Provide default value information in SerialDescriptor

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

It would be useful to retrieve the kotlin default value from the SerialDescriptor. Schema-based serialization formats that have the ability to specify a default value for a serialized field could use this information to enrich the generated schemas with informations about the default value.

Describe the solution you’d like

The SerialDescriptor should have an additional function that returns the “defaultValue” for an element.

Example:

@Serializable
data class Person(val name : String = "anonymous")
...
serialDescriptor.getElementDefaultValue(0) == "anonymous"

[qwwdfsad]

It still is not really possible. We were thinking about it back in the day and weren’t able to come up with an elegant, complete and sound solution that works consistently over various serialization use-cases.

E.g. consider the following class: @Serializable class Foo(val a: String, val b: String = a + " , but 'b'"). What should getElementDefaultValue(1) return?

And, as a library, we cannot provide an API in our very core that “works 50% of the time if the code is written in one way, but not in the other”, so, unfortunately, we cannot fix it.

[qwwdfsad]

It will be possible, but we are not going to do it for the same reasons: this is a half-baked solution that works 50% of the time. I realize that it solves your particular problem, but what the rest of the users should do?

What getElementDefaultValue should return? What type is it? How to distinguish default null from “this property actually doesn’t have a default value”? What should it return for complex default initializations? How to enforce this contract for authors of user-defined serializers and descriptors?