Add flag to enable intra-project parallel tasks

To enable parallel tasks execution within a project,
add 'kotlin.parallel.tasks.in.project=true'
to gradle.properties or local.properties file .

    #KT-28155 fixed

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

@@ -178,7 +178,8 @@ abstract class BaseGradleIT {
         val kotlinDaemonDebugPort: Int? = null,
         val usePreciseJavaTracking: Boolean? = null,
         val withBuildCache: Boolean = false,
-        val kaptOptions: KaptOptions? = null
+        val kaptOptions: KaptOptions? = null,
+        val parallelTasksInProject: Boolean? = null
     )
 
     data class KaptOptions(val verbose: Boolean, val useWorkers: Boolean)
@@ -446,6 +447,18 @@ abstract class BaseGradleIT {
         assertTasksUpToDate(tasks.toList())
     }
 
+    fun CompiledProject.assertTasksSubmittedWork(vararg tasks: String) {
+        for (task in tasks) {
+            assertContains("Starting Kotlin compiler work from task '$task'")
+        }
+    }
+
+    fun CompiledProject.assertTasksDidNotSubmitWork(vararg tasks: String) {
+        for (task in tasks) {
+            assertNotContains("Starting Kotlin compiler work from task '$task'")
+        }
+    }
+
     fun CompiledProject.getOutputForTask(taskName: String): String {
         val taskOutputRegex = ("\\[LIFECYCLE] \\[class org\\.gradle(?:\\.internal\\.buildevents)?\\.TaskExecutionLogger] :$taskName" +
                 "([\\s\\S]+?)" +
@@ -567,6 +580,10 @@ abstract class BaseGradleIT {
                 add("-Pkapt.use.worker.api=${kaptOptions.useWorkers}")
             }
 
+            options.parallelTasksInProject?.let {
+                add("-Pkotlin.parallel.tasks.in.project=$it")
+            }
+
             // Workaround: override a console type set in the user machine gradle.properties (since Gradle 4.3):
             add("--console=plain")
 

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

@@ -249,6 +249,35 @@ class NewMultiplatformIT : BaseGradleIT() {
         }
     }
 
+    @Test
+    fun testParallelTasks() {
+        parallelTasksImpl(isParallel = true)
+    }
+
+    @Test
+    fun testNoParallelTasks() {
+        parallelTasksImpl(isParallel = false)
+    }
+
+    private fun parallelTasksImpl(isParallel: Boolean) = with(Project("new-mpp-parallel", gradleVersion)) {
+        val options = defaultBuildOptions().copy(parallelTasksInProject = isParallel)
+        build("assemble", options = options) {
+            assertSuccessful()
+            val tasks = arrayOf(":compileKotlinMetadata", ":compileKotlinJvm", ":compileKotlinJs")
+            if (isParallel) {
+                assertTasksSubmittedWork(*tasks)
+            } else {
+                assertTasksDidNotSubmitWork(*tasks)
+            }
+            val expectedKotlinOutputFiles = listOf(
+                kotlinClassesDir(sourceSet = "metadata/main") + "common/A.kotlin_metadata",
+                kotlinClassesDir(sourceSet = "jvm/main") + "common/A.class",
+                kotlinClassesDir(sourceSet = "js/main") + "new-mpp-parallel.js"
+            )
+            expectedKotlinOutputFiles.forEach { assertFileExists(it) }
+        }
+    }
+
     @Test
     fun testLibWithTests() = with(Project("new-mpp-lib-with-tests", gradleVersion)) {
         build("check") {

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/new-mpp-parallel/build.gradle

@@ -0,0 +1,37 @@
+buildscript {
+	repositories {
+        mavenLocal()
+        jcenter()
+	}
+	dependencies {
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+	}
+}
+
+apply plugin: 'kotlin-multiplatform'
+
+repositories {
+    mavenLocal()
+    jcenter()
+}
+
+kotlin {
+    sourceSets {
+        commonMain {}
+        jvmMain {
+            dependencies {
+                implementation 'org.jetbrains.kotlin:kotlin-stdlib'
+            }
+        }
+        jsMain {
+            dependencies {
+                implementation 'org.jetbrains.kotlin:kotlin-stdlib-js'
+            }
+        }
+    }
+
+    targets {
+        fromPreset(presets.jvm, 'jvm')
+        fromPreset(presets.js, 'js')
+    }
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/new-mpp-parallel/src/commonMain/kotlin/A.kt

@@ -0,0 +1,9 @@
+/*
+ * 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 common
+
+class A(val x: Int)
+