Add tests for running incremental KAPT on JDK9

Add test for aggregating incremental annotation processors and JDK9.
This makes sure the implementation is not using any types that have
been removed in JDK 9.

libraries/tools/kotlin-gradle-plugin-integration-tests/build.gradle.kts

@@ -118,6 +118,7 @@ tasks.withType<Test> {
 
     systemProperty("kotlinVersion", rootProject.extra["kotlinVersion"] as String)
     systemProperty("runnerGradleVersion", gradle.gradleVersion)
+    systemProperty("jdk9Home", rootProject.extra["JDK_9"] as String)
     systemProperty("jdk10Home", rootProject.extra["JDK_10"] as String)
     systemProperty("jdk11Home", rootProject.extra["JDK_11"] as String)
 

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

@@ -8,7 +8,9 @@ package org.jetbrains.kotlin.gradle
 import org.jetbrains.kotlin.gradle.util.modify
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertTrue
+import org.junit.Assume
 import org.junit.Test
+import java.io.File
 import kotlin.test.assertFalse
 
 class KaptIncrementalWithAggregatingApt : KaptIncrementalIT() {
@@ -73,6 +75,32 @@ class KaptIncrementalWithAggregatingApt : KaptIncrementalIT() {
         }
     }
 
+    @Test
+    fun testIncrementalChangesWithJdk9() {
+        val javaHome = File(System.getProperty("jdk9Home")!!)
+        Assume.assumeTrue("JDK 9 isn't available", javaHome.isDirectory)
+        val options = defaultBuildOptions().copy(javaHome = javaHome)
+        val project = getProject()
+
+        project.build("clean", "build", options = options) {
+            assertSuccessful()
+        }
+
+        project.projectFile("useB.kt").modify { current -> "$current\nfun otherFunction() {}" }
+        project.build("build", options = options) {
+            assertSuccessful()
+
+            assertEquals(
+                setOf(
+                    fileInWorkingDir("build/tmp/kapt3/stubs/main/bar/UseBKt.java").canonicalPath,
+                    fileInWorkingDir("build/tmp/kapt3/stubs/main/bar/B.java").canonicalPath,
+                    fileInWorkingDir("build/tmp/kapt3/stubs/main/baz/UtilKt.java").canonicalPath,
+                    fileInWorkingDir("build/tmp/kapt3/stubs/main/foo/A.java").canonicalPath
+                ), getProcessedSources(output)
+            )
+        }
+    }
+
     @Test
     fun testClasspathChanges() {
         val project = Project(