Kapt: Support Java 9 in Gradle plugin infrastructure

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/AndroidSubplugin.kt

@@ -27,7 +27,6 @@ import org.gradle.api.Project
 import org.gradle.api.UnknownDomainObjectException
 import org.gradle.api.tasks.SourceSet
 import org.gradle.api.tasks.compile.AbstractCompile
-import com.intellij.openapi.util.text.StringUtil.*
 import org.jetbrains.kotlin.gradle.plugin.*
 import org.jetbrains.kotlin.gradle.plugin.android.AndroidGradleWrapper
 import org.jetbrains.kotlin.gradle.tasks.KotlinCompile

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/KaptTask.kt

@@ -11,6 +11,7 @@ import com.intellij.openapi.util.io.FileUtil
 import org.jetbrains.kotlin.compilerRunner.GradleCompilerEnvironment
 import org.jetbrains.kotlin.compilerRunner.GradleCompilerRunner
 import org.jetbrains.kotlin.compilerRunner.OutputItemsCollectorImpl
+import org.jetbrains.kotlin.gradle.plugin.compareVersionNumbers
 import org.jetbrains.kotlin.gradle.tasks.*
 import java.io.File
 
@@ -64,7 +65,7 @@ open class KaptTask : ConventionTask() {
         val messageCollector = GradleMessageCollector(logger)
         val outputItemCollector = OutputItemsCollectorImpl()
         val environment = GradleCompilerEnvironment(kotlinCompileTask.computedCompilerClasspath, messageCollector, outputItemCollector, args)
-        if (environment.toolsJar == null) {
+        if (environment.toolsJar == null && !isAtLeastJava9) {
             throw GradleException("Could not find tools.jar in system classpath, which is required for kapt to work")
         }
 
@@ -82,4 +83,12 @@ open class KaptTask : ConventionTask() {
         deleteRecursively()
         mkdirs()
     }
+
+    private val isAtLeastJava9: Boolean
+        get() = compareVersionNumbers(getJavaRuntimeVersion(), "9") >= 0
+
+    private fun getJavaRuntimeVersion(): String {
+        val rtVersion = System.getProperty("java.runtime.version")
+        return if (Character.isDigit(rtVersion[0])) rtVersion else System.getProperty("java.version")
+    }
 }

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

@@ -876,7 +876,7 @@ internal fun loadAndroidPluginVersion(): String? {
 }
 
 //Copied from StringUtil.compareVersionNumbers
-private fun compareVersionNumbers(v1: String?, v2: String?): Int {
+internal fun compareVersionNumbers(v1: String?, v2: String?): Int {
     if (v1 == null && v2 == null) {
         return 0
     }