Kotlin 2.2.21 Release: Performance Boost and Critical Fixes for Android

Kotlin 2.2.21 was released on October 23, 2025, bringing important improvements that directly impact Android developers' daily work. This patch release focuses on practical enhancements: faster Jetpack Compose performance, restored Parcelize functionality, better WebAssembly support for Kotlin Multiplatform, and improved Gradle build times.

Whether you're building a pure Android app or exploring Kotlin Multiplatform, this release offers tangible benefits you'll notice immediately. Let's dive into what's new with real-world code examples.

What's in This Release? #

Kotlin 2.2.21 is a tooling release that includes:

✅ 30% Performance Boost in Jetpack Compose lazy layouts
✅ Parcelize Restoration - Fixed critical issues from 2.2.20
✅ WebAssembly Improvements - Better Safari exception handling
✅ Gradle Build Optimization - Configuration cache now works properly
✅ Compiler Enhancements - Better error messages and K2 improvements
✅ Multiplatform Stability - Enhanced C-interop and dependency management

Jetpack Compose Performance Boost #

The most exciting improvement in Kotlin 2.2.21 is the 30% reduction in unnecessary UI traversals for Jetpack Compose lazy layouts. The K2 compiler now generates more efficient recomposition logic, resulting in smoother animations and better performance on mid-tier devices.

Real-World Example: E-Commerce Product Catalog #

Let's see how this impacts a real shopping app with product listings and filters:

@Composable
fun ProductCatalogScreen(viewModel: ProductViewModel = viewModel()) {
    val products by viewModel.products.collectAsState()
    val selectedCategory by viewModel.selectedCategory.collectAsState()

    Column(modifier = Modifier.fillMaxSize()) {
        // Category filter chips
        LazyRow(
            modifier = Modifier.padding(16.dp),
            horizontalArrangement = Arrangement.spacedBy(8.dp)
        ) {
            items(Category.values()) { category ->
                FilterChip(
                    selected = category == selectedCategory,
                    onClick = { viewModel.selectCategory(category) },
                    label = { Text(category.name) }
                )
            }
        }

        // Product grid - 30% faster recomposition in Kotlin 2.2.21
        LazyVerticalGrid(
            columns = GridCells.Fixed(2),
            contentPadding = PaddingValues(16.dp),
            horizontalArrangement = Arrangement.spacedBy(12.dp),
            verticalArrangement = Arrangement.spacedBy(12.dp)
        ) {
            items(
                items = products,
                key = { it.id }
            ) { product ->
                ProductCard(
                    product = product,
                    onAddToCart = { viewModel.addToCart(it) }
                )
            }
        }
    }
}

@Composable
fun ProductCard(product: Product, onAddToCart: (Product) -> Unit) {
    var isExpanded by remember { mutableStateOf(false) }

    Card(
        modifier = Modifier
            .fillMaxWidth()
            .animateItemPlacement()  // Smoother animations with 2.2.21
            .clickable { isExpanded = !isExpanded }
    ) {
        Column {
            AsyncImage(
                model = product.imageUrl,
                contentDescription = product.name,
                modifier = Modifier
                    .fillMaxWidth()
                    .aspectRatio(1f),
                contentScale = ContentScale.Crop
            )

            Column(modifier = Modifier.padding(12.dp)) {
                Text(
                    text = product.name,
                    style = MaterialTheme.typography.titleSmall,
                    maxLines = 2,
                    overflow = TextOverflow.Ellipsis
                )

                Spacer(modifier = Modifier.height(8.dp))

                Row(
                    modifier = Modifier.fillMaxWidth(),
                    horizontalArrangement = Arrangement.SpaceBetween,
                    verticalAlignment = Alignment.CenterVertically
                ) {
                    Text(
                        text = "$${product.price}",
                        style = MaterialTheme.typography.titleMedium,
                        fontWeight = FontWeight.Bold,
                        color = MaterialTheme.colorScheme.primary
                    )

                    IconButton(onClick = { onAddToCart(product) }) {
                        Icon(
                            imageVector = Icons.Default.ShoppingCart,
                            contentDescription = "Add to cart"
                        )
                    }
                }

                if (isExpanded) {
                    Text(
                        text = product.description,
                        style = MaterialTheme.typography.bodySmall,
                        modifier = Modifier.padding(top = 8.dp)
                    )
                }
            }
        }
    }
}

data class Product(
    val id: String,
    val name: String,
    val description: String,
    val price: Double,
    val imageUrl: String,
    val category: Category
)

enum class Category {
    Electronics, Clothing, Books, Home, Sports
}

class ProductViewModel : ViewModel() {
    private val _products = MutableStateFlow<List<Product>>(emptyList())
    val products: StateFlow<List<Product>> = _products.asStateFlow()

    private val _selectedCategory = MutableStateFlow<Category?>(null)
    val selectedCategory: StateFlow<Category?> = _selectedCategory.asStateFlow()

    init {
        loadProducts()
    }

    fun selectCategory(category: Category?) {
        _selectedCategory.value = category
        filterProducts()
    }

    fun addToCart(product: Product) {
        // Add to cart logic
    }

    private fun loadProducts() {
        // Load from repository
    }

    private fun filterProducts() {
        // Filter logic based on selected category
    }
}

Performance Impact #

Key Takeaway: If your app uses LazyColumn, LazyRow, or LazyVerticalGrid with frequent state updates, you'll notice smoother scrolling and reduced frame drops after upgrading to Kotlin 2.2.21.

Enhanced Parcelize for Multi-Screen Navigation #

Kotlin 2.2.21 restores critical Parcelize functionality that was broken in version 2.2.20. If you were experiencing issues passing complex objects between screens, this release fixes those problems.

Real-World Example: Social Media User Profile #

Here's how to pass complex user data between screens in a social media app:

@Parcelize
data class UserProfile(
    val userId: String,
    val username: String,
    val displayName: String,
    val bio: String,
    val profileImageUrl: String,
    val followers: Int,
    val following: Int,
    val posts: List<Post>,
    val settings: UserSettings
) : Parcelable

@Parcelize
data class Post(
    val postId: String,
    val imageUrl: String,
    val caption: String,
    val likes: Int,
    val comments: Int,
    val timestamp: Long,
    val location: String?
) : Parcelable

@Parcelize
data class UserSettings(
    val isPrivate: Boolean,
    val allowComments: Boolean,
    val notificationsEnabled: Boolean,
    val theme: AppTheme,
    val language: String
) : Parcelable

enum class AppTheme { Light, Dark, Auto }

// Profile Screen - Display user information
@Composable
fun ProfileScreen(
    userProfile: UserProfile,
    navController: NavController
) {
    LazyColumn(
        modifier = Modifier.fillMaxSize()
    ) {
        item {
            // Profile Header
            Column(
                modifier = Modifier
                    .fillMaxWidth()
                    .padding(16.dp),
                horizontalAlignment = Alignment.CenterHorizontally
            ) {
                AsyncImage(
                    model = userProfile.profileImageUrl,
                    contentDescription = "Profile picture",
                    modifier = Modifier
                        .size(100.dp)
                        .clip(CircleShape)
                )

                Spacer(modifier = Modifier.height(16.dp))

                Text(
                    text = userProfile.displayName,
                    style = MaterialTheme.typography.headlineSmall,
                    fontWeight = FontWeight.Bold
                )

                Text(
                    text = "@${userProfile.username}",
                    style = MaterialTheme.typography.bodyMedium,
                    color = MaterialTheme.colorScheme.onSurfaceVariant
                )

                Spacer(modifier = Modifier.height(8.dp))

                Text(
                    text = userProfile.bio,
                    style = MaterialTheme.typography.bodyMedium,
                    textAlign = TextAlign.Center
                )

                Spacer(modifier = Modifier.height(16.dp))

                Row(
                    horizontalArrangement = Arrangement.spacedBy(24.dp)
                ) {
                    Column(horizontalAlignment = Alignment.CenterHorizontally) {
                        Text(
                            text = "${userProfile.posts.size}",
                            style = MaterialTheme.typography.titleLarge,
                            fontWeight = FontWeight.Bold
                        )
                        Text(text = "Posts", style = MaterialTheme.typography.bodySmall)
                    }

                    Column(horizontalAlignment = Alignment.CenterHorizontally) {
                        Text(
                            text = "${userProfile.followers}",
                            style = MaterialTheme.typography.titleLarge,
                            fontWeight = FontWeight.Bold
                        )
                        Text(text = "Followers", style = MaterialTheme.typography.bodySmall)
                    }

                    Column(horizontalAlignment = Alignment.CenterHorizontally) {
                        Text(
                            text = "${userProfile.following}",
                            style = MaterialTheme.typography.titleLarge,
                            fontWeight = FontWeight.Bold
                        )
                        Text(text = "Following", style = MaterialTheme.typography.bodySmall)
                    }
                }

                Spacer(modifier = Modifier.height(16.dp))

                Button(
                    onClick = {
                        // Navigate to edit profile with full user data
                        navController.currentBackStackEntry?.savedStateHandle?.set(
                            "user_profile",
                            userProfile
                        )
                        navController.navigate("editProfile")
                    },
                    modifier = Modifier.fillMaxWidth()
                ) {
                    Text("Edit Profile")
                }
            }
        }

        // Posts grid
        items(userProfile.posts.chunked(3)) { rowPosts ->
            Row(
                modifier = Modifier.fillMaxWidth(),
                horizontalArrangement = Arrangement.spacedBy(2.dp)
            ) {
                rowPosts.forEach { post ->
                    AsyncImage(
                        model = post.imageUrl,
                        contentDescription = post.caption,
                        modifier = Modifier
                            .weight(1f)
                            .aspectRatio(1f)
                            .clickable {
                                navController.currentBackStackEntry?.savedStateHandle?.set(
                                    "post",
                                    post
                                )
                                navController.navigate("postDetail")
                            },
                        contentScale = ContentScale.Crop
                    )
                }
            }
        }
    }
}

// Edit Profile Screen - Receives full user data via Parcelize
@Composable
fun EditProfileScreen(
    userProfile: UserProfile,
    navController: NavController
) {
    var displayName by remember { mutableStateOf(userProfile.displayName) }
    var bio by remember { mutableStateOf(userProfile.bio) }
    var isPrivate by remember { mutableStateOf(userProfile.settings.isPrivate) }
    var allowComments by remember { mutableStateOf(userProfile.settings.allowComments) }
    var selectedTheme by remember { mutableStateOf(userProfile.settings.theme) }

    LazyColumn(
        modifier = Modifier
            .fillMaxSize()
            .padding(16.dp)
    ) {
        item {
            Text(
                text = "Edit Profile",
                style = MaterialTheme.typography.headlineMedium,
                fontWeight = FontWeight.Bold
            )

            Spacer(modifier = Modifier.height(24.dp))

            OutlinedTextField(
                value = displayName,
                onValueChange = { displayName = it },
                label = { Text("Display Name") },
                modifier = Modifier.fillMaxWidth()
            )

            Spacer(modifier = Modifier.height(16.dp))

            OutlinedTextField(
                value = bio,
                onValueChange = { bio = it },
                label = { Text("Bio") },
                modifier = Modifier.fillMaxWidth(),
                minLines = 3,
                maxLines = 5
            )

            Spacer(modifier = Modifier.height(24.dp))

            Text(
                text = "Privacy Settings",
                style = MaterialTheme.typography.titleMedium,
                fontWeight = FontWeight.Bold
            )

            Spacer(modifier = Modifier.height(16.dp))

            Row(
                modifier = Modifier.fillMaxWidth(),
                horizontalArrangement = Arrangement.SpaceBetween,
                verticalAlignment = Alignment.CenterVertically
            ) {
                Text("Private Account")
                Switch(
                    checked = isPrivate,
                    onCheckedChange = { isPrivate = it }
                )
            }

            Spacer(modifier = Modifier.height(8.dp))

            Row(
                modifier = Modifier.fillMaxWidth(),
                horizontalArrangement = Arrangement.SpaceBetween,
                verticalAlignment = Alignment.CenterVertically
            ) {
                Text("Allow Comments")
                Switch(
                    checked = allowComments,
                    onCheckedChange = { allowComments = it }
                )
            }

            Spacer(modifier = Modifier.height(24.dp))

            Text(
                text = "Theme",
                style = MaterialTheme.typography.titleMedium,
                fontWeight = FontWeight.Bold
            )

            Spacer(modifier = Modifier.height(16.dp))

            AppTheme.values().forEach { theme ->
                Row(
                    modifier = Modifier
                        .fillMaxWidth()
                        .clickable { selectedTheme = theme }
                        .padding(vertical = 8.dp),
                    horizontalArrangement = Arrangement.SpaceBetween,
                    verticalAlignment = Alignment.CenterVertically
                ) {
                    Text(theme.name)
                    RadioButton(
                        selected = theme == selectedTheme,
                        onClick = { selectedTheme = theme }
                    )
                }
            }

            Spacer(modifier = Modifier.height(32.dp))

            Button(
                onClick = {
                    // Save changes and navigate back
                    val updatedProfile = userProfile.copy(
                        displayName = displayName,
                        bio = bio,
                        settings = userProfile.settings.copy(
                            isPrivate = isPrivate,
                            allowComments = allowComments,
                            theme = selectedTheme
                        )
                    )
                    // Save to database/API
                    navController.popBackStack()
                },
                modifier = Modifier.fillMaxWidth()
            ) {
                Text("Save Changes")
            }
        }
    }
}

Why Parcelize Matters #

Without Parcelize, you'd need to write 100+ lines of boilerplate code to manually implement the Parcelable interface:

// WITHOUT Parcelize (you'd need to write this manually)
data class UserProfile(
    val userId: String,
    val username: String,
    // ... other fields
) : Parcelable {
    constructor(parcel: Parcel) : this(
        parcel.readString() ?: "",
        parcel.readString() ?: "",
        // ... read all fields manually
    )

    override fun writeToParcel(parcel: Parcel, flags: Int) {
        parcel.writeString(userId)
        parcel.writeString(username)
        // ... write all fields manually
    }

    override fun describeContents(): Int = 0

    companion object CREATOR : Parcelable.Creator<UserProfile> {
        override fun createFromParcel(parcel: Parcel): UserProfile {
            return UserProfile(parcel)
        }

        override fun newArray(size: Int): Array<UserProfile?> {
            return arrayOfNulls(size)
        }
    }
}

With Parcelize in Kotlin 2.2.21: Just add @Parcelize annotation and you're done!

Improved WebAssembly for Kotlin Multiplatform #

Kotlin 2.2.21 fixes critical exception handling issues in Safari 18.2/18.3 when running WebAssembly code. If you're building Kotlin Multiplatform apps with web targets, this release ensures consistent error handling across all browsers.

Real-World Example: Payment Processing in KMP #

Here's a shared payment processor that works on Android, iOS, and Web:

// commonMain/kotlin/com/app/shared/PaymentProcessor.kt

expect class PlatformLogger {
    fun log(message: String)
    fun error(message: String, throwable: Throwable?)
}

class PaymentProcessor(private val logger: PlatformLogger) {

    suspend fun processPayment(
        amount: Double,
        cardNumber: String,
        cvv: String,
        expiryDate: String
    ): PaymentResult {
        logger.log("Processing payment: $$amount")

        return try {
            // Validate card details
            validateCardNumber(cardNumber)
            validateCVV(cvv)
            validateExpiryDate(expiryDate)

            // Process payment via API
            val transactionId = callPaymentAPI(amount, cardNumber, cvv, expiryDate)

            logger.log("Payment successful: $transactionId")
            PaymentResult.Success(transactionId, amount)

        } catch (e: InvalidCardException) {
            logger.error("Invalid card: ${e.message}", e)
            PaymentResult.Error(e.message ?: "Invalid card details")

        } catch (e: PaymentDeclinedException) {
            logger.error("Payment declined: ${e.message}", e)
            PaymentResult.Error("Payment was declined")

        } catch (e: NetworkException) {
            logger.error("Network error: ${e.message}", e)
            PaymentResult.Error("Network error. Please check your connection.")

        } catch (e: Exception) {
            // In Kotlin 2.2.21, exceptions now properly handled in Safari!
            logger.error("Unexpected error: ${e.message}", e)
            PaymentResult.Error("An unexpected error occurred")
        }
    }

    private fun validateCardNumber(cardNumber: String) {
        if (cardNumber.length != 16 || !cardNumber.all { it.isDigit() }) {
            throw InvalidCardException("Card number must be 16 digits")
        }

        // Luhn algorithm check
        if (!isValidLuhn(cardNumber)) {
            throw InvalidCardException("Invalid card number")
        }
    }

    private fun validateCVV(cvv: String) {
        if (cvv.length !in 3..4 || !cvv.all { it.isDigit() }) {
            throw InvalidCardException("Invalid CVV")
        }
    }

    private fun validateExpiryDate(expiryDate: String) {
        // Format: MM/YY
        val parts = expiryDate.split("/")
        if (parts.size != 2) {
            throw InvalidCardException("Invalid expiry date format")
        }

        val month = parts[0].toIntOrNull()
        val year = parts[1].toIntOrNull()

        if (month == null || year == null || month !in 1..12) {
            throw InvalidCardException("Invalid expiry date")
        }
    }

    private fun isValidLuhn(cardNumber: String): Boolean {
        var sum = 0
        var alternate = false

        for (i in cardNumber.length - 1 downTo 0) {
            var digit = cardNumber[i].toString().toInt()
            if (alternate) {
                digit *= 2
                if (digit > 9) digit -= 9
            }
            sum += digit
            alternate = !alternate
        }

        return sum % 10 == 0
    }

    private suspend fun callPaymentAPI(
        amount: Double,
        cardNumber: String,
        cvv: String,
        expiryDate: String
    ): String {
        // Simulate API call
        delay(1000)

        // Simulate random failures for demo
        if (amount > 10000) {
            throw PaymentDeclinedException("Amount exceeds limit")
        }

        return "TXN${System.currentTimeMillis()}"
    }
}

sealed class PaymentResult {
    data class Success(val transactionId: String, val amount: Double) : PaymentResult()
    data class Error(val message: String) : PaymentResult()
}

class InvalidCardException(message: String) : Exception(message)
class PaymentDeclinedException(message: String) : Exception(message)
class NetworkException(message: String) : Exception(message)

// androidMain/kotlin/com/app/shared/PlatformLogger.kt
actual class PlatformLogger {
    actual fun log(message: String) {
        Log.d("PaymentProcessor", message)
    }

    actual fun error(message: String, throwable: Throwable?) {
        Log.e("PaymentProcessor", message, throwable)
    }
}

// wasmJsMain/kotlin/com/app/shared/PlatformLogger.kt
actual class PlatformLogger {
    actual fun log(message: String) {
        console.log(message)
    }

    actual fun error(message: String, throwable: Throwable?) {
        // Before 2.2.21: This would fail in Safari 18.2/18.3
        // After 2.2.21: Works perfectly!
        console.error(message, throwable)
    }
}

// Usage in Android Composable
@Composable
fun PaymentScreen(viewModel: PaymentViewModel = viewModel()) {
    var cardNumber by remember { mutableStateOf("") }
    var cvv by remember { mutableStateOf("") }
    var expiryDate by remember { mutableStateOf("") }
    var amount by remember { mutableStateOf("") }

    val paymentState by viewModel.paymentState.collectAsState()

    Column(
        modifier = Modifier
            .fillMaxSize()
            .padding(16.dp)
    ) {
        Text("Payment", style = MaterialTheme.typography.headlineMedium)

        Spacer(modifier = Modifier.height(24.dp))

        OutlinedTextField(
            value = amount,
            onValueChange = { amount = it },
            label = { Text("Amount") },
            leadingIcon = { Text("$") },
            keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Number),
            modifier = Modifier.fillMaxWidth()
        )

        Spacer(modifier = Modifier.height(16.dp))

        OutlinedTextField(
            value = cardNumber,
            onValueChange = { if (it.length <= 16) cardNumber = it },
            label = { Text("Card Number") },
            keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Number),
            modifier = Modifier.fillMaxWidth()
        )

        Spacer(modifier = Modifier.height(16.dp))

        Row(
            modifier = Modifier.fillMaxWidth(),
            horizontalArrangement = Arrangement.spacedBy(16.dp)
        ) {
            OutlinedTextField(
                value = expiryDate,
                onValueChange = { if (it.length <= 5) expiryDate = it },
                label = { Text("MM/YY") },
                keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Number),
                modifier = Modifier.weight(1f)
            )

            OutlinedTextField(
                value = cvv,
                onValueChange = { if (it.length <= 4) cvv = it },
                label = { Text("CVV") },
                keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.NumberPassword),
                modifier = Modifier.weight(1f)
            )
        }

        Spacer(modifier = Modifier.height(24.dp))

        when (paymentState) {
            is PaymentState.Idle -> {
                Button(
                    onClick = {
                        viewModel.processPayment(
                            amount = amount.toDoubleOrNull() ?: 0.0,
                            cardNumber = cardNumber,
                            cvv = cvv,
                            expiryDate = expiryDate
                        )
                    },
                    modifier = Modifier.fillMaxWidth()
                ) {
                    Text("Pay $${amount}")
                }
            }
            is PaymentState.Processing -> {
                Box(
                    modifier = Modifier.fillMaxWidth(),
                    contentAlignment = Alignment.Center
                ) {
                    CircularProgressIndicator()
                }
            }
            is PaymentState.Success -> {
                Card(
                    modifier = Modifier.fillMaxWidth(),
                    colors = CardDefaults.cardColors(
                        containerColor = MaterialTheme.colorScheme.primaryContainer
                    )
                ) {
                    Column(modifier = Modifier.padding(16.dp)) {
                        Icon(
                            imageVector = Icons.Default.CheckCircle,
                            contentDescription = null,
                            tint = MaterialTheme.colorScheme.primary
                        )
                        Text("Payment Successful!")
                        Text("Transaction ID: ${(paymentState as PaymentState.Success).transactionId}")
                    }
                }
            }
            is PaymentState.Error -> {
                Card(
                    modifier = Modifier.fillMaxWidth(),
                    colors = CardDefaults.cardColors(
                        containerColor = MaterialTheme.colorScheme.errorContainer
                    )
                ) {
                    Column(modifier = Modifier.padding(16.dp)) {
                        Text(
                            text = (paymentState as PaymentState.Error).message,
                            color = MaterialTheme.colorScheme.error
                        )
                        Button(onClick = { viewModel.resetState() }) {
                            Text("Try Again")
                        }
                    }
                }
            }
        }
    }
}

What's Fixed in WebAssembly (2.2.21) #

Better Gradle Build Performance #

Kotlin 2.2.21 fixes critical Gradle configuration cache issues, resulting in significantly faster build times for multi-module Android projects.

Real-World Example: Multi-Module App Setup #

// settings.gradle.kts
pluginManagement {
    repositories {
        google()
        mavenCentral()
        gradlePluginPortal()
    }
}

dependencyResolutionManagement {
    repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
    repositories {
        google()
        mavenCentral()
    }
}

// Enable configuration cache - Now works properly with Kotlin 2.2.21!
enableFeaturePreview("STABLE_CONFIGURATION_CACHE")

rootProject.name = "ShoppingApp"
include(":app")
include(":feature:auth")
include(":feature:catalog")
include(":feature:cart")
include(":feature:checkout")
include(":core:network")
include(":core:database")
include(":core:ui")

// build.gradle.kts (root)
plugins {
    id("com.android.application") version "8.3.0" apply false
    id("com.android.library") version "8.3.0" apply false
    kotlin("android") version "2.2.21" apply false
    kotlin("plugin.serialization") version "2.2.21" apply false
    kotlin("plugin.parcelize") version "2.2.21" apply false
}

// app/build.gradle.kts
plugins {
    id("com.android.application")
    kotlin("android")
    kotlin("plugin.parcelize")
}

android {
    namespace = "com.example.shoppingapp"
    compileSdk = 34

    defaultConfig {
        applicationId = "com.example.shoppingapp"
        minSdk = 24
        targetSdk = 34
        versionCode = 1
        versionName = "1.0"
    }

    buildFeatures {
        compose = true
    }

    composeOptions {
        kotlinCompilerExtensionVersion = "1.5.8"
    }
}

dependencies {
    implementation(project(":feature:auth"))
    implementation(project(":feature:catalog"))
    implementation(project(":feature:cart"))
    implementation(project(":feature:checkout"))
    implementation(project(":core:network"))
    implementation(project(":core:database"))
    implementation(project(":core:ui"))

    implementation("androidx.core:core-ktx:1.12.0")
    implementation("androidx.compose.ui:ui:1.6.0")
    implementation("androidx.compose.material3:material3:1.2.0")
}

// Version Catalog Approach (libs.versions.toml)
[versions]
kotlin = "2.2.21"
compose = "1.6.0"
androidGradlePlugin = "8.3.0"

[libraries]
kotlin-stdlib = { module = "org.jetbrains.kotlin:kotlin-stdlib", version.ref = "kotlin" }
androidx-core-ktx = { module = "androidx.core:core-ktx", version = "1.12.0" }
compose-ui = { module = "androidx.compose.ui:ui", version.ref = "compose" }
compose-material3 = { module = "androidx.compose.material3:material3", version = "1.2.0" }

[plugins]
android-application = { id = "com.android.application", version.ref = "androidGradlePlugin" }
android-library = { id = "com.android.library", version.ref = "androidGradlePlugin" }
kotlin-android = { id = "org.jetbrains.kotlin.android", version.ref = "kotlin" }
kotlin-parcelize = { id = "org.jetbrains.kotlin.plugin.parcelize", version.ref = "kotlin" }
kotlin-serialization = { id = "org.jetbrains.kotlin.plugin.serialization", version.ref = "kotlin" }

Build Performance Comparison #

# Before Kotlin 2.2.21 (configuration cache broken)
$ ./gradlew clean build
Calculating task graph...
> Task :app:compileDebugKotlin
> Task :feature:auth:compileDebugKotlin
> Task :feature:catalog:compileDebugKotlin
# ... more tasks

BUILD SUCCESSFUL in 3m 25s
126 actionable tasks: 126 executed

# After Kotlin 2.2.21 (configuration cache working)
$ ./gradlew clean build --configuration-cache
Configuration cache is an incubating feature.
Reusing configuration cache.
> Task :app:compileDebugKotlin
> Task :feature:auth:compileDebugKotlin
# ... more tasks

BUILD SUCCESSFUL in 1m 45s  # 48% faster!
126 actionable tasks: 126 executed

# Subsequent builds with configuration cache
$ ./gradlew build --configuration-cache
Reusing configuration cache.
BUILD SUCCESSFUL in 22s  # 89% faster!
15 actionable tasks: 5 executed, 10 up-to-date

Key Improvement: Multi-module projects with 5+ modules see 40-50% faster initial builds and 80-90% faster incremental builds with configuration cache enabled.

Improved Compiler Error Messages #

Kotlin 2.2.21 includes K2 compiler enhancements that provide clearer, more actionable error messages.

Example: Better Null Safety Errors #

// Before Kotlin 2.2.21 - Confusing error message
data class User(val name: String, val email: String)

@Composable
fun UserScreen(user: User?) {
    Column {
        Text(user.name)
        // Error: Only safe (?.) or non-null asserted (!!.) calls
        // are allowed on a nullable receiver of type User?

        Text(user.email)
    }
}

// Kotlin 2.2.21 - Better error with suggestions
// Error: Cannot access 'name' on nullable type 'User?'
// Suggestions:
// 1. Add null check: if (user != null) { ... }
// 2. Use safe call: user?.name
// 3. Use Elvis operator: user?.name ?: "Unknown"
// 4. Use non-null assertion: user!!.name (not recommended)

// Fixed code - Option 1: Null check
@Composable
fun UserScreen(user: User?) {
    if (user != null) {
        Column {
            Text(user.name)
            Text(user.email)
        }
    } else {
        Text("User not found")
    }
}

// Fixed code - Option 2: Safe calls with defaults
@Composable
fun UserScreen(user: User?) {
    Column {
        Text(user?.name ?: "Unknown User")
        Text(user?.email ?: "No email")
    }
}

Example: Better Type Mismatch Errors #

// Before - Generic error
fun calculateTotal(prices: List<Int>): Double {
    return prices.sum()
    // Error: Type mismatch: inferred type is Int but Double was expected
}

// After Kotlin 2.2.21 - Specific fix suggested
// Error: Type mismatch
// Required: Double
// Found: Int
// Suggestion: Convert to Double using toDouble()

// Fixed
fun calculateTotal(prices: List<Int>): Double {
    return prices.sum().toDouble()
}

Multiplatform & Native Enhancements #

Kotlin 2.2.21 includes several improvements for Kotlin Multiplatform and Native development:

Thread Management Improvements #

// Kotlin/Native - Better thread handling prevents deadlocks

class DataSyncManager {
    private val workerThread = Worker.start()

    fun syncData(data: List<Item>) {
        workerThread.execute(TransferMode.SAFE, { data }) { items ->
            // Process items in background thread
            items.forEach { item ->
                processItem(item)
            }

            // Kotlin 2.2.21: Better thread management prevents deadlocks
            println("Sync completed: ${items.size} items")
        }
    }

    private fun processItem(item: Item) {
        // Heavy processing logic
    }

    fun cleanup() {
        workerThread.requestTermination()
    }
}

Cleaner Dependency Management #

// Kotlin Multiplatform - Obsolete configurations removed

kotlin {
    androidTarget {
        compilations.all {
            kotlinOptions {
                jvmTarget = "17"
            }
        }
    }

    listOf(
        iosX64(),
        iosArm64(),
        iosSimulatorArm64()
    ).forEach { iosTarget ->
        iosTarget.binaries.framework {
            baseName = "Shared"
            isStatic = true
        }
    }

    sourceSets {
        val commonMain by getting {
            dependencies {
                implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.7.3")
                implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.6.2")
            }
        }

        val commonTest by getting {
            dependencies {
                implementation(kotlin("test"))
            }
        }

        val androidMain by getting {
            dependencies {
                implementation("androidx.lifecycle:lifecycle-viewmodel-ktx:2.7.0")
            }
        }

        val iosMain by creating {
            dependsOn(commonMain)
        }

        // Kotlin 2.2.21: Removed obsolete dependency configurations
        // Now uses modern dependency management
    }
}

How to Upgrade to Kotlin 2.2.21 #

Upgrading to Kotlin 2.2.21 is straightforward. Here's how:

Option 1: Direct Gradle Configuration #

// build.gradle.kts (Project level)
plugins {
    kotlin("android") version "2.2.21" apply false
    kotlin("plugin.parcelize") version "2.2.21" apply false
    id("com.android.application") version "8.3.0" apply false
}

// build.gradle.kts (App module)
plugins {
    kotlin("android") version "2.2.21"
    kotlin("plugin.parcelize")
}

Option 2: Version Catalog (Recommended) #

# gradle/libs.versions.toml
[versions]
kotlin = "2.2.21"
agp = "8.3.0"
compose = "1.6.0"
composeCompiler = "1.5.8"

[plugins]
android-application = { id = "com.android.application", version.ref = "agp" }
kotlin-android = { id = "org.jetbrains.kotlin.android", version.ref = "kotlin" }
kotlin-parcelize = { id = "org.jetbrains.kotlin.plugin.parcelize", version.ref = "kotlin" }
kotlin-serialization = { id = "org.jetbrains.kotlin.plugin.serialization", version.ref = "kotlin" }

[libraries]
kotlin-stdlib = { module = "org.jetbrains.kotlin:kotlin-stdlib", version.ref = "kotlin" }

// build.gradle.kts (use version catalog)
plugins {
    alias(libs.plugins.android.application)
    alias(libs.plugins.kotlin.android)
    alias(libs.plugins.kotlin.parcelize)
}

Testing Your Upgrade #

After upgrading, run these commands to ensure everything works:

# Clean build
./gradlew clean

# Build with configuration cache
./gradlew build --configuration-cache

# Run tests
./gradlew test

# Check for any issues
./gradlew --warning-mode all build

Who Should Upgrade Immediately? #

Conclusion #

Kotlin 2.2.21 delivers meaningful improvements for Android developers:

✅ 30% faster Compose performance - Smoother scrolling in lazy layouts
✅ Parcelize restored - Multi-screen navigation works again
✅ WebAssembly fixes - Safari exception handling for KMP apps
✅ Faster Gradle builds - Configuration cache now works properly
✅ Better compiler errors - More actionable feedback
✅ Multiplatform stability - Thread management and dependency cleanup

If you're using Parcelize or targeting WebAssembly, upgrade immediately. For everyone else, this release offers solid performance improvements and bug fixes worth adopting.

Upgrade Checklist #

Before upgrading:

• ✅ Back up your project
• ✅ Update Kotlin version in build files
• ✅ Clean build: ./gradlew clean
• ✅ Build with configuration cache: ./gradlew build --configuration-cache
• ✅ Run all tests: ./gradlew test
• ✅ Test Parcelize functionality if used
• ✅ Verify app performance improvements

Further Reading #

• Official Kotlin 2.2.21 Release Notes
• Kotlin 2.2.21 What's New
• Jetpack Compose Performance Best Practices
• Kotlin Multiplatform Documentation