error: `#[darling(flatten)]` can only be applied to one field
  --> tests/compile-fail/flatten_multiple_fields.rs:13:15
   |
13 |     #[darling(flatten)]
   |               ^^^^^^^

error: `#[darling(flatten)]` can only be applied to one field
  --> tests/compile-fail/flatten_multiple_fields.rs:15:15
   |
15 |     #[darling(flatten)]
   |               ^^^^^^^

error: `#[darling(flatten)]` can only be applied to one field
  --> tests/compile-fail/flatten_multiple_fields.rs:22:15
   |
22 |     #[darling(flatten)]
   |               ^^^^^^^

error: `#[darling(flatten)]` can only be applied to one field
  --> tests/compile-fail/flatten_multiple_fields.rs:24:15
   |
24 |     #[darling(flatten)]
   |               ^^^^^^^