Introduce KotlinJavaToolchain compile tasks input.

This task input provides a way to set different from current Gradle
JDK and use it for Kotlin files compilation. By default it provides
current Gradle JDK.

Provided JDK major version is used as task input, so on providing
different JDK user will see cache miss.

All required interfaces are located inside api module.

^KT-45611 In Progress

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/KotlinJavaToolchainTest.kt

@@ -0,0 +1,144 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * 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
+
+import org.gradle.internal.jvm.JavaInfo
+import org.gradle.internal.jvm.Jvm
+import org.gradle.testkit.runner.BuildResult
+import org.gradle.util.GradleVersion
+import org.jetbrains.kotlin.gradle.testbase.*
+import org.junit.jupiter.api.DisplayName
+import java.io.File
+
+class KotlinJavaToolchainTest : KGPBaseTest() {
+
+    @GradleTest
+    @DisplayName("Should use by default same jvm as Gradle daemon")
+    internal fun byDefaultShouldUseGradleJDK(gradleVersion: GradleVersion) {
+        project(
+            projectName = "simple".fullProjectName,
+            gradleVersion = gradleVersion,
+        ) {
+            build("assemble") {
+                assertDaemonIsUsingJdk(getUserJdk().javaExecutableRealPath)
+            }
+        }
+    }
+
+    @GradleTest
+    @DisplayName("Should use provided jdk location to compile Kotlin sources")
+    internal fun customJdkHomeLocation(gradleVersion: GradleVersion) {
+        project(
+            projectName = "simple".fullProjectName,
+            gradleVersion = gradleVersion,
+        ) {
+            useJdk9ToCompile()
+
+            build("assemble") {
+                assertDaemonIsUsingJdk(getJdk9().javaExecutableRealPath)
+            }
+        }
+    }
+
+    @GradleTest
+    @DisplayName("KotlinCompile task should use build cache when using provided JDK")
+    internal fun customJdkBuildCache(gradleVersion: GradleVersion) {
+        val buildCache = workingDir.resolve("custom-jdk-build-cache")
+        project(
+            projectName = "simple".fullProjectName,
+            gradleVersion = gradleVersion,
+            projectPathAdditionalSuffix = "1/cache-test",
+            buildOptions = defaultBuildOptions.copy(buildCacheEnabled = true)
+        ) {
+            enableLocalBuildCache(buildCache)
+            useJdk9ToCompile()
+
+            build("assemble")
+        }
+
+        project(
+            projectName = "simple".fullProjectName,
+            gradleVersion = gradleVersion,
+            projectPathAdditionalSuffix = "2/cache-test",
+            buildOptions = defaultBuildOptions.copy(buildCacheEnabled = true)
+        ) {
+            enableLocalBuildCache(buildCache)
+            useJdk9ToCompile()
+
+            build("assemble") {
+                assertTasksFromCache(":compileKotlin")
+            }
+        }
+    }
+
+    @GradleTest
+    @DisplayName("Kotlin compile task should not use build cache on using different JDK versions")
+    internal fun differentJdkBuildCacheMiss(gradleVersion: GradleVersion) {
+        val buildCache = workingDir.resolve("custom-jdk-build-cache")
+        project(
+            projectName = "simple".fullProjectName,
+            gradleVersion = gradleVersion,
+            projectPathAdditionalSuffix = "1/cache-test",
+            forceOutput = true,
+            buildOptions = defaultBuildOptions.copy(buildCacheEnabled = true)
+        ) {
+            enableLocalBuildCache(buildCache)
+            enableBuildCacheDebug()
+            useJdk9ToCompile()
+            build("assemble")
+        }
+
+        project(
+            projectName = "simple".fullProjectName,
+            gradleVersion = gradleVersion,
+            projectPathAdditionalSuffix = "2/cache-test",
+            forceOutput = true,
+            buildOptions = defaultBuildOptions.copy(buildCacheEnabled = true)
+        ) {
+            enableLocalBuildCache(buildCache)
+            enableBuildCacheDebug()
+            build("assemble") {
+                assertTasksExecuted(":compileKotlin")
+            }
+        }
+    }
+
+    private fun BuildResult.assertDaemonIsUsingJdk(
+        javaexecPath: String
+    ) = assertOutputContains("i: connected to the daemon. Daemon is using following 'java' executable to run itself: $javaexecPath")
+
+    private fun getUserJdk(): JavaInfo = Jvm.forHome(File(System.getenv("JAVA_HOME")))
+    private fun getJdk9(): JavaInfo = Jvm.forHome(File(System.getenv("JDK_9")))
+    private val JavaInfo.javaExecutableRealPath
+        get() = javaExecutable
+            .toPath()
+            .toRealPath()
+            .toAbsolutePath()
+            .toString()
+
+    private val String.fullProjectName get() = "kotlin-java-toolchain/$this"
+
+    private fun TestProject.useJdk9ToCompile() {
+        // replace required for windows paths so Groovy will not complain about unexpected char '\'
+        val jdk9Path = getJdk9().javaHome.absolutePath.replace("\\", "\\\\")
+        //language=Groovy
+        rootBuildGradle.append(
+            """
+            import org.gradle.api.JavaVersion
+            import org.jetbrains.kotlin.gradle.tasks.UsesKotlinJavaToolchain
+            
+            project.tasks
+                 .withType(UsesKotlinJavaToolchain.class)
+                 .configureEach {
+                      it.kotlinJavaToolchain.setJdkHome(
+                           "$jdk9Path",
+                           JavaVersion.VERSION_1_9
+                      )
+                 }
+            """.trimIndent()
+        )
+    }
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kotlin-java-toolchain/simple/build.gradle

@@ -0,0 +1,8 @@
+plugins {
+    id("org.jetbrains.kotlin.jvm")
+}
+
+repositories {
+    mavenLocal()
+    mavenCentral()
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kotlin-java-toolchain/simple/src/main/kotlin/main.kt

@@ -0,0 +1,3 @@
+fun main() {
+    println("I know what you've done last summer...")
+}