error: duplicate serde attribute `borrow`
 --> tests/ui/borrow/duplicate_variant.rs:9:15
  |
6 | #[derive(Deserialize)]
  |          ----------- in this derive macro expansion
...
9 |     S(#[serde(borrow)] Str<'a>),
  |               ^^^^^^
  |
  = note: this error originates in the derive macro `Deserialize` (in Nightly builds, run with -Z macro-backtrace for more info)