4.2.0 fails to compile on Kotlin 2.2.20 host

[azanium]

4.2.0 fails to compile on Kotlin 2.2.20 host — Unresolved reference 'AppodealBaseFlutterPlugin'

Summary

stack_appodeal_flutter 4.2.0 (and 4.1.0) fails to compile its own Android Kotlin sources when the host app uses Kotlin 2.2.20. The module-internal internal abstract class AppodealBaseFlutterPlugin is reported as an unresolved reference from AppodealConsentManager.kt, despite being declared in the same package and same Gradle module. Reverting to 3.12.0 compiles cleanly with no other changes.

Environment

	Version
Plugin	stack_appodeal_flutter 4.2.0 (also reproduced with 4.1.0 source)
Flutter	3.44.4 (stable, channel stable)
Dart	3.12.2
Kotlin (host)	2.2.20 (settings.gradle.kts: id("org.jetbrains.kotlin.android") version "2.2.20")
AGP	8.11.1
Gradle	8.14
Target	Android compileSdk/targetSdk = Flutter defaults (35), minSdk 24
OS	macOS (Darwin 25.5)

Error

> Task :stack_appodeal_flutter:compileDebugKotlin FAILED
e: .../stack_appodeal_flutter-4.2.0/android/src/main/kotlin/com/appodeal/appodeal_flutter/AppodealConsentManager.kt:16:32
   Unresolved reference 'AppodealBaseFlutterPlugin'.
e: .../AppodealConsentManager.kt:40:38 Unresolved reference 'activity'.
e: .../AppodealConsentManager.kt:85:42 Unresolved reference 'activity'.
e: .../AppodealConsentManager.kt:96:38 Unresolved reference 'activity'.
e: .../AppodealConsentManager.kt:127:45 Unresolved reference 'context'.
e: .../AppodealConsentManager.kt:143:38 Unresolved reference 'activity'.

FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':stack_appodeal_flutter:compileDebugKotlin'.
> Compilation error. See log for more details.

AppodealBaseFlutterPlugin is declared in AppodealBaseFlutterPlugin.kt (same package com.appodeal.appodeal_flutter, same module) as:

internal abstract class AppodealBaseFlutterPlugin :
    FlutterPlugin, MethodChannel.MethodCallHandler, ActivityAware {
    internal val activity: Activity get() = requireNotNull(activityReference.get())
    internal val context: Context get() = requireNotNull(activityReference.get() ?: contextReference.get())
    ...
}

and referenced by AppodealConsentManager.kt:

internal class AppodealConsentManager(
    private val flutterPlugin: AppodealBaseFlutterPlugin,   // <-- unresolved
    flutterPluginBinding: FlutterPlugin.FlutterPluginBinding
) : MethodChannel.MethodCallHandler { ... }

The 3.12.0 plugin has no such abstraction and compiles cleanly under the identical host config.

Reproduction

1. flutter create an app (Flutter 3.44.4).
2. Add stack_appodeal_flutter: ^4.2.0.
3. Keep the default Kotlin version resolved by Flutter 3.44 (2.2.20).
4. flutter build apk --debug → :stack_appodeal_flutter:compileDebugKotlin fails with the errors above.
5. Downgrade to stack_appodeal_flutter: ^3.12.0 (no other changes) → builds successfully.

Expected behavior

The 4.2.0 plugin compiles on a standard current Flutter/Kotlin toolchain (Kotlin 2.2.x).

Actual behavior

Compilation of the plugin's own Kotlin module fails on Kotlin 2.2.20.

Workaround that does not work

Pinning the host Kotlin down to 2.1.0 (the version in the plugin's own build.gradle ext.kotlin_version) resolves the AppodealBaseFlutterPlugin error, but breaks unrelated dependencies that require newer Kotlin metadata. In particular, google_mobile_ads: ^9.0.0 → play-services-ads:25.3.0 is published with Kotlin metadata version 2.3.0, which the 2.1.0 compiler cannot read:

e: .../play-services-ads-25.3.0-api.jar!/META-INF/...kotlin_module
   Module was compiled with an incompatible version of Kotlin.
   The binary version of its metadata is 2.3.0, expected version is 2.1.0.

So there is currently no single Kotlin version that compiles both stack_appodeal_flutter 4.2.0 and the current google_mobile_ads, forcing apps that use AdMob directly to stay on plugin 3.12.0.

Notes / suggested fix

• The regression was introduced in 4.x via the new AppodealBaseFlutterPlugin abstraction (absent in 3.12). Internal cross-file resolution of that class appears to break under Kotlin 2.2.20.
• Consider building/publishing the plugin against a current Kotlin (2.2.x / 2.3.x) and/or migrating to Flutter's built-in Kotlin (the dev.flutter.flutter-plugin-loader "Built-in Kotlin" path), which would decouple the plugin's Kotlin from the host and avoid this class of conflict.

Happy to provide a full flutter doctor -v, build logs, or a minimal repro repo on request. Thank you!

[da2gl]

Thanks for the very detailed report — it helped a lot. We've spent significant time trying to reproduce this, and we'd like to share what we found and ask for a few extra details, because we cannot reproduce the :stack_appodeal_flutter:compileDebugKotlin failure from the described steps.

What we tried

Fresh flutter create app + stack_appodeal_flutter: ^4.2.0 from pub.dev, then flutter build apk --debug, across this matrix:

Flutter	AGP	Kotlin	built-in Kotlin	google_mobile_ads
3.44.3 and 3.44.4	8.8.2 / 8.11.1 / 9.0.1	2.1.0 / 2.2.20 / 2.3.20	on / off	with / without

In every combination :stack_appodeal_flutter:compileDebugKotlin succeeds and the APK builds. We specifically matched your exact environment (Flutter 3.44.4, Kotlin 2.2.20) and it still builds cleanly.

One correction

AppodealBaseFlutterPlugin.kt is not new in 4.x — it already exists in 3.12.0 (byte-identical, same package, same module). So the abstraction itself doesn't look like the regression. The only relevant delta in 4.x is the Appodeal SDK bump and two new consent methods.

Our current hypothesis

"A class in the same module suddenly resolving as Unresolved reference" is a classic symptom of a stale K2 incremental-compilation cache rather than a source-level defect — which would explain why a clean reproduction doesn't fail for us.

Could you help us reproduce?

1. Full flutter doctor -v output.
2. Full settings.gradle(.kts) and the app-level build.gradle(.kts).
3. Whether it still fails after a clean run: flutter clean, delete <app>/android/.gradle and <app>/android/.kotlin, then flutter build apk --debug.
4. The complete Gradle log via flutter build apk --debug -v (not just the tail) — the first error higher up the stack is often the real cause, with the Unresolved reference lines being a cascade from it.
5. Your exact AGP version and whether android.builtInKotlin is set in gradle.properties.

With the clean-build result and the full log we should be able to pin down whether this is a caching issue on the toolchain side or something we need to fix in the plugin. Thanks again!