IR JS: support findAssociatedObject feature (KT-37418 fixed)

libraries/stdlib/js/src/kotlin/reflect/AssociatedObjects.kt

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2010-2020 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 kotlin.reflect
+
+import findAssociatedObject
+
+/**
+ * The experimental marker for associated objects API.
+ *
+ * Any usage of a declaration annotated with `@ExperimentalAssociatedObjects` must be accepted either by
+ * annotating that usage with the [OptIn] annotation, e.g. `@OptIn(ExperimentalAssociatedObjects::class)`,
+ * or by using the compiler argument `-Xopt-in=kotlin.reflect.ExperimentalAssociatedObjects`.
+ */
+@RequiresOptIn(level = RequiresOptIn.Level.ERROR)
+@Retention(value = AnnotationRetention.BINARY)
+public annotation class ExperimentalAssociatedObjects
+
+/**
+ * Makes the annotated annotation class an associated object key.
+ *
+ * An associated object key annotation should have single [KClass] parameter.
+ * When applied to a class with reference to an object declaration as an argument, it binds
+ * the object to the class, making this binding discoverable at runtime using [findAssociatedObject].
+ */
+@ExperimentalAssociatedObjects
+@Retention(AnnotationRetention.BINARY)
+@Target(AnnotationTarget.ANNOTATION_CLASS)
+public annotation class AssociatedObjectKey
+
+/**
+ * If [T] is an @[AssociatedObjectKey]-annotated annotation class and [this] class is annotated with @[T] (`S::class`),
+ * returns object `S`.
+ *
+ * Otherwise returns `null`.
+ */
+@ExperimentalAssociatedObjects
+public inline fun <reified T : Annotation> KClass<*>.findAssociatedObject(): Any? =
+    this.findAssociatedObject(T::class)

libraries/stdlib/js/src/kotlin/reflect/reflection.kt

@@ -75,4 +75,4 @@ internal fun <T : Any> getKClass1(jClass: JsClass<T>): KClass<T> {
     } else {
         SimpleKClassImpl(jClass)
     }
-}
+}