[Bug] Inline value class can be successfully serialized to a json string, but fails to be deserialized from a json string !

[hehua2008]

Describe the bug
A inline value class SpecificTool, implementing a sealed interface ToolChoice, can be successfully serialized to a json string, but fails to be deserialized from a json string !

Test code

import kotlinx.serialization.SerialName
import kotlinx.serialization.Serializable
import kotlinx.serialization.json.Json

@Serializable
data class Request(
    /**
     * Controls tool usage: `none`, `auto`, `required`, or specific tool.
     */
    @SerialName("tool_choice") val toolChoice: ToolChoice? = null,
)

@Serializable
sealed interface ToolChoice {
    @Serializable
    @JvmInline
    value class StringTool(val value: String) : ToolChoice

    @Serializable
    data class SpecificTool(
        /**
         * Type of tool choice: `function`.
         */
        @SerialName("type") val type: String = "function",
        /**
         * Function to call.
         */
        @SerialName("function") val function: FunctionChoice
    ) : ToolChoice {
        @Serializable
        data class FunctionChoice(
            /**
             * Name of the function to call.
             */
            @SerialName("name") val name: String
        )
    }
}

fun main() {
    val jsonDefault = Json {
        classDiscriminator = "json_class_type"
        ignoreUnknownKeys = true
        encodeDefaults = true
    }

    val stringTool = ToolChoice.StringTool("auto")
    val request1 = Request(stringTool)
    val request1_json = jsonDefault.encodeToString(request1)
    println(request1_json)

    val specificTool = ToolChoice.SpecificTool("function", ToolChoice.SpecificTool.FunctionChoice("testFunction"))
    val request2 = Request(specificTool)
    val request2_json = jsonDefault.encodeToString(request2)
    println(request2_json)

    val request2New = jsonDefault.decodeFromString<Request>(request2_json)
    println(request2New)

    val request1New = jsonDefault.decodeFromString<Request>(request1_json)
    println(request1New)
}

Test output

{"tool_choice":"auto"}
{"tool_choice":{"json_class_type":"ToolChoice.SpecificTool","type":"function","function":{"name":"testFunction"}}}
Request(toolChoice=SpecificTool(type=function, function=FunctionChoice(name=testFunction)))
Exception in thread "main" kotlinx.serialization.json.internal.JsonDecodingException: Expected JsonObject, but had JsonLiteral as the serialized body of ToolChoice at element: $.tool_choice
JSON input: "auto"
	at kotlinx.serialization.json.internal.JsonExceptionsKt.JsonDecodingException(JsonExceptions.kt:24)
	at kotlinx.serialization.json.internal.JsonExceptionsKt.JsonDecodingException(JsonExceptions.kt:32)
	at kotlinx.serialization.json.internal.StreamingJsonDecoder.decodeSerializableValue(StreamingJsonDecoder.kt:400)
	at kotlinx.serialization.encoding.AbstractDecoder.decodeSerializableValue(AbstractDecoder.kt:43)
	at kotlinx.serialization.encoding.AbstractDecoder.decodeNullableSerializableElement(AbstractDecoder.kt:78)
	at Request$$serializer.deserialize(main.kt:5)
	at Request$$serializer.deserialize(main.kt:5)
	at kotlinx.serialization.json.internal.StreamingJsonDecoder.decodeSerializableValue(StreamingJsonDecoder.kt:69)
	at kotlinx.serialization.json.Json.decodeFromString(Json.kt:149)
	at MainKt.main(main.kt:67)
	at MainKt.main(main.kt)

Expected behavior

{"tool_choice":"auto"}
{"tool_choice":{"json_class_type":"ToolChoice.SpecificTool","type":"function","function":{"name":"testFunction"}}}
Request(toolChoice=SpecificTool(type=function, function=FunctionChoice(name=testFunction)))
Request(toolChoice=StringTool(value=auto))

Environment

• Kotlin version: 2.1.0
• Library version: 1.8.0
• Kotlin platforms: JVM, may be same in JS, Native
• Gradle version: 8.9
• IDE version: Android Studio 2024.2.2
• Other relevant context [e.g. OS version, JRE version, ... ]

[sandwwraith]

Duplicate of #2835. See #2049 (comment) for context.