kotlin-tooling-agp9-migration

SKILL.md

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:

Read settings.gradle.kts (or .gradle) to find all modules

For each module, read its build.gradle.kts to identify which plugins are applied

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"

Read gradle/wrapper/gradle-wrapper.properties for the Gradle version

Check gradle.properties for any existing workarounds (android.enableLegacyVariantApi)

Check for org.jetbrains.kotlin.android plugin usage — AGP 9.0 has built-in Kotlin and this plugin must be removed

Check for org.jetbrains.kotlin.kapt plugin usage — incompatible with built-in Kotlin, must migrate to KSP or com.android.legacy-kapt

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:

Current plugins
Migration path

kotlin.multiplatform + com.android.library
Path A — Library plugin swap

kotlin.multiplatform + com.android.application
Path B — Mandatory Android split

kotlin.multiplatform with multiple platform entry points in one module
Path C — Full restructure (recommended)

com.android.application or com.android.library (no KMP)
See "Pure Android Tips" below

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:

Replace plugin: com.android.library → com.android.kotlin.multiplatform.library

Remove org.jetbrains.kotlin.android plugin if present (AGP 9.0 has built-in Kotlin support)

Migrate DSL: Move config from top-level android {} block into kotlin { android {} }:
kotlin {
    android {
        namespace = "com.example.lib"
        compileSdk = 35
        minSdk = 24
    }
}

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

Move dependencies from top-level dependencies {} into sourceSets:
kotlin {
    sourceSets {
        androidMain.dependencies {
            implementation("androidx.appcompat:appcompat:1.7.0")
        }
    }
}

Enable resources explicitly if the module uses Android or Compose Multiplatform resources:
kotlin {
    android {
        androidResources { enable = true }
    }
}

Enable Java compilation if module has .java source files:
kotlin {
    android {
        withJava()
    }
}

Enable tests explicitly if the module has unit or instrumented tests:
kotlin {
    android {
        withHostTest { isIncludeAndroidResources = true }
        withDeviceTest {
            instrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
        }
    }
}

Update Compose tooling dependency:
// Old: 
debugImplementation(libs.androidx.compose.ui.tooling)
// New:
androidRuntimeClasspath(libs.androidx.compose.ui.tooling)

Publish consumer ProGuard rules explicitly if applicable:
kotlin {
    android {
        consumerProguardFiles.add(file("consumer-rules.pro"))
    }
}

Resolve Sub-dependency Variants (Product Flavors / Build Types):
Because the new KMP Android library plugin enforces a single-variant architecture, it does not natively understand how to resolve dependencies that publish multiple variants (like debug/release build types, or product flavors like free/paid). Configure fallback behaviors using localDependencySelection:
kotlin {
    android {
        localDependencySelection {
            // Determine which build type to consume from Android library dependencies, in order of preference
            selectBuildTypeFrom.set(listOf("debug", "release"))
            
            // If the dependency has a 'tier' dimension, select the 'free' flavor
            productFlavorDimension("tier") {
                selectFrom.set(listOf("free"))
            }
        }
    }
}

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:

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)
}

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.)

Add to settings.gradle.kts: include(":androidApp")

Add to root build.gradle.kts: plugin declarations with apply false

Convert original module from application to library using Path A steps

Ensure different namespaces: app module and library module must have distinct namespaces

Remove from shared module: applicationId, targetSdk, versionCode, versionName

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

Apply Path B first — extract androidApp (mandatory for AGP 9.0)

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

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

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

Rename module from composeApp to shared:

Rename directory

Update settings.gradle.kts include

Update all dependency references across modules

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:

Gradle wrapper — update to 9.1.0+:

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

AGP version — update to 9.0.0+ and add the KMP library plugin.

With version catalog (gradle/libs.versions.toml):

[versions]
agp = "9.0.1"

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

Without version catalog — update com.android.* plugin versions and add in root build.gradle.kts:

plugins {
    id("com.android.application") version "9.0.1" apply false
    id("com.android.kotlin.multiplatform.library") version "9.0.1" apply false
}

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

SDK Build Tools — update to 36.0.0:

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

Review gradle.properties — remove error-causing properties and review changed defaults (see "Gradle Properties Default Changes" section)

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.

Step 1: Remove kotlin-android Plugin

Remove from all module-level and root-level build files:

// Remove from module build.gradle.kts
plugins {
    // REMOVE: alias(libs.plugins.kotlin.android)
    // REMOVE: id("org.jetbrains.kotlin.android")
}

// Remove from root build.gradle.kts
plugins {
    // REMOVE: alias(libs.plugins.kotlin.android) apply false
}

Remove from version catalog (gradle/libs.versions.toml):

[plugins]
# REMOVE: kotlin-android = { id = "org.jetbrains.kotlin.android", version.ref = "kotlin" }

Step 2: Migrate kapt to KSP or legacy-kapt

The org.jetbrains.kotlin.kapt plugin is incompatible with built-in Kotlin.

Preferred: Migrate to KSP — see the KSP migration guide for each annotation processor.

Fallback: Use com.android.legacy-kapt (same version as AGP):

# gradle/libs.versions.toml
[plugins]
legacy-kapt = { id = "com.android.legacy-kapt", version.ref = "agp" }

// Module build.gradle.kts — replace kotlin-kapt with legacy-kapt
plugins {
    // REMOVE: alias(libs.plugins.kotlin.kapt)
    alias(libs.plugins.legacy.kapt)
}

Step 3: Migrate kotlinOptions to compilerOptions

For pure Android modules (non-KMP), migrate android.kotlinOptions {} to the top-level
kotlin.compilerOptions {}:

// Old
android {
    kotlinOptions {
        jvmTarget = "11"
        languageVersion = "2.0"
        freeCompilerArgs += listOf("-Xopt-in=kotlin.RequiresOptIn")
    }
}

// New
kotlin {
    compilerOptions {
        jvmTarget.set(org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_11)
        languageVersion.set(org.jetbrains.kotlin.gradle.dsl.KotlinVersion.KOTLIN_2_0)
        optIn.add("kotlin.RequiresOptIn")
    }
}

Note: With built-in Kotlin, jvmTarget defaults to android.compileOptions.targetCompatibility, so it may be optional if you already set compileOptions.

Step 4: Migrate kotlin.sourceSets to android.sourceSets

With built-in Kotlin, only android.sourceSets {} with the kotlin set is supported:

// NOT SUPPORTED with built-in Kotlin:
kotlin.sourceSets.named("main") {
    kotlin.srcDir("additionalSourceDirectory/kotlin")
}

// Correct:
android.sourceSets.named("main") {
    kotlin.directories += "additionalSourceDirectory/kotlin"
}

For generated sources, use the Variant API:

androidComponents.onVariants { variant ->
    variant.sources.kotlin!!.addStaticSourceDirectory("additionalSourceDirectory/kotlin")
}

Per-Module Migration Strategy

For large projects, migrate module-by-module:

Disable globally: android.builtInKotlin=false in gradle.properties

Enable per migrated module by applying the opt-in plugin:
plugins {
    id("com.android.built-in-kotlin") version "AGP_VERSION"
}

Follow Steps 1-4 for that module

Once all modules are migrated, remove android.builtInKotlin=false and all com.android.built-in-kotlin plugins

Optional: Disable Kotlin for Non-Kotlin Modules

For modules that contain no Kotlin sources, disable built-in Kotlin to save build time:

android {
    enableKotlin = false
}

Opt-Out (Temporary)

If blocked by plugin incompatibilities, opt out temporarily:

# gradle.properties
android.builtInKotlin=false
android.newDsl=false  # also required if using new DSL opt-out

Warning: Ask the user if they want to opt out, and if so, remind them this is a temporary measure.

Plugin Compatibility

See references/PLUGIN-COMPATIBILITY.md for the full compatibility table with known compatible versions, opt-out flag workarounds, and broken plugins.

Before migrating, inventory all plugins in the project and check each against that table. If any plugin is broken without workaround, inform the user. If plugins need opt-out flags, add them togradle.properties and note them as temporary workarounds.

Gradle Properties Default Changes

AGP 9.0 changes the defaults for many Gradle properties. Check gradle.properties for any explicitly set values that may now conflict.
Key changes:

Property
Old Default
New Default
Action

android.uniquePackageNames
false
true
Ensure each library has a unique namespace

android.enableAppCompileTimeRClass
false
true
Refactor switch on R fields to if/else

android.defaults.buildfeatures.resvalues
true
false
Enable resValues = true where needed

android.defaults.buildfeatures.shaders
true
false
Enable shaders where needed

android.r8.optimizedResourceShrinking
false
true
Review R8 keep rules

android.r8.strictFullModeForKeepRules
false
true
Update keep rules to be explicit

android.proguard.failOnMissingFiles
false
true
Remove invalid ProGuard file references

android.r8.proguardAndroidTxt.disallowed
false
true
Use proguard-android-optimize.txt only

android.r8.globalOptionsInConsumerRules.disallowed
false
true
Remove global options from library consumer rules

android.sourceset.disallowProvider
false
true
Use Sources API on androidComponents

android.sdk.defaultTargetSdkToCompileSdkIfUnset
false
true
Specify targetSdk explicitly

android.onlyEnableUnitTestForTheTestedBuildType
false
true
Only if testing non-default build types

Check for and remove properties that now cause errors:

android.r8.integratedResourceShrinking — removed, always on

android.enableNewResourceShrinker.preciseShrinking — removed, always on

Pure Android Tips

For non-KMP Android modules upgrading to AGP 9.0, follow the "Built-in Kotlin Migration" steps above,
then review the "Gradle Properties Default Changes" table. Additional changes:

Review new DSL interfaces — BaseExtension is removed; use CommonExtension or specific extension types

Java default changed from Java 8 to Java 11 — ensure compileOptions reflects this

Verification

After migration, verify with the checklist. Key checks:

./gradlew build succeeds with no errors

All platform targets build successfully (Android, iOS via xcodebuild, Desktop, JS/Wasm)

./gradlew :shared:allTests and Android unit tests pass

No com.android.library or com.android.application in KMP modules

No org.jetbrains.kotlin.android in AGP 9.0 modules

Source sets use correct names (androidMain, androidHostTest, androidDeviceTest)

No deprecation warnings about variant API or DSL

Common Issues

See references/KNOWN-ISSUES.md for details. Key gotchas:

KMP Library Plugin Issues

BuildConfig unavailable in library modules — use DI/AppConfiguration interface, or use BuildKonfig or gradle-buildconfig-plugin for compile-time constants

No build variants — single variant architecture; compile-time constants can use BuildKonfig/gradle-buildconfig-plugin flavors, but variant-specific dependencies/resources/signing must move to app module

NDK/JNI unsupported in new plugin — extract to separate com.android.library module

Compose resources crash without androidResources { enable = true }

Consumer ProGuard rules silently dropped if not migrated to consumerProguardFiles.add(file(...)) in new DSL

KSP requires version 2.3.1+ for AGP 9.0 compatibility

AGP 9.0 General Issues

BaseExtension removed — convention plugins using old DSL types need rewriting to use CommonExtension

Variant APIs removed — applicationVariants, libraryVariants, variantFilter replaced by androidComponents

Convention plugins need refactoring — old android {} extension helpers are obsolete

Reference Files

DSL Reference — side-by-side old→new DSL mapping

Version Matrix — AGP/Gradle/KGP/Compose/IDE compatibility

Plugin Compatibility — third-party plugin status and workarounds