Wrap null values into serializable optional

Otherwise worker executor fails with NPE

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

@@ -6,9 +6,11 @@
 package org.jetbrains.kotlin.compilerRunner
 
 import org.gradle.api.Project
+import org.gradle.workers.ForkMode
 import org.gradle.workers.IsolationMode
 import org.gradle.workers.WorkerExecutor
 import org.jetbrains.kotlin.cli.common.arguments.CommonCompilerArguments
+import org.jetbrains.kotlin.gradle.utils.SerializableOptional
 
 internal class GradleCompilerRunnerWithWorkers(
     project: Project,
@@ -19,16 +21,20 @@ internal class GradleCompilerRunnerWithWorkers(
         compilerArgs: CommonCompilerArguments,
         environment: GradleCompilerEnvironment
     ) {
+        val icEnv = environment.incrementalCompilationEnvironment
+        val modulesInfo = icEnv?.let { buildModulesInfo(project.gradle) }
+
         workersExecutor.submit(KotlinCompilerRunnable::class.java) { config ->
             config.isolationMode = IsolationMode.NONE
+            config.forkMode = ForkMode.NEVER
             config.params(
                 ProjectFilesForCompilation(project),
                 environment.compilerFullClasspath,
                 compilerClassName,
                 ArgumentUtils.convertArgumentsToStringList(compilerArgs).toTypedArray(),
                 compilerArgs.verbose,
-                environment.incrementalCompilationEnvironment,
-                buildModulesInfo(project.gradle)
+                SerializableOptional(icEnv),
+                SerializableOptional(modulesInfo)
             )
         }
     }

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

@@ -30,6 +30,7 @@ import org.jetbrains.kotlin.daemon.client.CompileServiceSession
 import org.jetbrains.kotlin.daemon.common.*
 import org.jetbrains.kotlin.gradle.plugin.kotlinDebug
 import org.jetbrains.kotlin.gradle.tasks.*
+import org.jetbrains.kotlin.gradle.utils.SerializableOptional
 import org.jetbrains.kotlin.gradle.utils.newTmpFile
 import org.jetbrains.kotlin.gradle.utils.relativeToRoot
 import org.jetbrains.kotlin.incremental.*
@@ -130,8 +131,8 @@ internal open class GradleCompilerRunner(protected val project: Project) {
             compilerClassName = compilerClassName,
             compilerArgs = ArgumentUtils.convertArgumentsToStringList(compilerArgs).toTypedArray(),
             isVerbose = compilerArgs.verbose,
-            incrementalCompilationEnvironment = environment.incrementalCompilationEnvironment,
-            incrementalModuleInfo = buildModulesInfo(project.gradle)
+            incrementalCompilationEnvironment = SerializableOptional(environment.incrementalCompilationEnvironment),
+            incrementalModuleInfo = SerializableOptional(buildModulesInfo(project.gradle))
         )
         kotlinCompilerRunnable.run()
     }

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

@@ -16,6 +16,7 @@ import org.jetbrains.kotlin.daemon.common.*
 import org.jetbrains.kotlin.gradle.plugin.kotlinDebug
 import org.jetbrains.kotlin.gradle.tasks.GradleMessageCollector
 import org.jetbrains.kotlin.gradle.tasks.throwGradleExceptionIfError
+import org.jetbrains.kotlin.gradle.utils.SerializableOptional
 import org.jetbrains.kotlin.incremental.ChangedFiles
 import org.slf4j.LoggerFactory
 import java.io.ByteArrayOutputStream
@@ -48,15 +49,15 @@ internal class KotlinCompilerRunnable @Inject constructor(
     private val compilerClassName: String,
     private val compilerArgs: Array<String>,
     private val isVerbose: Boolean,
-    private val incrementalCompilationEnvironment: IncrementalCompilationEnvironment?,
-    private val incrementalModuleInfo: IncrementalModuleInfo?
+    private val incrementalCompilationEnvironment: SerializableOptional<IncrementalCompilationEnvironment>,
+    private val incrementalModuleInfo: SerializableOptional<IncrementalModuleInfo>
 ) : Runnable {
     private val log: KotlinLogger =
         SL4JKotlinLogger(LoggerFactory.getLogger("KotlinCompilerRunnable"))
     private val messageCollector = GradleMessageCollector(log)
 
     private val isIncremental: Boolean
-        get() = incrementalCompilationEnvironment != null
+        get() = incrementalCompilationEnvironment.value != null
 
     override fun run() {
         val exitCode = compileWithDaemonOrFallbackImpl()
@@ -165,7 +166,7 @@ internal class KotlinCompilerRunnable @Inject constructor(
         sessionId: Int,
         targetPlatform: CompileService.TargetPlatform
     ): CompileService.CallResult<Int> {
-        val icEnv = incrementalCompilationEnvironment ?: error("incrementalCompilationEnvironment is null!")
+        val icEnv = incrementalCompilationEnvironment.value ?: error("incrementalCompilationEnvironment is null!")
         val knownChangedFiles = icEnv.changedFiles as? ChangedFiles.Known
 
         val compilationOptions = IncrementalCompilationOptions(
@@ -181,7 +182,7 @@ internal class KotlinCompilerRunnable @Inject constructor(
             usePreciseJavaTracking = icEnv.usePreciseJavaTracking,
             localStateDirs = icEnv.localStateDirs,
             multiModuleICSettings = icEnv.multiModuleICSettings,
-            modulesInfo = incrementalModuleInfo!!
+            modulesInfo = incrementalModuleInfo.value!!
         )
 
         log.info("Options for KOTLIN DAEMON: $compilationOptions")

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

@@ -0,0 +1,14 @@
+/*
+ * 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.utils
+
+import java.io.Serializable
+
+internal class SerializableOptional<T>(val value: T?) : Serializable {
+    companion object {
+        const val serialVersionUID: Long = 0
+    }
+}