This is a partial implementation of the revised std::common_type rules
from P0435R1.
PR libstdc++/89102 (partial)
* include/std/type_traits (common_type<>): Define.
(common_type<T>): Derive from common_type<T, T>.
* testsuite/20_util/common_type/requirements/explicit_instantiation.cc:
Test zero-length template argument list.
* testsuite/20_util/common_type/requirements/sfinae_friendly_1.cc:
Test additional single argument cases.
* testsuite/20_util/common_type/requirements/sfinae_friendly_2.cc:
Adjust expected error.
Tested powerpc64le-linux, committed to trunk.
I think this could be backported to gcc-8-branch too.
I have a complete patch for stage 1 which I'll post in a minute.
commit e5f7ac8d78351f41edd752c94c92fe1a389bdca7
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Wed Feb 6 16:27:03 2019 +0000
PR libstdc++/89102 fix common_type<> and common_type<T> specializations
This is a partial implementation of the revised std::common_type rules
from P0435R1.
PR libstdc++/89102 (partial)
* include/std/type_traits (common_type<>): Define.
(common_type<T>): Derive from common_type<T, T>.
*
testsuite/20_util/common_type/requirements/explicit_instantiation.cc:
Test zero-length template argument list.
* testsuite/20_util/common_type/requirements/sfinae_friendly_1.cc:
Test additional single argument cases.
* testsuite/20_util/common_type/requirements/sfinae_friendly_2.cc:
Adjust expected error.
diff --git a/libstdc++-v3/include/std/type_traits
b/libstdc++-v3/include/std/type_traits
index f05a583cb04..bc2250d9dce 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -2132,9 +2132,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
struct __expanded_common_type_wrapper<__failure_type, _Args...>
{ typedef __failure_type type; };
+ template<>
+ struct common_type<>
+ { };
+
template<typename _Tp>
struct common_type<_Tp>
- { typedef typename decay<_Tp>::type type; };
+ : common_type<_Tp, _Tp>
+ { };
template<typename _Tp, typename _Up>
struct common_type<_Tp, _Up>
diff --git
a/libstdc++-v3/testsuite/20_util/common_type/requirements/explicit_instantiation.cc
b/libstdc++-v3/testsuite/20_util/common_type/requirements/explicit_instantiation.cc
index 28535a80d64..dc57ab5ad8e 100644
---
a/libstdc++-v3/testsuite/20_util/common_type/requirements/explicit_instantiation.cc
+++
b/libstdc++-v3/testsuite/20_util/common_type/requirements/explicit_instantiation.cc
@@ -30,6 +30,7 @@ namespace std
typedef void test_type5;
typedef const void test_type6;
+ template struct common_type<>;
template struct common_type<test_type1>;
template struct common_type<test_type1, test_type2>;
template struct common_type<test_type1, test_type2, test_type3>;
diff --git
a/libstdc++-v3/testsuite/20_util/common_type/requirements/sfinae_friendly_1.cc
b/libstdc++-v3/testsuite/20_util/common_type/requirements/sfinae_friendly_1.cc
index 372c1a58378..9b94eb13434 100644
---
a/libstdc++-v3/testsuite/20_util/common_type/requirements/sfinae_friendly_1.cc
+++
b/libstdc++-v3/testsuite/20_util/common_type/requirements/sfinae_friendly_1.cc
@@ -159,7 +159,10 @@ namespace std {
};
}
+static_assert(is_type<std::common_type<int>, int>(), "");
+static_assert(is_type<std::common_type<const int>, int>(), "");
static_assert(is_type<std::common_type<int, int>, int>(), "");
+static_assert(is_type<std::common_type<const int, int>, int>(), "");
static_assert(is_type<std::common_type<ScEn, ScEn>, ScEn>(), "");
static_assert(is_type<std::common_type<UnscEn, UnscEn>, UnscEn>(), "");
static_assert(is_type<std::common_type<UnscEn, int>, int>(), "");
@@ -180,6 +183,8 @@ static_assert(is_type<std::common_type<int*, const volatile
int*>,
const volatile int*>(), "");
static_assert(is_type<std::common_type<void*, const volatile int*>,
const volatile void*>(), "");
+static_assert(is_type<std::common_type<void>, void>(), "");
+static_assert(is_type<std::common_type<const void>, void>(), "");
static_assert(is_type<std::common_type<void, void>, void>(), "");
static_assert(is_type<std::common_type<const void, const void>, void>(), "");
static_assert(is_type<std::common_type<int&, int&&>, int>(), "");
@@ -316,6 +321,14 @@ static_assert(!has_type<std::common_type<UConv1,
Abstract&&>>(), "");
static_assert(!has_type<std::common_type<std::initializer_list<int>,
std::initializer_list<long>>>(), "");
+// PR libstdc++/89102
+static_assert(!has_type<std::common_type<int() &>>(), "");
+static_assert(!has_type<std::common_type<int() & noexcept>>(), "");
+static_assert(!has_type<std::common_type<int() const>>(), "");
+static_assert(!has_type<std::common_type<int(...) &>>(), "");
+static_assert(!has_type<std::common_type<int(...) & noexcept>>(), "");
+static_assert(!has_type<std::common_type<int(...) const>>(), "");
+
void test(int i)
{
auto local_lmd1 = [=](int, double) { return i + i; };
diff --git
a/libstdc++-v3/testsuite/20_util/common_type/requirements/sfinae_friendly_2.cc
b/libstdc++-v3/testsuite/20_util/common_type/requirements/sfinae_friendly_2.cc
index 64c8ea9339e..8f6f4ecd4d8 100644
---
a/libstdc++-v3/testsuite/20_util/common_type/requirements/sfinae_friendly_2.cc
+++
b/libstdc++-v3/testsuite/20_util/common_type/requirements/sfinae_friendly_2.cc
@@ -25,7 +25,7 @@ template<typename... Args>
constexpr
std::array<typename std::common_type<Args...>::type,
sizeof...(Args)>
-make_array(Args&&... args) // { dg-error "invalid use" }
+make_array(Args&&... args) // { dg-error "no type.*common_type<>" }
{
typedef typename std::common_type<Args...>::type CT;
return std::array<CT, sizeof...(Args)>{static_cast<CT>
