error: the `#[proc_macro_derive]` attribute may only be used on bare functions
  --> $DIR/issue-43106-gating-of-proc_macro_derive.rs:10:1
   |
LL | #[proc_macro_derive()]
   | ^^^^^^^^^^^^^^^^^^^^^^

error: the `#[proc_macro_derive]` attribute may only be used on bare functions
  --> $DIR/issue-43106-gating-of-proc_macro_derive.rs:18:17
   |
LL |     mod inner { #![proc_macro_derive()] }
   |                 ^^^^^^^^^^^^^^^^^^^^^^^

error: the `#[proc_macro_derive]` attribute is only usable with crates of the `proc-macro` crate type
  --> $DIR/issue-43106-gating-of-proc_macro_derive.rs:21:5
   |
LL |     #[proc_macro_derive()] fn f() { }
   |     ^^^^^^^^^^^^^^^^^^^^^^

error: the `#[proc_macro_derive]` attribute may only be used on bare functions
  --> $DIR/issue-43106-gating-of-proc_macro_derive.rs:24:5
   |
LL |     #[proc_macro_derive()] struct S;
   |     ^^^^^^^^^^^^^^^^^^^^^^

error: the `#[proc_macro_derive]` attribute may only be used on bare functions
  --> $DIR/issue-43106-gating-of-proc_macro_derive.rs:27:5
   |
LL |     #[proc_macro_derive()] type T = S;
   |     ^^^^^^^^^^^^^^^^^^^^^^

error: the `#[proc_macro_derive]` attribute may only be used on bare functions
  --> $DIR/issue-43106-gating-of-proc_macro_derive.rs:30:5
   |
LL |     #[proc_macro_derive()] impl S { }
   |     ^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to 6 previous errors