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Gradle - Kotlin Everything you didn’t want to know about the Gradle Kotlin APIs

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@MartinBonnin apollographql/apollo-android

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Disclaimer

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Once upon a time...

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GNU Make 1988 CC= gcc # gcc or g++ CFLAGS=-g -Wall -DNORMALUNIX -DLINUX # -DUSEASM LDFLAGS=-L/usr/X11R6/lib LIBS=-lXext -lX11 -lnsl -lm # subdirectory for objects O=linux # not too sophisticated dependency OBJS= \ $(O)/doomdef.o \ $(O)/doomstat.o \ all: $(O)/linuxxdoom clean: rm -f *.o *~ *.flc rm -f linux/* $(O)/linuxxdoom: $(OBJS) $(O)/i_main.o $(CC) $(CFLAGS) $(LDFLAGS) $(OBJS) $(O)/i_main.o \ -o $(O)/linuxxdoom $(LIBS) $(O)/%.o: %.c $(CC) $(CFLAGS) -c $< -o $@

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Maven 2004 4.0.0 com.apollographql.federation federation-parent 0.7.1-SNAPSHOT pom com.graphql-java graphql-java ${graphql-java.version} org.apache.maven.plugins maven-surefire-plugin ${maven-surefire-plugin.version} com.diffplug.spotless spotless-maven-plugin

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Gradle 2008 plugins { id 'build-logic' id 'org.jetbrains.kotlin.jvm' version '1.5.31' } repositories { mavenCentral() } dependencies { implementation('com.squareup.okio:okio:3.0.0') } kotlin { sourceSets { main { languageSettings.optIn('kotlin.RequiresOptIn') } } }

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Kotlin DSL 2018

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Differences

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plugins { id 'org.jetbrains.kotlin.jvm' version '1.5.31' } dependencies { implementation(’com.squareup.okio:okio:3.0.0’) } kotlin { explicitApi() } tasks { compileKotlin { kotlinOptions { apiVersion = '1.3' } } }

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plugins { id(”org.jetbrains.kotlin.jvm”).version(“1.5.31”) } dependencies { implementation("com.squareup.okio:okio:3.0.0") } kotlin { explicitApi() } tasks { compileKotlin { kotlinOptions { apiVersion = “1.3” } } }

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plugins { id 'org.jetbrains.kotlin.jvm' version '1.5.31' } dependencies { implementation(’com.squareup.okio:okio:3.0.0’) } kotlin { explicitApi() } tasks { compileKotlin { kotlinOptions { apiVersion = '1.3' } } }

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plugins { id 'org.jetbrains.kotlin.jvm' version '1.5.31' } dependencies { implementation(’com.squareup.okio:okio:3.0.0’) } kotlin { explicitApi() } tasks { compileKotlin { kotlinOptions { apiVersion = '1.3' } } } Dynamic Usages

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Groovy metaprogramming https://groovy-lang.org/metaprogramming.html class SomeGroovyClass { def invokeMethod(String name, Object args) { return "called invokeMethod $name $args" } def test() { return 'method exists' } }

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How does it work? With magic ✨

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How does it work? With magic autogenerated accessors✨

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plugins { id(”org.jetbrains.kotlin.jvm”).version(“1.5.31”) } dependencies { implementation("com.squareup.okio:okio:3.0.0") } kotlin { explicitApi() } tasks { compileKotlin { kotlinOptions { apiVersion = “1.3” } } } Configuration Extension Task

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The good news

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● Project ● Plugins ● Tasks ● Extension ● SourceSets ● Configurations The Gradle Model https://github.com/autonomousapps/gradle-glossary

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plugins { id(”org.jetbrains.kotlin.jvm”).version(“1.5.31”) } dependencies { implementation("com.squareup.okio:okio:3.0.0") } kotlin { explicitApi() } tasks { compileKotlin { kotlinOptions { apiVersion = “1.3” } } } Extension

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Extension https://docs.gradle.org/current/dsl/org.gradle.api.plugins.ExtensionAware.html

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Extension “Most plugins offer some configuration options for build scripts and other plugins to use to customize how the plugin works. Plugins do this using extension objects.” “An extension object is simply an object with Java Bean properties that represent the configuration.” https://docs.gradle.org/current/userguide/custom_plugins.html#sec:getting_input_from_the_build

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// When you're writing kotlin { explicitApi() }

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// When you're writing kotlin { explicitApi() } // What you're really doing is project.extensions.getByName("kotlin").apply { this as KotlinJvmProjectExtension explicitApi() }

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// When you're writing kotlin { explicitApi() } // What you're really doing is project.extensions.getByName("kotlin").apply { this as KotlinJvmProjectExtension explicitApi() } // Because Gradle generated an accessor: fun org.gradle.api.Project.`kotlin`(configure: Action): Unit = (this as org.gradle.api.plugins.ExtensionAware).extensions.configure("kotlin", configure)

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// You could also write configure { explicitApi() } // Or use 'the' the().apply { explicitApi() } // Even in imperative style, without lambda the().explicitApi() // It all works!

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Configuration https://github.com/gradle/gradle/blob/master/subprojects/dependency-management/src/main/java/or g/gradle/internal/component/external/descriptor/Configuration.java

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plugins { id(”org.jetbrains.kotlin.jvm”).version(“1.5.31”) } dependencies { implementation("com.squareup.okio:okio:3.0.0") } kotlin { explicitApi() } tasks { compileKotlin { kotlinOptions { apiVersion = “1.3” } } } Configuration

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Configuration https://docs.gradle.org/current/dsl/org.gradle.api.artifacts.Configuration.html

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Configuration “A Configuration represents a group of artifacts and their dependencies” “Configuration is an instance of a FileCollection that contains all dependencies but not artifacts” “configurations have at least 3 different roles: - to declare dependencies - as a consumer, to resolve a set of dependencies to files - as a producer, to expose artifacts and their dependencies” https://docs.gradle.org/current/dsl/org.gradle.api.artifacts.Configuration.html

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Configuration A list of dependencies Identified by “group:artifact:version” “implementation” is the name of a Configuration “api” too

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// When you’re writing dependencies { implementation("com.squareup.okio:okio:3.0.0") }

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// When you’re writing dependencies { implementation("com.squareup.okio:okio:3.0.0") } // What you’re really doing is dependencies { project.configurations .getByName("implementation") .dependencies .add(create("com.squareup.okio:okio:3.0.0")) }

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// When you’re writing dependencies { implementation("com.squareup.okio:okio:3.0.0") } // What you’re really doing is dependencies { project.configurations .getByName("implementation") .dependencies .add(create("com.squareup.okio:okio:3.0.0")) } // Because Gradle generated an accessor for you! fun DependencyHandler.`implementation`(dependencyNotation: Any): Dependency? = add("implementation", dependencyNotation)

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// You could also write dependencies { "implementation"("com.squareup.okio:okio:3.0.0") } // Or that too dependencies { add("implementation", "com.squareup.okio:okio:3.0.0") } // It’s all the same...

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Task “A Task represents a single atomic piece of work for a build, such as compiling classes or generating javadoc.” https://docs.gradle.org/current/dsl/org.gradle.api.Task.html

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plugins { id(”org.jetbrains.kotlin.jvm”).version(“1.5.31”) } dependencies { implementation("com.squareup.okio:okio:3.0.0") } kotlin { explicitApi() } tasks { compileKotlin { kotlinOptions { apiVersion = “1.3” } } } Task

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// When you're writing tasks { compileKotlin { kotlinOptions { apiVersion = "1.3" } } }

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// When you're writing tasks { compileKotlin { kotlinOptions { apiVersion = "1.3" } } } // What you’re really doing is project.tasks.named("compileKotlin", KotlinCompile::class).configure { kotlinOptions { apiVersion = "1.3" } }

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// When you're writing tasks { compileKotlin { kotlinOptions { apiVersion = "1.3" } } } // What you’re really doing is project.tasks.named("compileKotlin", KotlinCompile::class).configure { kotlinOptions { apiVersion = "1.3" } } // Because Gradle generated an accessor for you val TaskContainer.`compileKotlin`: TaskProvider get() = named("compileKotlin")

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Gradle Containers ● project.configurations ● project.extensions ● project.tasks ● project.sourceSets ● NamedDomainObjectContainer

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When are accessors generated?

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plugins { id(”org.jetbrains.kotlin.jvm”).version(“1.5.31”) } // Accessors are generated here dependencies { implementation("com.squareup.okio:okio:3.0.0") } kotlin { explicitApi() } tasks { compileKotlin { kotlinOptions { apiVersion = “1.3” } } Magic happens here ✨ ✨

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class KotlinPlugin: Plugin { override fun apply(target: Project) { target.configurations.create("kotlinCompilerClasspath") target.extensions.create("kotlin", KotlinJvmProjectExtension::class.java) target.tasks.register("compileKotlin", CompileKotlinTask::class.java) } } abstract class CompileKotlinTask: DefaultTask() { // } abstract class KotlinJvmProjectExtension { // } Pseudo Kotlin Plugin Code

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Accessors generation https://github.com/gradle/gradle/blob/master/subprojects/kotlin-dsl-provider-plugins/src/main/k otlin/org/gradle/kotlin/dsl/provider/plugins/DefaultProjectSchemaProvider.kt

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plugins { id(”org.jetbrains.kotlin.jvm”).version(“1.5.31”) } // Accessors are generated here dependencies { implementation("com.squareup.okio:okio:3.0.0") } kotlin { explicitApi() } tasks { compileKotlin { kotlinOptions { apiVersion = “1.3” } } } Kotlin build script

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buildscript { dependencies { classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:1.5.31") } } apply(plugin = "org.jetbrains.kotlin.jvm") dependencies { add("implementation", "com.squareup.okio:okio:3.0.0") } configure { explicitApi() } tasks.named("compileKotlin", KotlinCompile::class) { kotlinOptions { apiVersion = "1.3" } } } Kotlin build script

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Kotlin DSL != Kotlin build scripts

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Kotlin DSL ~= Kotlin build scripts + Generated Accessors + gradleKotlinDSL() + SamWithReceiver

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gradleKotlinDsl() dependency ● the() ● val commonMain by getting() ● val appleMain by creating() ● val myProperty: String by project ● closureOf {} ● ...

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SamWithReceiver val taskProvider = tasks.named("compileKotlin", KotlinCompile::class) taskProvider.configure { kotlinOptions { apiVersion = "1.3" } }

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SamWithReceiver val taskProvider = tasks.named("compileKotlin", KotlinCompile::class) taskProvider.configure { // How come the task is in 'this' and not 'it' ?? kotlinOptions { apiVersion = "1.3" } } // configure takes an Action public interface Action { void execute(T t); }

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https://kotlinlang.org/docs/sam-with-receiver-plugin.html @HasImplicitReceiver public interface Action { /** * Performs this action against the given object. * * @param t The object to perform the action on. */ void execute(T t); }

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Should I care?

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No content

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No content

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https://github.com/gradle/gradle/issues/15886#issuecomment-954833377

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“I can copy paste and it just works” “Yay, now I understand what’s going on!” “Well, maybe I can sacrifice type safety for build speed”

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apply plugin: 'com.android.library' apply plugin: 'kotlin-android' android { // lots of boilerplate } tasks.withType(KotlinCompile).configureEach { kotlinOptions { jvmTarget = JavaVersion.VERSION_11 } } Convention plugins plugins { id 'com.squareup.android.lib' } https://developer.squareup.com/blog/herding-elephants/

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● Kotlin DSL != Kotlin build scripts ● Use convention plugins for your Kotlin build logic: https://developer.squareup.com/blog/herding-elephants/ Takeaways

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Merci! @MartinBonnin 🎄 https://bit.ly/everything-you-didnt-want-to-know-about-gradle

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Resources ● https://docs.gradle.org/current/userguide/kotlin _dsl.html ● https://blog.mbonnin.net ● https://www.youtube.com/watch?v=XXoIzzcJr80 ● https://github.com/bernaferrari/GradleKotlinCo nverter