fix: [SDK-4511] fix Android build with Kotlin stdlib 2.2.x

android/README.md

@@ -0,0 +1,22 @@
+# OneSignal Capacitor Plugin – Android
+
+Thin Capacitor wrapper around the OneSignal Android SDK. Designed to be consumed as a Capacitor sub-project under both Capacitor 7 and Capacitor 8.
+
+## Kotlin / AGP toolchain
+
+The plugin module declares its own `buildscript` classpath for the Android Gradle Plugin and the Kotlin Gradle Plugin. This is required because Capacitor 7's host `build.gradle` does not classpath the Kotlin Gradle Plugin for sub-projects; without our own classpath the `kotlin-android` plugin would fail to resolve.
+
+Defaults live in [`gradle/libs.versions.toml`](gradle/libs.versions.toml):
+
+- `kotlin = "2.2.20"` – the compiler version used to build this module. Matches the Capacitor 8 upgrade guide's recommended `kotlin_version`, and a 2.2.x compiler reads `kotlin-stdlib` bytecode from both 1.x and 2.x, which is what makes a single artifact work on Capacitor 7 hosts (Kotlin 1.9.x stdlib) and Capacitor 8 hosts (Kotlin 2.2.x stdlib).
+- `androidGradlePlugin = "8.7.3"` – intentionally stays below Capacitor 8's recommended 8.13.0 so plugin-only Gradle invocations still work from a freshly scaffolded Capacitor 7 project (Gradle 8.11.1). In host builds the host's AGP wins regardless.
+
+Host apps that need to pin a different Kotlin compiler can do so via any standard Gradle property source — `rootProject.ext.kotlin_version` in their root `build.gradle`, `kotlin_version=…` in `gradle.properties`, or `-Pkotlin_version=…` on the command line. The plugin's buildscript block reads the value through `project.findProperty("kotlin_version")` and falls back to the catalog default.
+
+## SDK levels
+
+`compileSdk`, `minSdk`, and `targetSdk` default to the Capacitor 8 floors (36 / 24 / 36). Host apps override any of them by setting the matching `<name>Version` property through any Gradle property source (`rootProject.ext`, `gradle.properties`, or `-P`) — Capacitor 7 host apps that ship with `variables.gradle` defaults of 35 / 23 / 35 will continue to take precedence over the catalog defaults.
+
+## Library versions
+
+`androidx.appcompat`, `junit`, espresso, and the OneSignal native SDK versions also live in [`gradle/libs.versions.toml`](gradle/libs.versions.toml). `androidxAppCompatVersion` and `junitVersion` can be overridden per-project through any Gradle property source (`rootProject.ext`, `gradle.properties`, or `-P`).

android/build.gradle.kts

@@ -24,11 +24,23 @@ buildscript {
         return result ?: error("Version '$key' not found in ${catalogFile.name}")
     }
 
-    val kotlinVersion: String = if (project.hasProperty("kotlin_version")) {
-        rootProject.extra["kotlin_version"] as String
-    } else {
-        fromCatalog("kotlin")
-    }
+    // Both AGP and Kotlin Gradle Plugin are classpathed here so the plugin
+    // builds inside Capacitor 7 hosts, whose root build.gradle does not
+    // provide either for sub-projects. Capacitor 8 hosts that already pin
+    // their own kotlin_version can override via rootProject.ext.kotlin_version.
+    //
+    // The catalog default matches the Capacitor 8 upgrade guide's
+    // recommended kotlin_version (2.2.20). That matters because the host
+    // classpath can resolve kotlin-stdlib to 2.x; the 1.9 compiler can't
+    // read 2.x metadata, which is exactly what broke 1.0.2 on Capacitor 8
+    // (issue #18). A 2.2.x compiler reads both 1.x and 2.x stdlib bytecode,
+    // so the plugin works under Cap 7 and Cap 8.
+    // findProperty matches hasProperty's broad source set (extras, gradle.properties,
+    // -P flags, ORG_GRADLE_PROJECT_* env vars). Reading rootProject.extra directly
+    // would only see ext { ... } values and crash on the others with
+    // UnknownPropertyException, so prefer findProperty + toString().
+    val kotlinVersion: String =
+        project.findProperty("kotlin_version")?.toString() ?: fromCatalog("kotlin")
     val androidGradlePluginVersion: String = fromCatalog("androidGradlePlugin")
 
     repositories {
@@ -63,19 +75,14 @@ fun catalogVersion(key: String): String {
     return result ?: error("Version '$key' not found in ${toml.name}")
 }
 
+// See the kotlin_version note in buildscript {}: findProperty honors every property
+// source hasProperty does (extras, gradle.properties, -P, env), and toString()
+// avoids the String/Int cast hazard since gradle.properties values are always String.
 fun propertyOrCatalog(propertyName: String, catalogKey: String): String =
-    if (project.hasProperty(propertyName)) {
-        rootProject.extra[propertyName] as String
-    } else {
-        catalogVersion(catalogKey)
-    }
+    project.findProperty(propertyName)?.toString() ?: catalogVersion(catalogKey)
 
 fun intPropertyOrCatalog(propertyName: String, catalogKey: String): Int =
-    if (project.hasProperty(propertyName)) {
-        rootProject.extra[propertyName] as Int
-    } else {
-        catalogVersion(catalogKey).toInt()
-    }
+    project.findProperty(propertyName)?.toString()?.toInt() ?: catalogVersion(catalogKey).toInt()
 
 val junitVersion: String = propertyOrCatalog("junitVersion", "junit")
 val androidxAppCompatVersion: String = propertyOrCatalog("androidxAppCompatVersion", "androidxAppCompat")
@@ -108,7 +115,7 @@ configure<com.android.build.gradle.LibraryExtension> {
 }
 
 tasks.withType<org.jetbrains.kotlin.gradle.tasks.KotlinCompile>().configureEach {
-    kotlinOptions.jvmTarget = "17"
+    compilerOptions.jvmTarget.set(org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17)
 }
 
 repositories {

android/gradle/libs.versions.toml

@@ -1,21 +1,32 @@
 # Version catalog for the OneSignal Capacitor Android plugin.
-# Defaults below can be overridden by the consuming app via gradle
-# properties or rootProject.extra (see android/build.gradle.kts).
 #
-# compileSdk / minSdk / targetSdk / kotlin / appcompat / junit follow
-# Capacitor 7's required versions, not the OneSignal Android SDK's.
+# Host apps can override most defaults by setting the matching
+# rootProject.ext.<key> values; see android/build.gradle.kts for the
+# property-or-catalog lookup logic.
+#
+# kotlin: matches Capacitor 8's recommended kotlin_version (2.2.20, per
+#   Capacitor 8 upgrade docs). A 2.2.x compiler reads kotlin-stdlib bytecode
+#   from 1.x and 2.x without metadata version errors, which is what makes a
+#   single artifact compile under both Capacitor 7 hosts (Kotlin 1.9.x
+#   stdlib) and Capacitor 8 hosts (Kotlin 2.2.x stdlib).
+# androidGradlePlugin: kept at 8.7.3. Cap 8 recommends 8.13.0, but bumping
+#   here would force Gradle 8.13+ in standalone plugin builds, which a
+#   freshly scaffolded Cap 7 project (Gradle 8.11.1) cannot supply. In host
+#   builds the host's AGP wins regardless.
+# SDK levels / library versions: bumped to Capacitor 8's recommended floors
+#   for documentation parity. Host apps still override via rootProject.ext.
 
 [versions]
 androidGradlePlugin = "8.7.3"
-androidxAppCompat = "1.7.0"
-androidxEspresso = "3.6.1"
-androidxTestJunit = "1.2.1"
-compileSdk = "35"
+androidxAppCompat = "1.7.1"
+androidxEspresso = "3.7.0"
+androidxTestJunit = "1.3.0"
+compileSdk = "36"
 junit = "4.13.2"
-kotlin = "1.9.25"
-minSdk = "23"
+kotlin = "2.2.20"
+minSdk = "24"
 onesignal = "5.9.1"
-targetSdk = "35"
+targetSdk = "36"
 
 [libraries]
 androidx-appcompat = { module = "androidx.appcompat:appcompat", version.ref = "androidxAppCompat" }

examples/demo_cap7/.gitignore

@@ -0,0 +1,3 @@
+# Angular CLI cache + intermediate TS output
+.angular/
+out-tsc/

examples/demo_cap7/README.md

@@ -0,0 +1,45 @@
+# demo-cap7
+
+Minimal Capacitor 7 + Angular sample used to verify the OneSignal Capacitor plugin against the older Kotlin / AGP toolchain that Capacitor 7 ships with. Pairs with `examples/demo` (Capacitor 8, Ionic React).
+
+## Stack
+
+- Capacitor 7 (`@capacitor/core` `^7.4.3`)
+- Angular 18 standalone components, bootstrapped with `bootstrapApplication`
+- Angular CLI (`ng build` / `ng serve`) – no Ionic, no extra build tooling
+- Single root component with four buttons and a signal-backed log
+
+## What the demo does
+
+1. Initialize OneSignal
+2. Request notification permission
+3. Show the OneSignal user / push subscription id (paste it into the OneSignal dashboard to send a test push)
+4. Send Test Notification – POSTs `{ headings: 'Simple Notification', contents: 'This is a simple push notification' }` to the OneSignal REST API (`v1/notifications`) targeting the current push subscription id. Mirrors the Simple notification button in `examples/demo`; no REST API key needed since the call targets the device's own subscription id.
+
+## First-time setup
+
+The `android/` and `ios/` projects are committed (scaffolded via Capacitor 7's CLI, AGP 8.7.x, no root Kotlin Gradle Plugin classpath), so the only setup is dependencies and the plugin tarball.
+
+```bash
+# from the repo root: build + pack the plugin tarball
+vp run build
+vp pm pack && mv onesignal-capacitor-plugin-*.tgz onesignal-capacitor-plugin.tgz
+
+# in this folder: install deps and the local plugin tarball
+cd examples/demo_cap7
+bun install
+```
+
+The OneSignal plugin module compiles against the Kotlin 2.2.20 compiler it ships in its own buildscript classpath, which reads both 1.x and 2.x `kotlin-stdlib` bytecode.
+
+`ONESIGNAL_APP_ID` in `src/app/app.component.ts` defaults to the shared OneSignal demo app id (same one used by `examples/demo`). Swap it for your own app id before pointing the demo at a production environment.
+
+## Running
+
+```bash
+bun run build           # ng build → dist/browser
+bunx cap sync           # copy web + plugin into native projects
+bunx cap run android    # or: bunx cap run ios
+```
+
+The Angular CLI builder emits to `dist/browser/`; `capacitor.config.ts` points `webDir` there.

examples/demo_cap7/android/.gitignore

@@ -0,0 +1,101 @@
+# Using Android gitignore template: https://github.com/github/gitignore/blob/HEAD/Android.gitignore
+
+# Built application files
+*.apk
+*.aar
+*.ap_
+*.aab
+
+# Files for the ART/Dalvik VM
+*.dex
+
+# Java class files
+*.class
+
+# Generated files
+bin/
+gen/
+out/
+#  Uncomment the following line in case you need and you don't have the release build type files in your app
+# release/
+
+# Gradle files
+.gradle/
+build/
+
+# Local configuration file (sdk path, etc)
+local.properties
+
+# Proguard folder generated by Eclipse
+proguard/
+
+# Log Files
+*.log
+
+# Android Studio Navigation editor temp files
+.navigation/
+
+# Android Studio captures folder
+captures/
+
+# IntelliJ
+*.iml
+.idea/workspace.xml
+.idea/tasks.xml
+.idea/gradle.xml
+.idea/assetWizardSettings.xml
+.idea/dictionaries
+.idea/libraries
+# Android Studio 3 in .gitignore file.
+.idea/caches
+.idea/modules.xml
+# Comment next line if keeping position of elements in Navigation Editor is relevant for you
+.idea/navEditor.xml
+
+# Keystore files
+# Uncomment the following lines if you do not want to check your keystore files in.
+#*.jks
+#*.keystore
+
+# External native build folder generated in Android Studio 2.2 and later
+.externalNativeBuild
+.cxx/
+
+# Google Services (e.g. APIs or Firebase)
+# google-services.json
+
+# Freeline
+freeline.py
+freeline/
+freeline_project_description.json
+
+# fastlane
+fastlane/report.xml
+fastlane/Preview.html
+fastlane/screenshots
+fastlane/test_output
+fastlane/readme.md
+
+# Version control
+vcs.xml
+
+# lint
+lint/intermediates/
+lint/generated/
+lint/outputs/
+lint/tmp/
+# lint/reports/
+
+# Android Profiling
+*.hprof
+
+# Cordova plugins for Capacitor
+capacitor-cordova-android-plugins
+
+# Copied web assets
+app/src/main/assets/public
+
+# Generated Config files
+app/src/main/assets/capacitor.config.json
+app/src/main/assets/capacitor.plugins.json
+app/src/main/res/xml/config.xml

examples/demo_cap7/android/app/.gitignore

@@ -0,0 +1,2 @@
+/build/*
+!/build/.npmkeep

examples/demo_cap7/android/app/build.gradle

@@ -0,0 +1,54 @@
+apply plugin: 'com.android.application'
+
+android {
+    namespace "com.onesignal.example"
+    compileSdk rootProject.ext.compileSdkVersion
+    defaultConfig {
+        applicationId "com.onesignal.example"
+        minSdkVersion rootProject.ext.minSdkVersion
+        targetSdkVersion rootProject.ext.targetSdkVersion
+        versionCode 1
+        versionName "1.0"
+        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
+        aaptOptions {
+             // Files and dirs to omit from the packaged assets dir, modified to accommodate modern web apps.
+             // Default: https://android.googlesource.com/platform/frameworks/base/+/282e181b58cf72b6ca770dc7ca5f91f135444502/tools/aapt/AaptAssets.cpp#61
+            ignoreAssetsPattern '!.svn:!.git:!.ds_store:!*.scc:.*:!CVS:!thumbs.db:!picasa.ini:!*~'
+        }
+    }
+    buildTypes {
+        release {
+            minifyEnabled false
+            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
+        }
+    }
+}
+
+repositories {
+    flatDir{
+        dirs '../capacitor-cordova-android-plugins/src/main/libs', 'libs'
+    }
+}
+
+dependencies {
+    implementation fileTree(include: ['*.jar'], dir: 'libs')
+    implementation "androidx.appcompat:appcompat:$androidxAppCompatVersion"
+    implementation "androidx.coordinatorlayout:coordinatorlayout:$androidxCoordinatorLayoutVersion"
+    implementation "androidx.core:core-splashscreen:$coreSplashScreenVersion"
+    implementation project(':capacitor-android')
+    testImplementation "junit:junit:$junitVersion"
+    androidTestImplementation "androidx.test.ext:junit:$androidxJunitVersion"
+    androidTestImplementation "androidx.test.espresso:espresso-core:$androidxEspressoCoreVersion"
+    implementation project(':capacitor-cordova-android-plugins')
+}
+
+apply from: 'capacitor.build.gradle'
+
+try {
+    def servicesJSON = file('google-services.json')
+    if (servicesJSON.text) {
+        apply plugin: 'com.google.gms.google-services'
+    }
+} catch(Exception e) {
+    logger.info("google-services.json not found, google-services plugin not applied. Push Notifications won't work")
+}

examples/demo_cap7/android/app/proguard-rules.pro

@@ -0,0 +1,21 @@
+# Add project specific ProGuard rules here.
+# You can control the set of applied configuration files using the
+# proguardFiles setting in build.gradle.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}
+
+# Uncomment this to preserve the line number information for
+# debugging stack traces.
+#-keepattributes SourceFile,LineNumberTable
+
+# If you keep the line number information, uncomment this to
+# hide the original source file name.
+#-renamesourcefileattribute SourceFile