Turn off IC for multiplatform projects by default

Multiplatform IC is enabled when a corresponding platform property is enabled
and 'kotlin.incremental.multiplatform' is set to `true`.

See KT-20840

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

@@ -19,6 +19,8 @@ package org.jetbrains.kotlin.gradle
 import org.jetbrains.kotlin.gradle.plugin.EXPECTED_BY_CONFIG_NAME
 import org.jetbrains.kotlin.gradle.plugin.IMPLEMENT_CONFIG_NAME
 import org.jetbrains.kotlin.gradle.plugin.IMPLEMENT_DEPRECATION_WARNING
+import org.jetbrains.kotlin.gradle.util.allKotlinFiles
+import org.jetbrains.kotlin.gradle.util.getFileByName
 import org.jetbrains.kotlin.gradle.util.modify
 import org.junit.Test
 import java.io.File
@@ -121,4 +123,39 @@ class MultiplatformGradleIT : BaseGradleIT() {
             }
         }
     }
+
+    @Test
+    fun testNonIncrementalCompileByDefault(): Unit = Project("multiplatformProject", GRADLE_VERSION).run {
+        val compileCommonTask = ":lib:compileKotlinCommon"
+        val compileJsTask = ":libJs:compileKotlin2Js"
+        val compileJvmTask = ":libJvm:compileKotlin"
+        val allKotlinTasks = listOf(compileCommonTask, compileJsTask, compileJvmTask)
+
+        build("build") {
+            assertSuccessful()
+        }
+
+        val commonProjectDir = File(projectDir, "lib")
+        commonProjectDir.getFileByName("PlatformClass.kt").modify { it + "\n" }
+        build("build") {
+            assertSuccessful()
+            assertTasksExecuted(allKotlinTasks)
+        }
+
+        val jvmProjectDir = File(projectDir, "libJvm")
+        jvmProjectDir.getFileByName("PlatformClass.kt").modify { it + "\n" }
+        build("build") {
+            assertSuccessful()
+            assertTasksExecuted(listOf(compileJvmTask))
+            assertTasksUpToDate(listOf(compileCommonTask, compileJsTask))
+        }
+
+        val jsProjectDir = File(projectDir, "libJs")
+        jsProjectDir.getFileByName("PlatformClass.kt").modify { it + "\n" }
+        build("build") {
+            assertSuccessful()
+            assertTasksExecuted(listOf(compileJsTask))
+            assertTasksUpToDate(listOf(compileCommonTask, compileJvmTask))
+        }
+    }
 }

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

@@ -81,6 +81,16 @@ open class KotlinPlatformImplementationPluginBase(platformName: String) : Kotlin
                 }
             }
         }
+
+        val incrementalMultiplatform = PropertiesProvider(project).incrementalMultiplatform ?: false
+        project.afterEvaluate {
+            project.tasks.withType(AbstractKotlinCompile::class.java).all {
+                if (it.incremental && !incrementalMultiplatform) {
+                    project.logger.debug("IC is turned off for task '${it.path}' because multiplatform IC is not enabled")
+                }
+                it.incremental = it.incremental && incrementalMultiplatform
+            }
+        }
     }
 
     private var implementConfigurationIsUsed = false

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

@@ -25,27 +25,21 @@ import java.util.*
 import kotlin.reflect.KMutableProperty1
 
 fun mapKotlinTaskProperties(project: Project, task: AbstractKotlinCompile<*>) {
-    val properties = PropertiesProvider(project)
+    PropertiesProvider(project).apply {
+        coroutines?.let { task.coroutinesFromGradleProperties = it }
 
-    properties["kotlin.coroutines"]?.let {
-        task.coroutinesFromGradleProperties = Coroutines.byCompilerArgument(it)
-    }
-
-    if (task is KotlinCompile) {
-        properties["kotlin.incremental"]?.let {
-            task.incremental = it.toBoolean()
+        if (task is KotlinCompile) {
+            incrementalJvm?.let { task.incremental = it }
         }
-    }
 
-    if (task is Kotlin2JsCompile) {
-        properties["kotlin.incremental.js"]?.let {
-            task.incremental = it.toBoolean()
+        if (task is Kotlin2JsCompile) {
+            incrementalJs?.let { task.incremental = it }
         }
     }
 }
 
-private class PropertiesProvider(private val project: Project) {
-    val localProperties = Properties()
+internal class PropertiesProvider(private val project: Project) {
+    private val localProperties = Properties()
 
     init {
         val localPropertiesFile = project.rootProject.file("local.properties")
@@ -56,7 +50,22 @@ private class PropertiesProvider(private val project: Project) {
         }
     }
 
-    operator fun get(propName: String): String? =
+    val coroutines: Coroutines?
+        get() = property("kotlin.coroutines")?.let { Coroutines.byCompilerArgument(it) }
+
+    val incrementalJvm: Boolean?
+        get() = booleanProperty("kotlin.incremental")
+
+    val incrementalJs: Boolean?
+        get() = booleanProperty("kotlin.incremental.js")
+
+    val incrementalMultiplatform: Boolean?
+        get() = booleanProperty("kotlin.incremental.multiplatform")
+
+    private fun booleanProperty(propName: String): Boolean? =
+            property(propName)?.toBoolean()
+
+    private fun property(propName: String): String? =
             if (project.hasProperty(propName)) {
                 project.property(propName) as? String
             }