Add a recipe for showing the usage of onVariants API

Bug: n/a
Test: this is a test
Change-Id: Ifc56e46200e599bf38a284fa0b37c610b4d65415

BUILD

@@ -98,3 +98,7 @@ recipe_test(
 recipe_test(
     name = "transformAllClasses",
 )
+
+recipe_test(
+    name = "onVariants",
+)

recipes/onVariants/README.md

@@ -0,0 +1,58 @@
+# Registering callbacks using onVariants in plugin
+
+This recipe shows how to access and modify the variant objects in your project.
+Plugin demonstrates a possible usages of the onVariants() API in
+[CustomPlugin.kt](build-logic/plugins/src/main/kotlin/CustomPlugin.kt).
+
+
+| Module                     | Content                                                                  |
+|----------------------------|--------------------------------------------------------------------------|
+| [build-logic](build-logic) | Contains the Project plugin that is the core of the recipe.              |
+| [app](app)                 | An Android application that will be configured with additional variants. |
+
+
+The onVariants API differs from beforeVariants in that it gives access to the variants only after all the artifacts
+produced by AGP have been determined. This means the only values that can be modified are `Property` values, which
+are resolved during task execution. One of these properties is the application ID, which is used as an example in this
+recipe. These properties can then be wired up to providers from custom tasks, as this recipe demonstrates.
+
+## Details
+### Configuring variants
+Variants are set with two predefined build types `debug` and `release`.
+
+### onVariants
+The onVariants API also supports `VariantSelectors`.
+
+Recipe has multiple examples of usage onVariants API in Kotlin:
+
+Following snippet selects all variants with `release` build type and executes callback that
+updates the applicationId for those variants.
+
+```
+val releaseSelector = androidComponents.selector().withBuildType("release")
+
+androidComponents.onVariants(releaseSelector) { variant ->
+     variant.applicationId.set("newApplicationId")
+}
+```
+
+More examples are in [CustomPlugin.kt](build-logic/plugins/src/main/kotlin/CustomPlugin.kt).
+
+## To Run
+[`CustomPlugin`](build-logic/plugins/src/main/kotlin/CustomPlugin.kt) registers an instance of a task
+`CheckApplicationIdTask` per variant, and this task verifies and outputs a modified application ID corresponding to the
+variant name.
+
+To run the examples, you can just do
+
+```
+./gradlew checkDebugApplicationId
+```
+
+and you will see the output:
+
+```
+    Application ID for debug variant: debug.applicationId
+```
+
+Running with a different variant will produce the corresponding output.

recipes/onVariants/app/build.gradle.kts

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2022 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.
+ */
+
+plugins {
+    alias(libs.plugins.android.application)
+    alias(libs.plugins.kotlin.android)
+    id("android.recipes.on_variants")
+}
+
+android {
+    namespace = "com.example.android.recipes.onVariants"
+    compileSdk = $COMPILE_SDK
+    defaultConfig {
+        minSdk = $MINIMUM_SDK
+        targetSdk = $COMPILE_SDK
+    }
+}

recipes/onVariants/app/src/main/AndroidManifest.xml

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+    <!--
+         Copyright 2022 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
+              http://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.
+    -->
+    <application android:label="Minimal">
+    </application>
+</manifest>

recipes/onVariants/build-logic/gradle.properties

@@ -0,0 +1,2 @@
+# Gradle properties are not passed to included builds https://github.com/gradle/gradle/issues/2534
+org.gradle.parallel=true

recipes/onVariants/build-logic/gradle/libs.versions.toml

@@ -0,0 +1,9 @@
+[versions]
+androidGradlePlugin = $AGP_VERSION
+kotlin = $KOTLIN_VERSION
+
+[libraries]
+android-gradlePlugin-api = { group = "com.android.tools.build", name = "gradle-api", version.ref = "androidGradlePlugin" }
+
+[plugins]
+kotlin-jvm = { id = "org.jetbrains.kotlin.jvm", version.ref = "kotlin" }

recipes/onVariants/build-logic/plugins/build.gradle.kts

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2022 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.
+ */
+
+plugins {
+    `java-gradle-plugin`
+    alias(libs.plugins.kotlin.jvm)
+}
+
+java {
+    toolchain {
+        languageVersion.set(JavaLanguageVersion.of(17))
+    }
+}
+
+dependencies {
+    compileOnly(libs.android.gradlePlugin.api)
+    implementation(gradleKotlinDsl())
+}
+
+gradlePlugin {
+    plugins {
+        create("customPlugin") {
+            id = "android.recipes.on_variants"
+            implementationClass = "CustomPlugin"
+        }
+    }
+}

recipes/onVariants/build-logic/plugins/src/main/kotlin/CustomPlugin.kt

@@ -0,0 +1,86 @@
+/*
+ * Copyright 2022 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.
+ */
+
+import com.android.build.api.variant.ApplicationAndroidComponentsExtension
+import com.android.build.gradle.AppPlugin
+import org.gradle.api.DefaultTask
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.api.provider.Property
+import org.gradle.api.file.DirectoryProperty
+import org.gradle.api.tasks.Input
+import org.gradle.api.tasks.OutputDirectory
+import org.gradle.api.tasks.TaskAction
+import org.gradle.kotlin.dsl.register
+import java.lang.RuntimeException
+
+/**
+ * This custom plugin shows examples for the onVariants API which includes updating the application ID.
+ */
+class CustomPlugin : Plugin<Project> {
+    override fun apply(project: Project) {
+
+        // Registers a callback on the application of the Android Application plugin.
+        // This allows the CustomPlugin to work whether it's applied before or after
+        // the Android Application plugin.
+        project.plugins.withType(AppPlugin::class.java) {
+
+            // Queries for the extension set by the Android Application plugin.
+            // This is the second of two entry points into the Android Gradle plugin
+            val androidComponents =
+                project.extensions.getByType(ApplicationAndroidComponentsExtension::class.java)
+            // Registers a callback to be called, when a new variant is configured
+            androidComponents.onVariants { variant ->
+                variant.applicationId.set("${variant.name}.applicationId")
+                val taskName = "check${variant.name}ApplicationId"
+                project.tasks.register<CheckApplicationIdTask>(taskName) {
+                    output.set(
+                        project.layout.buildDirectory.dir("$taskName")
+                    )
+                    variantName.set(variant.name)
+                    applicationId.set(variant.applicationId)
+                }
+            }
+        }
+    }
+}
+
+/**
+ * This task checks and outputs the name of the application ID.
+ */
+abstract class CheckApplicationIdTask : DefaultTask() {
+
+    // In order of the task to be up-to-date when the inputs have not changed,
+    // the task must declare an output, even if it's not used. Tasks with no
+    // output are always run regardless of whether the inputs changed
+    @get:OutputDirectory
+    abstract val output: DirectoryProperty
+
+    @get:Input
+    abstract val variantName: Property<String>
+
+    @get:Input
+    abstract val applicationId: Property<String>
+
+    @TaskAction
+    fun taskAction() {
+        val expectedApplicationId = "${variantName.get()}.applicationId"
+        if (applicationId.get() != expectedApplicationId) {
+            throw RuntimeException("Expected application ID to be '$expectedApplicationId'")
+        }
+        println("Application ID for ${variantName.get()} variant: ${applicationId.get()}")
+    }
+}

recipes/onVariants/build-logic/settings.gradle.kts

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2022 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.
+ */
+
+rootProject.name = "build-logic"
+
+pluginManagement {
+    repositories {
+        $AGP_REPOSITORY
+        $PLUGIN_REPOSITORIES
+    }
+}
+
+dependencyResolutionManagement {
+    repositories {
+$AGP_REPOSITORY
+$DEPENDENCY_REPOSITORIES
+    }
+}
+
+include(":plugins")

recipes/onVariants/build.gradle.kts

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2022 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.
+ */
+
+plugins {
+    alias(libs.plugins.android.application) apply false
+    alias(libs.plugins.kotlin.android) apply false
+}

recipes/onVariants/gradle.properties

@@ -0,0 +1,23 @@
+# Project-wide Gradle settings.
+# IDE (e.g. Android Studio) users:
+# Gradle settings configured through the IDE *will override*
+# any settings specified in this file.
+# For more details on how to configure your build environment visit
+# http://www.gradle.org/docs/current/userguide/build_environment.html
+# Specifies the JVM arguments used for the daemon process.
+# The setting is particularly useful for tweaking memory settings.
+org.gradle.jvmargs=-Xmx2048m -Dfile.encoding=UTF-8
+# When configured, Gradle will run in incubating parallel mode.
+# This option should only be used with decoupled projects. More details, visit
+# http://www.gradle.org/docs/current/userguide/multi_project_builds.html#sec:decoupled_projects
+org.gradle.parallel=true
+# AndroidX package structure to make it clearer which packages are bundled with the
+# Android operating system, and which are packaged with your app's APK
+# https://developer.android.com/topic/libraries/support-library/androidx-rn
+android.useAndroidX=true
+# Kotlin code style for this project: "official" or "obsolete":
+kotlin.code.style=official
+# Enables namespacing of each library's R class so that its R class includes only the
+# resources declared in the library itself and none from the library's dependencies,
+# thereby reducing the size of the R class for that library
+android.nonTransitiveRClass=true

recipes/onVariants/gradle/libs.versions.toml

@@ -0,0 +1,9 @@
+[versions]
+androidGradlePlugin = $AGP_VERSION
+kotlin = $KOTLIN_VERSION
+
+[plugins]
+android-application = { id = "com.android.application", version.ref = "androidGradlePlugin" }
+kotlin-android = { id = "org.jetbrains.kotlin.android", version.ref = "kotlin" }
+
+

recipes/onVariants/recipe_metadata.toml

@@ -0,0 +1,22 @@
+title = "onVariants"
+
+description ="""
+   This sample shows how to use onVariants in Variant API.
+  """
+
+[agpVersion]
+min = "8.0.0"
+
+# Relevant Gradle tasks to run per recipe
+[gradleTasks]
+tasks = [
+    ":app:checkDebugApplicationId",
+    ":app:checkReleaseApplicationId"
+]
+
+# All the relevant metadata fields to create an index based on language/API/etc'
+[indexMetadata]
+index = [
+    "AndroidComponentsExtension.onVariants",
+    "variant.applicationId"
+]