Digamos que tengo estos alias de plantillas:

<code>enum class enabler {};

template <typename T>
using EnableIf = typename std::enable_if<T::value, enabler>::type;
template <typename T>
using DisableIf = typename std::enable_if<!T::value, enabler>::type;
</code>

Puedo hacer lo siguiente en GCC:

<code>#include <iostream>

template <typename T, EnableIf<std::is_polymorphic<T>> = {}>
void f(T) { std::cout << "is polymorphic\n"; }

template <typename T, DisableIf<std::is_polymorphic<T>> = {}>
void f(T) { std::cout << "is not polymorphic\n"; }

struct foo { virtual void g() {} };

int main() {
    f(foo {});
    f(int {});
}
</code>

Se imprime:

es polimorfo
no es polimorfo

Que coincide con mis expectativas.

Con clang ese código no se compila. Produce los siguientes mensajes de error.

<code>test.cpp:11:58: error: expected expression
template <typename T, EnableIf<std::is_polymorphic<T>> = {}>
                                                         ^
test.cpp:14:59: error: expected expression
template <typename T, DisableIf<std::is_polymorphic<T>> = {}>
                                                          ^
test.cpp:20:3: error: no matching function for call to 'f'
  f(foo {});
  ^
test.cpp:12:6: note: candidate template ignored: couldn't infer template argument ''
void f(T) { std::cout << "is polymorphic\n"; }
     ^
test.cpp:15:6: note: candidate template ignored: couldn't infer template argument ''
void f(T) { std::cout << "is not polymorphic\n"; }
     ^
test.cpp:21:3: error: no matching function for call to 'f'
  f(int {});
  ^
test.cpp:12:6: note: candidate template ignored: couldn't infer template argument ''
void f(T) { std::cout << "is polymorphic\n"; }
     ^
test.cpp:15:6: note: candidate template ignored: couldn't infer template argument ''
void f(T) { std::cout << "is not polymorphic\n"; }
     ^
4 errors generated.
</code>

¿Debería compilarlo? ¿Cuál de los dos compiladores es defectuoso?