[IR, Serialization] Support kotlinx-based (de)serialization of MFVC, nullable MFVC value assignment to nonnull variable

Signed-off-by: Evgeniy.Zhelenskiy <Evgeniy.Zhelenskiy@jetbrains.com>

#KT-1179

plugins/kotlinx-serialization/kotlinx-serialization.backend/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/IrPreGenerator.kt

@@ -12,6 +12,7 @@ import org.jetbrains.kotlin.ir.builders.declarations.addFunction
 import org.jetbrains.kotlin.ir.builders.declarations.addTypeParameter
 import org.jetbrains.kotlin.ir.builders.declarations.addValueParameter
 import org.jetbrains.kotlin.ir.declarations.IrClass
+import org.jetbrains.kotlin.ir.declarations.isSingleFieldValueClass
 import org.jetbrains.kotlin.ir.types.*
 import org.jetbrains.kotlin.ir.util.companionObject
 import org.jetbrains.kotlin.name.Name
@@ -102,7 +103,7 @@ class IrPreGenerator(
         if (irClass.hasCompanionObjectAsSerializer && irClass.companionObject()
                 ?.findPluginGeneratedMethod(SerialEntityNames.LOAD, compilerContext.afterK2) == null
         ) return
-        if (irClass.isValue) return
+        if (irClass.isSingleFieldValueClass) return
         if (irClass.findSerializableSyntheticConstructor() != null) return
         val ctor = irClass.addConstructor {
             origin = SERIALIZATION_PLUGIN_ORIGIN
@@ -121,7 +122,7 @@ class IrPreGenerator(
             ctor.addValueParameter(prop.name, prop.type.makeNullableIfNotPrimitive(), SERIALIZATION_PLUGIN_ORIGIN)
         }
 
-        ctor.addValueParameter(SerialEntityNames.dummyParamName, markerClassSymbol.defaultType, SERIALIZATION_PLUGIN_ORIGIN)
+        ctor.addValueParameter(SerialEntityNames.dummyParamName, markerClassSymbol.defaultType.makeNullable(), SERIALIZATION_PLUGIN_ORIGIN)
     }
 
     private fun IrType.makeNullableIfNotPrimitive() =

plugins/kotlinx-serialization/kotlinx-serialization.backend/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/IrPredicates.kt

@@ -253,4 +253,4 @@ fun IrSimpleType.argumentTypesOrUpperBounds(): List<IrType> {
 }
 
 internal inline fun IrClass.shouldHaveSpecificSyntheticMethods(functionPresenceChecker: () -> IrSimpleFunction?) =
-    !isValue && (isAbstractOrSealedSerializableClass || functionPresenceChecker() != null)
+    !isSingleFieldValueClass && (isAbstractOrSealedSerializableClass || functionPresenceChecker() != null)

plugins/kotlinx-serialization/kotlinx-serialization.backend/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializerIrGenerator.kt

@@ -634,7 +634,7 @@ open class SerializerIrGenerator(
                     irClass,
                     context
                 )
-                serializableDesc.isValue -> SerializerForInlineClassGenerator(irClass, context)
+                serializableDesc.isSingleFieldValueClass -> SerializerForInlineClassGenerator(irClass, context)
                 else -> SerializerIrGenerator(irClass, context, metadataPlugin)
             }
             generator.generate()

plugins/kotlinx-serialization/kotlinx-serialization.k2/src/org/jetbrains/kotlinx/serialization/compiler/fir/checkers/FirSerializationPluginClassChecker.kt

@@ -12,7 +12,7 @@ import org.jetbrains.kotlin.diagnostics.*
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.fir.analysis.checkers.declaration.FirClassChecker
-import org.jetbrains.kotlin.fir.analysis.checkers.isValueClass
+import org.jetbrains.kotlin.fir.analysis.checkers.isSingleFieldValueClass
 import org.jetbrains.kotlin.fir.analysis.checkers.toRegularClassSymbol
 import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.declarations.utils.*
@@ -485,7 +485,7 @@ object FirSerializationPluginClassChecker : FirClassChecker() {
     context(CheckerContext)
     @Suppress("IncorrectFormatting") // KTIJ-22227
     private val ConeKotlinType.isUnsupportedInlineType: Boolean
-        get() = isValueClass(session) && !isPrimitiveOrNullablePrimitive
+        get() = isSingleFieldValueClass(session) && !isPrimitiveOrNullablePrimitive
 
     context(CheckerContext)
     @Suppress("IncorrectFormatting") // KTIJ-22227

plugins/kotlinx-serialization/testData/boxIr/multiFieldValueClasses.kt

@@ -0,0 +1,68 @@
+// TARGET_BACKEND: JVM_IR
+// WITH_STDLIB
+// LANGUAGE: +ValueClasses
+
+import kotlinx.serialization.*
+import kotlinx.serialization.json.*
+import kotlinx.serialization.internal.*
+
+@Serializable
+sealed interface I
+
+@Serializable
+@JvmInline
+value class DPoint(val x: Double, val y: Double): I
+
+@Serializable
+@JvmInline
+value class DSegment(val p1: DPoint, val p2: DPoint): I
+
+@Serializable
+data class PointWrapper(val value: DPoint)
+
+@Serializable
+data class SegmentWrapper(val value: DSegment)
+
+fun box(): String {
+    val p1 = DPoint(1.0, 2.0)
+    val dSegment = DSegment(p1, DPoint(3.0, 4.0))
+    run {
+        val s = Json.encodeToString(DPoint.serializer(), p1)
+        if (s != """{"x":1.0,"y":2.0}""") return s
+        val decoded = Json.decodeFromString(DPoint.serializer(), s)
+        if (p1 != decoded) return decoded.toString()
+    }
+    run {
+        val s = Json.encodeToString(DSegment.serializer(), dSegment)
+        if (s != """{"p1":{"x":1.0,"y":2.0},"p2":{"x":3.0,"y":4.0}}""") return s
+        val decoded = Json.decodeFromString(DSegment.serializer(), s)
+        if (dSegment != decoded) return decoded.toString()
+    }
+    run {
+        val pointWrapper = PointWrapper(p1)
+        val s = Json.encodeToString(PointWrapper.serializer(), pointWrapper)
+        if (s != """{"value":{"x":1.0,"y":2.0}}""") return s
+        val decoded = Json.decodeFromString(PointWrapper.serializer(), s)
+        if (pointWrapper != decoded) return decoded.toString()
+    }
+    run {
+        val segmentWrapper = SegmentWrapper(dSegment)
+        val s = Json.encodeToString(SegmentWrapper.serializer(), segmentWrapper)
+        if (s != """{"value":{"p1":{"x":1.0,"y":2.0},"p2":{"x":3.0,"y":4.0}}}""") return s
+        val decoded = Json.decodeFromString(SegmentWrapper.serializer(), s)
+        if (segmentWrapper != decoded) return decoded.toString()
+    }
+    run {
+        val s = Json.encodeToString(I.serializer(), p1)
+        if (s != """{"type":"DPoint","x":1.0,"y":2.0}""") return s
+        val decoded = Json.decodeFromString(I.serializer(), s)
+        if (p1 != decoded) return decoded.toString()
+    }
+    run {
+        val s = Json.encodeToString(I.serializer(), dSegment)
+        if (s != """{"type":"DSegment","p1":{"x":1.0,"y":2.0},"p2":{"x":3.0,"y":4.0}}""") return s
+        val decoded = Json.decodeFromString(I.serializer(), s)
+        if (dSegment != decoded) return decoded.toString()
+    }
+    return "OK"
+}

plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationFirBlackBoxTestGenerated.java

@@ -93,6 +93,12 @@ public class SerializationFirBlackBoxTestGenerated extends AbstractSerialization
             runTest("plugins/kotlinx-serialization/testData/boxIr/metaSerializable.kt");
         }
 
+        @Test
+        @TestMetadata("multiFieldValueClasses.kt")
+        public void testMultiFieldValueClasses() throws Exception {
+            runTest("plugins/kotlinx-serialization/testData/boxIr/multiFieldValueClasses.kt");
+        }
+
         @Test
         @TestMetadata("multimoduleInheritance.kt")
         public void testMultimoduleInheritance() throws Exception {

plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationIrBoxTestGenerated.java

@@ -91,6 +91,12 @@ public class SerializationIrBoxTestGenerated extends AbstractSerializationIrBoxT
         runTest("plugins/kotlinx-serialization/testData/boxIr/metaSerializable.kt");
     }
 
+    @Test
+    @TestMetadata("multiFieldValueClasses.kt")
+    public void testMultiFieldValueClasses() throws Exception {
+        runTest("plugins/kotlinx-serialization/testData/boxIr/multiFieldValueClasses.kt");
+    }
+
     @Test
     @TestMetadata("multimoduleInheritance.kt")
     public void testMultimoduleInheritance() throws Exception {