// { dg-do assemble  }

template <class T> struct S1; // { dg-error "" } previous declaration

template <class T, class U> struct S1 {}; // { dg-error "" } used 1 template parameter

template <class T = int> // { dg-error "" } original def of default
struct S2; 

template <class T = int> struct S2; // { dg-error "" } redefinition of default

template <class T> // { dg-error "" } template parameter
struct S3;

template <int I> struct S3; // { dg-error "" } redeclared here

template <template <class T> class C> struct S3; // { dg-error "" } redeclared here