error: can only derive `Function` for `struct`s with precisely one field
 --> tests/function/field_count.rs:3:10
  |
3 | #[derive(Function)]
  |          ^^^^^^^^
  |
  = note: this error originates in the derive macro `Function` (in Nightly builds, run with -Z macro-backtrace for more info)

error: can only derive `Function` for `struct`s with precisely one field
 --> tests/function/field_count.rs:6:10
  |
6 | #[derive(Function)]
  |          ^^^^^^^^
  |
  = note: this error originates in the derive macro `Function` (in Nightly builds, run with -Z macro-backtrace for more info)

error: can only derive `Function` for `struct`s with precisely one field
  --> tests/function/field_count.rs:10:20
   |
10 | struct Unnamed2<F>(F, bool);
   |                    ^^^^^^^

error: can only derive `Function` for `struct`s with precisely one field
  --> tests/function/field_count.rs:12:10
   |
12 | #[derive(Function)]
   |          ^^^^^^^^
   |
   = note: this error originates in the derive macro `Function` (in Nightly builds, run with -Z macro-backtrace for more info)

error: can only derive `Function` for `struct`s with precisely one field
  --> tests/function/field_count.rs:17:5
   |
17 | /     x: bool,
18 | |     y: u32,
   | |___________^