add device id to feature flag context by default

[msiebert]

This pull request introduces support for a new device_id field (mapped to anonymousId) in the Mixpanel Feature Flag system. The changes ensure that device_id is properly handled in both the main application logic and the associated tests.

Feature enhancements:

• src/main/java/com/mixpanel/android/mpmetrics/FeatureFlagDelegate.java: Added a new method getAnonymousId() to the FeatureFlagDelegate interface to retrieve the device_id.
• src/main/java/com/mixpanel/android/mpmetrics/FeatureFlagManager.java: Updated _performFetchRequest() to include device_id in the request context JSON. [1] [2]

Test updates:

• src/androidTest/java/com/mixpanel/android/mpmetrics/FeatureFlagManagerTest.java:
  • Modified MockFeatureFlagDelegate to support anonymousIdToReturn. [1] [2]
  • Updated tests (testRequestBodyConstruction_performFetchRequest, testRequestBodyConstruction_withNullContext, testRequestBodyConstruction_withEmptyDistinctId, testFlagsConfigContextUsage_emptyContext) to verify the inclusion and correctness of the device_id field in the request context. [1] [2] [3] [4] [5]

[Copilot]

Pull Request Overview

This PR adds the device’s anonymous ID to the feature-flag fetch request context by default.

• Introduces getAnonymousId() in the FeatureFlagDelegate interface and uses it in FeatureFlagManager to populate a new device_id field in the request payload.
• Updates tests in FeatureFlagManagerTest to verify device_id is present and correct in various scenarios.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/main/java/com/mixpanel/android/mpmetrics/FeatureFlagManager.java	Retrieve anonymous ID and insert device_id into the fetch request JSON context.
src/main/java/com/mixpanel/android/mpmetrics/FeatureFlagDelegate.java	Add new abstract getAnonymousId() method to the delegate interface.
src/androidTest/java/com/mixpanel/android/mpmetrics/FeatureFlagManagerTest.java	Extend mock delegate and assertions to cover device_id presence and value.

Comments suppressed due to low confidence (1)

src/main/java/com/mixpanel/android/mpmetrics/FeatureFlagDelegate.java:12

• Adding a new abstract method to the existing interface is a breaking change for all current implementers. Consider providing a default implementation (Java 8 interface default) or a shim to maintain backward compatibility.

    String getAnonymousId();