[Gradle, JS] Activate legacy plugin and new plugin via gradle property

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

@@ -77,6 +77,8 @@ abstract class KotlinBasePluginWrapper(
 
         kotlinGradleBuildServices.detectKotlinPluginLoadedInMultipleProjects(project, kotlinPluginVersion)
 
+        defineExtension(project)
+
         project.createKotlinExtension(projectExtensionClass).apply {
             fun kotlinSourceSetContainer(factory: NamedDomainObjectFactory<KotlinSourceSet>) =
                 project.container(KotlinSourceSet::class.java, factory)
@@ -107,6 +109,9 @@ abstract class KotlinBasePluginWrapper(
         project: Project,
         kotlinGradleBuildServices: KotlinGradleBuildServices
     ): Plugin<Project>
+
+    protected open fun defineExtension(project: Project) {
+    }
 }
 
 open class KotlinPluginWrapper @Inject constructor(
@@ -156,11 +161,28 @@ open class Kotlin2JsPluginWrapper @Inject constructor(
 open class KotlinJsPluginWrapper @Inject constructor(
     fileResolver: FileResolver
 ) : KotlinBasePluginWrapper(fileResolver) {
-    override fun getPlugin(project: Project, kotlinGradleBuildServices: KotlinGradleBuildServices): Plugin<Project> =
+    override fun getPlugin(project: Project, kotlinGradleBuildServices: KotlinGradleBuildServices): Plugin<Project> {
-        KotlinJsPlugin(kotlinPluginVersion)
+        val propertiesProvider = PropertiesProvider(project)
 
-    override val projectExtensionClass: KClass<out KotlinJsProjectExtension>
+        return when (propertiesProvider.jsMode) {
-        get() = KotlinJsProjectExtension::class
+            JsMode.IR -> KotlinJsIrPlugin(kotlinPluginVersion)
+            JsMode.LEGACY -> KotlinJsPlugin(kotlinPluginVersion)
+            JsMode.MIXED -> KotlinJsPlugin(kotlinPluginVersion)
+        }
+    }
+
+    override lateinit var projectExtensionClass: KClass<out KotlinProjectExtension>
+
+    override fun defineExtension(project: Project) {
+        val propertiesProvider = PropertiesProvider(project)
+
+        when (propertiesProvider.jsMode) {
+            JsMode.IR -> projectExtensionClass = KotlinJsIrProjectExtension::class
+            JsMode.LEGACY -> projectExtensionClass = KotlinJsProjectExtension::class
+            JsMode.MIXED -> {
+            } //TODO MIXED MODE
+        }
+    }
 
     override fun createTestRegistry(project: Project) = KotlinTestsRegistry(project, "test")
 }

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

@@ -168,6 +168,12 @@ internal class PropertiesProvider private constructor(private val project: Proje
     val jsDiscoverTypes: Boolean?
         get() = booleanProperty("kotlin.js.experimental.discoverTypes")
 
+    /**
+     * Use Kotlin/JS backend mode
+     */
+    val jsMode: JsMode
+        get() = property("kotlin.js.mode")?.let { JsMode.byCompilerArgument(it) } ?: JsMode.IR
+
     private fun propertyWithDeprecatedVariant(propName: String, deprecatedPropName: String): String? {
         val deprecatedProperty = property(deprecatedPropName)
         if (deprecatedProperty != null) {
@@ -201,3 +207,14 @@ internal class PropertiesProvider private constructor(private val project: Proje
             }
     }
 }
+
+internal enum class JsMode {
+    LEGACY,
+    IR,
+    MIXED;
+
+    companion object {
+        fun byCompilerArgument(argument: String): JsMode? =
+            JsMode.values().firstOrNull { it.name.equals(argument, ignoreCase = true) }
+    }
+}

libraries/tools/kotlin-gradle-plugin/src/main/resources/META-INF/gradle-plugins/org.jetbrains.kotlin.js.properties

@@ -1 +1 @@
-implementation-class=org.jetbrains.kotlin.gradle.plugin.KotlinJsIrPluginWrapper
+implementation-class=org.jetbrains.kotlin.gradle.plugin.KotlinJsPluginWrapper