Is decltype (foo (1)) allowed to view the body of foo if a return type is declared?

Question

The following code compiles with gcc and MSVC, but does not work using clang I, verified with clang-3.5 and the current trunk).

template <typename T> constexpr auto wrong = false; template <typename T> constexpr auto foo(const T t) -> int { static_assert(wrong<T>, ""); return {}; } using F = decltype(foo(1)); int main() {} 

clang creates an instance of the function body and stumbles upon static_assert . gcc and MSVC just look at the function declaration and ignore static_assert in the body.

If you remove constexpr, all compilers will compile the code just fine.

Question:
Is decltype allowed to view function body if return type is declared?

I am looking for a link to the corresponding section in the standard.