Attribute Macro compose 

#[compose]

Inject a cx: &mut UiScope first parameter into the annotated function.

The attribute exists to keep infrastructure out of the signature the user reads:

#[compose]
fn counter_button(sig: Signal<i32>) {
    ui! {
        View (bg_color: ColorToken::Primary)
        on Tap { sig.update(|n| *n += 1); }
        { Text($sig) }
    };
}

Every ui! invocation inside the function body reads cx.world_mut() / cx.parent() implicitly; callers pass their existing cx through the paired ui!(func(args)) form so no site ever spells out world and parent again.

The attribute rejects three shapes at expansion time:

• non-function items — annotate a fn, or reach for mold!(Name { ... }) when you want a full widget class.
• async fn — cross-await UI state is a separate topic (v0.41+).
• generic fn — parameter monomorphisation is deferred to a later release.

It also errors out if the user already declared a parameter named cx, so double-injection can’t silently pass through.