error: duplicate diagnostic item in crate `p2`: `Foo`
   |
   = note: the diagnostic item is first defined in crate `p1`

error: duplicate diagnostic item in crate `duplicate_diagnostic`: `Foo`
  --> $DIR/duplicate-diagnostic.rs:12:1
   |
LL | pub struct Foo {}
   | ^^^^^^^^^^^^^^
   |
   = note: the diagnostic item is first defined in crate `p2`

error: aborting due to 2 previous errors