error: expected one of `)` or `,`, found `(`
  --> $DIR/test.rs:4:26
   |
LL |     struct S2(pub((foo)) ());
   |                         -^ expected one of `)` or `,`
   |                         |
   |                         help: missing `,`

error[E0412]: cannot find type `foo` in this scope
  --> $DIR/test.rs:4:20
   |
LL |     struct S2(pub((foo)) ());
   |                    ^^^ not found in this scope

error: aborting due to 2 previous errors

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