Macro declarative_component 

macro_rules! declarative_component {
    ($ty:ty) => { ... };
}

Emit a no-op ExecutableNode impl for a declarative-only component (W.5.1). The generated runtime calls on_callback unconditionally, so a component instantiated into a generated binary must impl ExecutableNode; components without callback bodies use this to satisfy that contract:

pub struct Node;
impl nros::Node for Node { /* register(...) */ }
nros::declarative_component!(Node);