kotlin-tooling-agp9-migration

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name: kotlin-tooling-agp9-migration description: > Migrates Kotlin Multiplatform (KMP) projects to Android Gradle Plugin 9.0+. Handles plugin replacement (com.android.kotlin.multiplatform.library), module splitting, DSL migration, and the new default project structure. Use when upgrading AGP, when build fails due to KMP+AGP incompatibility, or when the user mentions AGP 9.0, android multiplatform plugin, KMP migration, or com.android.kotlin.multiplatform.library. license: Apache-2.0 metadata: author: JetBrains version: "1.0.0"

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:

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:

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 or Compose Multiplatform 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:
   androidRuntimeClasspath(libs.androidx.compose.ui.tooling)
   

10. Publish consumer ProGuard rules explicitly if applicable:

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

11. 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:

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+ 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
   }
   

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

4. SDK Build Tools — update to 36.0.0:

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

5. 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:

1. Disable globally: android.builtInKotlin=false in gradle.properties
2. Enable per migrated module by applying the opt-in plugin:

   plugins {
       id("com.android.built-in-kotlin") version "AGP_VERSION"
   }
   

3. Follow Steps 1-4 for that module
4. 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:

1. ./gradlew build succeeds with no errors
2. All platform targets build successfully (Android, iOS via xcodebuild, Desktop, JS/Wasm)
3. ./gradlew :shared:allTests and Android unit tests pass
4. No com.android.library or com.android.application in KMP modules
5. No org.jetbrains.kotlin.android in AGP 9.0 modules
6. Source sets use correct names (androidMain, androidHostTest, androidDeviceTest)
7. 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