Make value class with Serializable property automatically Serializable

[Cyberavater]

What is your use-case and why do you need this feature?
example

value class Color(val value: ULong) 

This value class parameter is already serializable, but when we have another wrapper class that we need to be Serializable!

@Serializable
data class Note(
    val title: String,
    val content: String,
    val color: Color,
    val timestamp: Instant = Clock.System.now(),
    @PrimaryKey(autoGenerate = true) val id: Int,
)

Serializer has not been found for type 'Color'. To use context serializer as fallback, explicitly annotate type or property with @Contextual
We need to write a verbose KSerializer, which could be avoided entirely

Describe the solution you'd like
Serialization compiler to be able to properly generate/understand value class without manually writing KSerializer

[JohannesTeichert]

I have the same issue with Instant

[sandwwraith]

While the request itself is reasonable enough, there are fundamental Kotlin compiler plugin limitations — the inability to process a specific class if it is not annotated. Also, the @Serializable annotation can affect class API/ABI, so I think it would be better to write it explicitly on the class.

Maybe it is possible to produce a diagnostic on value class without @Serializable annotation (with serializable property). But I think the lack of annotation will be quite obvious from other compiler errors.

[sandwwraith]

(may be reopened in the future, but no plans for now)