IC: add destination dir to start of classpath instead of end

Otherwise IC fails when a project declares a class with the same name
as in one of its dependencies.
The issue is relevant only for non-JPS IC (Gradle, Maven, etc.),
but I added the test for JPS too.

  #KT-20516 fixed

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

@@ -22,6 +22,21 @@ class IncrementalCompilationMultiProjectIT : BaseGradleIT() {
     override fun defaultBuildOptions(): BuildOptions =
             super.defaultBuildOptions().copy(withDaemon = true, incremental = true)
 
+    @Test
+    fun testDuplicatedClass() {
+        val project = Project("duplicatedClass")
+        project.build("build") {
+            assertSuccessful()
+        }
+
+        val usagesFiles = listOf("useBuzz.kt", "useA.kt").map { project.projectFile(it) }
+        usagesFiles.forEach { file -> file.modify { "$it\n " } }
+
+        project.build("build") {
+            assertSuccessful()
+            assertCompiledKotlinSources(project.relativize(usagesFiles))
+        }
+    }
 
     @Test
     fun testMoveFunctionFromLib() {

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/duplicatedClass/app/build.gradle

@@ -0,0 +1,5 @@
+apply plugin: 'kotlin'
+
+dependencies {
+    compile project(':lib')
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/duplicatedClass/app/src/main/kotlin/A.kt

@@ -0,0 +1,3 @@
+class A {
+    fun buzz() {}
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/duplicatedClass/app/src/main/kotlin/useA.kt

@@ -0,0 +1,3 @@
+fun useA(a: A) {
+    A().buzz()
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/duplicatedClass/app/src/main/kotlin/useBuzz.kt

@@ -0,0 +1,3 @@
+fun useBuzz() {
+    buzz()
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/duplicatedClass/app/src/main/kotlin/utils.kt

@@ -0,0 +1 @@
+fun buzz() {}

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

@@ -0,0 +1,9 @@
+buildscript {
+    repositories {
+        mavenLocal()
+        mavenCentral()
+    }
+    dependencies {
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+    }
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/duplicatedClass/lib/build.gradle

@@ -0,0 +1 @@
+apply plugin: 'kotlin'

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/duplicatedClass/lib/src/main/kotlin/A.kt

@@ -0,0 +1,3 @@
+class A {
+    fun fizz() {}
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/duplicatedClass/lib/src/main/kotlin/utils.kt

@@ -0,0 +1 @@
+fun fizz() {}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/duplicatedClass/settings.gradle

@@ -0,0 +1 @@
+include ':lib', ':app'

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

@@ -19,6 +19,8 @@ package org.jetbrains.kotlin.incremental
 import org.gradle.api.Project
 import java.io.File
 
+// todo: Move all files under org.jetbrains.kotlin.gradle package to avoid class clash (KT-18621, KT-20516)
+
 internal fun File.isJavaFile() =
         extension.equals("java", ignoreCase = true)