1// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify
2
3// This is a test for an egregious hack in Clang that works around
4// an issue with GCC's <type_traits> implementation. std::common_type
5// relies on pre-standard rules for decltype(), in which it doesn't
6// produce reference types so frequently.
7
8#ifdef BE_THE_HEADER
9
10#pragma GCC system_header
11namespace std {
12  template<typename T> T &&declval();
13
14  template<typename...Ts> struct common_type {};
15  template<typename A, typename B> struct common_type<A, B> {
16    // Under the rules in the standard, this always produces a
17    // reference type.
18    typedef decltype(true ? declval<A>() : declval<B>()) type;
19  };
20}
21
22#else
23
24#define BE_THE_HEADER
25#include "libstdcxx_common_type_hack.cpp"
26
27using T = int;
28using T = std::common_type<int, int>::type;
29
30using U = int; // expected-note {{here}}
31using U = decltype(true ? std::declval<int>() : std::declval<int>()); // expected-error {{different types}}
32
33#endif
34