error: this returns a `Result<_, ()>`
  --> tests/ui/result_unit_error_no_std.rs:12:1
   |
LL | pub fn returns_unit_error_lint() -> Result<u32, ()> {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: use a custom `Error` type instead
   = note: `-D clippy::result-unit-err` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(clippy::result_unit_err)]`

error: aborting due to 1 previous error