[Wasm] Support for Associated Objects feature

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

@@ -0,0 +1,43 @@
+/*
+ * 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 kotlin.wasm.internal.wasmClassId
+import kotlin.wasm.internal.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 `-opt-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
+@Suppress("NON_PUBLIC_CALL_FROM_PUBLIC_INLINE")
+public inline fun <reified T : Annotation> KClass<*>.findAssociatedObject(): Any? =
+    findAssociatedObject(this, wasmClassId<T>())

libraries/stdlib/wasm/src/kotlin/reflect/KClassImpl.kt

@@ -23,7 +23,7 @@ internal object ErrorKClass : KClass<Nothing> {
     override fun isInstance(value: Any?): Boolean = error("Can's check isInstance on ErrorKClass")
 }
 
-internal class KClassImpl<T : Any>(private val typeData: TypeInfoData) : KClass<T> {
+internal class KClassImpl<T : Any>(internal val typeData: TypeInfoData) : KClass<T> {
     override val simpleName: String get() = typeData.typeName
     override val qualifiedName: String =
         if (typeData.packageName.isEmpty()) typeData.typeName else "${typeData.packageName}.${typeData.typeName}"

libraries/stdlib/wasm/src/kotlin/reflect/associatedObjectsImpl.kt

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2010-2023 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.wasm.internal
+
+import kotlin.reflect.wasm.internal.KClassImpl
+import kotlin.reflect.KClass
+
+internal var associatedObjects: Map<ULong, Any>? = null
+
+@PublishedApi
+internal fun findAssociatedObject(klass: KClass<*>, key: Int): Any? {
+    val klassId = (klass as? KClassImpl<*>)?.typeData?.typeId ?: return null
+
+    val map = associatedObjects ?: run {
+        val newMap: MutableMap<ULong, Any> = mutableMapOf()
+        initAssociatedObjects(newMap)
+        associatedObjects = newMap
+        newMap
+    }
+
+    return map[packIntoULong(klassId, key)]
+}
+
+internal fun packIntoULong(a: Int, b: Int): ULong =
+    (a.toUInt().toULong() shl Int.SIZE_BITS) or b.toUInt().toULong()
+
+internal fun addAssociatedObject(
+    mapToInit: MutableMap<ULong, Any>,
+    klassId: Int,
+    keyId: Int,
+    instance: Any
+) {
+    mapToInit[packIntoULong(klassId, keyId)] = instance
+}
+
+internal fun initAssociatedObjects(@Suppress("UNUSED_PARAMETER") mapToInit: MutableMap<ULong, Any>) {
+    // Init implicitly with AssociatedObjectsLowering
+    // addAssociatedObject(mapToInit, ...)
+}