error: `derive` may only be applied to structs, enums and unions
  --> $DIR/issue-43106-gating-of-derive.rs:4:1
   |
LL | #![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:7:1
   |
LL | #[derive(Debug)]
   | ^^^^^^^^^^^^^^^^

error: `derive` may only be applied to structs, enums and unions
  --> $DIR/issue-43106-gating-of-derive.rs:10:17
   |
LL |     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:13:5
   |
LL |     #[derive(Debug)]
   |     ^^^^^^^^^^^^^^^^

error: `derive` may only be applied to structs, enums and unions
  --> $DIR/issue-43106-gating-of-derive.rs:26:5
   |
LL |     #[derive(Debug)]
   |     ^^^^^^^^^^^^^^^^

error: `derive` may only be applied to structs, enums and unions
  --> $DIR/issue-43106-gating-of-derive.rs:30:5
   |
LL |     #[derive(Debug)]
   |     ^^^^^^^^^^^^^^^^

error: aborting due to 6 previous errors