Support generation of relative path in JS source maps in JPS builder

See KT-20820

jps-plugin/jps-tests/test/org/jetbrains/kotlin/jps/build/KotlinJpsBuildTest.kt

@@ -366,6 +366,18 @@ open class KotlinJpsBuildTest : AbstractKotlinJpsBuildTestCase() {
         assertTrue("Source map for stdlib should be copied to $librarySourceMapFile", librarySourceMapFile.exists())
     }
 
+    fun testKotlinJavaScriptProjectWithSourceMapRelativePaths() {
+        initProject(JS_STDLIB)
+        buildAllModules().assertSuccessful()
+
+        val sourceMapContent = File(getOutputDir(PROJECT_NAME), "$PROJECT_NAME.js.map").readText()
+        val expectedPath = "../../../src/pkg/test1.kt"
+        assertTrue("Source map file should contain relative path ($expectedPath)", sourceMapContent.contains("\"$expectedPath\""))
+
+        val librarySourceMapFile = File(getOutputDir(PROJECT_NAME), "lib/kotlin.js.map")
+        assertTrue("Source map for stdlib should be copied to $librarySourceMapFile", librarySourceMapFile.exists())
+    }
+
     fun testKotlinJavaScriptProjectWithTwoModules() {
         initProject(JS_STDLIB)
         buildAllModules().assertSuccessful()

jps-plugin/src/org/jetbrains/kotlin/jps/build/KotlinBuilder.kt

@@ -648,10 +648,21 @@ class KotlinBuilder : ModuleLevelBuilder(BuilderCategory.SOURCE_PROCESSOR) {
         val compilerSettings = JpsKotlinCompilerSettings.getCompilerSettings(representativeModule)
         val k2JsArguments = JpsKotlinCompilerSettings.getK2JsCompilerArguments(representativeModule)
 
-        val sourceRoots = representativeModule.contentRootsList.urls
-                .map { URI.create(it) }
-                .filter { it.scheme == "file" }
-                .map { File(it.path) }
+        // Compiler starts to produce path relative to base dirs in source maps if at least one statement is true:
+        // 1) base dirs are specified;
+        // 2) prefix is specified (i.e. non-empty)
+        // Otherwise compiler produces paths relative to source maps location.
+        // We don't have UI to configure base dirs, but we have UI to configure prefix.
+        // If prefix is not specified (empty) in UI, we want to produce paths relative to source maps location
+        val sourceRoots = if (k2JsArguments.sourceMapPrefix.isNullOrBlank()) {
+            emptyList()
+        }
+        else {
+            representativeModule.contentRootsList.urls
+                    .map { URI.create(it) }
+                    .filter { it.scheme == "file" }
+                    .map { File(it.path) }
+        }
 
         val friendPaths = KotlinBuilderModuleScriptGenerator.getProductionModulesWhichInternalsAreVisible(representativeTarget).mapNotNull {
             val file = getOutputMetaFile(it, false)

jps-plugin/testData/general/KotlinJavaScriptProjectWithSourceMapRelativePaths/kotlinProject.ipr

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="CompilerConfiguration">
+    <option name="DEFAULT_COMPILER" value="Javac" />
+  </component>
+  <component name="Kotlin2JsCompilerArguments">
+    <option name="sourceMap" value="true" />
+  </component>
+  <component name="ProjectModuleManager">
+    <modules>
+      <module fileurl="file://$PROJECT_DIR$/kotlinProject.iml" filepath="$PROJECT_DIR$/kotlinProject.iml" />
+    </modules>
+  </component>
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_1_6" assert-keyword="true" jdk-15="true" project-jdk-name="IDEA_JDK" project-jdk-type="JavaSDK">
+    <output url="file://$PROJECT_DIR$/out" />
+  </component>
+</project>

jps-plugin/testData/general/KotlinJavaScriptProjectWithSourceMapRelativePaths/src/pkg/test1.kt

@@ -0,0 +1,7 @@
+package pkg
+
+var log = ""
+
+fun foo(x: String) {
+    log += "$x;"
+}