Properly handle top-level value classes in encodeToJsonElement (#1777)

Fixes #1774

Author: sandwwraith

formats/json/commonMain/src/kotlinx/serialization/json/internal/TreeJsonEncoder.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2020 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ * Copyright 2017-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
  */
 @file:OptIn(ExperimentalSerializationApi::class)
 
@@ -69,7 +69,7 @@ private sealed class AbstractJsonTreeEncoder(
 
     override fun <T> encodeSerializableValue(serializer: SerializationStrategy<T>, value: T) {
         // Writing non-structured data (i.e. primitives) on top-level (e.g. without any tag) requires special output
-        if (currentTagOrNull != null || serializer.descriptor.kind !is PrimitiveKind && serializer.descriptor.kind !== SerialKind.ENUM) {
+        if (currentTagOrNull != null || !serializer.descriptor.carrierDescriptor(serializersModule).requiresTopLevelTag) {
             encodePolymorphically(serializer, value) { polymorphicDiscriminator = it }
         } else JsonPrimitiveEncoder(json, nodeConsumer).apply {
             encodeSerializableValue(serializer, value)
@@ -139,6 +139,9 @@ private sealed class AbstractJsonTreeEncoder(
     }
 }
 
+private val SerialDescriptor.requiresTopLevelTag: Boolean
+    get() = kind is PrimitiveKind || kind === SerialKind.ENUM
+
 internal const val PRIMITIVE_TAG = "primitive" // also used in JsonPrimitiveInput
 
 private class JsonPrimitiveEncoder(

formats/json/commonMain/src/kotlinx/serialization/json/internal/WriteMode.kt

@@ -1,15 +1,15 @@
 /*
- * Copyright 2017-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ * Copyright 2017-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
  */
 @file:OptIn(ExperimentalSerializationApi::class)
 
 package kotlinx.serialization.json.internal
 
 import kotlinx.serialization.*
 import kotlinx.serialization.descriptors.*
-import kotlinx.serialization.json.Json
-import kotlinx.serialization.modules.SerializersModule
-import kotlin.jvm.JvmField
+import kotlinx.serialization.json.*
+import kotlinx.serialization.modules.*
+import kotlin.jvm.*
 
 internal enum class WriteMode(@JvmField val begin: Char, @JvmField val end: Char) {
     OBJ(BEGIN_OBJ, END_OBJ),
@@ -47,6 +47,6 @@ internal inline fun <T, R1 : T, R2 : T> Json.selectMapMode(
 
 internal fun SerialDescriptor.carrierDescriptor(module: SerializersModule): SerialDescriptor = when {
     kind == SerialKind.CONTEXTUAL -> module.getContextualDescriptor(this)?.carrierDescriptor(module) ?: this
-    isInline -> getElementDescriptor(0)
+    isInline -> getElementDescriptor(0).carrierDescriptor(module)
     else     -> this
 }

formats/json/commonTest/src/kotlinx/serialization/features/inline/InlineClassesTest.kt

@@ -15,6 +15,7 @@ import kotlinx.serialization.*
 import kotlinx.serialization.builtins.*
 import kotlinx.serialization.encoding.*
 import kotlinx.serialization.json.*
+import kotlinx.serialization.modules.*
 import kotlinx.serialization.test.*
 import kotlin.jvm.*
 import kotlin.test.*
@@ -72,11 +73,60 @@ value class ResourceId(val id: String)
 value class ResourceType(val type: String)
 
 @Serializable
-data class ResourceIdentifier(val id: ResourceId, val type: ResourceType)
+@JvmInline
+value class ResourceKind(val kind: SampleEnum)
+
+@Serializable
+data class ResourceIdentifier(val id: ResourceId, val type: ResourceType, val type2: ValueWrapper)
+
+@Serializable @JvmInline
+value class ValueWrapper(val wrapped: ResourceType)
 
 class InlineClassesTest : JsonTestBase() {
     private val precedent: UInt = Int.MAX_VALUE.toUInt() + 10.toUInt()
 
+    @Test
+    fun testTopLevel() = noLegacyJs {
+        assertJsonFormAndRestored(
+            ResourceType.serializer(),
+            ResourceType("foo"),
+            """"foo"""",
+        )
+    }
+
+    @Test
+    fun testTopLevelOverEnum() = noLegacyJs {
+        assertJsonFormAndRestored(
+            ResourceKind.serializer(),
+            ResourceKind(SampleEnum.OptionC),
+            """"OptionC"""",
+        )
+    }
+
+    @Test
+    fun testTopLevelWrapper() = noLegacyJs {
+        assertJsonFormAndRestored(
+            ValueWrapper.serializer(),
+            ValueWrapper(ResourceType("foo")),
+            """"foo"""",
+        )
+    }
+
+    @Test
+    fun testTopLevelContextual() = noLegacyJs {
+        val module = SerializersModule {
+            contextual<ResourceType>(ResourceType.serializer())
+        }
+        val json = Json(default) { serializersModule = module }
+        assertJsonFormAndRestored(
+            ContextualSerializer(ResourceType::class),
+            ResourceType("foo"),
+            """"foo"""",
+            json
+        )
+    }
+
+
     @Test
     fun testSimpleContainer() = noLegacyJs {
         assertJsonFormAndRestored(
@@ -106,8 +156,8 @@ class InlineClassesTest : JsonTestBase() {
     fun testInlineClassesWithStrings() = noLegacyJs {
         assertJsonFormAndRestored(
             ResourceIdentifier.serializer(),
-            ResourceIdentifier(ResourceId("resId"), ResourceType("resType")),
-            """{"id":"resId","type":"resType"}"""
+            ResourceIdentifier(ResourceId("resId"), ResourceType("resType"), ValueWrapper(ResourceType("wrappedType"))),
+            """{"id":"resId","type":"resType","type2":"wrappedType"}"""
         )
     }