[Gradle, JS] Add test with webpack + es modules

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

@@ -174,7 +174,7 @@ class Kotlin2JsIrGradlePluginIT : AbstractKotlin2JsGradlePluginIT(true) {
 
                 assertEquals(
                     setOf(
-                        projectPath.resolve("build/js/packages/kotlin-js-browser-app/kotlin/kotlin-js-browser-base-js-ir.js").toFile(),
+                        projectPath.resolve("build/js/packages/kotlin-js-browser-app/kotlin/kotlin-js-browser-base-js-ir.mjs").toFile(),
                         projectPath.resolve("build/js/packages/kotlin-js-browser-app/kotlin/foo/foo.txt").toFile(),
                     ),
                     modified.toSet()
@@ -487,6 +487,42 @@ class Kotlin2JsIrGradlePluginIT : AbstractKotlin2JsGradlePluginIT(true) {
         }
     }
 
+    @DisplayName("Webpack works with ES modules")
+    @GradleTest
+    fun testWebpackWorksWithEsModules(gradleVersion: GradleVersion) {
+        project("kotlin-js-browser-project", gradleVersion) {
+            buildGradleKts.modify(::transformBuildScriptWithPluginsDsl)
+
+            subProject("app").buildGradleKts.modify { originalScript ->
+                buildString {
+                    append(originalScript)
+                    append(
+                        """
+                        |
+                        |tasks.named<org.jetbrains.kotlin.gradle.targets.js.ir.KotlinJsIrLink>("compileDevelopmentExecutableKotlinJs") {
+                        |   kotlinOptions {
+                        |       moduleKind = "es"
+                        |   }
+                        |}
+                        |
+                        |tasks.named<org.jetbrains.kotlin.gradle.targets.js.ir.KotlinJsIrLink>("compileProductionExecutableKotlinJs") {
+                        |   kotlinOptions {
+                        |       moduleKind = "es"
+                        |   }
+                        |}
+                        |
+                        """.trimMargin()
+                    )
+                }
+            }
+
+            build("browserProductionWebpack") {
+                assertTasksExecuted(":app:browserProductionWebpack")
+                assertFileExists(subProject("app").projectPath.resolve("build/${Distribution.DIST}/js/productionExecutable/app.js"))
+            }
+        }
+    }
+
     @DisplayName("Multiple targets works without clash")
     @GradleTest
     fun testMultipleJsTargets(gradleVersion: GradleVersion) {

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kotlin-js-browser-project/app/build.gradle.kts

@@ -1,4 +1,5 @@
 import org.jetbrains.kotlin.gradle.targets.js.NpmVersions
+import org.jetbrains.kotlin.gradle.targets.js.ir.KotlinJsIrLink
 import javax.inject.Inject
 
 plugins {
@@ -76,3 +77,9 @@ tasks.named<org.jetbrains.kotlin.gradle.dsl.KotlinJsCompile>("compileKotlinJs")
 tasks.named<org.jetbrains.kotlin.gradle.dsl.KotlinJsCompile>("compileTestKotlinJs") {
     kotlinOptions.freeCompilerArgs += "-Xforce-deprecated-legacy-compiler-usage"
 }
+
+tasks.withType<org.jetbrains.kotlin.gradle.targets.js.ir.KotlinJsIrLink>().configureEach {
+    kotlinOptions {
+        moduleKind = "es"
+    }
+}