json: Use @SerialName of inline polymorphic children

formats/json-tests/commonTest/src/kotlinx/serialization/features/sealed/SealedInterfacesInlineSerialNameTest.kt

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2017-2024 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.serialization.features.sealed
+
+import kotlinx.serialization.*
+import kotlinx.serialization.json.*
+import kotlin.jvm.*
+import kotlin.test.*
+
+class SealedInterfacesInlineSerialNameTest : JsonTestBase() {
+    @Serializable
+    data class Child1Value(
+        val a: Int,
+        val b: String
+    )
+
+    @Serializable
+    data class Child2Value(
+        val c: Int,
+        val d: String
+    )
+
+    @Serializable
+    sealed interface Parent
+
+    @Serializable
+    @SerialName("child1")
+    @JvmInline
+    value class Child1(val value: Child1Value) : Parent
+
+    @Serializable
+    @SerialName("child2")
+    @JvmInline
+    value class Child2(val value: Child2Value) : Parent
+
+    // From https://github.com/Kotlin/kotlinx.serialization/issues/2288
+    @Test
+    fun testSealedInterfaceInlineSerialName() {
+        val messages = listOf(
+            Child1(Child1Value(1, "one")),
+            Child2(Child2Value(2, "two"))
+        )
+        assertJsonFormAndRestored(
+            serializer(),
+            messages,
+            """[{"type":"child1","a":1,"b":"one"},{"type":"child2","c":2,"d":"two"}]"""
+        )
+    }
+}

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

@@ -43,6 +43,7 @@ internal class StreamingJsonEncoder(
     // Forces serializer to wrap all values into quotes
     private var forceQuoting: Boolean = false
     private var polymorphicDiscriminator: String? = null
+    private var polymorphicSerialName: String? = null
 
     init {
         val i = mode.ordinal
@@ -66,12 +67,12 @@ internal class StreamingJsonEncoder(
         }
     }
 
-    private fun encodeTypeInfo(descriptor: SerialDescriptor) {
+    private fun encodeTypeInfo(discriminator: String, serialName: String) {
         composer.nextItem()
-        encodeString(polymorphicDiscriminator!!)
+        encodeString(discriminator)
         composer.print(COLON)
         composer.space()
-        encodeString(descriptor.serialName)
+        encodeString(serialName)
     }
 
     override fun beginStructure(descriptor: SerialDescriptor): CompositeEncoder {
@@ -81,9 +82,11 @@ internal class StreamingJsonEncoder(
             composer.indent()
         }
 
-        if (polymorphicDiscriminator != null) {
-            encodeTypeInfo(descriptor)
+        val discriminator = polymorphicDiscriminator
+        if (discriminator != null) {
+            encodeTypeInfo(discriminator, polymorphicSerialName ?: descriptor.serialName)
             polymorphicDiscriminator = null
+            polymorphicSerialName = null
         }
 
         if (mode == newMode) {
@@ -160,6 +163,7 @@ internal class StreamingJsonEncoder(
         when {
             descriptor.isUnsignedNumber -> StreamingJsonEncoder(composerAs(::ComposerForUnsignedNumbers), json, mode, null)
             descriptor.isUnquotedLiteral -> StreamingJsonEncoder(composerAs(::ComposerForUnquotedLiterals), json, mode, null)
+            polymorphicDiscriminator != null -> apply { polymorphicSerialName = descriptor.serialName }
             else                        -> super.encodeInline(descriptor)
         }
 

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

@@ -35,7 +35,8 @@ internal fun <T> Json.readPolymorphicJson(
 
 private sealed class AbstractJsonTreeDecoder(
     override val json: Json,
-    open val value: JsonElement
+    open val value: JsonElement,
+    protected val polymorphicDiscriminator: String? = null
 ) : NamedValueDecoder(), JsonDecoder {
 
     override val serializersModule: SerializersModule
@@ -63,7 +64,7 @@ private sealed class AbstractJsonTreeDecoder(
                 { JsonTreeMapDecoder(json, cast(currentObject, descriptor)) },
                 { JsonTreeListDecoder(json, cast(currentObject, descriptor)) }
             )
-            else -> JsonTreeDecoder(json, cast(currentObject, descriptor))
+            else -> JsonTreeDecoder(json, cast(currentObject, descriptor), polymorphicDiscriminator)
         }
     }
 
@@ -159,11 +160,15 @@ private sealed class AbstractJsonTreeDecoder(
 
     override fun decodeInline(descriptor: SerialDescriptor): Decoder {
         return if (currentTagOrNull != null) super.decodeInline(descriptor)
-        else JsonPrimitiveDecoder(json, value).decodeInline(descriptor)
+        else JsonPrimitiveDecoder(json, value, polymorphicDiscriminator).decodeInline(descriptor)
     }
 }
 
-private class JsonPrimitiveDecoder(json: Json, override val value: JsonElement) : AbstractJsonTreeDecoder(json, value) {
+private class JsonPrimitiveDecoder(
+    json: Json,
+    override val value: JsonElement,
+    polymorphicDiscriminator: String? = null
+) : AbstractJsonTreeDecoder(json, value, polymorphicDiscriminator) {
 
     init {
         pushTag(PRIMITIVE_TAG)
@@ -180,9 +185,9 @@ private class JsonPrimitiveDecoder(json: Json, override val value: JsonElement)
 private open class JsonTreeDecoder(
     json: Json,
     override val value: JsonObject,
-    private val polyDiscriminator: String? = null,
+    polymorphicDiscriminator: String? = null,
     private val polyDescriptor: SerialDescriptor? = null
-) : AbstractJsonTreeDecoder(json, value) {
+) : AbstractJsonTreeDecoder(json, value, polymorphicDiscriminator) {
     private var position = 0
     private var forceNull: Boolean = false
     /*
@@ -251,7 +256,7 @@ private open class JsonTreeDecoder(
         // in endStructure can filter polyDiscriminator out.
         if (descriptor === polyDescriptor) {
             return JsonTreeDecoder(
-                json, cast(currentObject(), polyDescriptor), polyDiscriminator, polyDescriptor
+                json, cast(currentObject(), polyDescriptor), polymorphicDiscriminator, polyDescriptor
             )
         }
 
@@ -271,7 +276,7 @@ private open class JsonTreeDecoder(
         }
 
         for (key in value.keys) {
-            if (key !in names && key != polyDiscriminator) {
+            if (key !in names && key != polymorphicDiscriminator) {
                 throw UnknownKeyException(key, value.toString())
             }
         }

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

@@ -35,6 +35,7 @@ private sealed class AbstractJsonTreeEncoder(
     protected val configuration = json.configuration
 
     private var polymorphicDiscriminator: String? = null
+    private var polymorphicSerialName: String? = null
 
     override fun elementName(descriptor: SerialDescriptor, index: Int): String =
         descriptor.getJsonElementName(json, index)
@@ -112,8 +113,12 @@ private sealed class AbstractJsonTreeEncoder(
         }
 
     override fun encodeInline(descriptor: SerialDescriptor): Encoder {
-        return if (currentTagOrNull != null) super.encodeInline(descriptor)
-        else JsonPrimitiveEncoder(json, nodeConsumer).encodeInline(descriptor)
+        return if (currentTagOrNull != null) {
+            if (polymorphicDiscriminator != null) polymorphicSerialName = descriptor.serialName
+            super.encodeInline(descriptor)
+        } else {
+            JsonPrimitiveEncoder(json, nodeConsumer).encodeInline(descriptor)
+        }
     }
 
     @SuppressAnimalSniffer // Long(Integer).toUnsignedString(long)
@@ -148,9 +153,11 @@ private sealed class AbstractJsonTreeEncoder(
             else -> JsonTreeEncoder(json, consumer)
         }
 
-        if (polymorphicDiscriminator != null) {
-            encoder.putElement(polymorphicDiscriminator!!, JsonPrimitive(descriptor.serialName))
+        val discriminator = polymorphicDiscriminator
+        if (discriminator != null) {
+            encoder.putElement(discriminator, JsonPrimitive(polymorphicSerialName ?: descriptor.serialName))
             polymorphicDiscriminator = null
+            polymorphicSerialName = null
         }
 
         return encoder