error: `derive` may only be applied to structs, enums and unions
  --> $DIR/issue-43106-gating-of-derive.rs:14:1
   |
14 | #![derive(Debug)]
   | ^^^^^^^^^^^^^^^^^ help: try an outer attribute: `#[derive(Debug)]`

error: `derive` may only be applied to structs, enums and unions
  --> $DIR/issue-43106-gating-of-derive.rs:17:1
   |
17 | #[derive(Debug)]
   | ^^^^^^^^^^^^^^^^

error: `derive` may only be applied to structs, enums and unions
  --> $DIR/issue-43106-gating-of-derive.rs:20:17
   |
20 |     mod inner { #![derive(Debug)] }
   |                 ^^^^^^^^^^^^^^^^^ help: try an outer attribute: `#[derive(Debug)]`

error: `derive` may only be applied to structs, enums and unions
  --> $DIR/issue-43106-gating-of-derive.rs:23:5
   |
23 |     #[derive(Debug)]
   |     ^^^^^^^^^^^^^^^^

error: `derive` may only be applied to structs, enums and unions
  --> $DIR/issue-43106-gating-of-derive.rs:36:5
   |
36 |     #[derive(Debug)]
   |     ^^^^^^^^^^^^^^^^

error: `derive` may only be applied to structs, enums and unions
  --> $DIR/issue-43106-gating-of-derive.rs:40:5
   |
40 |     #[derive(Debug)]
   |     ^^^^^^^^^^^^^^^^

error: aborting due to 6 previous errors