[IR] Made currentDeclarationParent nullable

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/IrElementTransformerVoidWithContext.kt

@@ -99,7 +99,7 @@ abstract class IrElementTransformerVoidWithContext : IrElementTransformerVoid()
     protected val currentScope get() = scopeStack.peek()
     protected val parentScope get() = if (scopeStack.size < 2) null else scopeStack[scopeStack.size - 2]
     protected val allScopes get() = scopeStack
-    protected val currentDeclarationParent get() = allScopes.last { it.irElement is IrDeclarationParent }.irElement as IrDeclarationParent
+    protected val currentDeclarationParent get() = scopeStack.lastOrNull { it.irElement is IrDeclarationParent }?.irElement as? IrDeclarationParent
 
     fun printScopeStack() {
         scopeStack.forEach { println(it.scope.scopeOwner) }

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

@@ -118,7 +118,7 @@ private class AddContinuationLowering(private val context: JvmBackendContext) :
                     irBlock {
                         +generateContinuationClassForLambda(
                             info,
-                            currentDeclarationParent,
+                            currentDeclarationParent ?: error("No current declaration parent at ${expression.dump()}"),
                             (currentFunction?.irElement as? IrFunction)?.isInline == true
                         )
                         val constructor = info.constructor

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

@@ -137,7 +137,7 @@ internal class CallableReferenceLowering(private val context: JvmBackendContext)
             origin = if (isLambda) JvmLoweredDeclarationOrigin.LAMBDA_IMPL else JvmLoweredDeclarationOrigin.FUNCTION_REFERENCE_IMPL
             name = SpecialNames.NO_NAME_PROVIDED
         }.apply {
-            parent = currentDeclarationParent
+            parent = currentDeclarationParent ?: error("No current declaration parent at ${irFunctionReference.dump()}")
             superTypes += superType
             if (samSuperType == null)
                 superTypes += functionSuperClass.typeWith(parameterTypes)

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

@@ -83,7 +83,7 @@ internal class InlineCallableReferenceToLambdaPhase(val context: JvmBackendConte
                 returnType = field.type
                 isSuspend = false
             }.apply {
-                parent = currentDeclarationParent
+                parent = currentDeclarationParent ?: error("No current declaration parent at ${expression.dump()}")
                 val boundReceiver = expression.dispatchReceiver ?: expression.extensionReceiver
 
                 val receiver =
@@ -140,7 +140,7 @@ internal class InlineCallableReferenceToLambdaPhase(val context: JvmBackendConte
                 returnType = referencedFunction.returnType
                 isSuspend = referencedFunction.isSuspend
             }.apply {
-                parent = currentDeclarationParent
+                parent = currentDeclarationParent!!
                 for ((index, argumentType) in argumentTypes.withIndex()) {
                     addValueParameter {
                         name = Name.identifier("p$index")