Hello world Kotlin Jetpack Compose Example; Fixes:com-lihaoyi#3550

example/kotlinlib/android/2-jetpack-compose-hello-world/app/AndroidManifest.xml

@@ -0,0 +1,12 @@
+<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.helloworld.app">
+    <uses-sdk android:minSdkVersion="21" android:targetSdkVersion="35"/>
+    <application android:label="Hello World" android:debuggable="true">
+        <activity android:name=".MainActivity"
+                android:exported="true">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN"/>
+                <category android:name="android.intent.category.LAUNCHER"/>
+            </intent-filter>
+        </activity>
+    </application>
+</manifest>

example/kotlinlib/android/2-jetpack-compose-hello-world/app/src/main/kotlin/com/helloworld/app/MainActivity.kt

@@ -0,0 +1,21 @@
+package com.helloworld.app
+
+import android.os.Bundle
+import androidx.activity.ComponentActivity
+import androidx.activity.compose.setContent
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+
+class MainActivity : ComponentActivity() {
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        setContent {
+            Greeting("Hello, World!")
+        }
+    }
+}
+
+@Composable
+fun Greeting(name: String) {
+    Text(text = name)
+}

example/kotlinlib/android/2-jetpack-compose-hello-world/build.mill

@@ -0,0 +1,45 @@
+//// SNIPPET:BUILD
+package build
+
+import mill._
+import kotlinlib._
+import coursier.maven.MavenRepository
+import mill.kotlinlib.android.AndroidAppKotlinModule
+import mill.javalib.android.AndroidSdkModule
+
+val maven_google = Seq(
+  MavenRepository("https://maven.google.com/"),
+  MavenRepository("https://repo1.maven.org/maven2")
+)
+
+object androidSdkModule0 extends AndroidSdkModule {
+  def buildToolsVersion = "35.0.0"
+}
+
+object app extends AndroidAppKotlinModule {
+  def kotlinVersion = "2.0.20"
+  def androidSdkModule = mill.define.ModuleRef(androidSdkModule0)
+
+  override def mandatoryIvyDeps: T[Agg[Dep]] = Task {
+    super.mandatoryIvyDeps() ++ Agg(
+      // Jetpack Compose dependencies
+      ivy"androidx.compose.compiler:compiler:1.5.15",
+      ivy"androidx.activity:activity:1.8.2",
+      ivy"androidx.activity:activity-compose:1.8.2",
+      ivy"androidx.compose.runtime:runtime:1.3.1",
+      ivy"androidx.compose.material3:material3:1.0.1"
+    )
+  }
+
+  def repositoriesTask = T.task { super.repositoriesTask() ++ maven_google }
+
+}
+
+////SNIPPET:END
+
+/** Usage
+
+> ./mill show app.androidApk
+".../out/app/androidApk.dest/app.apk"
+
+*/

kotlinlib/src/mill/kotlinlib/android/AndroidAppKotlinModule.scala

@@ -2,6 +2,9 @@ package mill.kotlinlib.android
 
 import mill.kotlinlib.KotlinModule
 import mill.javalib.android.AndroidAppModule
+import mill._
+import coursier.Type
+import upickle.default.ReadWriter
 
 /**
  * Trait for building Android applications using the Mill build tool.
@@ -18,4 +21,66 @@ import mill.javalib.android.AndroidAppModule
  * [[https://developer.android.com/studio Android Studio Documentation]]
  */
 @mill.api.experimental
-trait AndroidAppKotlinModule extends AndroidAppModule with KotlinModule {}
+trait AndroidAppKotlinModule extends AndroidAppModule with KotlinModule {
+
+  /**
+   * Implicit `ReadWriter` for serializing and deserializing `coursier.Type` values.
+   * Converts a `coursier.Type` to a `String` and vice versa.
+   */
+  implicit val coursierTypeRW: ReadWriter[Type] = upickle.default.readwriter[String].bimap(
+    _.value, // Serialize coursier.Type to String
+    Type(_) // Deserialize String to coursier.Type
+  )
+
+  /**
+   * Implicit `ReadWriter` for handling `Set[coursier.Type]`, allowing conversion
+   * between a set of `coursier.Type` and a set of `String`.
+   */
+  implicit val coursierTypeSetRW: ReadWriter[Set[Type]] =
+    upickle.default.readwriter[Set[String]].bimap(
+      _.map(_.value), // Serialize Set[coursier.Type] to Set[String]
+      _.map(Type(_)) // Deserialize Set[String] to Set[coursier.Type]
+    )
+
+  /**
+   * Adds the "aar" type to the set of artifact types handled by this module.
+   *
+   * @return A task that yields an updated set of artifact types including "aar".
+   */
+  override def artifactTypes: T[Set[Type]] =
+    T { super.artifactTypes() + coursier.Type("aar") }
+
+  /**
+   * Task to extract `classes.jar` files from AAR files in the classpath.
+   *
+   * @return A sequence of `PathRef` pointing to the extracted JAR files.
+   */
+  def recompileAARs: T[Seq[PathRef]] = Task {
+    val aarFiles = super.compileClasspath().map(_.path).filter(_.ext == "aar").toSeq
+
+    aarFiles.map { aarFile =>
+      val extractDir = T.dest / aarFile.baseName
+      os.call(Seq("unzip", aarFile.toString, "-d", extractDir.toString))
+      PathRef(extractDir / "classes.jar")
+    }
+  }
+
+  /**
+   * Updates the compile classpath by removing `.aar` files and including the
+   * extracted `.jar` files from the AARs.
+   *
+   * @return A task yielding the updated classpath with `.jar` files.
+   */
+  def updatedCompileClasspath: T[Agg[PathRef]] = Task {
+    super.compileClasspath().filter(_.path.ext == "jar") ++ Agg.from(recompileAARs())
+  }
+
+  /**
+   * Overrides the compile classpath to replace `.aar` files with the extracted
+   * `.jar` files.
+   *
+   * @return The updated classpath with `.jar` files only.
+   */
+  override def compileClasspath: T[Agg[PathRef]] = updatedCompileClasspath()
+
+}