[K/JS] Throw error when a module contains file with the same name and package (ignoring case)

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

@@ -359,6 +359,27 @@ class Kotlin2JsIrGradlePluginIT : AbstractKotlin2JsGradlePluginIT(true) {
         }
     }
 
+    @DisplayName("per-file with the  declarations validation")
+    @GradleTest
+    fun testPerFileProjectWithResultFilesClash(gradleVersion: GradleVersion) {
+        project("kotlin-js-invalid-per-file-project", gradleVersion) {
+            buildAndFail("compileDevelopmentExecutableKotlinJs") {
+                assertTasksFailed(":compileDevelopmentExecutableKotlinJs")
+                assertOutputContains("""
+                   |There are two files in module '<kotlin-js-invalid-per-file-project>' that have the similar package and file names.
+                   |  - Package "com.example" and
+                """.trimMargin())
+            }
+            buildAndFail("compileProductionExecutableKotlinJs") {
+                assertTasksFailed(":compileProductionExecutableKotlinJs")
+                assertOutputContains("""
+                   |There are two files in module '<kotlin-js-invalid-per-file-project>' that have the similar package and file names.
+                   |  - Package "com.example" and path
+                """.trimMargin())
+            }
+        }
+    }
+
     @DisplayName("fully qualified names can be used in the sourcemap")
     @GradleTest
     fun testKotlinJsSourceMapGenerateFqNames(gradleVersion: GradleVersion) {

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kotlin-js-invalid-per-file-project/build.gradle.kts

@@ -0,0 +1,16 @@
+plugins {
+    kotlin("js")
+}
+
+repositories {
+    mavenLocal()
+    mavenCentral()
+}
+
+kotlin {
+    js(IR) {
+        useEsModules()
+        binaries.executable()
+        nodejs()
+    }
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kotlin-js-invalid-per-file-project/gradle.properties

@@ -0,0 +1,8 @@
+kotlin.tests.individualTaskReports=true
+kotlin.js.ir.output.granularity=per-file
+kotlin.incremental=false
+kotlin.incremental.js=false
+kotlin.incremental.js.ir=false
+kotlin.incremental.js.klib=false
+kotlin.incremental.multiplatform=false
+kotlin.incremental.useClasspathSnapshot=false

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kotlin-js-invalid-per-file-project/src/main/kotlin/base1/Base.kt

@@ -0,0 +1,16 @@
+/*
+ * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package com.example
+
+@JsExport
+fun best(): Int {
+    return 42
+}
+
+@JsExport
+fun simpleBest(): Int {
+    return 73
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kotlin-js-invalid-per-file-project/src/main/kotlin/base2/base.kt

@@ -0,0 +1,9 @@
+/*
+ * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package com.example
+
+@JsExport
+public val foo = 44

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/targets/js/ir/CompilerFlags.kt

@@ -24,6 +24,7 @@ internal const val MINIMIZED_MEMBER_NAMES = "-Xir-minimized-member-names"
 
 internal const val KLIB_MODULE_NAME = "-Xir-module-name"
 
+internal const val PER_FILE = "-Xir-per-file"
 internal const val PER_MODULE = "-Xir-per-module"
 internal const val PER_MODULE_OUTPUT_NAME = "-Xir-per-module-output-name"
 

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/targets/js/ir/OutputGranularity.kt

@@ -7,7 +7,8 @@ package org.jetbrains.kotlin.gradle.targets.js.ir
 
 enum class KotlinJsIrOutputGranularity {
     WHOLE_PROGRAM,
-    PER_MODULE;
+    PER_MODULE,
+    PER_FILE;
 
     companion object {
         fun byArgument(argument: String): KotlinJsIrOutputGranularity? =
@@ -17,6 +18,9 @@ enum class KotlinJsIrOutputGranularity {
 }
 
 fun KotlinJsIrOutputGranularity.toCompilerArgument(): String {
-    val perModule = this == KotlinJsIrOutputGranularity.PER_MODULE
-    return "$PER_MODULE=$perModule"
+    return when (this) {
+        KotlinJsIrOutputGranularity.PER_FILE -> PER_FILE
+        KotlinJsIrOutputGranularity.PER_MODULE -> PER_MODULE
+        KotlinJsIrOutputGranularity.WHOLE_PROGRAM -> ""
+    }
 }