those using non-primitive keys, correctly trigger a ParseError. This enhancement improves the diagnostic capabilities and reliability of the flag resolution process.

Highlights

• Improved Error Handling for Invalid Targeting: The system now explicitly throws a "ParseError" when a flag's targeting rule is invalid, specifically when the JsonLogic evaluation results in a non-primitive type (like an object or array) for a variant selector.
• Enhanced Robustness in JsonLogic Evaluation: A try-catch block has been added around the JsonLogic.Apply method to gracefully handle exceptions during rule processing, converting them into a FeatureProviderException with ErrorType.ParseError.
• Corrected Flag Evaluation Response: This fix prevents scenarios where an invalid targeting configuration would previously lead to an incorrect "Flag not found" response, instead providing a more accurate ParseError.

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[gemini-code-assist]

Code Review

This pull request correctly addresses an issue where invalid targeting rules in flagd were not producing a parse error. The added validation for the JsonLogic evaluation result is a good improvement. My review includes a suggestion to fix a bug in the handling of null evaluation results and to refactor the logic for better readability. I've also included a minor point about catching generic exceptions.

[chrfwow]

Could you please add a test to verify the new behaviour is what we expect?

[kylejuliandev]

Could you please add a test to verify the new behaviour is what we expect?

Yep will add it later today! It was late last night 😆