error: expected one of `)` or `,`, found `(`
  --> $DIR/test3.rs:5:27
   |
LL |         struct S3(pub($t) ());
   |                           ^ expected one of `)` or `,`
...
LL |     define_struct! { foo }
   |     ---------------------- in this macro invocation

error[E0412]: cannot find type `foo` in this scope
  --> $DIR/test3.rs:11:22
   |
LL |     define_struct! { foo }
   |                      ^^^ not found in this scope

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0412`.