Extracted some common code.

Sometimes it would be nice to know context during IR rewriting, this is when
IrElementTransformerVoidWithContext comes in handy.

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

@@ -0,0 +1,44 @@
+package org.jetbrains.kotlin.backend.common
+
+import org.jetbrains.kotlin.descriptors.ClassDescriptor
+import org.jetbrains.kotlin.descriptors.FunctionDescriptor
+import org.jetbrains.kotlin.ir.IrStatement
+import org.jetbrains.kotlin.ir.declarations.IrClass
+import org.jetbrains.kotlin.ir.declarations.IrFunction
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
+
+abstract class IrElementTransformerVoidWithContext(): IrElementTransformerVoid() {
+    private fun <E> MutableList<E>.push(element: E) = this.add(element)
+
+    private fun <E> MutableList<E>.pop() = this.removeAt(size - 1)
+
+    private fun <E> MutableList<E>.peek(): E? = if (size == 0) null else this[size - 1]
+
+    private val functionsStack = mutableListOf<FunctionDescriptor>()
+    private val classesStack = mutableListOf<ClassDescriptor>()
+
+    override final fun visitFunction(declaration: IrFunction): IrStatement {
+        functionsStack.push(declaration.descriptor)
+        val result = visitFunctionNew(declaration)
+        functionsStack.pop()
+        return result
+    }
+
+    override final fun visitClass(declaration: IrClass): IrStatement {
+        classesStack.push(declaration.descriptor)
+        val result = visitClassNew(declaration)
+        classesStack.pop()
+        return result
+    }
+
+    protected val currentFunction get() = functionsStack.peek()
+    protected val currentClass get() = classesStack.peek()
+
+    open fun visitFunctionNew(declaration: IrFunction) : IrStatement {
+        return super.visitFunction(declaration)
+    }
+
+    open fun visitClassNew(declaration: IrClass) : IrStatement {
+        return super.visitClass(declaration)
+    }
+}

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/lower/InnerClassLowering.kt

@@ -1,14 +1,13 @@
 package org.jetbrains.kotlin.backend.konan.lower
 
 import org.jetbrains.kotlin.backend.common.ClassLoweringPass
+import org.jetbrains.kotlin.backend.common.IrElementTransformerVoidWithContext
 import org.jetbrains.kotlin.backend.common.lower.callsSuper
 import org.jetbrains.kotlin.backend.konan.Context
 import org.jetbrains.kotlin.descriptors.*
-import org.jetbrains.kotlin.ir.IrStatement
 import org.jetbrains.kotlin.ir.declarations.IrClass
 import org.jetbrains.kotlin.ir.declarations.IrConstructor
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationOriginImpl
-import org.jetbrains.kotlin.ir.declarations.IrFunction
 import org.jetbrains.kotlin.ir.declarations.impl.IrFieldImpl
 import org.jetbrains.kotlin.ir.expressions.IrBlockBody
 import org.jetbrains.kotlin.ir.expressions.IrExpression
@@ -17,7 +16,6 @@ import org.jetbrains.kotlin.ir.expressions.impl.IrGetFieldImpl
 import org.jetbrains.kotlin.ir.expressions.impl.IrGetValueImpl
 import org.jetbrains.kotlin.ir.expressions.impl.IrSetFieldImpl
 import org.jetbrains.kotlin.ir.util.transformFlat
-import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
 import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
 import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.scopes.receivers.ImplicitClassReceiver
@@ -84,22 +82,7 @@ internal class InnerClassLowering(val context: Context) : ClassLoweringPass {
         }
 
         private fun lowerOuterThisReferences() {
-            irClass.transformChildrenVoid(object : IrElementTransformerVoid() {
+            irClass.transformChildrenVoid(object : IrElementTransformerVoidWithContext() {
-                private fun <E> MutableList<E>.push(element: E) = this.add(element)
-
-                private fun <E> MutableList<E>.pop() = this.removeAt(size - 1)
-
-                private fun <E> MutableList<E>.peek(): E? = if (size == 0) null else this[size - 1]
-
-                private val functionsStack = mutableListOf<FunctionDescriptor>()
-
-                override fun visitFunction(declaration: IrFunction): IrStatement {
-                    functionsStack.push(declaration.descriptor)
-                    val result = super.visitFunction(declaration)
-                    functionsStack.pop()
-                    return result
-                }
-
                 override fun visitGetValue(expression: IrGetValue): IrExpression {
                     expression.transformChildrenVoid(this)
 
@@ -108,7 +91,7 @@ internal class InnerClassLowering(val context: Context) : ClassLoweringPass {
 
                     if (implicitThisClass == classDescriptor) return expression
 
-                    val constructorDescriptor = functionsStack.peek()!! as? ConstructorDescriptor
+                    val constructorDescriptor = currentFunction!! as? ConstructorDescriptor
 
                     val startOffset = expression.startOffset
                     val endOffset = expression.endOffset