I'm not sure if we should use DiscordPartialGuild for this. This rather seems to be a union of DiscordUnavailableGuild (which represents this) and DiscordGuild. We might instead introduce a sealed superclass for these two and decide on whether to deserialize it as a DiscordGuild or a DiscordUnavailableGuild based on the presence and true value of the unavailable field.

So something like this:

// supertype for DiscordUnavailableGuild and DiscordGuild
@Serializable(with = DiscordGuildCreateGuildSerializer::class)
public sealed interface DiscordGuildCreateGuild {
    public val id: Snowflake
}

private object DiscordGuildCreateGuildSerializer : JsonContentPolymorphicSerializer<DiscordGuildCreateGuild>(DiscordGuildCreateGuild::class) {
    override fun selectDeserializer(element: JsonElement) =
        when (element.jsonObject["unavailable"]?.jsonPrimitive?.boolean) {
            true -> DiscordUnavailableGuild.serializer()
            false, null -> DiscordGuild.serializer()
        }
}

DiscordGuild.unavailable could then also be removed.

This at least works for the available case in the basic test I did (unavailable is hard to reproduce).

do we even need a super type 🤔

I mean what should we put in the event class if there is no supertype? We don't have union types.

this also supports my suggestion: discord/discord-api-docs@745685b