Simple stage layers + enforce model

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

@@ -112,7 +112,7 @@ fun DeclarationContainerLoweringPass.runOnFilePostfix(irFile: IrFile) {
     this.lower(irFile as IrDeclarationContainer)
 }
 
-fun BodyLoweringPass.runOnFilePostfix(irFile: IrFile, withLocalDeclarations: Boolean = false) {
+fun BodyLoweringPass.runOnFilePostfix(irFile: IrFile, withLocalDeclarations: Boolean = false, allowDeclarationModification: Boolean = false) {
     ArrayList(irFile.declarations).forEach {
         it.accept(object : IrElementVisitor<Unit, IrDeclaration?> {
             override fun visitElement(element: IrElement, data: IrDeclaration?) {
@@ -131,8 +131,13 @@ fun BodyLoweringPass.runOnFilePostfix(irFile: IrFile, withLocalDeclarations: Boo
 
             override fun visitBody(body: IrBody, data: IrDeclaration?) {
                 if (withLocalDeclarations) body.acceptChildren(this, null)
-
-                lower(body, data!!)
+                if (allowDeclarationModification) {
+                    lower(body, data!!)
+                } else {
+                    stageController.bodyLowering {
+                        lower(body, data!!)
+                    }
+                }
             }
         }, null)
     }
@@ -160,7 +165,9 @@ interface DeclarationTransformer: FileLoweringPass {
 }
 
 fun DeclarationTransformer.transformFlatRestricted(declaration: IrDeclaration): List<IrDeclaration>? {
-    return transformFlat(declaration)
+    return stageController.restrictTo(declaration) {
+        transformFlat(declaration)
+    }
 }
 
 fun DeclarationTransformer.toFileLoweringPass(): FileLoweringPass {

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

@@ -366,7 +366,9 @@ fun IrType.remapTypeParameters(
 
 /* Copied from K/N */
 fun IrDeclarationContainer.addChild(declaration: IrDeclaration) {
-    this.declarations += declaration
+    stageController.unrestrictDeclarationListsAccess {
+        this.declarations += declaration
+    }
     declaration.accept(SetDeclarationsParentVisitor, this)
 }
 
@@ -443,6 +445,7 @@ fun IrClass.simpleFunctions() = declarations.flatMap {
     }
 }
 
+
 fun IrClass.createParameterDeclarations() {
     assert(thisReceiver == null)
 

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/InitializersLowering.kt

@@ -64,7 +64,8 @@ open class InitializersLowering(context: CommonBackendContext) : InitializersLow
 
 abstract class InitializersLoweringBase(open val context: CommonBackendContext) {
     protected fun extractInitializers(irClass: IrClass, filter: (IrDeclaration) -> Boolean) =
-        irClass.declarations.filter(filter).mapNotNull {
+        // TODO What about fields that were added by lowerings? e.g. captured outer class or locals?
+        ArrayList(irClass.declarations).mapNotNull { if (it is IrProperty) it.backingField else it }.filter(filter).mapNotNull {
             when (it) {
                 is IrField -> handleField(irClass, it)
                 is IrAnonymousInitializer -> handleAnonymousInitializer(it)

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/InnerClassesLowering.kt

@@ -34,7 +34,9 @@ class InnerClassesLowering(val context: BackendContext) : DeclarationTransformer
     override fun transformFlat(declaration: IrDeclaration): List<IrDeclaration>? {
 
         if (declaration is IrClass && declaration.isInner) {
-            declaration.declarations += context.declarationFactory.getOuterThisField(declaration)
+            stageController.unrestrictDeclarationListsAccess {
+                declaration.declarations += context.declarationFactory.getOuterThisField(declaration)
+            }
         } else if (declaration is IrConstructor) {
             val irClass = declaration.parentAsClass
             if (!irClass.isInner) return null

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/LocalClassPopupLowering.kt

@@ -15,7 +15,7 @@ import org.jetbrains.kotlin.ir.expressions.impl.IrCompositeImpl
 //This lower takes part of old LocalDeclarationLowering job to pop up local classes from functions
 open class LocalClassPopupLowering(val context: BackendContext) : BodyLoweringPass {
     override fun lower(irFile: IrFile) {
-        runOnFilePostfix(irFile, withLocalDeclarations = true)
+        runOnFilePostfix(irFile, withLocalDeclarations = true, allowDeclarationModification = true)
     }
 
     override fun lower(irBody: IrBody, container: IrDeclaration) {

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/LocalDeclarationsLowering.kt

@@ -95,6 +95,10 @@ class LocalDeclarationsLowering(
 ) :
     BodyLoweringPass {
 
+    override fun lower(irFile: IrFile) {
+        runOnFilePostfix(irFile, allowDeclarationModification = true)
+    }
+
     object DECLARATION_ORIGIN_FIELD_FOR_CAPTURED_VALUE :
         IrDeclarationOriginImpl("FIELD_FOR_CAPTURED_VALUE", isSynthetic = true)