Macro impl_managed_callback 

macro_rules! impl_managed_callback {
    (
        wrapper:        $wrapper:ty,
        info_ty:        $info_ty:ty,
        return_ty:      $ret:ty,
        default_ret:    $default:expr,
        invoker_static: $invoker_static:ident,
        invoker_ty:     $invoker_ty:ident,
        thunk_fn:       $thunk_fn:ident,
        setter_fn:      $setter_fn:ident,
        from_handle_fn: $from_handle_fn:ident,
    ) => { ... };
    (
        wrapper:        $wrapper:ty,
        info_ty:        $info_ty:ty,
        return_ty:      $ret:ty,
        default_ret:    $default:expr,
        invoker_static: $invoker_static:ident,
        invoker_ty:     $invoker_ty:ident,
        thunk_fn:       $thunk_fn:ident,
        setter_fn:      $setter_fn:ident,
        from_handle_fn: $from_handle_fn:ident,
        extra_args:     [ $( $extra_name:ident : $extra_ty:ty ),* $(,)? ] $(,)?
    ) => { ... };
}

Macro that expands to the per-callback-kind boilerplate: a static thunk (compiled into libazul) that the framework calls with by-value args, a <Wrapper>::create_from_host_handle(u64) constructor, and an AzApp_set<Kind>Invoker setter the host calls once at module load.

All identifiers are passed in explicitly so we don’t need a proc-macro dependency just to concatenate idents. Codegen emits invocations of this macro from ir.callback_typedefs.

Caller responsibilities:

• The wrapper type must have public fields cb: <typedef> and ctx: OptionRefAny — that’s the standard shape every callback wrapper in the framework already follows.
• info_ty must expose a .get_ctx() -> OptionRefAny method (also standard for *CallbackInfo types).
• default_ret is returned when:
  • the framework invokes the thunk with OptionRefAny::None ctx (host called the typedef directly without going through this path),
  • the ctx isn’t a host-handle (host registered the wrapper but the ctx came from somewhere else),
  • or no invoker has been registered yet for this kind. Pick a value that can’t be confused with a “real” return — typically the kind’s “do nothing” / “empty body” default.