[IR] Mark IrClassImpl with an opt-in annotation

KT-59318

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

@@ -31,7 +31,6 @@ import org.jetbrains.kotlin.fileClasses.JvmMultifileClassPartInfo
 import org.jetbrains.kotlin.fileClasses.JvmSimpleFileClassInfo
 import org.jetbrains.kotlin.ir.PsiIrFileEntry
 import org.jetbrains.kotlin.ir.declarations.*
-import org.jetbrains.kotlin.ir.declarations.impl.IrClassImpl
 import org.jetbrains.kotlin.ir.expressions.IrConst
 import org.jetbrains.kotlin.ir.expressions.IrConstKind
 import org.jetbrains.kotlin.ir.expressions.IrConstructorCall
@@ -98,17 +97,18 @@ private class FileClassLowering(val context: JvmBackendContext) : FileLoweringPa
                 IrDeclarationOrigin.FILE_CLASS
             else
                 IrDeclarationOrigin.SYNTHETIC_FILE_CLASS
-        return IrClassImpl(
-            0, fileEntry.maxOffset,
-            fileClassOrigin,
-            symbol = IrClassSymbolImpl(),
+        return context.irFactory.createClass(
+            startOffset = 0,
+            endOffset = fileEntry.maxOffset,
+            origin = fileClassOrigin,
             name = fileClassInfo.fileClassFqName.shortName(),
-            kind = ClassKind.CLASS,
             visibility = if (isMultifilePart || onlyPrivateDeclarationsAndFeatureIsEnabled)
                 JavaDescriptorVisibilities.PACKAGE_VISIBILITY
             else
                 DescriptorVisibilities.PUBLIC,
-            modality = Modality.FINAL
+            symbol = IrClassSymbolImpl(),
+            kind = ClassKind.CLASS,
+            modality = Modality.FINAL,
         ).apply {
             superTypes = listOf(context.irBuiltIns.anyType)
             parent = irFile

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmFileFacadeClass.kt

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.backend.jvm
 
 import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.ir.IrImplementationDetail
 import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
 import org.jetbrains.kotlin.ir.declarations.IrClass
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
@@ -14,6 +15,7 @@ import org.jetbrains.kotlin.ir.symbols.impl.IrClassSymbolImpl
 import org.jetbrains.kotlin.ir.util.DeserializableClass
 import org.jetbrains.kotlin.name.Name
 
+@OptIn(IrImplementationDetail::class)
 class JvmFileFacadeClass(
     origin: IrDeclarationOrigin,
     name: Name,

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

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.ir.declarations.impl
 
 import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.ir.IrImplementationDetail
 import org.jetbrains.kotlin.ir.ObsoleteDescriptorBasedAPI
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.expressions.IrConstructorCall
@@ -15,7 +16,7 @@ import org.jetbrains.kotlin.ir.types.IrSimpleType
 import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.name.Name
 
-open class IrClassImpl(
+open class IrClassImpl @IrImplementationDetail constructor(
     override val startOffset: Int,
     override val endOffset: Int,
     override var origin: IrDeclarationOrigin,

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/impl/IrErrorClassImpl.kt

@@ -7,6 +7,7 @@ package org.jetbrains.kotlin.ir.types.impl
 
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.ir.IrFileEntry
+import org.jetbrains.kotlin.ir.IrImplementationDetail
 import org.jetbrains.kotlin.ir.ObsoleteDescriptorBasedAPI
 import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
 import org.jetbrains.kotlin.ir.declarations.*
@@ -19,6 +20,8 @@ import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.utils.addToStdlib.shouldNotBeCalled
 
+
+@OptIn(IrImplementationDetail::class)
 object IrErrorClassImpl : IrClassImpl(
     UNDEFINED_OFFSET, UNDEFINED_OFFSET, IrDeclarationOrigin.ERROR_CLASS, IrClassSymbolImpl(),
     Name.special("<error>"), ClassKind.CLASS, DescriptorVisibilities.DEFAULT_VISIBILITY, Modality.FINAL