Change default output dir in JS DCE Gradle plugin

See KT-21328

Compiler removes all files from its output directory.
Due to this reason (and some other reasons) it't not a good idea
to put DCE output to `classes` dir.
Therefore we changed output dir to `$buildDir/kotlin-js-min`.
Additionally, we now allow to customize output dir.
In particular, this fixes issues with webpack in multi-project build +
continuous Gradle build.

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/K2JSDceArguments.kt

@@ -26,6 +26,7 @@ class K2JSDceArguments : CommonToolArguments() {
             valueDescription = "<path>",
             description = "Output directory"
     )
+    @GradleOption(DefaultValues.StringNullDefault::class)
     var outputDirectory: String? by FreezableVar(null)
 
     @Argument(

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/Kotlin2JsGradlePluginIT.kt

@@ -221,6 +221,30 @@ class Kotlin2JsGradlePluginIT : BaseGradleIT() {
     fun testDce() {
         val project = Project("kotlin2JsDceProject", "2.10", minLogLevel = LogLevel.INFO)
 
+        project.build("runRhino") {
+            assertSuccessful()
+            val pathPrefix = "mainProject/build/kotlin-js-min/main"
+            assertFileExists("$pathPrefix/exampleapp.js.map")
+            assertFileExists("$pathPrefix/examplelib.js.map")
+            assertFileContains("$pathPrefix/exampleapp.js.map", "\"../../../src/main/kotlin/exampleapp/main.kt\"")
+
+            assertFileExists("$pathPrefix/kotlin.js")
+            assertTrue(fileInWorkingDir("$pathPrefix/kotlin.js").length() < 500 * 1000, "Looks like kotlin.js file was not minified by DCE")
+        }
+    }
+
+    @Test
+    fun testDceOutputPath() {
+        val project = Project("kotlin2JsDceProject", "2.10", minLogLevel = LogLevel.INFO)
+
+        project.setupWorkingDir()
+        File(project.projectDir, "mainProject/build.gradle").modify {
+            it + "\n" +
+            "runDceKotlinJs.dceOptions.outputDirectory = \"\${buildDir}/min\"\n" +
+            "runRhino.args = [\"-f\", \"min/kotlin.js\", \"-f\", \"min/examplelib.js\", \"-f\", \"min/exampleapp.js\"," +
+                "\"-f\", \"../check.js\"]\n"
+        }
+
         project.build("runRhino") {
             assertSuccessful()
             val pathPrefix = "mainProject/build/min"
@@ -245,10 +269,10 @@ class Kotlin2JsGradlePluginIT : BaseGradleIT() {
 
         project.build("runRhino") {
             assertSuccessful()
-            val pathPrefix = "mainProject/build/min"
+            val pathPrefix = "mainProject/build/kotlin-js-min/main"
             assertFileExists("$pathPrefix/exampleapp.js.map")
             assertFileExists("$pathPrefix/examplelib.js.map")
-            assertFileContains("$pathPrefix/exampleapp.js.map", "\"../../src/main/kotlin/exampleapp/main.kt\"")
+            assertFileContains("$pathPrefix/exampleapp.js.map", "\"../../../src/main/kotlin/exampleapp/main.kt\"")
 
             assertFileExists("$pathPrefix/kotlin.js")
             assertTrue(fileInWorkingDir("$pathPrefix/kotlin.js").length() > 1000 * 1000, "Looks like kotlin.js file was minified by DCE")

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kotlin2JsDceProject/mainProject/build.gradle

@@ -32,7 +32,11 @@ task runRhino(type: JavaExec) {
     classpath = sourceSets.main.runtimeClasspath
     workingDir = "${buildDir}"
     main = 'org.mozilla.javascript.tools.shell.Main'
-    args = ["-opt", "-1", "-f", "min/kotlin.js", "-f", "min/examplelib.js", "-f", "min/exampleapp.js", "-f", "../check.js"]
+    args = ["-opt", "-1",
+            "-f", "kotlin-js-min/main/kotlin.js",
+            "-f", "kotlin-js-min/main/examplelib.js",
+            "-f", "kotlin-js-min/main/exampleapp.js",
+            "-f", "../check.js"]
 }
 
 runRhino.dependsOn(runDceKotlinJs)

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

@@ -5,8 +5,14 @@ package org.jetbrains.kotlin.gradle.dsl
 interface KotlinJsDceOptions  : org.jetbrains.kotlin.gradle.dsl.KotlinCommonToolOptions {
 
     /**
-     * Development mode: don't strip out any code, just copy dependencies and remap source maps
+     * Development mode: don't strip out any code, just copy dependencies
      * Default value: false
      */
      var devMode: kotlin.Boolean
+
+    /**
+     * Output directory
+     * Default value: null
+     */
+     var outputDirectory: kotlin.String?
 }

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

@@ -24,11 +24,17 @@ internal abstract class KotlinJsDceOptionsBase : org.jetbrains.kotlin.gradle.dsl
         get() = devModeField ?: false
         set(value) { devModeField = value }
 
+    private var outputDirectoryField: kotlin.String?? = null
+    override var outputDirectory: kotlin.String?
+        get() = outputDirectoryField ?: null
+        set(value) { outputDirectoryField = value }
+
     internal open fun updateArguments(args: org.jetbrains.kotlin.cli.common.arguments.K2JSDceArguments) {
         allWarningsAsErrorsField?.let { args.allWarningsAsErrors = it }
         suppressWarningsField?.let { args.suppressWarnings = it }
         verboseField?.let { args.verbose = it }
         devModeField?.let { args.devMode = it }
+        outputDirectoryField?.let { args.outputDirectory = it }
     }
 }
 
@@ -37,4 +43,5 @@ internal fun org.jetbrains.kotlin.cli.common.arguments.K2JSDceArguments.fillDefa
     suppressWarnings = false
     verbose = false
     devMode = false
+    outputDirectory = null
 }

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

@@ -43,7 +43,7 @@ class KotlinJsDcePlugin : Plugin<Project> {
         }
 
         project.afterEvaluate {
-            val outputDir = File(kotlinTask.outputFile).parentFile
+            val outputDir = File(File(project.buildDir, DEFAULT_OUT_DIR), sourceSet.name)
 
             val configuration = project.configurations.findByName(sourceSet.compileConfigurationName)
             val dceInputTrees = listOf(project.fileTree(kotlinTask.outputFile)) + configuration.map { project.fileTree(it) }
@@ -51,7 +51,7 @@ class KotlinJsDcePlugin : Plugin<Project> {
 
             with (dceTask) {
                 classpath = sourceSet.compileClasspath
-                destinationDir = File(outputDir, "min")
+                destinationDir = dceTask.dceOptions.outputDirectory?.let { File(it) } ?: outputDir
                 source(dceInputFiles)
             }
         }
@@ -60,5 +60,6 @@ class KotlinJsDcePlugin : Plugin<Project> {
     companion object {
         private const val TASK_SUFFIX = "kotlinJs"
         private const val DCE_TASK_PREFIX = "runDce"
+        private const val DEFAULT_OUT_DIR = "kotlin-js-min"
     }
 }