error: `proc-macro` crate types cannot export any items other than functions tagged with `#[proc_macro_derive]` currently
  --> $DIR/pub-at-crate-root.rs:8:1
   |
LL | / pub mod a {
LL | |     use proc_macro::TokenStream;
LL | |
LL | |     #[proc_macro_derive(B)]
...  |
LL | |     }
LL | | }
   | |_^

error: functions tagged with `#[proc_macro_derive]` must currently reside in the root of the crate
  --> $DIR/pub-at-crate-root.rs:12:5
   |
LL | /     pub fn bar(a: TokenStream) -> TokenStream {
LL | |
LL | |         a
LL | |     }
   | |_____^

error: functions tagged with `#[proc_macro_derive]` must be `pub`
  --> $DIR/pub-at-crate-root.rs:19:1
   |
LL | / fn bar(a: proc_macro::TokenStream) -> proc_macro::TokenStream {
LL | |
LL | |     a
LL | | }
   | |_^

error: aborting due to 3 previous errors