extension View {
    /// Adds an action to be performed before this view appears.
    ///
    /// The exact moment that the action gets called is an internal detail and
    /// may change at any time, but it is guaranteed to be after accessing the
    /// view's ``View/body`` and before the view appears on screen. Currently,
    /// if these docs have been kept up to date, the action gets called just
    /// before creating the view's widget.
    ///
    /// - Parameter action: The action to perform when this view appears.
    public func onAppear(perform action: @escaping @MainActor () -> Void) -> some View {
        OnAppearModifier(body: TupleView1(self), action: action)
    }
}

struct OnAppearModifier<Content: View>: View {
    var body: TupleView1<Content>
    var action: @MainActor () -> Void

    func asWidget<Backend: BaseAppBackend>(
        _ children: any ViewGraphNodeChildren,
        backend: Backend
    ) -> Backend.Widget {
        action()
        return defaultAsWidget(children, backend: backend)
    }
}