[Commonizer] Initial implementation for nullable return type commonization

^KT-48567

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

@@ -5,21 +5,21 @@
 
 package org.jetbrains.kotlin.commonizer.core
 
-import org.jetbrains.kotlin.commonizer.cir.CirFunctionOrProperty
-import org.jetbrains.kotlin.commonizer.cir.CirName
+import org.jetbrains.kotlin.commonizer.cir.*
 import org.jetbrains.kotlin.commonizer.mergedtree.CirKnownClassifiers
+import org.jetbrains.kotlin.commonizer.utils.safeCastValues
 import org.jetbrains.kotlin.descriptors.CallableMemberDescriptor
 import org.jetbrains.kotlin.descriptors.CallableMemberDescriptor.Kind.DELEGATION
 import org.jetbrains.kotlin.descriptors.CallableMemberDescriptor.Kind.SYNTHESIZED
 
 abstract class AbstractFunctionOrPropertyCommonizer<T : CirFunctionOrProperty>(
     classifiers: CirKnownClassifiers
-) : AbstractStandardCommonizer<T, T>() {
+) : AbstractStandardCommonizer<T, T?>() {
     protected lateinit var name: CirName
     protected val modality = ModalityCommonizer()
     protected val visibility = VisibilityCommonizer.lowering()
     protected val extensionReceiver = ExtensionReceiverCommonizer(classifiers)
-    protected val returnType = TypeCommonizer(classifiers).asCommonizer()
+    protected val returnType = ReturnTypeCommonizer(classifiers).asCommonizer()
     protected lateinit var kind: CallableMemberDescriptor.Kind
     protected val typeParameters = TypeParameterListCommonizer(classifiers)
 
@@ -35,6 +35,29 @@ abstract class AbstractFunctionOrPropertyCommonizer<T : CirFunctionOrProperty>(
                 && modality.commonizeWith(next.modality)
                 && visibility.commonizeWith(next)
                 && extensionReceiver.commonizeWith(next.extensionReceiver)
-                && returnType.commonizeWith(next.returnType)
+                && returnType.commonizeWith(next)
                 && typeParameters.commonizeWith(next.typeParameters)
 }
+
+private class ReturnTypeCommonizer(
+    private val classifiers: CirKnownClassifiers,
+) : NullableContextualSingleInvocationCommonizer<CirFunctionOrProperty, CirType> {
+    override fun invoke(values: List<CirFunctionOrProperty>): CirType? {
+        if (values.isEmpty()) return null
+        val isTopLevel = values.all { it.containingClass == null }
+        val returnTypes = if (isTopLevel) makeNullableIfNecessary(values.map { it.returnType }) else values.map { it.returnType }
+        return TypeCommonizer(classifiers).asCommonizer().commonize(returnTypes)
+    }
+
+    private fun makeNullableIfNecessary(types: List<CirType>): List<CirType> {
+        val simpleTypes = types.safeCastValues<CirType, CirSimpleType>() ?: return types
+
+        if (
+            simpleTypes.all { type -> type.isMarkedNullable } ||
+            simpleTypes.none { type -> type.isMarkedNullable }
+        ) return types
+
+        return simpleTypes.map { type -> type.makeNullable() }
+    }
+}
+

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

@@ -13,7 +13,7 @@ class FunctionCommonizer(classifiers: CirKnownClassifiers) : AbstractFunctionOrP
     private val modifiers = FunctionModifiersCommonizer()
     private val valueParameters = CallableValueParametersCommonizer(classifiers)
 
-    override fun commonizationResult(): CirFunction {
+    override fun commonizationResult(): CirFunction? {
         val valueParameters = valueParameters.result
         valueParameters.patchCallables()
 
@@ -27,7 +27,7 @@ class FunctionCommonizer(classifiers: CirKnownClassifiers) : AbstractFunctionOrP
             valueParameters = valueParameters.valueParameters,
             hasStableParameterNames = valueParameters.hasStableParameterNames,
             extensionReceiver = extensionReceiver.result,
-            returnType = returnType.result,
+            returnType = returnType.result ?: return null,
             kind = kind,
             modifiers = modifiers.result
         )

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

@@ -19,4 +19,21 @@ fun <T : Any> NullableSingleInvocationCommonizer<T>.asCommonizer(): Commonizer<T
         collectedValues.add(next)
         return true
     }
-}
+}
+
+
+interface NullableContextualSingleInvocationCommonizer<T : Any, R : Any> {
+    operator fun invoke(values: List<T>): R?
+}
+
+fun <T : Any, R: Any> NullableContextualSingleInvocationCommonizer<T, R>.asCommonizer(): Commonizer<T, R?> = object : Commonizer<T, R?> {
+    private val collectedValues = mutableListOf<T>()
+
+    override val result: R?
+        get() = this@asCommonizer.invoke(collectedValues)
+
+    override fun commonizeWith(next: T): Boolean {
+        collectedValues.add(next)
+        return true
+    }
+}

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

@@ -17,7 +17,7 @@ class PropertyCommonizer(classifiers: CirKnownClassifiers) : AbstractFunctionOrP
     private var isExternal = true
     private lateinit var constCommonizationState: ConstCommonizationState
 
-    override fun commonizationResult(): CirProperty {
+    override fun commonizationResult(): CirProperty? {
         val modality = modality.result
 
         val setter = setter.result?.takeIf { setter ->
@@ -36,7 +36,7 @@ class PropertyCommonizer(classifiers: CirKnownClassifiers) : AbstractFunctionOrP
             containingClass = null, // does not matter
             isExternal = isExternal,
             extensionReceiver = extensionReceiver.result,
-            returnType = returnType.result,
+            returnType = returnType.result ?: return null,
             kind = kind,
             isVar = setter != null,
             isLateInit = false,

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

@@ -122,3 +122,21 @@ inline fun <T> Array<T>.fastForEach(action: (T) -> Unit) {
         action(this[index])
     }
 }
+
+@Suppress("unchecked_cast")
+internal inline fun <T, reified R> List<T>.safeCastValues(): List<R>? {
+    fastForEach { if (it !is R) return null }
+    return this as List<R>
+}
+
+
+internal fun <T : Any> List<T>.singleDistinctValueOrNull(): T? = singleDistinctValueOrNull { it }
+
+internal inline fun <T : Any, R> List<T>.singleDistinctValueOrNull(selector: (T) -> R): R? {
+    if (isEmpty()) return null
+    val value = selector(this[0])
+    for (index in 1 until size) {
+        if (value != selector(this[index])) return null
+    }
+    return value
+}

native/commonizer/tests/org/jetbrains/kotlin/commonizer/AbstractInlineSourcesCommonizationTest.kt

@@ -96,6 +96,10 @@ abstract class AbstractInlineSourcesCommonizationTest : KtInlineSourceCommonizer
             }
         }
 
+        infix fun String.withSource(@Language("kotlin") sourceContent: String) {
+            simpleSingleSourceTarget(this, sourceContent)
+        }
+
         @InlineSourcesCommonizationTestDsl
         fun simpleSingleSourceTarget(target: String, @Language("kotlin") sourceCode: String) {
             simpleSingleSourceTarget(parseCommonizerTarget(target), sourceCode)