The code is as follow:

struct T;

template <typename U>
void f()
{
 try
 {}
 catch(T const &)
 {}
}

struct T
{};

int main()
{
 f<int>();
 return 0;
}

g++ accepts, but clang++ rejects it:

code0.cpp:8:17: error: cannot catch reference to incomplete type 'const T'
 catch(T const &)
                ^
code0.cpp:1:8: note: forward declaration of 'T'
struct T;
       ^
1 error generated.


15.3 Handling an exception [except.handle]

1 The exception-declaration in a handler describes the type(s) of exceptions that can cause that handler to be entered. The exception-declaration shall not denote an incomplete type or an rvalue reference type. The exception-declaration shall not denote a pointer or reference to an incomplete type, other than void*, const void*, volatile void*, or const volatile void*.