[IR] Mark IrAnonymousInitializerImpl with an opt-in annotation

KT-59318

compiler/ir/backend.jvm/lower/src/org/jetbrains/kotlin/backend/jvm/lower/MoveCompanionObjectFieldsLowering.kt

@@ -14,11 +14,8 @@ import org.jetbrains.kotlin.backend.jvm.ir.replaceThisByStaticReference
 import org.jetbrains.kotlin.backend.jvm.propertiesPhase
 import org.jetbrains.kotlin.descriptors.DescriptorVisibilities
 import org.jetbrains.kotlin.ir.builders.declarations.addField
-import org.jetbrains.kotlin.ir.builders.declarations.addProperty
-import org.jetbrains.kotlin.ir.builders.declarations.buildField
 import org.jetbrains.kotlin.ir.builders.irCall
 import org.jetbrains.kotlin.ir.declarations.*
-import org.jetbrains.kotlin.ir.declarations.impl.IrAnonymousInitializerImpl
 import org.jetbrains.kotlin.ir.expressions.*
 import org.jetbrains.kotlin.ir.expressions.impl.IrExpressionBodyImpl
 import org.jetbrains.kotlin.ir.expressions.impl.IrGetFieldImpl
@@ -100,7 +97,7 @@ private class MoveOrCopyCompanionObjectFieldsLowering(val context: JvmBackendCon
         with(oldInitializer) {
             val oldParent = parentAsClass
             val newSymbol = IrAnonymousInitializerSymbolImpl(newParent.symbol)
-            IrAnonymousInitializerImpl(startOffset, endOffset, origin, newSymbol, isStatic = true).apply {
+            factory.createAnonymousInitializer(startOffset, endOffset, origin, newSymbol, isStatic = true).apply {
                 parent = newParent
                 body = this@with.body.patchDeclarationParents(newParent)
                 replaceThisByStaticReference(context.cachedDeclarations.fieldsForObjectInstances, oldParent, oldParent.thisReceiver!!)

compiler/ir/backend.jvm/lower/src/org/jetbrains/kotlin/backend/jvm/lower/ScriptLowering.kt

@@ -1031,7 +1031,7 @@ private inline fun IrClass.addAnonymousInitializer(builder: IrFunctionBuilder.()
     IrFunctionBuilder().run {
         builder()
         returnType = defaultType
-        IrAnonymousInitializerImpl(
+        factory.createAnonymousInitializer(
             startOffset, endOffset, origin,
             IrAnonymousInitializerSymbolImpl()
         )

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/IrImplementationDetail.kt

@@ -0,0 +1,17 @@
+/*
+ * 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 org.jetbrains.kotlin.ir
+
+import org.jetbrains.kotlin.ir.declarations.IrFactory
+
+/**
+ * IR implementation classes annotated with this annotation are not expected to be used directly.
+ *
+ * [IrFactory] should be the preferred way to create instances of such classes.
+ */
+@RequiresOptIn("Use IrFactory instead of creating IR nodes directly", level = RequiresOptIn.Level.ERROR)
+@Target(AnnotationTarget.CONSTRUCTOR)
+annotation class IrImplementationDetail

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrAnonymousInitializerImpl.kt

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.ir.declarations.impl
 
 import org.jetbrains.kotlin.descriptors.ClassDescriptor
+import org.jetbrains.kotlin.ir.IrImplementationDetail
 import org.jetbrains.kotlin.ir.ObsoleteDescriptorBasedAPI
 import org.jetbrains.kotlin.ir.declarations.IrAnonymousInitializer
 import org.jetbrains.kotlin.ir.declarations.IrFactory
@@ -15,7 +16,7 @@ import org.jetbrains.kotlin.ir.expressions.IrBlockBody
 import org.jetbrains.kotlin.ir.expressions.IrConstructorCall
 import org.jetbrains.kotlin.ir.symbols.IrAnonymousInitializerSymbol
 
-class IrAnonymousInitializerImpl(
+class IrAnonymousInitializerImpl @IrImplementationDetail constructor(
     override val startOffset: Int,
     override val endOffset: Int,
     override var origin: IrDeclarationOrigin,

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFactoryImpl.kt

@@ -6,7 +6,7 @@
 package org.jetbrains.kotlin.ir.declarations.impl
 
 import org.jetbrains.kotlin.descriptors.*
-import org.jetbrains.kotlin.ir.IrStatement
+import org.jetbrains.kotlin.ir.IrImplementationDetail
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.expressions.IrBlockBody
 import org.jetbrains.kotlin.ir.expressions.IrExpression
@@ -23,6 +23,7 @@ object IrFactoryImpl : AbstractIrFactoryImpl() {
     override val stageController: StageController = StageController()
 }
 
+@OptIn(IrImplementationDetail::class)
 abstract class AbstractIrFactoryImpl : IrFactory {
 
     override fun createAnonymousInitializer(