Kotlin Tooling Agp9 Migration

KMP AGP 9.0 Migration

Android Gradle Plugin 9.0 makes the Android application and library plugins incompatible with the Kotlin Multiplatform plugin in the same module. This skill guides you through the migration.

Step 0: Analyze the Project

Before making any changes, understand the project structure:

1. Read settings.gradle.kts (or .gradle) to find all modules
2. For each module, read its build.gradle.kts to identify which plugins are applied
3. Check if the project uses a Gradle version catalog (gradle/libs.versions.toml). If it exists, read it for current AGP/Gradle/Kotlin versions. If not, find versions directly in build.gradle.kts files (typically in the root buildscript {} or plugins {} block). Adapt all examples in this guide accordingly — version catalog examples use alias(libs.plugins.xxx) while direct usage uses id("plugin.id") version "x.y.z"
4. Read gradle/wrapper/gradle-wrapper.properties for the Gradle version
5. Check gradle.properties for any existing workarounds (android.enableLegacyVariantApi)
6. Check for org.jetbrains.kotlin.android plugin usage — AGP 9.0 has built-in Kotlin and this plugin must be removed
7. Check for org.jetbrains.kotlin.kapt plugin usage — incompatible with built-in Kotlin, must migrate to KSP or com.android.legacy-kapt
8. Check for third-party plugins that may be incompatible with AGP 9.0 (see "Plugin Compatibility" section below)

If Bash is available, run scripts/analyze-project.sh from this skill's directory to get a structured summary.

Classify Each Module

For each module, determine its type:

Determine Scope

• Path B is mandatory for any module combining KMP + Android application plugin
• Path C is recommended when the project has a monolithic composeApp (or similar) module containing entry points for multiple platforms (Android, Desktop, Web). This aligns with the new JetBrains default project structure where each platform gets its own app module.
• Ask the user whether they want Path B only (minimum required) or Path C (recommended full restructure)

Path A: Library Module Migration

Use this when a module applies kotlin.multiplatform + com.android.library.

See references/MIGRATION-LIBRARY.md for full before/after code.

Summary:

1. Replace plugin: com.android.library → com.android.kotlin.multiplatform.library
2. Remove org.jetbrains.kotlin.android plugin if present (AGP 9.0 has built-in Kotlin support)
3. Migrate DSL: Move config from top-level android {} block into kotlin { android {} }:

   kotlin {
       android {
           namespace = "com.example.lib"
           compileSdk = 35
           minSdk = 24
       }
   }

4. Rename source directories (only if the module uses classic Android layout instead of KMP layout):
   • src/main → src/androidMain
   • src/test → src/androidHostTest
   • src/androidTest → src/androidDeviceTest
   • If the module already uses src/androidMain/, no directory renames are needed
5. Move dependencies from top-level dependencies {} into sourceSets:

   kotlin {
       sourceSets {
           androidMain.dependencies {
               implementation("androidx.appcompat:appcompat:1.7.0")
           }
       }
   }

6. Enable resources explicitly if the module uses Android resources:

   kotlin {
       android {
           androidResources { enable = true }
       }
   }

7. Enable Java compilation if module has .java source files:

   kotlin {
       android {
           withJava()
       }
   }

8. Enable tests explicitly if the module has unit or instrumented tests:

   kotlin {
       android {
           withHostTest { isIncludeAndroidResources = true }
           withDeviceTest {
               instrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
           }
       }
   }

9. Update Compose tooling dependency:

   // Old: debugImplementation(libs.androidx.compose.ui.tooling)
   // New:
   dependencies {
       androidRuntimeClasspath(libs.androidx.compose.ui.tooling)
   }

10. Publish consumer ProGuard rules explicitly if applicable:

    kotlin {
        android {
            consumerProguardFiles.add(file("consumer-rules.pro"))
        }
    }

Path B: Android App + Shared Module Split

Use this when a module applies kotlin.multiplatform + com.android.application. This is mandatory for AGP 9.0 compatibility.

See references/MIGRATION-APP-SPLIT.md for full guide.

Summary:

1. Create androidApp module with its own build.gradle.kts:

   plugins {
       alias(libs.plugins.androidApplication)
       // Do NOT apply kotlin-android — AGP 9.0 includes Kotlin support
       alias(libs.plugins.composeMultiplatform)  // if using Compose
       alias(libs.plugins.composeCompiler)       // if using Compose
   }
   
   android {
       namespace = "com.example.app"
       compileSdk = 35
       defaultConfig {
           applicationId = "com.example.app"
           minSdk = 24
           targetSdk = 35
           versionCode = 1
           versionName = "1.0"
       }
       buildFeatures { compose = true }
   }
   
   dependencies {
       implementation(projects.shared)  // or whatever the shared module is named
       implementation(libs.androidx.activity.compose)
   }

2. Move Android entry point code from src/androidMain/ to androidApp/src/main/:
   • MainActivity.kt (and any other Activities/Fragments)
   • AndroidManifest.xml (app-level manifest with <application> and launcher <activity>) — verify android:name on <activity> uses the fully qualified class name in its new location
   • Android Application class if present
   • App-level resources (launcher icons, theme, etc.)
3. Add to settings.gradle.kts: include(":androidApp")
4. Add to root build.gradle.kts: plugin declarations with apply false
5. Convert original module from application to library using Path A steps
6. Ensure different namespaces: app module and library module must have distinct namespaces
7. Remove from shared module: applicationId, targetSdk, versionCode, versionName
8. Update IDE run configurations: change the module from the old module to androidApp

Path C: Full Restructure (Recommended)

Use this when the project has a monolithic module (typically composeApp) containing entry points for multiple platforms. This is optional but aligns with the new JetBrains default.

See references/MIGRATION-FULL-RESTRUCTURE.md for full guide.

Target Structure

project/
├── shared/              ← KMP library (was composeApp), pure shared code
├── androidApp/          ← Android entry point only
├── desktopApp/          ← Desktop entry point only (if desktop target exists)
├── webApp/              ← Wasm/JS entry point only (if web target exists)
├── iosApp/              ← iOS Xcode project (usually already separate)
└── ...

Steps

1. Apply Path B first — extract androidApp (mandatory for AGP 9.0)
2. Extract desktopApp (if desktop target exists):
   • Create module with org.jetbrains.compose and application {} plugin
   • Move main() function from desktopMain to desktopApp/src/main/kotlin/
   • Move compose.desktop { application { ... } } config to desktopApp/build.gradle.kts
   • Add dependency on shared module
3. Extract webApp (if wasmJs/js target exists):
   • Create module with appropriate Kotlin/JS or Kotlin/Wasm configuration
   • Move web entry point from wasmJsMain/jsMain to webApp/src/wasmJsMain/kotlin/
   • Move browser/distribution config to webApp/build.gradle.kts
   • Add dependency on shared module
4. iOS — typically already in a separate iosApp directory. Verify:
   • Framework export config (binaries.framework) stays in shared module
   • Xcode project references the correct framework path
5. Rename module from composeApp to shared:
   • Rename directory
   • Update settings.gradle.kts include
   • Update all dependency references across modules
6. Clean up shared module: remove all platform entry point code and app-specific config that was moved to the platform app modules

Variant: Native UI

If some platforms use native UI (e.g., SwiftUI for iOS), split shared into:

• sharedLogic — business logic consumed by ALL platforms
• sharedUI — Compose Multiplatform UI consumed only by platforms using shared UI

Variant: Server

If the project includes a server target:

• Add server module at the root
• Move all client modules under an app/ directory
• Add core module for code shared between server and client (models, validation)

Version Updates

These are required regardless of migration path:

1. Gradle wrapper — update to 9.1.0+:

   # gradle/wrapper/gradle-wrapper.properties
   distributionUrl=https\://services.gradle.org/distributions/gradle-9.1.0-bin.zip

2. AGP version — update to 9.0.0+.

   If using a version catalog (gradle/libs.versions.toml):

   [versions]
   agp = "9.0.0"

   If versions are set directly in build files, update all com.android.* plugin version strings:

   // root build.gradle.kts
   plugins {
       id("com.android.application") version "9.0.0" apply false
   }

3. Add the KMP library plugin.

   With version catalog:

   [plugins]
   android-kotlin-multiplatform-library = { id = "com.android.kotlin.multiplatform.library", version.ref = "agp" }

   Without version catalog — use the plugin ID directly in build files:

   // root build.gradle.kts
   plugins {
       id("com.android.kotlin.multiplatform.library") version "9.0.0" apply false
   }
   // module build.gradle.kts
   plugins {
       id("com.android.kotlin.multiplatform.library")
   }

4. Root build.gradle.kts — add apply false for new plugin (see examples above)

5. JDK — ensure JDK 17+ is used (required by AGP 9.0)

6. SDK Build Tools — update to 36.0.0:

   Install via SDK Manager or configure in android { buildToolsVersion = "36.0.0" }

7. Remove legacy workarounds from gradle.properties:

   • Remove android.enableLegacyVariantApi=true (removed in AGP 9.0, causes error if present)
   • Remove android.r8.integratedResourceShrinking (removed in AGP 9.0, causes error if present)
   • Remove android.enableNewResourceShrinker.preciseShrinking (removed in AGP 9.0, causes error if present)
   • Remove android.builtInKotlin=false (unless needed for plugin compatibility — see Plugin Compatibility)
   • Remove android.newDsl=false (unless needed for plugin compatibility)

8. Review gradle.properties defaults — see "Gradle Properties Default Changes" section for properties whose defaults changed in AGP 9.0

Built-in Kotlin Migration

AGP 9.0 enables built-in Kotlin support by default for all com.android.application and com.android.library modules. The org.jetbrains.kotlin.android plugin is no longer needed and will conflict if applied.

Important: Built-in Kotlin does NOT replace KMP support. KMP library modules still need org.jetbrains.kotlin.multiplatform + com.android.kotlin.multiplatform.library.

Detection

Check if the project uses org.jetbrains.kotlin.android or kotlin-android in any build files. If found, this migration is needed. If not, check gradle.properties for android.builtInKotlin=false which may indicate a previous opt-out.