For the time being we are forced to use `java.time...

# codereview

[arve]

For the time being we are forced to use java.time.Instant over kotlinx.datetime. We are leveraging the typealias trick to make Instant @Serializable.
This has been working just fine up until now, but today i was writing a specific test and came over something surprising:

When using the aliased type inside a @Serializable data class, it works as expected. But when trying to serialize a naked MyInstant i get an exception 🤯

typealias MyInstant = @Serializable(InstantSerializer::class) java.time.Instant


@Serializable
data class Test(val i: MyInstant)

fun main() {
    val epoch = MyInstant.EPOCH
    println(Json.encodeToString(Test(epoch)))  // {"i":"1970-01-01T00:00:00Z"}
    println(Json.encodeToString(epoch))        // kotlinx.serialization.SerializationException: Serializer for class 'Instant' is not found.
}

[CLOVIS]

The typealias is removed at compile-time, and the typeOf<T>() function that is used within encodeToString() doesn't know about it. Whereas the compiler plugin which generates the @Serializable data class does see it.

[arve]

aah!

[arve]

thanks, that makes sense

[CLOVIS]

Same reason why

@Serializable
data class Test(val i: @Serializable(InstantSerializer::class) MyInstant)

works but

println(Json.encodeToString(@Serializable(InstantSerializer::class) epoch))

doesn't