kmp-build-setup

KMP Build Setup (Gradle)

Overview

The Kotlin Multiplatform Gradle plugin's kotlin {} block declares targets; from the declared targets it generates a source-set hierarchy (commonMain → intermediate iosMain → leaf iosArm64Main) via the default hierarchy template. Shared code lives in commonMain, platform code in the platform source sets. Requires Kotlin 1.9.20+ (hierarchy template); current line is Kotlin 2.1.x.

When to use

• New or broken shared/build.gradle.kts
• Adding a target (iosArm64, jvm, js, wasmJs) or a source set
• "source set not found" or dependency-wiring issues across commonMain/iosMain
• Configuring the android {} block for androidTarget

Plugins + targets

plugins {
    kotlin("multiplatform") version "2.1.x"
    id("com.android.library") version "8.x"
}

kotlin {
    androidTarget()          // Android target
    iosArm64()               // real devices
    iosSimulatorArm64()      // Apple-silicon simulator
    iosX64()                 // Intel simulator (optional)

    // The default hierarchy template runs automatically.
    // Call explicitly only when you customize the hierarchy:
    // applyDefaultHierarchyTemplate()

    sourceSets {
        commonMain.dependencies {
            implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:<v>")
        }
        androidMain.dependencies { /* OkHttp, Android-only libs */ }
        iosMain.dependencies     { /* Darwin engine, Apple-only libs */ }
        commonTest.dependencies  { implementation(kotlin("test")) }
    }
}

android {
    namespace = "com.example.shared"
    compileSdk = 35
    defaultConfig { minSdk = 24 }
}

Source-set hierarchy (auto-generated)

commonMain ─┬─ androidMain
            └─ iosMain ─┬─ iosArm64Main
                        ├─ iosSimulatorArm64Main
                        └─ iosX64Main

Declaring iosArm64() + iosSimulatorArm64() makes the plugin create the shared iosMain intermediate set automatically — put shared iOS actual code there, not in a single leaf set.