How to send a `vararg variadicArguments: kotlin.Any?` to a GObject native call with Kotlin Native?

Question

I'm working on a GIR generator to create Kotlin Native bindings for GTK and other GObject based libraries. I reached a stage where I can almost compile the bindings for GLib but I'm stuck with the handling of varargs.

For example g_string_append_printf, which is mapped with this:

kotlinx.cinterop.internal.CCall public external fun g_string_append_printf(string: kotlinx.cinterop.CValuesRef<native.glib.GString /* = native.glib._GString */>?, @kotlinx.cinterop.internal.CCall.CString format: kotlin.String?, vararg variadicArguments: kotlin.Any?): kotlin.Unit { /* compiled code */ }

It seems to expect a vararg variadicArguments: kotlin.Any?, but if I send that to it like this:

    public fun appendPrintf(format: String, vararg variadicArguments: Any): Unit {
        g_string_append_printf(cPointer.reinterpret(), format, variadicArguments)
    }

I get this error when I build the module:

type kotlin.Array<out kotlin.Any>  is not supported here: doesn't correspond to any C type

The GIR parameter only gives a name (...) and has a tag varargs:

          <parameter name="..." transfer-ownership="none">
            <doc xml:space="preserve"
                 filename="glib-2.0.c"
                 line="32361">the parameters to insert into the format string</doc>
            <varargs/>
          </parameter>

But there are no other information about the type.

What should this vararg variadicArguments: kotlin.Any? be converted to?

Answer 1

EDIT: this is not supported in Kotlin/Native at the moment, see https://youtrack.jetbrains.com/issue/KT-56164

Original answer:

I'm not very experienced in Kotlin/Native nor CInterop, but I know that to pass an array to a function that expects a vararg, you have to explicitly spread it (unlike in Java) using the spread operator (*variadicArguments):

public fun appendPrintf(format: String, vararg variadicArguments: Any): Unit {
    g_string_append_printf(cPointer.reinterpret(), format, *variadicArguments)
}

Here is the relevant piece of the doc:

If you already have an array and want to pass its contents to the function, use the spread operator (prefix the array with *)