Provide preset-like factory functions for creating targets in new MPP

* Pull the `targets` and `presets` properties of the `kotlin` extension
  up to an interface in `kotlin-gradle-plugin-api`

* Generate the code: we need type-safe statically-typed functions for
  different target type, which seems to be only possible to achieve by
  providing a function per preset.

* Place these functions in the top-level `kotlin` Gradle extension,
  rather than extension functions for `kotlin.targets`:

  - `kotlin.jvm { ... }` will work, while `kotlin.targets.jvm { ... }`
    won't, the extension function needs to be somehow brought into scope

  - reducing the nesting level by one seems to be a good move here

Issue #KT-26389 Fixed

libraries/tools/kotlin-gradle-plugin-api/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinTarget.kt

@@ -45,5 +45,7 @@ interface KotlinTarget: Named, HasAttributes {
     fun mavenPublication(action: Closure<Unit>)
     fun mavenPublication(action: Action<MavenPublication>)
 
+    val preset: KotlinTargetPreset<out KotlinTarget>?
+
     override fun getName(): String = targetName
 }

libraries/tools/kotlin-gradle-plugin-api/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinTargetsContainer.kt

@@ -0,0 +1,16 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.gradle.plugin
+
+import org.gradle.api.NamedDomainObjectCollection
+
+interface KotlinTargetsContainer {
+    val targets: NamedDomainObjectCollection<KotlinTarget>
+}
+
+interface KotlinTargetsContainerWithPresets : KotlinTargetsContainer {
+    val presets: NamedDomainObjectCollection<KotlinTargetPreset<*>>
+}

libraries/tools/kotlin-gradle-plugin-dsl-codegen/build.gradle.kts

@@ -0,0 +1,28 @@
+import org.gradle.jvm.tasks.Jar
+
+plugins {
+    kotlin("jvm")
+}
+
+dependencies {
+    compile(gradleApi())
+    compile(project(":kotlin-gradle-plugin-api"))
+    compile(project(":kotlin-native:kotlin-native-utils"))
+}
+
+val generateMppTargetContainerWithPresets by generator(
+    "org.jetbrains.kotlin.generators.gradle.dsl.MppPresetFunctionsCodegenKt",
+    sourceSets["main"]
+)
+
+generateMppTargetContainerWithPresets.run {
+    systemProperty(
+        "org.jetbrains.kotlin.generators.gradle.dsl.outputSourceRoot",
+        project(":kotlin-gradle-plugin").projectDir.resolve("src/main/kotlin").absolutePath
+    )
+}
+
+// Workaround: 'java -jar' refuses to read the original dotted filename on Windows, 'Unable to access jarFile org.jetbrains.kotlin....jar'
+tasks.named<Jar>(generateMppTargetContainerWithPresets.name + "WriteClassPath").configure {
+    archiveName = generateMppTargetContainerWithPresets.name
+}

libraries/tools/kotlin-gradle-plugin-dsl-codegen/src/main/kotlin/org/jetbrains/kotlin/generators/gradle/dsl/codegenUtils.kt

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.generators.gradle.dsl
+
+internal data class TypeName(val fqName: String, val typeArguments: List<TypeName>)
+
+internal fun typeName(fqName: String, vararg typeArgumentFlatFqNames: String): TypeName {
+    require(typeArgumentFlatFqNames.none { "<" in it }) { "generics won't render to short type names properly, use the full constructor" }
+    return TypeName(
+        fqName,
+        typeArgumentFlatFqNames.map {
+            TypeName(
+                it,
+                emptyList()
+            )
+        })
+}
+
+internal fun TypeName.shortName() = fqName.split(".").last()
+
+internal fun TypeName.packageName() = fqName.substringBeforeLast(".")
+
+internal fun TypeName.renderShort(): String =
+    shortName() + typeArguments.takeIf { it.isNotEmpty() }?.joinToString(", ", "<", ">") { it.renderShort() }.orEmpty()
+
+internal fun TypeName.renderErased(): String =
+    shortName() + typeArguments.takeIf { it.isNotEmpty() }?.joinToString(", ", "<", ">") { "*" }.orEmpty()
+
+internal fun TypeName.collectFqNames(): Set<String> =
+    setOf(fqName) + typeArguments.flatMap { it.collectFqNames() }.toSet()
+

libraries/tools/kotlin-gradle-plugin-dsl-codegen/src/main/kotlin/org/jetbrains/kotlin/generators/gradle/dsl/mppPresetFunctionsCodegen.kt

@@ -0,0 +1,74 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.generators.gradle.dsl
+
+import org.jetbrains.kotlin.gradle.plugin.KotlinTargetsContainerWithPresets
+import java.io.File
+
+fun main() {
+    generateKotlinTargetContainerWithPresetFunctionsInterface()
+}
+
+private val parentInterface = KotlinTargetsContainerWithPresets::class
+
+private val presetsProperty = KotlinTargetsContainerWithPresets::presets.name
+
+private fun generateKotlinTargetContainerWithPresetFunctionsInterface() {
+    // Generate KotlinMutliplatformExtension subclass with member functions for the presets:
+    val functions = allPresetEntries.map {
+        generatePresetFunction(it, presetsProperty, "configureOrCreate")
+    }
+
+    val parentInterfaceName =
+        typeName(parentInterface.java.canonicalName)
+
+    val className =
+        typeName("org.jetbrains.kotlin.gradle.dsl.KotlinTargetContainerWithPresetFunctions")
+
+    val imports = allPresetEntries
+        .flatMap { it.typeNames() }
+        .plus(parentInterfaceName)
+        .filter { it.packageName() != className.packageName() }
+        .flatMap { it.collectFqNames() }
+        .toSortedSet()
+        .joinToString("\n") { "import $it" }
+
+    val generatedCodeWarning = "// DO NOT EDIT MANUALLY! Generated by ${object {}.javaClass.enclosingClass.name}"
+
+    val code = listOf(
+        "package ${className.packageName()}",
+        imports,
+        generatedCodeWarning,
+        "interface ${className.renderShort()} : ${parentInterfaceName.renderShort()} {",
+        functions.joinToString("\n\n") { it.indented(4) },
+        "}"
+    ).joinToString("\n\n")
+
+    val outputSourceRoot = System.getProperties()["org.jetbrains.kotlin.generators.gradle.dsl.outputSourceRoot"]
+    val targetFile = File("$outputSourceRoot/${className.fqName.replace(".", "/")}.kt")
+    targetFile.writeText(code)
+}
+
+private fun generatePresetFunction(
+    presetEntry: KotlinPresetEntry,
+    getPresetsExpression: String,
+    configureOrCreateFunctionName: String
+): String = """
+    fun ${presetEntry.presetName}(
+        name: String = "${presetEntry.presetName}",
+        configure: ${presetEntry.targetType.renderShort()}.() -> Unit = { }
+    ): ${presetEntry.targetType.renderShort()} =
+        $configureOrCreateFunctionName(
+            name,
+            $getPresetsExpression.getByName("${presetEntry.presetName}") as ${presetEntry.presetType.renderErased()},
+            configure
+        )
+""".trimIndent()
+
+private fun String.indented(nSpaces: Int = 4): String {
+    val spaces = String(CharArray(nSpaces) { ' ' })
+    return lines().joinToString("\n") { "$spaces$it"  }
+}

libraries/tools/kotlin-gradle-plugin-dsl-codegen/src/main/kotlin/org/jetbrains/kotlin/generators/gradle/dsl/presetEntries.kt

@@ -0,0 +1,62 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.generators.gradle.dsl
+
+import org.jetbrains.kotlin.konan.target.HostManager
+import org.jetbrains.kotlin.konan.target.presetName
+
+internal class KotlinPresetEntry(
+    val presetName: String,
+    val presetType: TypeName,
+    val targetType: TypeName
+)
+
+internal fun KotlinPresetEntry.typeNames(): Set<TypeName> = setOf(presetType, targetType)
+
+private const val MPP_PACKAGE = "org.jetbrains.kotlin.gradle.plugin.mpp"
+
+private const val KOTLIN_NATIVE_TARGET_PRESET_CLASS_FQNAME = "$MPP_PACKAGE.KotlinNativeTargetPreset"
+private const val KOTLIN_NATIVE_TARGET_CLASS_FQNAME = "$MPP_PACKAGE.KotlinNativeTarget"
+
+private const val KOTLIN_ONLY_TARGET_CLASS_FQNAME = "$MPP_PACKAGE.KotlinOnlyTarget"
+
+internal val jvmPresetEntry = KotlinPresetEntry(
+    "jvm",
+    typeName("$MPP_PACKAGE.KotlinJvmTargetPreset"),
+    typeName(
+        KOTLIN_ONLY_TARGET_CLASS_FQNAME,
+        "$MPP_PACKAGE.KotlinJvmCompilation"
+    )
+)
+
+internal val jsPresetEntry = KotlinPresetEntry(
+    "js",
+    typeName("$MPP_PACKAGE.KotlinJsTargetPreset"),
+    typeName(
+        KOTLIN_ONLY_TARGET_CLASS_FQNAME,
+        "$MPP_PACKAGE.KotlinJsCompilation"
+    )
+)
+
+internal val androidPresetEntry = KotlinPresetEntry(
+    "android",
+    typeName("$MPP_PACKAGE.KotlinAndroidTargetPreset"),
+    typeName("$MPP_PACKAGE.KotlinAndroidTarget")
+)
+
+internal val nativePresetEntries = HostManager().targets.map { (_, target) ->
+    KotlinPresetEntry(
+        target.presetName,
+        typeName(KOTLIN_NATIVE_TARGET_PRESET_CLASS_FQNAME),
+        typeName(KOTLIN_NATIVE_TARGET_CLASS_FQNAME)
+    )
+}
+
+internal val allPresetEntries = listOf(
+    jvmPresetEntry,
+    jsPresetEntry,
+    androidPresetEntry
+) + nativePresetEntries

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/dsl/KotlinMultiplatformExtension.kt

@@ -5,17 +5,64 @@
 
 package org.jetbrains.kotlin.gradle.dsl
 
+import org.gradle.api.InvalidUserCodeException
 import org.gradle.api.NamedDomainObjectCollection
 import org.jetbrains.kotlin.gradle.plugin.KotlinTarget
 import org.jetbrains.kotlin.gradle.plugin.KotlinTargetPreset
+import org.jetbrains.kotlin.gradle.plugin.KotlinTargetsContainerWithPresets
+import org.jetbrains.kotlin.gradle.plugin.mpp.KotlinCommonCompilation
+import org.jetbrains.kotlin.gradle.plugin.mpp.KotlinMultiplatformPlugin
+import org.jetbrains.kotlin.gradle.plugin.mpp.KotlinOnlyTarget
 
-open class KotlinMultiplatformExtension : KotlinProjectExtension() {
+open class KotlinMultiplatformExtension : KotlinProjectExtension(), KotlinTargetContainerWithPresetFunctions {
-    lateinit var presets: NamedDomainObjectCollection<KotlinTargetPreset<*>>
+    override lateinit var presets: NamedDomainObjectCollection<KotlinTargetPreset<*>>
         internal set
 
-    lateinit var targets: NamedDomainObjectCollection<KotlinTarget>
+    override lateinit var targets: NamedDomainObjectCollection<KotlinTarget>
         internal set
 
     internal var isGradleMetadataAvailable: Boolean = false
     internal var isGradleMetadataExperimental: Boolean = false
+
+    fun metadata(configure: KotlinOnlyTarget<KotlinCommonCompilation>.() -> Unit = { }): KotlinOnlyTarget<KotlinCommonCompilation> =
+        @Suppress("UNCHECKED_CAST")
+        (targets.getByName(KotlinMultiplatformPlugin.METADATA_TARGET_NAME) as KotlinOnlyTarget<KotlinCommonCompilation>).also(configure)
+
+    fun <T : KotlinTarget> targetFromPreset(
+        preset: KotlinTargetPreset<T>,
+        name: String = preset.name,
+        configure: T.() -> Unit = { }
+    ): T = configureOrCreate(name, preset, configure)
+}
+
+internal fun KotlinTarget.isProducedFromPreset(kotlinTargetPreset: KotlinTargetPreset<*>): Boolean =
+    preset == kotlinTargetPreset
+
+internal fun <T : KotlinTarget> KotlinTargetsContainerWithPresets.configureOrCreate(
+    targetName: String,
+    targetPreset: KotlinTargetPreset<T>,
+    configure: T.() -> Unit
+): T {
+    val existingTarget = targets.findByName(targetName)
+    when {
+        existingTarget?.isProducedFromPreset(targetPreset) ?: false -> {
+            @Suppress("UNCHECKED_CAST")
+            configure(existingTarget as T)
+            return existingTarget
+        }
+        existingTarget == null -> {
+            val newTarget = targetPreset.createTarget(targetName)
+            targets.add(newTarget)
+            configure(newTarget)
+            return newTarget
+        }
+        else -> {
+            throw InvalidUserCodeException(
+                "The target '$targetName' already exists, but it was not created with the '${targetPreset.name}' preset. " +
+                        "To configure it, access it by name in `kotlin.targets`" +
+                        " or use the preset function '${existingTarget.preset?.name}'"
+                            .takeIf { existingTarget.preset != null }
+            )
+        }
+    }
 }

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/dsl/KotlinTargetContainerWithPresetFunctions.kt

@@ -0,0 +1,160 @@
+package org.jetbrains.kotlin.gradle.dsl
+
+import org.jetbrains.kotlin.gradle.plugin.KotlinTargetsContainerWithPresets
+import org.jetbrains.kotlin.gradle.plugin.mpp.*
+
+// DO NOT EDIT MANUALLY! Generated by org.jetbrains.kotlin.generators.gradle.dsl.MppPresetFunctionsCodegenKt
+
+interface KotlinTargetContainerWithPresetFunctions : KotlinTargetsContainerWithPresets {
+
+    fun jvm(
+        name: String = "jvm",
+        configure: KotlinOnlyTarget<KotlinJvmCompilation>.() -> Unit = { }
+    ): KotlinOnlyTarget<KotlinJvmCompilation> =
+        configureOrCreate(
+            name,
+            presets.getByName("jvm") as KotlinJvmTargetPreset,
+            configure
+        )
+
+    fun js(
+        name: String = "js",
+        configure: KotlinOnlyTarget<KotlinJsCompilation>.() -> Unit = { }
+    ): KotlinOnlyTarget<KotlinJsCompilation> =
+        configureOrCreate(
+            name,
+            presets.getByName("js") as KotlinJsTargetPreset,
+            configure
+        )
+
+    fun android(
+        name: String = "android",
+        configure: KotlinAndroidTarget.() -> Unit = { }
+    ): KotlinAndroidTarget =
+        configureOrCreate(
+            name,
+            presets.getByName("android") as KotlinAndroidTargetPreset,
+            configure
+        )
+
+    fun androidNativeArm32(
+        name: String = "androidNativeArm32",
+        configure: KotlinNativeTarget.() -> Unit = { }
+    ): KotlinNativeTarget =
+        configureOrCreate(
+            name,
+            presets.getByName("androidNativeArm32") as KotlinNativeTargetPreset,
+            configure
+        )
+
+    fun androidNativeArm64(
+        name: String = "androidNativeArm64",
+        configure: KotlinNativeTarget.() -> Unit = { }
+    ): KotlinNativeTarget =
+        configureOrCreate(
+            name,
+            presets.getByName("androidNativeArm64") as KotlinNativeTargetPreset,
+            configure
+        )
+
+    fun iosArm32(
+        name: String = "iosArm32",
+        configure: KotlinNativeTarget.() -> Unit = { }
+    ): KotlinNativeTarget =
+        configureOrCreate(
+            name,
+            presets.getByName("iosArm32") as KotlinNativeTargetPreset,
+            configure
+        )
+
+    fun iosArm64(
+        name: String = "iosArm64",
+        configure: KotlinNativeTarget.() -> Unit = { }
+    ): KotlinNativeTarget =
+        configureOrCreate(
+            name,
+            presets.getByName("iosArm64") as KotlinNativeTargetPreset,
+            configure
+        )
+
+    fun iosX64(
+        name: String = "iosX64",
+        configure: KotlinNativeTarget.() -> Unit = { }
+    ): KotlinNativeTarget =
+        configureOrCreate(
+            name,
+            presets.getByName("iosX64") as KotlinNativeTargetPreset,
+            configure
+        )
+
+    fun linuxX64(
+        name: String = "linuxX64",
+        configure: KotlinNativeTarget.() -> Unit = { }
+    ): KotlinNativeTarget =
+        configureOrCreate(
+            name,
+            presets.getByName("linuxX64") as KotlinNativeTargetPreset,
+            configure
+        )
+
+    fun linuxArm32Hfp(
+        name: String = "linuxArm32Hfp",
+        configure: KotlinNativeTarget.() -> Unit = { }
+    ): KotlinNativeTarget =
+        configureOrCreate(
+            name,
+            presets.getByName("linuxArm32Hfp") as KotlinNativeTargetPreset,
+            configure
+        )
+
+    fun linuxMips32(
+        name: String = "linuxMips32",
+        configure: KotlinNativeTarget.() -> Unit = { }
+    ): KotlinNativeTarget =
+        configureOrCreate(
+            name,
+            presets.getByName("linuxMips32") as KotlinNativeTargetPreset,
+            configure
+        )
+
+    fun linuxMipsel32(
+        name: String = "linuxMipsel32",
+        configure: KotlinNativeTarget.() -> Unit = { }
+    ): KotlinNativeTarget =
+        configureOrCreate(
+            name,
+            presets.getByName("linuxMipsel32") as KotlinNativeTargetPreset,
+            configure
+        )
+
+    fun mingwX64(
+        name: String = "mingwX64",
+        configure: KotlinNativeTarget.() -> Unit = { }
+    ): KotlinNativeTarget =
+        configureOrCreate(
+            name,
+            presets.getByName("mingwX64") as KotlinNativeTargetPreset,
+            configure
+        )
+
+    fun macosX64(
+        name: String = "macosX64",
+        configure: KotlinNativeTarget.() -> Unit = { }
+    ): KotlinNativeTarget =
+        configureOrCreate(
+            name,
+            presets.getByName("macosX64") as KotlinNativeTargetPreset,
+            configure
+        )
+
+    fun wasm32(
+        name: String = "wasm32",
+        configure: KotlinNativeTarget.() -> Unit = { }
+    ): KotlinNativeTarget =
+        configureOrCreate(
+            name,
+            presets.getByName("wasm32") as KotlinNativeTargetPreset,
+            configure
+        )
+
+}

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/kotlinTargetPresets.kt

@@ -42,6 +42,7 @@ abstract class KotlinOnlyTargetPreset<T : KotlinCompilation>(
         val result = KotlinOnlyTarget<T>(project, platformType).apply {
             targetName = name
             disambiguationClassifier = name
+            preset = this@KotlinOnlyTargetPreset
 
             val compilationFactory = createCompilationFactory(this)
             compilations = project.container(compilationFactory.itemClass, compilationFactory)
@@ -177,6 +178,7 @@ class KotlinAndroidTargetPreset(
     override fun createTarget(name: String): KotlinAndroidTarget {
         val result = KotlinAndroidTarget(name, project).apply {
             disambiguationClassifier = name
+            preset = this@KotlinAndroidTargetPreset
         }
 
         KotlinAndroidPlugin.applyToTarget(
@@ -204,6 +206,7 @@ class KotlinJvmWithJavaTargetPreset(
 
         val target = KotlinWithJavaTarget(project, KotlinPlatformType.jvm, name).apply {
             disambiguationClassifier = name
+            preset = this@KotlinJvmWithJavaTargetPreset
         }
 
         AbstractKotlinPlugin.configureTarget(target) { compilation ->
@@ -314,6 +317,7 @@ class KotlinNativeTargetPreset(
         val result = KotlinNativeTarget(project, konanTarget).apply {
             targetName = name
             disambiguationClassifier = name
+            preset = this@KotlinNativeTargetPreset
 
             val compilationFactory = KotlinNativeCompilationFactory(project, this)
             compilations = project.container(compilationFactory.itemClass, compilationFactory)

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/kotlinTargets.kt

@@ -108,6 +108,9 @@ abstract class AbstractKotlinTarget(
 
     override fun mavenPublication(action: Closure<Unit>) =
         mavenPublication(ConfigureUtil.configureUsing(action))
+
+    override var preset: KotlinTargetPreset<out KotlinTarget>? = null
+        internal set
 }
 
 internal fun KotlinTarget.disambiguateName(simpleName: String) =

settings.gradle

@@ -157,6 +157,7 @@ include ":kotlin-build-common",
         ":tools:kotlin-stdlib-gen",
         ":tools:kotlinp",
         ":kotlin-gradle-plugin-api",
+        ":kotlin-gradle-plugin-dsl-codegen",
         ":kotlin-gradle-plugin",
         ":kotlin-gradle-plugin-model",
         ":kotlin-gradle-plugin-test-utils-embeddable",
@@ -293,6 +294,7 @@ project(':tools:kotlin-stdlib-js-merger').projectDir = "$rootDir/libraries/tools
 project(':tools:kotlin-stdlib-gen').projectDir = "$rootDir/libraries/tools/kotlin-stdlib-gen" as File
 project(':tools:kotlinp').projectDir = "$rootDir/libraries/tools/kotlinp" as File
 project(':kotlin-gradle-plugin-api').projectDir = "$rootDir/libraries/tools/kotlin-gradle-plugin-api" as File
+project(':kotlin-gradle-plugin-dsl-codegen').projectDir = "$rootDir/libraries/tools/kotlin-gradle-plugin-dsl-codegen" as File
 project(':kotlin-gradle-plugin').projectDir = "$rootDir/libraries/tools/kotlin-gradle-plugin" as File
 project(':kotlin-gradle-plugin-model').projectDir = "$rootDir/libraries/tools/kotlin-gradle-plugin-model" as File
 project(':kotlin-gradle-plugin-test-utils-embeddable').projectDir = "$rootDir/libraries/tools/kotlin-gradle-plugin-test-utils-embeddable" as File