fix(flutter): forward subscriptionProductReplacementParams on Android

[hyochan]

Summary

• RequestSubscriptionAndroidProps.subscriptionProductReplacementParams was declared in types.dart and parsed correctly by the Android plugin, but flutter_inapp_purchase.dart never copied the field onto the method-channel payload when translating the Dart props into the native call. Any value callers passed was silently dropped, so Google Play fell back to its default replacement mode (WITHOUT_PRORATION) regardless of what the Dart side requested.
• Forwards the field through the channel payload and adds a channel test asserting that the serialized oldProductId / replacementMode reach the native call, so the wiring can't silently regress again.

Reported via #96 (comment). The legacy replacementMode int path was already wired correctly; this PR only fixes the newer per-product SubscriptionProductReplacementParams path (Billing Library 8.1.0+).

Test plan

• flutter analyze — no issues
• flutter test — 243 tests pass (new forwards subscriptionProductReplacementParams on Android subscription test included)
• Format check: dart format --page-width 80 --set-exit-if-changed clean

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Added support for Android subscription product replacement parameters during in-app purchase requests, enabling configuration when requesting subscriptions.

• Tests

  • Added test coverage verifying proper handling of subscription product replacement parameters in Android purchase requests.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 5161b558-3a64-4ed2-9dcc-59db797541b6

📥 Commits

Reviewing files that changed from the base of the PR and between d54f868 and 040e22a.

📒 Files selected for processing (2)

• libraries/flutter_inapp_purchase/lib/flutter_inapp_purchase.dart
• libraries/flutter_inapp_purchase/test/flutter_inapp_purchase_channel_test.dart

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📝 Walkthrough

Walkthrough

This pull request adds support for Android subscription product replacement parameters during purchase requests. A new nullable subscriptionProductReplacementParams variable is introduced in the Dart layer, extracted from subscription request properties, serialized to JSON, and forwarded to the native Android requestPurchase method. A corresponding test verifies correct parameter forwarding and serialization.

Changes

Cohort / File(s)	Summary
Android Subscription Replacement Parameters libraries/flutter_inapp_purchase/lib/flutter_inapp_purchase.dart	Introduces subscriptionProductReplacementParams variable initialization logic that extracts replacement parameters from subscription requests and appends serialized JSON to the native requestPurchase payload.
Subscription Replacement Parameters Testing libraries/flutter_inapp_purchase/test/flutter_inapp_purchase_channel_test.dart	Adds comprehensive test case for Android subscription purchases that validates subscriptionProductReplacementParams forwarding, including verification of nested field serialization (oldProductId and replacementMode).

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• fix(google): handle DEFERRED replacement mode correctly #25: Updates subscription replacement parameter handling and requestPurchase usage for DEFERRED/numeric replacement modes.
• fix(google): correct SubscriptionProductReplacementParams Replacement… #72: Fixes native Android-side mapping and handling of replacementMode values for subscription product replacement.

Suggested labels

🛠 bugfix

Poem

🐰 A parameter hops through the Android maze,
From Dart to native in a modern craze,
Subscriptions replaced with graceful care,
JSON serialized through the air! ✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main change: forwarding subscriptionProductReplacementParams on Android, which is the core fix implemented in the pull request.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/flutter-subscription-product-replacement-params-channel

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[gemini-code-assist]

Code Review

This pull request adds support for subscriptionProductReplacementParams to the Android implementation of the Flutter In-App Purchase library, enabling item-level replacements as introduced in Billing Library 8.1.0. The changes include updating the purchase request logic to serialize these parameters into the platform channel payload and adding a corresponding test case to verify the integration. I have no feedback to provide.