Adds R8 use cases to the repo

.idea/codeStyles/Project.xml

@@ -12,6 +12,7 @@
       </option>
       <option name="IMPORT_LAYOUT_TABLE">
         <value>
+          <package name="" withSubpackages="true" static="false" module="true" />
           <package name="" withSubpackages="true" static="false" />
           <emptyLine />
           <package name="javax" withSubpackages="true" static="false" />

app/build.gradle.kts

@@ -45,7 +45,7 @@ android {
         release {
             isMinifyEnabled = true
             applicationIdSuffix = NiaBuildType.RELEASE.applicationIdSuffix
-            proguardFiles(getDefaultProguardFile("proguard-android-optimize.txt"))
+            proguardFiles(getDefaultProguardFile("proguard-android-optimize.txt"), "proguard-rules.pro")
 
             // To publish on the Play store a private signing key is required, but to allow anyone
             // who clones the code to sign and run the release variant, use the debug signing key.
@@ -71,6 +71,7 @@ android {
 
 dependencies {
     implementation(projects.app.nativelib)
+    implementation(projects.app.mylibrary)
     implementation(projects.feature.interests)
     implementation(projects.feature.foryou)
     implementation(projects.feature.bookmarks)

app/mylibrary/build.gradle.kts

@@ -0,0 +1,35 @@
+plugins {
+    id("com.android.library")
+    kotlin("android")
+}
+
+android {
+    namespace = "com.example.mylibrary"
+    compileSdk = 33
+
+    defaultConfig {
+        minSdk = 21
+        targetSdk = 33
+
+        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
+        consumerProguardFiles("consumer-rules.pro")
+    }
+
+    buildTypes {
+        release {
+            isMinifyEnabled = false
+            proguardFiles(getDefaultProguardFile("proguard-android-optimize.txt"), "proguard-rules.pro")
+        }
+    }
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_1_8
+        targetCompatibility = JavaVersion.VERSION_1_8
+    }
+    kotlinOptions {
+        jvmTarget = "1.8"
+    }
+}
+
+dependencies {
+    implementation(projects.app.videolibrary)
+}

app/mylibrary/consumer-rules.pro

@@ -0,0 +1,27 @@
+# In your library's consumer-proguard-rules.pro
+-keep, allowoptimization class * implements com.example.mylibrary.MyWorker {
+    <init>();
+}
+
+-keepattributes *Annotation*
+
+-keep @interface com.example.mylibrary.OnEvent
+
+-keepclasseswithmembers class * {
+    @com.example.mylibrary.OnEvent <methods>;
+}
+
+-keep @interface com.example.mylibrary.ReflectiveExecutor
+
+-keep @com.example.mylibrary.ReflectiveExecutor class *{
+    # Keep the public, no-argument constructor so that an instance of the class can be created.
+    # <init> is the internal name for a constructor.
+    public <init>();
+
+    # Keep the public execute() method that has no parameters.
+    # This is critical because TaskRunner calls getMethod("execute").
+    # If this method is renamed (obfuscated) or removed (shrunk), your app will crash.
+    public void execute();
+}
+
+

app/mylibrary/proguard-rules.pro

@@ -0,0 +1,21 @@
+# Add project specific ProGuard rules here.
+# You can control the set of applied configuration files using the
+# proguardFiles setting in build.gradle.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}
+
+# Uncomment this to preserve the line number information for
+# debugging stack traces.
+#-keepattributes SourceFile,LineNumberTable
+
+# If you keep the line number information, uncomment this to
+# hide the original source file name.
+#-renamesourcefileattribute SourceFile

app/mylibrary/src/androidTest/java/com/example/mylibrary/ExampleInstrumentedTest.kt

@@ -0,0 +1,24 @@
+package com.example.mylibrary
+
+import androidx.test.platform.app.InstrumentationRegistry
+import androidx.test.ext.junit.runners.AndroidJUnit4
+
+import org.junit.Test
+import org.junit.runner.RunWith
+
+import org.junit.Assert.*
+
+/**
+ * Instrumented test, which will execute on an Android device.
+ *
+ * See [testing documentation](http://d.android.com/tools/testing).
+ */
+@RunWith(AndroidJUnit4::class)
+class ExampleInstrumentedTest {
+    @Test
+    fun useAppContext() {
+        // Context of the app under test.
+        val appContext = InstrumentationRegistry.getInstrumentation().targetContext
+        assertEquals("com.example.mylibrary.test", appContext.packageName)
+    }
+}

app/mylibrary/src/main/AndroidManifest.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+
+</manifest>

app/mylibrary/src/main/java/com/example/mylibrary/Event.kt

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2025 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.mylibrary
+
+import android.util.Log
+import kotlin.annotation.AnnotationRetention.RUNTIME
+
+// In your library:
+@Retention(RUNTIME)
+@Target(AnnotationTarget.FUNCTION)
+annotation class OnEvent
+
+class EventBus {
+    fun dispatch(listener: Any) {
+        Log.e("EventBus", "Dispatching event to $listener")
+        // Find all methods annotated with @OnEvent and invoke them
+        listener::class.java.declaredMethods.forEach { method ->
+            if (method.isAnnotationPresent(OnEvent::class.java)) {
+                try {
+                    method.invoke(listener)
+                } catch (e: Exception) { /* ... */ }
+            }
+        }
+    }
+}
+
+

app/mylibrary/src/main/java/com/example/mylibrary/TaskRunner.kt

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2025 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.mylibrary
+
+import android.util.Log
+
+/**
+ * This annotation is now targeted at classes.
+ */
+@Retention(AnnotationRetention.RUNTIME)
+@Target(AnnotationTarget.CLASS)
+annotation class ReflectiveExecutor
+
+class TaskRunner {
+    fun process(task: Any) {
+        Log.e("R8","TaskRunner processing " + task.toString())
+        // Get the Java Class object for the instance
+        val taskClass = task::class.java
+        // 1. Check if the CLASS is annotated with @ReflectiveExecutor
+        if (taskClass.isAnnotationPresent(ReflectiveExecutor::class.java)) {
+            // 2. If it's annotated, we assume a contract: the class must have a public method named "execute".
+            // We use getMethod() to find that specific method.
+            val methodToCall = taskClass.getMethod("execute") // Throws an exception if not found
+
+            // 3. Invoke the "execute" method on the provided 'task' instance.
+            methodToCall.invoke(task)
+        }
+    }
+}

app/mylibrary/src/main/java/com/example/mylibrary/Worker.kt

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2025 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.mylibrary
+
+
+
+// This is an example of loading a class by name and running its doWork method.
+
+interface MyWorker {
+    fun doWork()
+}
+
+object WorkerLoader {
+    fun loadAndRun(className: String) {
+        val workerClass = Class.forName(className)
+        val worker = workerClass.getDeclaredConstructor().newInstance() as MyWorker
+        worker.doWork()
+    }
+}
+

app/mylibrary/src/test/java/com/example/mylibrary/ExampleUnitTest.kt

@@ -0,0 +1,17 @@
+package com.example.mylibrary
+
+import org.junit.Test
+
+import org.junit.Assert.*
+
+/**
+ * Example local unit test, which will execute on the development machine (host).
+ *
+ * See [testing documentation](http://d.android.com/tools/testing).
+ */
+class ExampleUnitTest {
+    @Test
+    fun addition_isCorrect() {
+        assertEquals(4, 2 + 2)
+    }
+}

app/src/main/kotlin/com/google/samples/apps/nowinandroid/MainActivity.kt

@@ -36,6 +36,12 @@ import androidx.lifecycle.lifecycleScope
 import androidx.lifecycle.repeatOnLifecycle
 import androidx.metrics.performance.JankStats
 import androidx.tracing.trace
+import com.example.mylibrary.EventBus
+import com.example.mylibrary.MyWorker
+import com.example.mylibrary.OnEvent
+import com.example.mylibrary.ReflectiveExecutor
+import com.example.mylibrary.TaskRunner
+import com.example.mylibrary.WorkerLoader
 import com.google.samples.apps.nowinandroid.MainActivityUiState.Loading
 import com.google.samples.apps.nowinandroid.core.analytics.AnalyticsHelper
 import com.google.samples.apps.nowinandroid.core.analytics.LocalAnalyticsHelper
@@ -53,7 +59,6 @@ import kotlinx.coroutines.flow.distinctUntilChanged
 import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.flow.onEach
 import kotlinx.coroutines.launch
-import com.example.nativelib.NativeLib
 
 import javax.inject.Inject
 import kotlin.reflect.KVisibility
@@ -85,7 +90,21 @@ class MainActivity : ComponentActivity() {
         val splashScreen = installSplashScreen()
         super.onCreate(savedInstanceState)
 
-        accessSecretMessage(LibraryClass())
+
+        val workerClassName = "com.google.samples.apps.nowinandroid.CrashTestWorker"
+        WorkerLoader.loadAndRun(workerClassName)
+        val eventBus = EventBus()
+
+        val listener = CustomListener()
+        eventBus.dispatch(listener)
+
+        val runner = TaskRunner()
+        val task1 = ImportantBackgroundTask()
+
+
+        runner.process(task1) // This will be executed.
+
+
 
         // We keep this as a mutable state, so that we can track changes inside the composition.
         // This allows us to react to dark/light mode changes.
@@ -196,3 +215,25 @@ data class ThemeSettings(
     val androidTheme: Boolean,
     val disableDynamicTheming: Boolean,
 )
+
+class CrashTestWorker : MyWorker {
+    override fun doWork() {
+        // This log will never appear in a release build because the class won't be found
+        Log.d("CrashTestWorker", "Important work is being done!")
+    }
+}
+
+class CustomListener {
+    @OnEvent
+    fun onSomethingHappened() {
+        // This method will be removed by R8 without a keep rule
+        Log.e(TAG, "🎉 Event received!")
+    }
+}
+
+@ReflectiveExecutor
+class ImportantBackgroundTask {
+    fun execute() {
+        Log.e("ImportantBackgroundTask", "Executing the important background task... ✅")
+    }
+}

app/videolibrary/build.gradle.kts

@@ -0,0 +1,31 @@
+plugins {
+    id("com.android.library")
+    kotlin("android")
+}
+
+android {
+    namespace = "com.example.videolibrary"
+    compileSdk = 33
+
+    defaultConfig {
+        minSdk = 21
+        targetSdk = 33
+
+        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
+        consumerProguardFiles("consumer-rules.pro")
+    }
+
+    buildTypes {
+        release {
+            isMinifyEnabled = false
+            proguardFiles(getDefaultProguardFile("proguard-android-optimize.txt"), "proguard-rules.pro")
+        }
+    }
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_1_8
+        targetCompatibility = JavaVersion.VERSION_1_8
+    }
+    kotlinOptions {
+        jvmTarget = "1.8"
+    }
+}

app/videolibrary/src/main/java/com/example/analytics/video/VideoEventTracker.kt

@@ -0,0 +1,6 @@
+package com.example.analytics.video
+
+class VideoEventTracker {
+    // This constructor must be kept for the reflection call to succeed.
+    init { /* ... */ }
+}

core/datastore/consumer-proguard-rules.pro

@@ -3,7 +3,7 @@
    <fields>;
 }
 
--keepclassmembers,includedescriptorclasses class com.google.samples.apps.nowinandroid.LibraryClass {
+-keepclassmembers class com.google.samples.apps.nowinandroid.LibraryClass {
     private * secretMessage;
 }
 

settings.gradle.kts

@@ -84,3 +84,5 @@ check(JavaVersion.current().isCompatibleWith(JavaVersion.VERSION_17)) {
     """.trimIndent()
 }
 include(":app:nativelib")
+include(":app:mylibrary")
+include(":app:videolibrary")