Function gtk_source_annotation_provider_populate_hover_async 

pub unsafe extern "C" fn gtk_source_annotation_provider_populate_hover_async(
    self_: *mut GtkSourceAnnotationProvider,
    annotation: *mut GtkSourceAnnotation,
    display: *mut GtkSourceHoverDisplay,
    cancellable: *mut GCancellable,
    callback: GAsyncReadyCallback,
    user_data: gpointer,
)

Available on crate feature v5_18 only.