[Commonizer] Prototype: Commonize TypeAliases with Classes

^KT-45992 Fixed
^KT-46061 Fixed

native/commonizer/src/org/jetbrains/kotlin/commonizer/cir/ArtificialCirDeclaration.kt

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this delegate code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.commonizer.cir
+
+/**
+ * Marker for classifiers that are made up to support commonization.
+ * E.g. TypeAliases might create artificial classes for the types they are pointing to.
+ */
+internal interface ArtificialCirDeclaration : CirDeclaration
+
+internal class ArtificialCirModule(val delegate: CirModule) : CirModule by delegate, ArtificialCirDeclaration
+
+internal fun CirModule.markedArtificial() = ArtificialCirModule(this)
+
+internal class ArtificialCirClass(val delegate: CirClass) : CirClass by delegate, ArtificialCirDeclaration
+
+internal fun CirClass.markedArtificial(): ArtificialCirClass = ArtificialCirClass(this)
+
+internal class ArtificialCirClassConstructor(val delegate: CirClassConstructor) : CirClassConstructor by delegate, ArtificialCirDeclaration
+
+internal fun CirClassConstructor.markedArtificial() = ArtificialCirClassConstructor(this)
+
+internal class ArtificialCirFunction(val delegate: CirFunction) : CirFunction by delegate, ArtificialCirDeclaration
+
+internal fun CirFunction.markedArtificial() = ArtificialCirFunction(this)
+
+internal class ArtificialCirProperty(val delegate: CirProperty) : CirProperty by delegate, ArtificialCirDeclaration
+
+internal fun CirProperty.markedArtificial() = ArtificialCirProperty(this)

native/commonizer/src/org/jetbrains/kotlin/commonizer/cir/CirClassConstructor.kt

@@ -18,6 +18,8 @@ interface CirClassConstructor :
     val isPrimary: Boolean
     override val containingClass: CirContainingClass // non-nullable
 
+    override fun withContainingClass(containingClass: CirContainingClass): CirClassConstructor
+
     companion object {
         @Suppress("NOTHING_TO_INLINE")
         inline fun create(
@@ -48,4 +50,8 @@ data class CirClassConstructorImpl(
     override var valueParameters: List<CirValueParameter>,
     override var hasStableParameterNames: Boolean,
     override val isPrimary: Boolean
-) : CirClassConstructor
+) : CirClassConstructor {
+    override fun withContainingClass(containingClass: CirContainingClass): CirClassConstructor {
+        return copy(containingClass = containingClass)
+    }
+}

native/commonizer/src/org/jetbrains/kotlin/commonizer/cir/CirDeclaration.kt

@@ -41,8 +41,13 @@ interface CirHasModality {
     val modality: Modality
 }
 
+
 interface CirMaybeCallableMemberOfClass {
     val containingClass: CirContainingClass? // null assumes no containing class
+
+    fun withContainingClass(containingClass: CirContainingClass): CirMaybeCallableMemberOfClass = object : CirMaybeCallableMemberOfClass {
+        override val containingClass: CirContainingClass = containingClass
+    }
 }
 
 /**

native/commonizer/src/org/jetbrains/kotlin/commonizer/cir/CirFunction.kt

@@ -12,6 +12,8 @@ import org.jetbrains.kotlin.descriptors.Visibility
 interface CirFunction : CirFunctionOrProperty, CirCallableMemberWithParameters {
     val modifiers: CirFunctionModifiers
 
+    override fun withContainingClass(containingClass: CirContainingClass): CirFunction
+
     companion object {
         @Suppress("NOTHING_TO_INLINE")
         inline fun create(
@@ -57,4 +59,8 @@ data class CirFunctionImpl(
     override val returnType: CirType,
     override val kind: CallableMemberDescriptor.Kind,
     override val modifiers: CirFunctionModifiers
-) : CirFunction
+) : CirFunction {
+    override fun withContainingClass(containingClass: CirContainingClass): CirFunction {
+        return copy(containingClass = containingClass)
+    }
+}

native/commonizer/src/org/jetbrains/kotlin/commonizer/cir/CirProperty.kt

@@ -21,6 +21,8 @@ interface CirProperty : CirFunctionOrProperty, CirLiftedUpDeclaration {
     val delegateFieldAnnotations: List<CirAnnotation>
     val compileTimeInitializer: CirConstantValue
 
+    override fun withContainingClass(containingClass: CirContainingClass): CirProperty
+
     companion object {
         @Suppress("NOTHING_TO_INLINE")
         inline fun create(
@@ -90,4 +92,8 @@ data class CirPropertyImpl(
 ) : CirProperty {
     // const property in "common" fragment is already lifted up
     override val isLiftedUp get() = isConst
+
+    override fun withContainingClass(containingClass: CirContainingClass): CirProperty {
+        return copy(containingClass = containingClass)
+    }
 }

native/commonizer/src/org/jetbrains/kotlin/commonizer/core/TypeAliasCommonizer.kt

@@ -16,26 +16,21 @@ import org.jetbrains.kotlin.descriptors.Modality
  *
  * Secondary (less optimistic) branch:
  * - Make sure that all TAs are identical, so the resulting TA can be lifted up into "common" fragment.
- *
- * Tertiary (backup) branch:
- * - Produce an "expect class" for "common" fragment and the corresponding "actual typealias" declarations for each platform fragment.
  */
 class TypeAliasCommonizer(classifiers: CirKnownClassifiers) : AbstractStandardCommonizer<CirTypeAlias, CirClassifier>() {
     private val primary = TypeAliasShortCircuitingCommonizer(classifiers)
     private val secondary = TypeAliasLiftingUpCommonizer(classifiers)
-    private val tertiary = TypeAliasExpectClassCommonizer()
 
-    override fun commonizationResult(): CirClassifier = primary.resultOrNull ?: secondary.resultOrNull ?: tertiary.result
+    override fun commonizationResult(): CirClassifier = primary.resultOrNull ?: secondary.result
 
     override fun initialize(first: CirTypeAlias) = Unit
 
     override fun doCommonizeWith(next: CirTypeAlias): Boolean {
         val primaryResult = primary.commonizeWith(next)
         val secondaryResult = secondary.commonizeWith(next)
-        val tertiaryResult = tertiary.commonizeWith(next)
 
         // Note: don't call commonizeWith() functions in return statement to avoid short-circuiting!
-        return primaryResult || secondaryResult || tertiaryResult
+        return primaryResult || secondaryResult
     }
 }
 
@@ -94,9 +89,6 @@ private class TypeAliasLiftingUpCommonizer(classifiers: CirKnownClassifiers) : A
         )
     }
 
-    val resultOrNull: CirTypeAlias?
-        get() = if (hasResult) commonizationResult() else null
-
     override fun initialize(first: CirTypeAlias) {
         name = first.name
     }
@@ -106,43 +98,3 @@ private class TypeAliasLiftingUpCommonizer(classifiers: CirKnownClassifiers) : A
                 && underlyingType.commonizeWith(next.underlyingType)
                 && visibility.commonizeWith(next)
 }
-
-private class TypeAliasExpectClassCommonizer : AbstractStandardCommonizer<CirTypeAlias, CirClass>() {
-    private lateinit var name: CirName
-    private val classVisibility = VisibilityCommonizer.equalizing()
-
-    override fun commonizationResult(): CirClass = CirClass.create(
-        annotations = emptyList(),
-        name = name,
-        typeParameters = emptyList(),
-        visibility = classVisibility.result,
-        modality = Modality.FINAL,
-        kind = ClassKind.CLASS,
-        companion = null,
-        isCompanion = false,
-        isData = false,
-        isValue = false,
-        isInner = false,
-        isExternal = false
-    )
-
-    override fun initialize(first: CirTypeAlias) {
-        name = first.name
-    }
-
-    override fun doCommonizeWith(next: CirTypeAlias): Boolean {
-        if (next.typeParameters.isNotEmpty())
-            return false // TAs with declared type parameters can't be commonized
-
-        val underlyingType = next.underlyingType as? CirClassType ?: return false // right-hand side could have only class
-        return hasNoArguments(underlyingType) // TAs with functional types or types with arguments at the right-hand side can't be commonized
-                && classVisibility.commonizeWith(underlyingType) // the visibilities of the right-hand classes should be equal
-    }
-
-    private tailrec fun hasNoArguments(type: CirClassType?): Boolean =
-        when {
-            type == null -> true
-            type.arguments.isNotEmpty() -> false
-            else -> hasNoArguments(type.outerType)
-        }
-}

native/commonizer/src/org/jetbrains/kotlin/commonizer/core/TypeCommonizer.kt

@@ -8,6 +8,7 @@ package org.jetbrains.kotlin.commonizer.core
 import org.jetbrains.kotlin.commonizer.cir.*
 import org.jetbrains.kotlin.commonizer.core.CommonizedTypeAliasAnswer.Companion.FAILURE_MISSING_IN_SOME_TARGET
 import org.jetbrains.kotlin.commonizer.core.CommonizedTypeAliasAnswer.Companion.SUCCESS_FROM_DEPENDENCY_LIBRARY
+import org.jetbrains.kotlin.commonizer.core.CommonizedTypeAliasAnswer.Companion.create
 import org.jetbrains.kotlin.commonizer.mergedtree.CirKnownClassifiers
 import org.jetbrains.kotlin.commonizer.utils.isUnderKotlinNativeSyntheticPackages
 import org.jetbrains.kotlin.descriptors.Visibility
@@ -203,16 +204,9 @@ private fun commonizeClass(classId: CirEntityId, classifiers: CirKnownClassifier
         return true
     }
 
-    return when (val node = classifiers.commonizedNodes.classNode(classId)) {
+    // Looking for a a node that provides a non-null (successfully commonized) classifier declaration
-        null -> {
+    return (classifiers.commonizedNodes.classNode(classId)?.commonDeclaration?.invoke()
-            // No node means that the type alias was not subject for commonization. It is missing in some target(s) => not commonized.
+        ?: classifiers.commonizedNodes.typeAliasNode(classId)?.commonDeclaration?.invoke()) != null
-            false
-        }
-        else -> {
-            // Common declaration in node is not null -> successfully commonized.
-            (node.commonDeclaration() != null)
-        }
-    }
 }
 
 private fun commonizeTypeAlias(typeAliasId: CirEntityId, classifiers: CirKnownClassifiers): CommonizedTypeAliasAnswer {
@@ -221,16 +215,14 @@ private fun commonizeTypeAlias(typeAliasId: CirEntityId, classifiers: CirKnownCl
         return SUCCESS_FROM_DEPENDENCY_LIBRARY
     }
 
-    return when (val node = classifiers.commonizedNodes.typeAliasNode(typeAliasId)) {
+    val typeAliasNode = classifiers.commonizedNodes.typeAliasNode(typeAliasId)
-        null -> {
+    val classNode = classifiers.commonizedNodes.classNode(typeAliasId)
-            // No node means that the type alias was not subject for commonization. It is missing in some target(s) => not commonized.
+
-            FAILURE_MISSING_IN_SOME_TARGET
+    if (typeAliasNode == null && classNode == null) {
-        }
+        return FAILURE_MISSING_IN_SOME_TARGET
-        else -> {
-            // Common declaration in node is not null -> successfully commonized.
-            CommonizedTypeAliasAnswer.create(node.commonDeclaration())
-        }
     }
+
+    return create(typeAliasNode?.commonDeclaration?.invoke() ?: classNode?.commonDeclaration?.invoke())
 }
 
 private class CommonizedTypeAliasAnswer(val commonized: Boolean, val commonClassifier: CirClassifier?) {

native/commonizer/src/org/jetbrains/kotlin/commonizer/core/typeAliasUtils.kt

@@ -18,8 +18,7 @@ internal tailrec fun computeSuitableUnderlyingType(
     return when (underlyingType) {
         is CirClassType -> underlyingType.withCommonizedArguments(classifiers)
         is CirTypeAliasType -> if (classifiers.commonDependencies.hasClassifier(underlyingType.classifierId))
-            underlyingType.withCommonizedArguments(classifiers)
+            underlyingType.withCommonizedArguments(classifiers) else
-        else
             computeSuitableUnderlyingType(classifiers, underlyingType.underlyingType)
     }
 }

native/commonizer/src/org/jetbrains/kotlin/commonizer/facade.kt

@@ -16,6 +16,8 @@ import org.jetbrains.kotlin.commonizer.mergedtree.CirNode.Companion.indexOfCommo
 import org.jetbrains.kotlin.commonizer.mergedtree.CirNode.Companion.targetIndices
 import org.jetbrains.kotlin.commonizer.mergedtree.CirRootNode
 import org.jetbrains.kotlin.commonizer.metadata.CirTreeSerializer.serializeSingleTarget
+import org.jetbrains.kotlin.commonizer.transformer.Checked.Companion.invoke
+import org.jetbrains.kotlin.commonizer.transformer.InlineTypeAliasCirNodeTransformer
 import org.jetbrains.kotlin.commonizer.tree.CirTreeRoot
 import org.jetbrains.kotlin.commonizer.tree.assembleCirTree
 import org.jetbrains.kotlin.commonizer.tree.deserializeCirTree
@@ -50,6 +52,7 @@ private fun commonize(
     )
 
     val mergedTree = merge(storageManager, classifiers, cirTrees) ?: return null
+    InlineTypeAliasCirNodeTransformer(storageManager, classifiers).invoke(mergedTree)
     mergedTree.accept(CommonizationVisitor(classifiers, mergedTree), Unit)
     parameters.logProgress("Commonized declarations for $target")
 

native/commonizer/src/org/jetbrains/kotlin/commonizer/mergedtree/CommonizerCondition.kt

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2010-2021 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.commonizer.mergedtree
+
+import org.jetbrains.kotlin.commonizer.cir.CirDeclaration
+import org.jetbrains.kotlin.storage.NullableLazyValue
+
+
+internal fun interface CommonizerCondition {
+
+    fun allowCommonization(): Boolean
+
+    infix fun and(other: CommonizerCondition) = CommonizerCondition { allowCommonization() && other.allowCommonization() }
+
+    companion object Factory {
+        fun none(): CommonizerCondition = NoneCommonizerCondition
+
+        fun nodeIsNotCommonized(node: CirNode<*, *>) = CommonizerCondition { node.commonDeclaration() == null }
+
+        fun parent(parent: CirNode<*, *>): ParentNodeCommonizerCondition = ParentNodeCommonizerCondition(parent.commonDeclaration)
+
+        fun parent(parent: CirNode<*, *>?): CommonizerCondition = if (parent == null) none() else parent(parent)
+    }
+}
+
+private object NoneCommonizerCondition : CommonizerCondition {
+    override fun allowCommonization(): Boolean = true
+}
+
+internal class ParentNodeCommonizerCondition(
+    private val parentNodeCommonDeclaration: NullableLazyValue<CirDeclaration>
+) : CommonizerCondition {
+    override fun allowCommonization(): Boolean = parentNodeCommonDeclaration() != null
+}

native/commonizer/src/org/jetbrains/kotlin/commonizer/mergedtree/nodeBuilders.kt

@@ -20,6 +20,7 @@ internal fun buildRootNode(
 ): CirRootNode = buildNode(
     storageManager = storageManager,
     size = size,
+    commonizerCondition = CommonizerCondition.none(),
     commonizerProducer = ::RootCommonizer,
     nodeProducer = ::CirRootNode
 )
@@ -30,6 +31,7 @@ internal fun buildModuleNode(
 ): CirModuleNode = buildNode(
     storageManager = storageManager,
     size = size,
+    commonizerCondition = CommonizerCondition.none(),
     commonizerProducer = ::ModuleCommonizer,
     nodeProducer = ::CirModuleNode
 )
@@ -40,6 +42,7 @@ internal fun buildPackageNode(
 ): CirPackageNode = buildNode(
     storageManager = storageManager,
     size = size,
+    commonizerCondition = CommonizerCondition.none(),
     commonizerProducer = ::PackageCommonizer,
     nodeProducer = ::CirPackageNode
 )
@@ -48,11 +51,11 @@ internal fun buildPropertyNode(
     storageManager: StorageManager,
     size: Int,
     classifiers: CirKnownClassifiers,
-    parentCommonDeclaration: NullableLazyValue<*>?
+    condition: CommonizerCondition = CommonizerCondition.none(),
 ): CirPropertyNode = buildNode(
     storageManager = storageManager,
     size = size,
-    parentCommonDeclaration = parentCommonDeclaration,
+    commonizerCondition = condition,
     commonizerProducer = { PropertyCommonizer(classifiers) },
     nodeProducer = ::CirPropertyNode
 )
@@ -61,11 +64,11 @@ internal fun buildFunctionNode(
     storageManager: StorageManager,
     size: Int,
     classifiers: CirKnownClassifiers,
-    parentCommonDeclaration: NullableLazyValue<*>?
+    condition: CommonizerCondition = CommonizerCondition.none(),
 ): CirFunctionNode = buildNode(
     storageManager = storageManager,
     size = size,
-    parentCommonDeclaration = parentCommonDeclaration,
+    commonizerCondition = condition,
     commonizerProducer = { FunctionCommonizer(classifiers) },
     nodeProducer = ::CirFunctionNode
 )
@@ -74,12 +77,12 @@ internal fun buildClassNode(
     storageManager: StorageManager,
     size: Int,
     classifiers: CirKnownClassifiers,
-    parentCommonDeclaration: NullableLazyValue<*>?,
+    condition: CommonizerCondition = CommonizerCondition.none(),
     classId: CirEntityId
 ): CirClassNode = buildNode(
     storageManager = storageManager,
     size = size,
-    parentCommonDeclaration = parentCommonDeclaration,
+    commonizerCondition = condition,
     commonizerProducer = { ClassCommonizer(classifiers) },
     recursionMarker = CirClassRecursionMarker,
     nodeProducer = { targetDeclarations, commonDeclaration ->
@@ -89,15 +92,16 @@ internal fun buildClassNode(
     }
 )
 
+
 internal fun buildClassConstructorNode(
     storageManager: StorageManager,
     size: Int,
     classifiers: CirKnownClassifiers,
-    parentCommonDeclaration: NullableLazyValue<*>?
+    condition: ParentNodeCommonizerCondition,
 ): CirClassConstructorNode = buildNode(
     storageManager = storageManager,
     size = size,
-    parentCommonDeclaration = parentCommonDeclaration,
+    commonizerCondition = condition,
     commonizerProducer = { ClassConstructorCommonizer(classifiers) },
     nodeProducer = ::CirClassConstructorNode
 )
@@ -110,6 +114,7 @@ internal fun buildTypeAliasNode(
 ): CirTypeAliasNode = buildNode(
     storageManager = storageManager,
     size = size,
+    commonizerCondition = CommonizerCondition.none(),
     commonizerProducer = { TypeAliasCommonizer(classifiers) },
     recursionMarker = CirClassifierRecursionMarker,
     nodeProducer = { targetDeclarations, commonDeclaration ->
@@ -122,14 +127,14 @@ internal fun buildTypeAliasNode(
 private fun <T : CirDeclaration, R : CirDeclaration, N : CirNode<T, R>> buildNode(
     storageManager: StorageManager,
     size: Int,
-    parentCommonDeclaration: NullableLazyValue<*>? = null,
+    commonizerCondition: CommonizerCondition,
     commonizerProducer: () -> Commonizer<T, R>,
     recursionMarker: R? = null,
     nodeProducer: (CommonizedGroup<T>, NullableLazyValue<R>) -> N
 ): N {
     val targetDeclarations = CommonizedGroup<T>(size)
 
-    val commonComputable = { commonize(parentCommonDeclaration, targetDeclarations, commonizerProducer()) }
+    val commonComputable = { commonize(commonizerCondition, targetDeclarations, commonizerProducer()) }
 
     val commonLazyValue = if (recursionMarker != null)
         storageManager.createRecursionTolerantNullableLazyValue(commonComputable, recursionMarker)
@@ -153,14 +158,13 @@ internal fun <T : Any, R> commonize(
 
 @Suppress("NOTHING_TO_INLINE")
 private inline fun <T : Any, R> commonize(
-    parentCommonDeclaration: NullableLazyValue<*>?,
+    commonizerCondition: CommonizerCondition,
     targetDeclarations: CommonizedGroup<T>,
     commonizer: Commonizer<T, R>
 ): R? {
-    if (parentCommonDeclaration != null && parentCommonDeclaration.invoke() == null) {
+    if (commonizerCondition.allowCommonization()) {
-        // don't commonize declaration if it's parent failed to commonize
+        return commonize(targetDeclarations, commonizer)
-        return null
     }
 
-    return commonize(targetDeclarations, commonizer)
+    return null
 }

native/commonizer/src/org/jetbrains/kotlin/commonizer/metadata/CirTreeSerializer.kt

@@ -143,6 +143,7 @@ private class CirTreeSerializationVisitor(
         classContext: CirTreeSerializationContext
     ): KmClass? {
         val cirClass = classContext.get<CirClass>(node) ?: return null
+
         val classTypeParametersCount = cirClass.typeParameters.size
         val fullClassName = classContext.currentPath.toString()
 
@@ -403,7 +404,8 @@ internal data class CirTreeSerializationContext(
     }
 
     inline fun <reified T : CirDeclaration> get(node: CirNode<*, *>): T? {
-        return (if (isCommon) node.commonDeclaration() else node.targetDeclarations[targetIndex]) as T?
+        return ((if (isCommon) node.commonDeclaration() else node.targetDeclarations[targetIndex]) as T?)
+            .takeIf { it !is ArtificialCirDeclaration }
     }
 
     inline fun <reified T : CirDeclaration> get(node: CirNodeWithLiftingUp<*, *>): T? {
@@ -411,7 +413,7 @@ internal data class CirTreeSerializationContext(
             isCommon -> node.commonDeclaration() as T?
             node.isLiftedUp -> null
             else -> node.targetDeclarations[targetIndex] as T?
-        }
+        }.takeIf { it !is ArtificialCirDeclaration }
     }
 
     companion object {

native/commonizer/src/org/jetbrains/kotlin/commonizer/transformer/CirDeclarationCount.kt

@@ -0,0 +1,87 @@
+/*
+ * Copyright 2010-2021 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.
+ */
+
+/*
+ * Copyright 2010-2021 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.commonizer.transformer
+
+import org.jetbrains.kotlin.commonizer.cir.ArtificialCirDeclaration
+import org.jetbrains.kotlin.commonizer.mergedtree.*
+
+internal data class CirDeclarationCount(
+    val artificialNodeCount: Int,
+    val nonArtificialNodeCount: Int
+)
+
+internal data class MutableCirDeclarationCount(
+    var artificialNodeCount: Int = 0,
+    var nonArtificialNodeCount: Int = 0
+) {
+    fun toCirDeclarationCount() = CirDeclarationCount(
+        artificialNodeCount = artificialNodeCount,
+        nonArtificialNodeCount = nonArtificialNodeCount
+    )
+}
+
+internal fun CirNode<*, *>.countCirDeclarations(): CirDeclarationCount {
+    val counter = MutableCirDeclarationCount()
+    accept(CirNodeCounterVisitor, counter)
+    return counter.toCirDeclarationCount()
+}
+
+private object CirNodeCounterVisitor : CirNodeVisitor<MutableCirDeclarationCount, Unit> {
+
+    private operator fun MutableCirDeclarationCount.plusAssign(node: CirNode<*, *>) {
+        node.targetDeclarations.forEach { declaration ->
+            if (declaration == null) return@forEach
+            if (declaration is ArtificialCirDeclaration) artificialNodeCount++ else nonArtificialNodeCount++
+        }
+    }
+
+    override fun visitRootNode(node: CirRootNode, data: MutableCirDeclarationCount) {
+        data += node
+        node.modules.forEach { (_, module) -> module.accept(this, data) }
+    }
+
+    override fun visitModuleNode(node: CirModuleNode, data: MutableCirDeclarationCount) {
+        data += node
+        node.packages.forEach { (_, pkg) -> pkg.accept(this, data) }
+    }
+
+    override fun visitPackageNode(node: CirPackageNode, data: MutableCirDeclarationCount) {
+        data += node
+        node.typeAliases.forEach { (_, typeAlias) -> typeAlias.accept(this, data) }
+        node.properties.forEach { (_, property) -> property.accept(this, data) }
+        node.functions.forEach { (_, function) -> function.accept(this, data) }
+        node.classes.forEach { (_, clazz) -> clazz.accept(this, data) }
+    }
+
+    override fun visitPropertyNode(node: CirPropertyNode, data: MutableCirDeclarationCount) {
+        data += node
+    }
+
+    override fun visitFunctionNode(node: CirFunctionNode, data: MutableCirDeclarationCount) {
+        data += node
+    }
+
+    override fun visitClassNode(node: CirClassNode, data: MutableCirDeclarationCount) {
+        data += node
+        node.properties.forEach { (_, property) -> property.accept(this, data) }
+        node.functions.forEach { (_, function) -> function.accept(this, data) }
+        node.constructors.forEach { (_, constructor) -> constructor.accept(this, data) }
+        node.classes.forEach { (_, clazz) -> clazz.accept(this, data) }
+    }
+
+    override fun visitClassConstructorNode(node: CirClassConstructorNode, data: MutableCirDeclarationCount) {
+        data += node
+    }
+
+    override fun visitTypeAliasNode(node: CirTypeAliasNode, data: MutableCirDeclarationCount) {
+        data += node
+    }
+}

native/commonizer/src/org/jetbrains/kotlin/commonizer/transformer/CirNodeTransformer.kt

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2010-2021 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.commonizer.transformer
+
+import org.jetbrains.kotlin.commonizer.mergedtree.CirRootNode
+
+internal fun interface CirNodeTransformer {
+
+    sealed class Context {
+        object Unchecked : Context()
+    }
+
+    operator fun Context.invoke(root: CirRootNode)
+}
+
+internal class Checked private constructor() : CirNodeTransformer.Context() {
+    companion object {
+        private val areAssertionsEnabled = this::class.java.desiredAssertionStatus()
+
+        operator fun CirNodeTransformer.invoke(cirRootNode: CirRootNode) {
+            val context = if (areAssertionsEnabled) Checked() else Unchecked
+            val declarationCountBefore = if (areAssertionsEnabled) cirRootNode.countCirDeclarations() else null
+
+            with(this) {
+                context.invoke(cirRootNode)
+            }
+
+            if (declarationCountBefore != null) {
+                val declarationCountAfter = cirRootNode.countCirDeclarations()
+                if (declarationCountAfter.nonArtificialNodeCount > declarationCountBefore.nonArtificialNodeCount) {
+                    throw AssertionError(
+                        "$this attached declarations not marked as artificial\n" +
+                                "Declaration Count before: $declarationCountBefore\n" +
+                                "Declaration Count after: $declarationCountAfter"
+                    )
+                }
+            }
+        }
+    }
+}

native/commonizer/src/org/jetbrains/kotlin/commonizer/transformer/InlineTypeAliasCirNodeTransformer.kt

@@ -0,0 +1,143 @@
+/*
+ * Copyright 2010-2021 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.commonizer.transformer
+
+import org.jetbrains.kotlin.commonizer.cir.*
+import org.jetbrains.kotlin.commonizer.mergedtree.*
+import org.jetbrains.kotlin.commonizer.transformer.CirNodeTransformer.Context
+import org.jetbrains.kotlin.descriptors.ClassKind
+import org.jetbrains.kotlin.descriptors.Modality
+import org.jetbrains.kotlin.storage.StorageManager
+
+internal class InlineTypeAliasCirNodeTransformer(
+    private val storageManager: StorageManager,
+    private val classifiers: CirKnownClassifiers
+) : CirNodeTransformer {
+    override fun Context.invoke(root: CirRootNode) {
+        root.modules.values.forEach(::invoke)
+    }
+
+    private operator fun invoke(module: CirModuleNode) {
+        val classNodeIndex = ClassNodeIndex(module)
+
+        module.packages.values.forEach { packageNode ->
+            packageNode.typeAliases.values.forEach { typeAliasNode ->
+                val targetClassNode = classNodeIndex[typeAliasNode.id] ?: packageNode.createArtificialClassNode(typeAliasNode)
+                inlineTypeAliasIfPossible(classNodeIndex, typeAliasNode, targetClassNode)
+            }
+        }
+    }
+
+    private fun inlineTypeAliasIfPossible(classes: ClassNodeIndex, fromTypeAliasNode: CirTypeAliasNode, intoClassNode: CirClassNode) {
+        fromTypeAliasNode.targetDeclarations.forEachIndexed { targetIndex, typeAlias ->
+            if (typeAlias != null) {
+                inlineTypeAliasIfPossible(classes, typeAlias, intoClassNode, targetIndex)
+            }
+        }
+    }
+
+    private fun inlineTypeAliasIfPossible(
+        classes: ClassNodeIndex, fromTypeAlias: CirTypeAlias, intoClassNode: CirClassNode, targetIndex: Int
+    ) {
+        if (fromTypeAlias.typeParameters.isNotEmpty()) {
+            // Inlining parameterized TAs is not supported yet
+            return
+        }
+
+        if (fromTypeAlias.underlyingType.arguments.isNotEmpty() ||
+            fromTypeAlias.underlyingType.run { this as? CirClassType }?.outerType?.arguments?.isNotEmpty() == true
+        ) {
+            // Inlining TAs with parameterized underlying types is not supported yet
+            return
+        }
+
+        if (intoClassNode.targetDeclarations[targetIndex] != null) {
+            // No empty spot to inline the type-alias into
+            return
+        }
+
+        val fromAliasedClassNode = classes[fromTypeAlias.expandedType.classifierId]
+
+        val intoArtificialClass = ArtificialAliasedCirClass(
+            pointingTypeAlias = fromTypeAlias,
+            pointedClass = fromAliasedClassNode?.targetDeclarations?.get(targetIndex) ?: fromTypeAlias.toArtificialCirClass()
+        )
+
+        intoClassNode.targetDeclarations[targetIndex] = intoArtificialClass
+
+        if (fromAliasedClassNode != null && !fromTypeAlias.expandedType.isMarkedNullable) {
+            inlineArtificialMembers(fromAliasedClassNode, intoClassNode, intoArtificialClass, targetIndex)
+        }
+    }
+
+    private fun inlineArtificialMembers(
+        fromAliasedClassNode: CirClassNode,
+        intoClassNode: CirClassNode,
+        intoClass: CirClass,
+        targetIndex: Int
+    ) {
+        val targetSize = intoClassNode.targetDeclarations.size
+
+        fromAliasedClassNode.constructors.forEach { (key, aliasedConstructorNode) ->
+            val aliasedConstructor = aliasedConstructorNode.targetDeclarations[targetIndex] ?: return@forEach
+            intoClassNode.constructors.getOrPut(key) {
+                buildClassConstructorNode(storageManager, targetSize, classifiers, CommonizerCondition.parent(intoClassNode))
+            }.targetDeclarations[targetIndex] = aliasedConstructor.withContainingClass(intoClass).markedArtificial()
+        }
+
+        fromAliasedClassNode.functions.forEach { (key, aliasedFunctionNode) ->
+            val aliasedFunction = aliasedFunctionNode.targetDeclarations[targetIndex] ?: return@forEach
+            intoClassNode.functions.getOrPut(key) {
+                buildFunctionNode(storageManager, targetSize, classifiers, CommonizerCondition.parent(intoClassNode))
+            }.targetDeclarations[targetIndex] = aliasedFunction.withContainingClass(intoClass).markedArtificial()
+        }
+
+        fromAliasedClassNode.properties.forEach { (key, aliasedPropertyNode) ->
+            val aliasedProperty = aliasedPropertyNode.targetDeclarations[targetIndex] ?: return@forEach
+            intoClassNode.properties.getOrPut(key) {
+                buildPropertyNode(storageManager, targetSize, classifiers, CommonizerCondition.parent(intoClassNode))
+            }.targetDeclarations[targetIndex] = aliasedProperty.withContainingClass(intoClass).markedArtificial()
+        }
+    }
+
+    private fun CirPackageNode.createArtificialClassNode(typeAliasNode: CirTypeAliasNode): CirClassNode {
+        val classNode = buildClassNode(
+            storageManager = storageManager,
+            size = typeAliasNode.targetDeclarations.size,
+            classifiers = classifiers,
+            // This artificial class node should only try to commonize if the package node is commonized
+            //  and if the original typeAliasNode cannot be commonized.
+            //  Therefore, this artificial class node acts as a fallback with the original type-alias being still the preferred
+            //  option for commonization
+            condition = CommonizerCondition.parent(this) and CommonizerCondition.nodeIsNotCommonized(typeAliasNode),
+            classId = typeAliasNode.id
+        )
+        this.classes[typeAliasNode.classifierName] = classNode
+        return classNode
+    }
+}
+
+private typealias ClassNodeIndex = Map<CirEntityId, CirClassNode>
+
+private fun ClassNodeIndex(module: CirModuleNode): ClassNodeIndex = module.packages.values
+    .flatMap { pkg -> pkg.classes.values }
+    .associateBy { clazz -> clazz.id }
+
+private data class ArtificialAliasedCirClass(
+    val pointingTypeAlias: CirTypeAlias,
+    val pointedClass: CirClass
+) : CirClass by pointedClass, ArtificialCirDeclaration {
+    override val name: CirName = pointingTypeAlias.name
+    override var companion: CirName?
+        get() = null
+        set(_) = throw UnsupportedOperationException("Can't set companion on artificial class (pointed by $pointingTypeAlias)")
+}
+
+private fun CirTypeAlias.toArtificialCirClass(): CirClass = CirClass.create(
+    annotations = emptyList(), name = name, typeParameters = typeParameters,
+    visibility = this.visibility, modality = Modality.FINAL, kind = ClassKind.CLASS,
+    companion = null, isCompanion = false, isData = false, isValue = false, isInner = false, isExternal = false
+).also { it.supertypes = emptyList() }.markedArtificial()

native/commonizer/src/org/jetbrains/kotlin/commonizer/tree/mergeCirTree.kt

@@ -52,7 +52,7 @@ internal fun CirNodeWithMembers<*, *>.buildClass(
     context: TargetBuildingContext, treeClass: CirTreeClass, parent: CirNode<*, *>? = null
 ) {
     val classNode = classes.getOrPut(treeClass.clazz.name) {
-        buildClassNode(context.storageManager, context.targets, context.classifiers, parent?.commonDeclaration, treeClass.id)
+        buildClassNode(context.storageManager, context.targets, context.classifiers, CommonizerCondition.parent(parent), treeClass.id)
     }
     classNode.targetDeclarations[context.targetIndex] = treeClass.clazz
     treeClass.functions.forEach { function -> classNode.buildFunction(context, function, classNode) }
@@ -65,7 +65,7 @@ internal fun CirNodeWithMembers<*, *>.buildFunction(
     context: TargetBuildingContext, treeFunction: CirTreeFunction, parent: CirNode<*, *>? = null
 ) {
     val functionNode = functions.getOrPut(treeFunction.approximationKey) {
-        buildFunctionNode(context.storageManager, context.targets, context.classifiers, parent?.commonDeclaration)
+        buildFunctionNode(context.storageManager, context.targets, context.classifiers, CommonizerCondition.parent(parent))
     }
     functionNode.targetDeclarations[context.targetIndex] = treeFunction.function
 }
@@ -74,16 +74,16 @@ internal fun CirNodeWithMembers<*, *>.buildProperty(
     context: TargetBuildingContext, treeProperty: CirTreeProperty, parent: CirNode<*, *>? = null
 ) {
     val propertyNode = properties.getOrPut(treeProperty.approximationKey) {
-        buildPropertyNode(context.storageManager, context.targets, context.classifiers, parent?.commonDeclaration)
+        buildPropertyNode(context.storageManager, context.targets, context.classifiers, CommonizerCondition.parent(parent))
     }
     propertyNode.targetDeclarations[context.targetIndex] = treeProperty.property
 }
 
 internal fun CirClassNode.buildConstructor(
-    context: TargetBuildingContext, treeConstructor: CirTreeClassConstructor, parent: CirNode<*, *>?
+    context: TargetBuildingContext, treeConstructor: CirTreeClassConstructor, parent: CirNode<*, *>
 ) {
     val constructorNode = constructors.getOrPut(treeConstructor.approximationKey) {
-        buildClassConstructorNode(context.storageManager, context.targets, context.classifiers, parent?.commonDeclaration)
+        buildClassConstructorNode(context.storageManager, context.targets, context.classifiers, CommonizerCondition.parent(parent))
     }
     constructorNode.targetDeclarations[context.targetIndex] = treeConstructor.constructor
 }
@@ -94,4 +94,3 @@ internal fun CirPackageNode.buildTypeAlias(context: TargetBuildingContext, treeT
     }
     typeAliasNode.targetDeclarations[context.targetIndex] = treeTypeAlias.typeAlias
 }
-

native/commonizer/testData/classifierCommonization/typeAliases/commonized/common/package_root.kt

@@ -1,5 +1,4 @@
 expect class A()
-
 // Lifted up type aliases:
 typealias B = A // class at the RHS
 typealias C = A // TA at the RHS, expanded to the same class
@@ -40,10 +39,11 @@ typealias U = A // same nullability of the RHS class
 
 expect class V // different nullability of the RHS class
 typealias W = A // same nullability of the RHS TA
+expect class X // different nullability of the RHS TA
 typealias Y = V // TA at the RHS with the different nullability of own RHS
 
 // Supertypes:
-expect class FILE : kotlinx.cinterop.CStructVar
+expect class FILE expect constructor(): kotlinx.cinterop.CStructVar
 
 typealias uuid_t = kotlinx.cinterop.CArrayPointer<kotlinx.cinterop.UByteVar>
 typealias __darwin_uuid_t = kotlinx.cinterop.CArrayPointer<kotlinx.cinterop.UByteVar>

native/commonizer/testData/classifierCommonization/visibility/commonized/common/package_root.kt

@@ -6,18 +6,18 @@ public typealias E1 = A1
 protected typealias E2 = A1
 internal typealias E3 = A1
 
-public expect class E4
+public expect class E4()
 
 protected typealias F1 = A1
 
-public expect class F2
+public expect class F2()
-public expect class F3
+public expect class F3()
 
 internal typealias G1 = A1
 
-public expect class G2
+public expect class G2()
 
-public expect class H1
+public expect class H1()
 
 public typealias I1 = A1
 public typealias I2 = B1

native/commonizer/testData/generalCommonization/annotations/commonized/common/package_root.kt

@@ -19,4 +19,4 @@ expect class AnnotatedClass(value: String) {
 }
 typealias AnnotatedLiftedUpTypeAlias = AnnotatedClass
 
-expect class AnnotatedNonLiftedUpTypeAlias
+expect class AnnotatedNonLiftedUpTypeAlias expect constructor(expect val value: String)

native/commonizer/tests/org/jetbrains/kotlin/commonizer/core/TypeCommonizerTest.kt

@@ -272,14 +272,6 @@ class TypeCommonizerTest : AbstractCommonizerTest<CirType, CirType>() {
         shouldFailOnFirstVariant = true
     )
 
-    @Test
-    // why success: expect class/actual TAs
-    fun taTypesInUserPackageWithDifferentClasses() = doTestSuccess(
-        expected = mockClassType("org/sample/FooAlias"),
-        mockTAType("org/sample/FooAlias") { mockClassType("org/sample/Foo") },
-        mockTAType("org/sample/FooAlias") { mockClassType("org/sample/Bar") }
-    )
-
     @Test
     // why success: short-circuiting & lifting up
     fun multilevelTATypesInUserPackageWithSameNameAndRightHandSideClass1() = doTestSuccess(
@@ -338,28 +330,6 @@ class TypeCommonizerTest : AbstractCommonizerTest<CirType, CirType>() {
         }
     )
 
-    @Test
-    // why success: lifting up outer TA and expect class for inner TA
-    fun multilevelTATypesInUserPackageWithSameNameAndRightHandSideClass4() = doTestSuccess(
-        expected = mockTAType("org/sample/FooAlias") {
-            mockTAType("org/sample/FooAliasL2") {
-                mockClassType("org/sample/Foo")
-            }
-        },
-
-        mockTAType("org/sample/FooAlias") {
-            mockTAType("org/sample/FooAliasL2") {
-                mockClassType("org/sample/Bar")
-            }
-        },
-
-        mockTAType("org/sample/FooAlias") {
-            mockTAType("org/sample/FooAliasL2") {
-                mockClassType("org/sample/Baz")
-            }
-        }
-    )
-
     @Test
     // why success: types with the same nullability are treated as equal
     fun taTypesInKotlinPackageWithSameNullability1() = doTestSuccess(
@@ -432,30 +402,16 @@ class TypeCommonizerTest : AbstractCommonizerTest<CirType, CirType>() {
     fun taTypesInUserPackageWithDifferentNullability1() = doTestFailure(
         mockTAType("org/sample/FooAlias", nullable = false) { mockClassType("org/sample/Foo") },
         mockTAType("org/sample/FooAlias", nullable = false) { mockClassType("org/sample/Foo") },
-        mockTAType("org/sample/FooAlias", nullable = true) { mockClassType("org/sample/Foo") }
+        mockTAType("org/sample/FooAlias", nullable = true) { mockClassType("org/sample/Foo") },
+        shouldFailOnFirstVariant = true
     )
 
     @Test(expected = IllegalCommonizerStateException::class)
     fun taTypesInUserPackageWithDifferentNullability2() = doTestFailure(
         mockTAType("org/sample/FooAlias", nullable = true) { mockClassType("org/sample/Foo") },
         mockTAType("org/sample/FooAlias", nullable = true) { mockClassType("org/sample/Foo") },
-        mockTAType("org/sample/FooAlias", nullable = false) { mockClassType("org/sample/Foo") }
+        mockTAType("org/sample/FooAlias", nullable = false) { mockClassType("org/sample/Foo") },
-    )
+        shouldFailOnFirstVariant = true
-
-    @Test
-    // why success: nullability of underlying type does not matter if expect class/actual TAs created
-    fun taTypesInUserPackageWithDifferentNullability3() = doTestSuccess(
-        expected = mockClassType("org/sample/FooAlias"),
-        mockTAType("org/sample/FooAlias") { mockClassType("org/sample/Foo", nullable = false) },
-        mockTAType("org/sample/FooAlias") { mockClassType("org/sample/Foo", nullable = true) }
-    )
-
-    @Test
-    // why success: nullability of underlying type does not matter if expect class/actual TAs created
-    fun taTypesInUserPackageWithDifferentNullability4() = doTestSuccess(
-        expected = mockClassType("org/sample/FooAlias"),
-        mockTAType("org/sample/FooAlias") { mockClassType("org/sample/Foo", nullable = true) },
-        mockTAType("org/sample/FooAlias") { mockClassType("org/sample/Foo", nullable = false) }
     )
 
     private fun prepareCache(variants: Array<out CirClassOrTypeAliasType>) {
@@ -469,7 +425,7 @@ class TypeCommonizerTest : AbstractCommonizerTest<CirType, CirType>() {
                             storageManager = LockBasedStorageManager.NO_LOCKS,
                             size = variants.size,
                             classifiers = classifiers,
-                            parentCommonDeclaration = null,
+                            condition = CommonizerCondition.none(),
                             classId = type.classifierId
                         )
                     }

native/commonizer/tests/org/jetbrains/kotlin/commonizer/hierarchical/HierarchicalClassAndTypeAliasCommonizationTest.kt

@@ -104,4 +104,141 @@ class HierarchicalClassAndTypeAliasCommonizationTest : AbstractInlineSourcesComm
         """.trimIndent()
         )
     }
+
+    fun `test follow typeAlias on both platforms`() {
+        val result = commonize {
+            outputTarget("(a, b)")
+            simpleSingleSourceTarget(
+                "a", """
+                class A {
+                    val x: Int = 42
+                }
+                typealias X = A
+            """.trimIndent()
+            )
+
+            simpleSingleSourceTarget(
+                "b", """
+                class B {
+                    val x: Int = 42
+                }
+                typealias X = B
+                """.trimIndent()
+            )
+        }
+
+        result.assertCommonized(
+            "(a, b)", """
+                expect class X expect constructor() {
+                    expect val x: Int
+                }
+            """.trimIndent()
+        )
+    }
+
+    fun `test follow exact same typeAlias on both platforms`() {
+        val result = commonize {
+            outputTarget("(a, b)")
+            simpleSingleSourceTarget(
+                "a", """
+                class AB {
+                    val x: Int = 42
+                }
+                typealias X = AB
+            """.trimIndent()
+            )
+
+            simpleSingleSourceTarget(
+                "b", """
+                class AB {
+                    val x: Int = 42
+                }
+                typealias X = AB
+                """.trimIndent()
+            )
+        }
+
+        result.assertCommonized(
+            "(a, b)", """
+                expect class AB expect constructor() {
+                    expect val x: Int
+                }
+                typealias X = AB
+            """.trimIndent()
+        )
+    }
+
+    fun `test aliased class with companion`() {
+        val result = commonize {
+            outputTarget("(a, b)")
+            simpleSingleSourceTarget(
+                "a", """
+                    class A {
+                        companion object
+                    }
+                    
+                    typealias X = A
+                """.trimIndent()
+            )
+            simpleSingleSourceTarget(
+                "b", """
+                    class X {
+                        companion object
+                    }
+                """.trimIndent()
+            )
+        }
+
+        result.assertCommonized("(a, b)", """expect class X expect constructor()""")
+    }
+
+    fun `test typeAlias with nullability`() {
+        val result = commonize {
+            outputTarget("(a, b)")
+            simpleSingleSourceTarget(
+                "a", """
+                    class A
+                    typealias X = A?
+                """.trimIndent()
+            )
+
+            simpleSingleSourceTarget(
+                "b", """
+                    class B
+                    typealias X = B
+                """.trimIndent()
+            )
+        }
+
+        result.assertCommonized("(a, b)", """expect class X""")
+    }
+
+    fun `test typeAlias chain with nullability`() {
+        val result = commonize {
+            outputTarget("(a, b)")
+            simpleSingleSourceTarget(
+                "a", """
+                    class AB
+                    typealias V = AB?
+                    typealias Y = V
+                """.trimIndent()
+            )
+
+            simpleSingleSourceTarget(
+                "b", """
+                    class AB
+                    typealias V = AB
+                    typealias Y = V
+                """.trimIndent()
+            )
+        }
+
+        result.assertCommonized(
+            "(a, b)", """
+                expect class AB expect constructor()
+                expect class V
+                typealias Y = V
+            """.trimIndent()
+        )
+    }
 }

native/commonizer/tests/org/jetbrains/kotlin/commonizer/hierarchical/HierarchicalTypeAliasCommonizationTest.kt

@@ -111,7 +111,7 @@ class HierarchicalTypeAliasCommonizationTest : AbstractInlineSourcesCommonizatio
             "(e,f)", """expect class x expect constructor()"""
         )
 
-        result.assertCommonized("((a,b), (c,d))", """expect class x""")
+        result.assertCommonized("((a,b), (c,d))", """expect class x expect constructor()""")
-        result.assertCommonized("(((a,b), (c,d)), (e,f))", """expect class x""")
+        result.assertCommonized("(((a,b), (c,d)), (e,f))", """expect class x expect constructor()""")
     }
 }

native/commonizer/tests/org/jetbrains/kotlin/commonizer/transformer/RunTransformationTest.kt

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2010-2021 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.commonizer.transformer
+
+import org.jetbrains.kotlin.commonizer.cir.CirModule
+import org.jetbrains.kotlin.commonizer.cir.CirName
+import org.jetbrains.kotlin.commonizer.cir.markedArtificial
+import org.jetbrains.kotlin.commonizer.mergedtree.buildModuleNode
+import org.jetbrains.kotlin.commonizer.mergedtree.buildRootNode
+import org.jetbrains.kotlin.commonizer.transformer.Checked.Companion.invoke
+import org.jetbrains.kotlin.storage.LockBasedStorageManager
+import org.junit.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+import kotlin.test.assertIs
+
+class RunTransformationTest {
+
+    private val storageManager = LockBasedStorageManager("test")
+
+    @Test
+    fun `fails when attaching non-artificial declarations`() {
+        val badTransformer = CirNodeTransformer { root ->
+            root.modules[CirName.create("bad-module")] = buildModuleNode(storageManager, 1).also { moduleNode ->
+                moduleNode.targetDeclarations[0] = CirModule.create(CirName.create("bad-module"))
+            }
+        }
+
+        val node = buildRootNode(storageManager, 0)
+        assertFailsWith<AssertionError> { badTransformer(node) }
+    }
+
+    @Test
+    fun `when attaching non-artificial declarations`() {
+        val goodTransformer = CirNodeTransformer { root ->
+            assertIs<Checked>(this, "Expected 'Checked' context")
+
+            root.modules[CirName.create("artificial-module")] = buildModuleNode(storageManager, 1).also { moduleNode ->
+                moduleNode.targetDeclarations[0] = CirModule.create(CirName.create("artificial-module")).markedArtificial()
+            }
+        }
+
+        val node = buildRootNode(storageManager, 0)
+        goodTransformer(node)
+
+        assertEquals(CirName.create("artificial-module"), node.modules.values.single().targetDeclarations.single()?.name)
+    }
+}