possibly lazyweb but are there IR APIs for calling...

# compiler

[Zac Sweers]

possibly lazyweb but are there IR APIs for calling expected defaults functions/constructors? This is specifically for cases where the calling generated code is computing the mask values itself at runtime. Currently I'm simulating the existence of the constructor by creating a synthetic one to link against during code gen, but I'm sure there's better ways. With functions I imagine this gets a bit more complex with defaults being static

[bnorm]

Call site default argument transformation happens as a lowering in IR which is performed after IrGenerationExtension. If you set the arguments at the call site to be null, the compiler should automatically convert that to a call to the synthetic function/constructor and calculate all the mask/marker information needed.

Call-site lowering for JVM: https://github.com/JetBrains/kotlin/blob/266fcba624f8e93102ee8aa3ee5f6a4942fc7510/[…]tbrains/kotlin/backend/jvm/lower/JvmDefaultParameterInjector.kt
Declaration-site lowering for JVM: https://github.com/JetBrains/kotlin/blob/266fcba624f8e93102ee8aa3ee5f6a4942fc7510/[…]ins/kotlin/backend/jvm/lower/JvmDefaultArgumentStubGenerator.kt

[Zac Sweers]

Yep I knew about the null args too, unfortunately this is a case where I’m generating a class that doesn’t know the absent args at compile time but also doesn’t want to do reflection heh

[bnorm]

Okay, let me know if I'm understanding this correctly. You have the following class you are trying to generate a JsonAdapter for:

@JsonClass(generateAdapter = true)
value class ValueClass(val i: Int = 0)

And the issues is the adapter should use the default value from the constructor if it is not found when parsing JSON?

class ValueClassJsonAdapter : JsonAdapter<ValueClass>() {
    override fun fromJson(reader: JsonReader): ValueClass? {
        val i = if (reader.hasNext()) reader.nextInt() else /* use default from constructor */
        return ValueClass(i)
    }

    override fun toJson(writer: JsonWriter, value: ValueClass?) {
        if (value != null) writer.value(value.i)
    }
}

[Zac Sweers]

right yeah, though not just for value classes but rather a class with any number of properties

[Zac Sweers]

and since their present values are computed at runtime, this relies on being able to compute the mask at runtime and call the defaults constructor directly

[bnorm]

So kotlinx-serialization achieves this by coping the default IrExpression from the constructor: https://github.com/JetBrains/kotlin/blob/master/plugins/kotlinx-serialization/kotl[…]kotlinx/serialization/compiler/backend/ir/DefaultValuesUtils.kt.
In your case, are you generating the JsonAdaptor as a nested class or a top-level class?

[Zac Sweers]

it's a top-level class currently. Could move it but it would def break where moshi expects the class to be and thus a breaking change 😓

[Zac Sweers]

maybe something for moshi 2 in the future