error: a macro named `foo` has already been exported
  --> $DIR/issue-38715.rs:5:1
   |
LL | macro_rules! foo { () => {} }
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `foo` already exported
   |
   = note: `#[deny(duplicate_macro_exports)]` on by default
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in the 2018 edition!
   = note: for more information, see issue #35896 <https://github.com/rust-lang/rust/issues/35896>
note: previous macro export is now shadowed
  --> $DIR/issue-38715.rs:2:1
   |
LL | macro_rules! foo { ($i:ident) => {} }
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error