error: #[serde(transparent)] requires at least one field that is neither skipped nor has a default
  --> $DIR/de_at_least_one.rs:5:1
   |
5  | / #[serde(transparent)]
6  | | struct S {
7  | |     #[serde(skip)]
8  | |     a: u8,
9  | |     #[serde(default)]
10 | |     b: u8,
11 | | }
   | |_^

error: aborting due to previous error