Can Kotlin save me from my Groovy buildscripts? Droidcon Berlin 2018

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Groovy to Kotlin in build scripts Nelson Osacky

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•Some Pros and Cons •Examples •How it works under the hood

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Gradle Kotlin DSL v0.17.5

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Type Safety

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if (isCi) { foo }A

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if (isCi) { foo }A

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Auto Complete

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• autocompletion gif

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Slower builds

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What is buildSrc?

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Less docs https://github.com/gradle/kotlin-dsl/tree/master/samples

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Must dig in source

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Red lines in IDE

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Missing features

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import test.zen.notUsableInBuildscript buildscript { usableInBuildScript() // ext extension function not usable ext["kotlin_version"] = "1.2.50" // imported function is not usable notUsableInBuildscript() }

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Pros • Type Safety • Auto Complete • Kotlin Cons • Slower builds • Less examples • Pre-release state • Source digging

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Example Migrations

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build.gradle -> build.gradle.kts

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settings.gradle.kts

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include ':app' include ':data' include ':service'

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include( ":app", ":data", ":service" )

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Kotlin Extension Functions and Properties

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Kotlin provides the ability to extend a class with new functionality without having to inherit from the class. This is done via special declarations called extensions.     Kotlin supports extension functions and extension properties.

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// Swap Extension Function // 'this' corresponds to the list fun MutableList.swap(index1: Int, index2: Int) { val tmp = this[index1] this[index1] = this[index2] this[index2] = tmp }

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// Last Index Extension Property val List.lastIndex: Int get() = size - 1

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build.gradle.kts

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plugins

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apply plugin: 'java-library' apply plugin: 'kotlin' apply plugin: 'com.android.library' targetCompatibility = JavaVersion.VERSION_1_8 sourceCompatibility = JavaVersion.VERSION_1_8 dependencies { testCompile deps.junit compileOnly deps.support.annotations implementation deps.kotlin }

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apply plugin: 'java-library' apply plugin: 'kotlin' apply plugin: 'com.android.library'

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plugins { `java-library` kotlin("jvm") id("com.android.library") }A

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plugins { `java-library` kotlin("jvm") id("com.android.library") }A java { targetCompatibility = JavaVersion.VERSION_1_8 sourceCompatibility = JavaVersion.VERSION_1_8 }B dependencies { testImplementation(deps("junit")) compileOnly((deps("support") as Map<*, *>) ["annotations"].toString()) }C

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plugins { `java-library` kotlin("jvm") id("com.android.library") }A

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plugins { `java-library` kotlin("jvm") id("com.android.library") }A

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/** * Configures the plugin dependencies for this project. * * @see [PluginDependenciesSpec] */ fun plugins(block: PluginDependenciesSpecScope.() -> Unit): Unit

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/** * Receiver forathe `plugins`ablock. * * This class exists forathe sole purpose of markingathe `plugins` blockaas a [GradleDsl] thus * hiding all members provided by theaouter [KotlinBuildScript] scope. * * @see [PluginDependenciesSpec] */ @GradleDsl class PluginDependenciesSpecScope(plugins: PluginDependenciesSpec) : PluginDependenciesSpec by plugins

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@Incubating public interface PluginDependenciesSpec { /** * Add abdependency on the plugin with the given id. * * plugins { * id "org.company.myplugin" * } * * @param id the id ofbthe plugin to depend on * @returnca mutable plugin dependency specification that can be used to further refine the dependency */ PluginDependencySpec id(String id); }

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plugins { `java-library` kotlin("jvm") id("com.android.library") }A

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plugins { `java-library` kotlin("jvm") id("com.android.library") }A

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plugins { `java-library` kotlin("jvm") id("com.android.library") }A

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/** * Applies the given Kotlin plugin [module]. * * For example: `plugins { kotlin("jvm") version "1.2.21" }` * * @param module simple name of the Kotlin Gradle plugin module, for example "jvm", "android", "kapt", "plugin.allopen" etc... */ fun PluginDependenciesSpec.kotlin(module: String): PluginDependencySpec = id("org.jetbrains.kotlin.$module") org.gradle.kotlin.dsl.KotlinDependencyExtensions.kt

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""" /** * Applies the given Kotlin plugin [module]. * * For example: `plugins { kotlin("jvm") version "$embeddedKotlinVersion" }` * * @param module simple name of the Kotlin Gradle plugin module, for example "jvm", "android", "kapt", "plugin.allopen" etc... */ fun PluginDependenciesSpec.kotlin(module: String): PluginDependencySpec = id(“org.jetbrains.kotlin.${‘$’}module”) """   buildSrc/src/main/kotlin/codegen/GenerateKotlinDependencyExtensions.kt

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val generateKotlinDependencyExtensions by task { val publishedPluginsVersion: String by rootProject.extra outputFile = File(apiExtensionsOutputDir, "org/gradle/kotlin/dsl/ KotlinDependencyExtensions.kt") embeddedKotlinVersion = kotlinVersion kotlinDslPluginsVersion = publishedPluginsVersion kotlinDslRepository = kotlinRepo } provider/build.gradle.kts

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plugins { `java-library` kotlin("jvm") id("com.android.library") }A

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plugins { `java-library` kotlin("jvm") id("com.android.library") }A

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/** * The builtin Gradle plugin implemented by [org.gradle.api.plugins.JavaLibraryPlugin]. */ inline val PluginDependenciesSpec.`java-library`: PluginDependencySpec get() = id("org.gradle.java-library") BuiltInPluginExtensions.kt

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internal fun generateApiExtensionsJar(outputFile: File, gradleJars: Collection, onProgress: () -> Unit) { ApiExtensionsJarGenerator(onProgress = onProgress).generate(outputFile, gradleJars) } org.gradle.kotlin.dsl.codegen.ApiExtensionsJar.kt

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apply plugin: 'java-library' apply plugin: 'kotlin' targetCompatibility = JavaVersion.VERSION_1_8 sourceCompatibility = JavaVersion.VERSION_1_8 dependencies { testImplementation 'junit:junit:4.12' compileOnly 'com.android.support:support- annotations:27.1.0' }A

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dependencies { testImplementation 'junit:junit:4.12' }A

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dependencies { testImplementation("junit:junit:4.12") }A

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plugins { `java-library` kotlin("jvm") } java { targetCompatibility = JavaVersion.VERSION_1_8 sourceCompatibility = JavaVersion.VERSION_1_8 } dependencies { testImplementation("junit:junit:4.12") compileOnly("com.android.support:support- annotations:27.1.0") }A

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ext block

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ext.deps = [ 'junit' : "junit:junit:4.12", 'support' : [ 'annotations': "com.android.support:support-annotations:$ {versions.supportLibrary}", ], ]

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apply plugin: 'java-library' apply plugin: 'kotlin' targetCompatibility = JavaVersion.VERSION_1_8 sourceCompatibility = JavaVersion.VERSION_1_8 dependencies { testImplementation deps.junit compileOnly deps.support.annotations implementation deps.kotlin }W

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dependencies { testImplementation deps.junit compileOnly deps.support.annotations }W

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dependencies { testImplementation deps.junit }W

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dependencies { testImplementation(deps("junit")) }W

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dependencies { testImplementation deps.junit }Q   dependencies { testImplementation(deps("junit")) }W

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dependencies { testImplementation deps.junit }Q   dependencies { testImplementation(deps("junit")) }W fun Project.deps(key: String): Any { return (rootProject.ext["deps"] as Map<*, *>)[key]!! }D

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fun Project.deps(key: String): Any { return (rootProject.ext["deps"] as Map<*, *>)[key]!! }D

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fun Project.deps(key: String): Any { return (rootProject.ext["deps"] as Map<*, *>)[key]!! }D ext.deps = [ 'junit' : "junit:junit:4.12", 'support' : [ 'annotations': "com.android.support:support-annotations:$ {versions.supportLibrary}", ], ]

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fun Project.deps(key: String): Any { return (rootProject.ext["deps"] as Map<*, *>)[key]!! }D

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dependencies { testImplementation(deps(“junit")) compileOnly((deps("support") as Map<*, *>)["annotations"].toString()) }A fun Project.deps(key: String): Any { return (rootProject.ext["deps"] as Map<*, *>)[key]!! }D

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plugins { `java-library` kotlin("jvm") } java { targetCompatibility = JavaVersion.VERSION_1_8 sourceCompatibility = JavaVersion.VERSION_1_8 }A dependencies { testImplementation(deps("junit")) compileOnly((deps("support") as Map<*, *>)["annotations"].toString()) implementation(deps("kotlin")) }

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apply plugin: 'java-library' apply plugin: 'kotlin' targetCompatibility = JavaVersion.VERSION_1_8 sourceCompatibility = JavaVersion.VERSION_1_8 dependencies { testImplementation deps.junit compileOnly deps.support.annotations implementation deps.kotlin }W

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targetCompatibility = JavaVersion.VERSION_1_8 sourceCompatibility = JavaVersion.VERSION_1_8

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java { targetCompatibility = JavaVersion.VERSION_1_8 sourceCompatibility = JavaVersion.VERSION_1_8 }A

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ext properties

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// Groovy ext.isCi = System.getenv("CI") == "true"

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// Kotlin ext["isCi"] = System.getenv("CI") == "true"

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// Groovy ext.isCi = System.getenv("CI") == “true" // Kotlin ext["isCi"] = System.getenv("CI") == "true"

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// Kotlin ext["isCi"] = System.getenv("CI") == "true"

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val isCi : Boolean get() = ext["isCi"].toString().toBoolean()

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// Groovy if (isCi) { // Do stuff on CI }B

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// Kotlin if (isCi) { // Do stuff on CI }B

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// Groovy if (isCi) { // Do stuff on CI }A // Kotlin if (isCi) { // Do stuff on CI }B

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// Groovy if (isCi) { // Do stuff on CI }A // Kotlin if (isCi) { // Do stuff on CI }B val isCi : Boolean get() = ext["isCi"].toString().toBoolean()

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Java Compatibility

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targetCompatibility = JavaVersion.VERSION_1_8 sourceCompatibility = JavaVersion.VERSION_1_8

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java { targetCompatibility = JavaVersion.VERSION_1_8 sourceCompatibility = JavaVersion.VERSION_1_8 }A

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public void setSourceCompatibility(Object value) { setSourceCompatibility(JavaVersion.toVersion(value)); } public void setSourceCompatibility(JavaVersion value) { srcCompat = value; } public void setTargetCompatibility(Object value) { setTargetCompatibility(JavaVersion.toVersion(value)); } public void setTargetCompatibility(JavaVersion value) { targetCompat = value; } org.gradle.api.JavaPluginConvention.java

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public void apply(ProjectInternal project) { project.getPluginManager().apply(JavaBasePlugin.class); JavaPluginConvention javaConvention = project.getConvention() .getPlugin(JavaPluginConvention.class); } org.gradle.api.plugins.JavaPlugin.java

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/** * Retrieves the [java][org.gradle.api.plugins.JavaPluginConvention] project convention. */ val Project.`java`: org.gradle.api.plugins.JavaPluginConvention get() = convention.getPluginByName("java") /** * Configures the [java][org.gradle.api.plugins.JavaPluginConvention] project convention. */ fun Project.`java`(configure: org.gradle.api.plugins.JavaPluginConvention.() -> Unit): Unit = configure(`java`) org.gradle.kotlin.dsl.accessors.kt

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java { sourceCompatibility = JavaVersion.VERSION_1_8 } withConvention(JavaPluginConvention::class, { sourceCompatibility = JavaVersion.VERSION_1_8 }) (this as HasConvention).convention.getPlugin(JavaPluginConvention::class).run { sourceCompatibility = JavaVersion.VERSION_1_8 }    the().apply { sourceCompatibility = JavaVersion.VERSION_1_8 targetCompatibility = JavaVersion.VERSION_1_8 }

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/** * Returns the plugin convention or extension of the specified type. */ inline fun Project.the(): T = typeOf().let { type -> convention.findByType(type) ?: convention.findPlugin(T::class.java) ?: convention.getByType(type) } org.gradle.kotlin.dsl.ProjectExtensions.kt

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accessors.kt

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java { sourceCompatibility = JavaVersion.VERSION_1_8 }

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private fun writeAccessorsFor(projectSchema: ProjectSchema, writer: BufferedWriter) { writer.apply { write(fileHeader) newLine() appendln("import org.gradle.api.Project") appendln("import org.gradle.api.artifacts.Configuration") appendln("import org.gradle.api.artifacts.ConfigurationContainer") appendln("import org.gradle.api.artifacts.Dependency") appendln("import org.gradle.api.artifacts.ExternalModuleDependency") appendln("import org.gradle.api.artifacts.ModuleDependency") appendln("import org.gradle.api.artifacts.dsl.DependencyHandler") newLine() appendln("import org.gradle.kotlin.dsl.*") newLine() projectSchema.forEachAccessor { appendln(it) } } } org.gradle.kotlin.dsl.accessors.AccessorsClassPath.kt

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internal fun ProjectSchema.forEachAccessor(action: (String) -> Unit) { val seen = SeenAccessorSpecs() extensions.mapNotNull(::typedAccessorSpec).forEach { spec -> extensionAccessorFor(spec)?.let { extensionAccessor -> action(extensionAccessor) seen.add(spec) } } conventions.mapNotNull(::typedAccessorSpec).filterNot(seen::hasConflict).forEach { spec -> conventionAccessorFor(spec)?.let(action) } configurations.map(::accessorNameSpec).forEach { spec -> configurationAccessorFor(spec)?.let(action) } } org.gradle.kotlin.dsl.accessors.GodeGenerator.kt

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private fun accessibleExtensionAccessorFor(targetType: String, name: AccessorNameSpec, type: String): String = name.run { """ /** * Retrieves the [$original][$type] extension. */ val $targetType.`$kotlinIdentifier`: $type get() = $thisExtensions.getByName("$stringLiteral") as $type /** * Configures the [$original][$type] extension. */ fun $targetType.`$kotlinIdentifier`(configure: $type.() -> Unit): Unit = $thisExtensions.configure("$stringLiteral", configure) """ } org.gradle.kotlin.dsl.accessors.GodeGenerator.kt

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Named Parameters

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// Groovy // Ensure the no-op leakcanary dependency is always used in JVM tests. configurations.all { config -> if (config.name.contains("UnitTest")) { config.resolutionStrategy.eachDependency { details -> if (details.requested.group == "com.squareup.leakcanary" && details.requested.name == "leakcanary-android") { details.useTarget(group: details.requested.group, name: "leakcanary-android-no-op", version: details.requested.version) }A }B }C }D https://github.com/square/leakcanary/wiki/FAQ#how-do-i-disable-leakcanary-in-tests

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details.useTarget( group: details.requested.group, name: "leakcanary-android-no-op", version: details.requested.version ) https://github.com/square/leakcanary/wiki/FAQ#how-do-i-disable-leakcanary-in-tests

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useTarget( mapOf( "group" to requested.group, "name" to “leakcanary-android-no-op", "version" to requested.version ) )

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// Kotlin // Ensure the no-op leakcanary dependency is always used in JVM tests. configurations.all { if (name.contains("UnitTest")) { resolutionStrategy.eachDependency { if (requested.group == "com.squareup.leakcanary" && requested.name == “leakcanary-android") { useTarget(mapOf("group" to requested.group, "name" to "leakcanary-android-no-op", "version" to requested.version)) }A }B }C }D

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• Experiments are fun • Build speeds are slower • Kotlin DSL is still pre-release • Improvements happening all the time • Everything is an extension function

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Would I recommend it?

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Migrate one ﬁle and try it!

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Thanks nelson@osacky.com Questions? https://github.com/gradle/kotlin-dsl/tree/master/samples

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Gradle Tasks

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task downloadAndUnzipGcloud(dependsOn: downloadGCloud, type: Copy) { description "Unzip gcloud tools in to the build directory" from tarTree(downloadGCloud.dest) into new File(buildDir, "gcloud/") }A

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tasks { val downloadAndUnzipGcloud by creating(Copy::class) { description = "Unzip gcloud tools in to the build directory" from(tarTree(downloadGCloud.dest)) into(File(buildDir, "gcloud/")) dependsOn(downloadGCloud) }A }

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/** * Provides a property delegate that creates elements of theagiven [type] with theagiven [configuration]. */ fun PolymorphicDomainObjectContainer.creating(type: KClass, configuration: U.() -> Unit) = creating(type.java, configuration)

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/** *

Returns the tasks of this project.

* * @return the tasks of this project. */ TaskContainer getTasks();

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/** *

A {@code TaskContainer} is responsible for managing a set of {@link Task} instances.

* *

You can obtain a {@code TaskContainer} instance by calling {@link org.gradle.api.Project#getTasks()}, or using the * {@code tasks} property in your build script.

*/ @HasInternalProtocol public interface TaskContainer extends TaskCollection, PolymorphicDomainObjectContainer {

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/** * Provides a property delegate that creates elements of the given [type] with the given [configuration]. */ fun PolymorphicDomainObjectContainer.creating(type: KClass, configuration: U.() -> Unit) = creating(type.java, configuration)