error: at most one variant can be the default
  --> $DIR/duplicated_default_variant.rs:4:1
   |
4  | / pub enum Enum {
5  | |     #[ibuilder(default)]
6  | |     Var1,
7  | |     #[ibuilder(default)]
8  | |     Var2,
9  | |     Var3,
10 | | }
   | |_^