Remap source maps in JS DCE. Improve JS DCE error logging

See KT-19821

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

@@ -225,6 +225,9 @@ class Kotlin2JsGradlePluginIT : BaseGradleIT() {
         project.build("runRhino") {
             println(output)
             assertSuccessful()
+            val pathPrefix = "mainProject/build/min"
+            assertFileExists("$pathPrefix/exampleapp.js.map")
+            assertFileExists("$pathPrefix/examplelib.js.map")
         }
     }
 

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

@@ -18,10 +18,12 @@ dependencies {
 }
 
 compileKotlin2Js.kotlinOptions.outputFile = "${buildDir}/examplelib.js"
+compileKotlin2Js.kotlinOptions.sourceMap = true
 
 jar {
     from buildDir
     include "**/*.js"
+    include "**/*.js.map"
 }
 
 jar.dependsOn(compileKotlin2Js)

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

@@ -68,8 +68,8 @@ class KotlinJsDcePlugin : Plugin<Project> {
 
         val zippedFiles = UnionFileCollection(configuration.map { project.zipTree(it) })
         val files = project.fileTree(tmpDir)
-                .filter { it.path.endsWith(".js") }
-                .filter { File(it.path.removeSuffix(".js") + ".meta.js").exists() }
+                .filter { file -> SUFFIXES.any { file.path.endsWith(it) } }
+                .filter { file -> SUFFIXES.any { File(file.path.removeSuffix(it) + ".meta.js").exists() } }
 
         // This intermediate task is needed due to bug in Gradle that causes infinite loops in continuous build mode
         val unpackName = sourceSet.getTaskName(UNPACK_DEPENDENCIES_TASK_PREFIX, TASK_SUFFIX)
@@ -93,5 +93,6 @@ class KotlinJsDcePlugin : Plugin<Project> {
         private const val UNPACK_DEPENDENCIES_TASK_PREFIX = "unpackDependencies"
         private const val DEPENDENCIES_TASK_PREFIX = "copyDependencies"
         private const val DCE_TASK_PREFIX = "runDce"
+        private val SUFFIXES = listOf(".js", ".js.map")
     }
 }

libraries/tools/kotlin-stdlib-js-merger/src/FileMerger.kt

@@ -43,14 +43,14 @@ fun main(args: Array<String>) {
     fun File.relativizeIfNecessary(): String = baseDir.relativize(canonicalFile.toPath()).toString()
 
     val wrapperFile = File(args[2])
-    val wrapper = parse(wrapperFile.readText(), ThrowExceptionOnErrorReporter, program.scope, wrapperFile.relativizeIfNecessary())
+    val wrapper = parse(wrapperFile.readText(), ThrowExceptionOnErrorReporter, program.scope, wrapperFile.relativizeIfNecessary())!!
     val insertionPlace = wrapper.createInsertionPlace()
 
     val allFiles = mutableListOf<File>()
     args.drop(3).map { File(it) }.forEach { collectFiles(it, allFiles) }
 
     for (file in allFiles) {
-        val statements = parse(file.readText(), ThrowExceptionOnErrorReporter, program.scope, file.relativizeIfNecessary())
+        val statements = parse(file.readText(), ThrowExceptionOnErrorReporter, program.scope, file.relativizeIfNecessary())!!
         val block = JsBlock(statements)
         block.fixForwardNameReferences()