[Commonizer] Split type substitution into forward and backwards

^KT-48288

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

@@ -85,3 +85,32 @@ internal tailrec fun computeExpandedType(underlyingType: CirClassOrTypeAliasType
 
 @Suppress("unused", "NOTHING_TO_INLINE")
 internal inline fun CirDeclaration.unsupported(): Nothing = error("This method should never be called on ${this::class.java}, $this")
+
+internal fun CirClassOrTypeAliasType.withParentArguments(
+    parentArguments: List<CirTypeProjection>, parentIsMarkedNullable: Boolean
+): CirClassOrTypeAliasType {
+    val newIsMarkedNullable = isMarkedNullable || parentIsMarkedNullable
+
+    val newArguments = arguments.map { oldArgument ->
+        if (oldArgument is CirRegularTypeProjection) {
+            val oldArgumentType = oldArgument.type
+            if (oldArgumentType is CirTypeParameterType) {
+                return@map parentArguments[oldArgumentType.index]
+            }
+        }
+        oldArgument
+    }
+
+    return when (val newUnderlyingType = makeNullableIfNecessary(newIsMarkedNullable).withArguments(newArguments)) {
+        this -> this
+        is CirClassType -> newUnderlyingType
+        is CirTypeAliasType -> newUnderlyingType.withUnderlyingType(
+            newUnderlyingType.underlyingType.withParentArguments(newArguments, newIsMarkedNullable)
+        )
+    }
+}
+
+internal tailrec fun CirClassOrTypeAliasType.expandedType(): CirClassType = when (this) {
+    is CirClassType -> this
+    is CirTypeAliasType -> this.underlyingType.expandedType()
+}

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

@@ -92,44 +92,51 @@ internal class ClassOrTypeAliasTypeCommonizer(
         }
     }
 
+    @Suppress("KotlinConstantConditions") // Improved readability
     private fun selectClassifierId(types: List<CirClassOrTypeAliasType>): CirEntityId? {
         types.singleDistinctValueOrNull { it.classifierId }?.let { return it }
 
-        if (typeCommonizer.options.enableTypeAliasSubstitution) {
-            val commonId = types.singleDistinctValueOrNull {
-                classifiers.commonClassifierIdResolver.findCommonId(it.classifierId)
-            } ?: return null
+        val forwardSubstitutionAllowed = typeCommonizer.options.enableForwardTypeAliasSubstitution
+        val backwardsSubstitutionAllowed = typeCommonizer.options.enableBackwardsTypeAliasSubstitution
 
-            return commonId.aliases.maxByOrNull { candidate -> types.count { it.classifierId == candidate } }!!
-        } else return null
-    }
-}
-
-private fun CirClassOrTypeAliasType.withParentArguments(
-    parentArguments: List<CirTypeProjection>, parentIsMarkedNullable: Boolean
-): CirClassOrTypeAliasType {
-    val newIsMarkedNullable = isMarkedNullable || parentIsMarkedNullable
-
-    val newArguments = arguments.map { oldArgument ->
-        if (oldArgument is CirRegularTypeProjection) {
-            val oldArgumentType = oldArgument.type
-            if (oldArgumentType is CirTypeParameterType) {
-                return@map parentArguments[oldArgumentType.index]
-            }
+        /* No substitution allowed in any direction */
+        if (!forwardSubstitutionAllowed && !backwardsSubstitutionAllowed) {
+            return null
         }
-        oldArgument
+
+        val commonId = types.singleDistinctValueOrNull {
+            classifiers.commonClassifierIdResolver.findCommonId(it.classifierId)
+        } ?: return null
+
+        val candidates = when {
+            forwardSubstitutionAllowed && backwardsSubstitutionAllowed -> commonId.aliases
+
+            /* Only forward substitutions allowed -> Only substitute with any underlying type */
+            forwardSubstitutionAllowed -> commonId.aliases.filter { candidate ->
+                types.all { type -> type.isAnyUnderlyingClassifier(candidate) }
+            }
+
+            /* Only backward substitutions allowed -> Only substitute with any typealias pointing to this types */
+            backwardsSubstitutionAllowed -> commonId.aliases.filter { candidate ->
+                types.none { type -> type.isAnyUnderlyingClassifier(candidate) }
+            }
+
+            else -> error("Failed to select classifierId: Unexpected when branch")
+        }
+
+        if (candidates.isEmpty()) return null
+
+        return candidates.maxByOrNull { candidate -> types.count { it.classifierId == candidate } }!!
     }
 
-    return when (val newUnderlyingType = makeNullableIfNecessary(newIsMarkedNullable).withArguments(newArguments)) {
-        this -> this
-        is CirClassType -> newUnderlyingType
-        is CirTypeAliasType -> newUnderlyingType.withUnderlyingType(
-            newUnderlyingType.underlyingType.withParentArguments(newArguments, newIsMarkedNullable)
-        )
+    private fun CirClassOrTypeAliasType.isAnyUnderlyingClassifier(classifierId: CirEntityId): Boolean {
+        return when (this) {
+            is CirClassType -> false
+            is CirTypeAliasType -> this.isAnyUnderlyingClassifier(classifierId)
+        }
+    }
+
+    private fun CirTypeAliasType.isAnyUnderlyingClassifier(classifierId: CirEntityId): Boolean {
+        return underlyingType.classifierId == classifierId || underlyingType.isAnyUnderlyingClassifier(classifierId)
     }
 }
-
-internal tailrec fun CirClassOrTypeAliasType.expandedType(): CirClassType = when (this) {
-    is CirClassType -> this
-    is CirTypeAliasType -> this.underlyingType.expandedType()
-}

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

@@ -18,7 +18,7 @@ class TypeAliasCommonizer(
 ) : NullableSingleInvocationCommonizer<CirTypeAlias> {
 
     private val typeCommonizer = typeCommonizer.withOptions {
-        withTypeAliasSubstitutionEnabled(false).withOptimisticNumberTypeCommonizationEnabled(true)
+        withBackwardsTypeAliasSubstitutionEnabled(false).withOptimisticNumberTypeCommonizationEnabled(true)
     }
 
     override fun invoke(values: List<CirTypeAlias>): CirTypeAlias? {

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

@@ -36,7 +36,8 @@ class TypeCommonizer(
     data class Options(
         val enableOptimisticNumberTypeCommonization: Boolean = false,
         val enableCovariantNullabilityCommonization: Boolean = false,
-        val enableTypeAliasSubstitution: Boolean = true
+        val enableForwardTypeAliasSubstitution: Boolean = true,
+        val enableBackwardsTypeAliasSubstitution: Boolean = true,
     ) {
 
         fun withOptimisticNumberTypeCommonizationEnabled(enabled: Boolean = true): Options {
@@ -49,9 +50,18 @@ class TypeCommonizer(
             else copy(enableCovariantNullabilityCommonization = enabled)
         }
 
+        fun withForwardTypeAliasSubstitutionEnabled(enabled: Boolean = true): Options {
+            return if (enableForwardTypeAliasSubstitution == enabled) this
+            else copy(enableForwardTypeAliasSubstitution = enabled)
+        }
+
+        fun withBackwardsTypeAliasSubstitutionEnabled(enabled: Boolean = true): Options {
+            return if (enableBackwardsTypeAliasSubstitution == enabled) this
+            else copy(enableBackwardsTypeAliasSubstitution = enabled)
+        }
+
         fun withTypeAliasSubstitutionEnabled(enabled: Boolean = true): Options {
-            return if (enableTypeAliasSubstitution == enabled) this
-            else copy(enableTypeAliasSubstitution = enabled)
+            return withForwardTypeAliasSubstitutionEnabled(enabled).withBackwardsTypeAliasSubstitutionEnabled(enabled)
         }
 
         companion object {

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

@@ -6,11 +6,7 @@
 package org.jetbrains.kotlin.commonizer.transformer
 
 import org.jetbrains.kotlin.commonizer.TargetDependent
-import org.jetbrains.kotlin.commonizer.cir.CirEntityId
-import org.jetbrains.kotlin.commonizer.cir.CirName
-import org.jetbrains.kotlin.commonizer.cir.CirType
-import org.jetbrains.kotlin.commonizer.cir.CirTypeAliasType
-import org.jetbrains.kotlin.commonizer.core.expandedType
+import org.jetbrains.kotlin.commonizer.cir.*
 import org.jetbrains.kotlin.commonizer.mergedtree.CirClassifierIndex
 import org.jetbrains.kotlin.commonizer.mergedtree.CirTypeSubstitutor
 import org.jetbrains.kotlin.commonizer.mergedtree.findTypeAlias

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

@@ -618,7 +618,7 @@ class HierarchicalOptimisticNumbersTypeCommonizerTest : AbstractInlineSourcesCom
                 @UnsafeNumber(["a: kotlin.Int", "b: kotlin.Long"])
                 typealias B = A
                 @UnsafeNumber(["a: kotlin.Int", "b: kotlin.Long"])
-                typealias X = Int
+                typealias X = A
             """.trimIndent()
         )
     }