kmp-migration

name

kmp-migration

description

Use this skill whenever a user wants to migrate a Kotlin Multiplatform (KMP) or Compose Multiplatform project from the old single-module structure (with a `composeApp` module) to the new default structure (with a `shared` library module and separate `androidApp`, `desktopApp`, `webApp` application modules). Also trigger for questions about the new KMP project structure, what changed in the KMP wizard, how to split `composeApp` into separate modules, stale Android Studio or IntelliJ run configurations that still show `composeApp`, or how to comply with Android Gradle Plugin (AGP) 9.0's requirement to separate app and library code. Use this even if the user phrases it casually, e.g. "how do I update my KMP project structure", "split my composeApp module", "composeApp still appears in Edit Configurations", or "AGP 9.0 breaking my KMP build".

KMP Project Structure Migration

Helps users migrate a Kotlin Multiplatform project from the old composeApp single-module structure to the new shared + separate app-module structure introduced in May 2026.

Background: What Changed and Why

The old structure used a single composeApp Gradle module that acted as both a KMP library (holding shared code) and the application entry point for Android, desktop, and web. This caused several problems:

• Mixed responsibilities made it hard to understand the build configuration
• AGP 9.0 requires the Android app entry point to be in a separate module from shared code
• iOS was already in a separate iosApp folder — the other platforms were inconsistently co-located
• Amper-based projects already used separate modules per app; Gradle projects were out of step

The new structure separates concerns clearly. For variant configurations (native UI, server), see references/configurations.md.

---

Migration Workflow

Step 1 — Understand the user's project

Before doing anything, ask or infer:

1. Which targets does the project support? (Android, iOS, desktop, web/WASM)
2. Does it have a server module? If yes, see references/configurations.md
3. Does it use native UI on any platform? (e.g. SwiftUI for iOS)
4. What AGP version is in use? If AGP 9.0+, the migration is mandatory for Android targets.
5. Can they share their settings.gradle.kts and build.gradle.kts files? Reading the actual files makes the migration more accurate.
6. Does the IDE still show composeApp after migration? If yes, inspect .idea metadata as part of cleanup.

---

Step 2 — Create the shared module

Extract the KMP library portions from composeApp. Move all source sets (commonMain, androidMain, iosMain, desktopMain, wasmJsMain), shared dependencies, and resources. Do NOT move: com.android.application plugin, desktop application {} block, or app-specific signing/package config.

shared/build.gradle.kts skeleton:

plugins {
    alias(libs.plugins.kotlinMultiplatform)
    alias(libs.plugins.composeMultiplatform)
    alias(libs.plugins.composeCompiler)
    alias(libs.plugins.androidLibrary)   // library, not application
}

kotlin {
    androidTarget()
    iosX64(); iosArm64(); iosSimulatorArm64()
    jvm("desktop")
    wasmJs { browser() }

    sourceSets {
        commonMain.dependencies {
            implementation(compose.runtime)
            implementation(compose.foundation)
            implementation(compose.material3)
            implementation(compose.components.resources)
        }
    }
}

android {
    namespace = "com.example.myapp.shared"
    compileSdk = libs.versions.android.compileSdk.get().toInt()
}

---

Step 3 — Create androidApp module

Standard Android application module that depends on shared.

plugins {
    alias(libs.plugins.androidApplication)
    alias(libs.plugins.kotlinAndroid)
    alias(libs.plugins.composeCompiler)
}

android {
    namespace = "com.example.myapp"
    defaultConfig {
        applicationId = "com.example.myapp"
        versionCode = 1
        versionName = "1.0"
    }
}

dependencies {
    implementation(projects.shared)
    implementation(libs.androidx.activity.compose)
}

Move AndroidManifest.xml, MainActivity.kt, and res/ from composeApp/src/androidMain/. MainActivity just calls the shared App() composable.

---

Step 4 — Create desktopApp module (if applicable)

plugins {
    alias(libs.plugins.kotlinJvm)
    alias(libs.plugins.composeMultiplatform)
    alias(libs.plugins.composeCompiler)
}

dependencies {
    implementation(projects.shared)
    implementation(compose.desktop.currentOs)
}

compose.desktop {
    application { mainClass = "com.example.myapp.MainKt" }
}

Move main() from composeApp/src/desktopMain/ into desktopApp/src/main/kotlin/.

---

Step 5 — Create webApp module (if applicable)

plugins {
    alias(libs.plugins.kotlinMultiplatform)
    alias(libs.plugins.composeMultiplatform)
    alias(libs.plugins.composeCompiler)
}

kotlin {
    wasmJs {
        moduleName = "webApp"
        browser { commonWebpackConfig { outputFileName = "webApp.js" } }
        binaries.executable()
    }
    sourceSets {
        commonMain.dependencies { implementation(projects.shared) }
    }
}

---

Step 6 — Update settings.gradle.kts

include(":shared")
include(":androidApp")
include(":desktopApp")   // if applicable
include(":webApp")       // if applicable

Remove the old :composeApp include.

If composeApp still appears in Android Studio / IntelliJ, verify this file first. The IDE will keep importing composeApp as long as settings.gradle.kts still contains:

include(":composeApp")

Replace it with only the modules that actually exist. Do not add desktopApp or webApp unless those modules were created.

---

Step 7 — Update iOS references

iosApp/ stays as-is structurally, but renaming the module concept from composeApp to shared requires updating several iOS-side references. Both lowercase composeApp and uppercase ComposeApp must be searched — the uppercase form is used as the framework baseName and Swift import.

7a — Update the Gradle framework baseName

In shared/build.gradle.kts (or the root build file), find the XCFramework / framework configuration and change the baseName:

// Before
kotlin {
    iosX64 { binaries.framework { baseName = "ComposeApp" } }
    // ...
}

// After
kotlin {
    iosX64 { binaries.framework { baseName = "Shared" } }
    // ...
}

7b — Update the Xcode build phase

In Xcode → Build Phases → "Compile Kotlin Framework", update the Gradle task:

./gradlew :shared:assembleXCFramework

7c — Update Swift imports

Search iosApp/ for import ComposeApp and replace with import Shared:

rg -n "ComposeApp" iosApp/ --glob '*.swift'

Update every occurrence in .swift files — typically iOSApp.swift and ContentView.swift.

7d — Update Podfile or SPM manifest (if applicable)

If using CocoaPods, update the pod name in iosApp/Podfile:

# Before
pod 'ComposeApp', :path => '../'

# After
pod 'Shared', :path => '../'

If using Swift Package Manager, update the target dependency name accordingly.

7e — Verify with xcodebuild, not just Gradle

A successful ./gradlew :shared:assembleXCFramework does not guarantee the Xcode build works. Always verify with an actual Xcode build:

xcodebuild -project iosApp/iosApp.xcodeproj \
  -scheme iosApp \
  -destination 'platform=iOS Simulator,name=iPhone 15' \
  build

Or simply build from Xcode IDE to catch any remaining ComposeApp references.

---

Step 8 — Clean up

• Delete the old composeApp/ directory after verifying the build
• Update CI scripts referencing :composeApp tasks
• Search the project for stale module references before declaring the migration done:

rg -n "composeApp|ComposeApp" . --hidden \
  --glob 'settings.gradle.kts' \
  --glob '**/*.gradle.kts' \
  --glob '.idea/**' \
  --glob '.github/**' \
  --glob 'gradle/**' \
  --glob 'iosApp/**'

• Update IDE metadata and run configurations. IntelliJ / Android Studio may keep showing composeApp even after the source migration if any of these files still reference it:

  • .idea/gradle.xml module entries such as $PROJECT_DIR$/composeApp
  • .idea/runConfigurations/*.xml and .idea/workspace.xml run manager entries
  • .idea/deploymentTargetSelector.xml entries such as runConfigName="composeApp"
  • .idea/artifacts/composeApp_*.xml generated artifact definitions

• Exact run configuration field mappings — update each stale config as follows:

  Field	Old value	New value
  Android run config name	Android App.composeApp	Android App.androidApp
  Android module field	Breeze.composeApp	Breeze.androidApp
  Desktop config (hot reload)	composeApp [jvm, hot]	desktopApp [jvm, hot]
  Desktop config (standard)	composeApp [jvm]	desktopApp [jvm]
  Web config (JS)	composeApp [js]	webApp [js]
  Web config (WASM)	composeApp [wasmJs]	webApp [wasmJs]
  Gradle project path (desktop)	$PROJECT_DIR$/composeApp	$PROJECT_DIR$/desktopApp
  Gradle project path (web)	$PROJECT_DIR$/composeApp	$PROJECT_DIR$/webApp
  Desktop hot-reload task	hotRunJvm	hotRun
  Desktop standard task	jvmRun	run

• If the IDE files are not intentionally versioned, the pragmatic shortcut is to close the IDE, delete stale .idea/runConfigurations/*.xml, .idea/artifacts/composeApp_*.xml, and the composeApp entries in .idea/gradle.xml, .idea/deploymentTargetSelector.xml, and .idea/workspace.xml, then re-open and sync Gradle.

• Commit updated shared IDE files if the repository tracks them, so teammates do not keep importing or launching composeApp.

---

Step 9 — Sync and verify before finishing

Do not end the migration immediately after editing files. Finish with a project synchronization and validation pass:

1. Run ./gradlew projects and confirm the output lists the new modules and does not list :composeApp.
2. Run the relevant compile/build tasks for the targets that exist, for example:

./gradlew :shared:compileKotlinMetadata
./gradlew :androidApp:assembleDebug
./gradlew :desktopApp:compileKotlin
./gradlew :webApp:compileKotlinJs
./gradlew :webApp:compileKotlinWasmJs
./gradlew :shared:compileKotlinIosSimulatorArm64

3. For iOS, verify with xcodebuild (see Step 7e) in addition to the Gradle tasks above.
4. Search for stale module references one last time:

rg -n "composeApp|ComposeApp" . --hidden --glob '!**/build/**' --glob '!**/.gradle/**' --glob '!**/.kotlin/**'

5. In the final response, explicitly tell the user to run File → Sync Project with Gradle Files in Android Studio / IntelliJ, or close and reopen the IDE if stale composeApp configurations still appear. There is no reliable repository-only edit that forces an already open IDE window to complete a Gradle sync.

---

Common Issues

"Cannot apply com.android.application to a multiplatform module" → AGP 9.0 error. Move the app plugin to androidApp.

Duplicate resources / composeResources not found → Keep compose.components.resources only in shared; app modules depend on projects.shared.

expect/actual not resolved → Source set names in shared must match what they were in composeApp.

iOS build fails after rename → Search for both composeApp and ComposeApp in iosApp/. The uppercase form is the framework baseName and Swift import — update baseName = "Shared" in the Gradle build file, replace import ComposeApp with import Shared in all Swift files, update any Podfile or SPM references, and verify with xcodebuild rather than Gradle alone.

composeApp still appears in Edit Configurations or the Gradle tool window → First check settings.gradle.kts; if it still has include(":composeApp"), replace it with include(":shared"), include(":androidApp"), and any created desktopApp / webApp modules. Then search .idea for composeApp. Remove or update stale entries in .idea/gradle.xml, .idea/runConfigurations/*.xml, .idea/workspace.xml, .idea/deploymentTargetSelector.xml, and .idea/artifacts/composeApp_*.xml, then re-sync Gradle.

Run configuration still launches :composeApp (or fails with "Task ':composeApp:…' not found") → IDE run configurations were not updated. Use the field mapping table in Step 8 to update each config's name, module, Gradle project path, and task name. Or delete the stale XML files and let the IDE recreate them on next sync.

Edits look correct but the IDE still shows old modules → Run File → Sync Project with Gradle Files. If Android Studio / IntelliJ was open during the migration and still shows stale entries after sync, close and reopen the project so it reloads settings.gradle.kts and the updated .idea metadata.

---

References

• references/configurations.md — native UI and server-module variants
• Official migration guide: https://kotlinlang.org/docs/multiplatform/multiplatform-project-recommended-structure.html
• AGP 9.0 changes: https://blog.jetbrains.com/kotlin/2026/01/update-your-projects-for-agp9/
• KMP wizard: https://kmp.new