error[E0428]: the name `Foo` is defined multiple times
  --> tests/fail/no_allow_same_name_twice.rs:22:5
   |
20 |     Foo,
   |     --- previous definition of the type `Foo` here
21 |     #[mh(code = 0x1, hasher = FooHasher)]
22 |     Foo,
   |     ^^^ `Foo` redefined here
   |
   = note: `Foo` must be defined only once in the type namespace of this enum