[libc++] Implement LWG 2510

Summary:
LWG2510 makes tag types like allocator_arg_t explicitly default
constructible instead of implicitly default constructible. It also
makes the constructors for std::pair and std::tuple conditionally
explicit based on the explicit-ness of the default constructibility
for the pair/tuple's elements.

Reviewers: mclow.lists, EricWF

Subscribers: christof, jkorous, dexonsmith, libcxx-commits

Tags: #libc

Differential Revision: https://reviews.llvm.org/D65161

llvm-svn: 372777

14 files changed, 306 insertions, 10 deletions

diff --git a/libcxx/test/libcxx/type_traits/is_implicitly_default_constructible.pass.cpp b/libcxx/test/libcxx/type_traits/is_implicitly_default_constructible.pass.cpp
new file mode 100644
index 00000000000..19719a79c0c
--- /dev/null
+++ b/libcxx/test/libcxx/type_traits/is_implicitly_default_constructible.pass.cpp
@@ -0,0 +1,56 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03
+
+// <type_traits>
+
+// __is_implicitly_default_constructible<Tp>
+
+#include <type_traits>
+
+
+struct ExplicitlyDefaultConstructible1 {
+    explicit ExplicitlyDefaultConstructible1() = default;
+};
+
+struct ExplicitlyDefaultConstructible2 {
+    explicit ExplicitlyDefaultConstructible2() { }
+};
+
+struct ImplicitlyDefaultConstructible1 {
+    ImplicitlyDefaultConstructible1() { }
+};
+
+struct ImplicitlyDefaultConstructible2 {
+    ImplicitlyDefaultConstructible2() = default;
+};
+
+struct NonDefaultConstructible1 {
+    NonDefaultConstructible1() = delete;
+};
+
+struct NonDefaultConstructible2 {
+    explicit NonDefaultConstructible2() = delete;
+};
+
+struct NonDefaultConstructible3 {
+    NonDefaultConstructible3(NonDefaultConstructible3&&) { }
+};
+
+static_assert(!std::__is_implicitly_default_constructible<ExplicitlyDefaultConstructible1>::value, "");
+static_assert(!std::__is_implicitly_default_constructible<ExplicitlyDefaultConstructible2>::value, "");
+static_assert(std::__is_implicitly_default_constructible<ImplicitlyDefaultConstructible1>::value, "");
+static_assert(std::__is_implicitly_default_constructible<ImplicitlyDefaultConstructible2>::value, "");
+static_assert(!std::__is_implicitly_default_constructible<NonDefaultConstructible1>::value, "");
+static_assert(!std::__is_implicitly_default_constructible<NonDefaultConstructible2>::value, "");
+static_assert(!std::__is_implicitly_default_constructible<NonDefaultConstructible3>::value, "");
+
+int main(int, char**) {
+    return 0;
+}
diff --git a/libcxx/test/std/language.support/support.dynamic/nothrow_t.fail.cpp b/libcxx/test/std/language.support/support.dynamic/nothrow_t.fail.cpp
new file mode 100644
index 00000000000..c1092c3516b
--- /dev/null
+++ b/libcxx/test/std/language.support/support.dynamic/nothrow_t.fail.cpp
@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03
+
+// struct nothrow_t {
+//   explicit nothrow_t() = default;
+// };
+// extern const nothrow_t nothrow;
+
+// This test checks for LWG 2510.
+
+#include <new>
+
+
+std::nothrow_t f() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+
+int main(int, char**) {
+    return 0;
+}
diff --git a/libcxx/test/std/language.support/support.dynamic/nothrow_t.pass.cpp b/libcxx/test/std/language.support/support.dynamic/nothrow_t.pass.cpp
new file mode 100644
index 00000000000..3a6231329f0
--- /dev/null
+++ b/libcxx/test/std/language.support/support.dynamic/nothrow_t.pass.cpp
@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// struct nothrow_t {
+//   explicit nothrow_t() = default;
+// };
+// extern const nothrow_t nothrow;
+
+#include <new>
+
+
+int main(int, char**) {
+  std::nothrow_t x = std::nothrow;
+  (void)x;
+
+  return 0;
+}
diff --git a/libcxx/test/std/thread/thread.mutex/thread.lock/types.fail.cpp b/libcxx/test/std/thread/thread.mutex/thread.lock/types.fail.cpp
new file mode 100644
index 00000000000..56fbc90a63d
--- /dev/null
+++ b/libcxx/test/std/thread/thread.mutex/thread.lock/types.fail.cpp
@@ -0,0 +1,31 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03
+
+// UNSUPPORTED: libcpp-has-no-threads
+
+// <mutex>
+
+// struct defer_lock_t { explicit defer_lock_t() = default; };
+// struct try_to_lock_t { explicit try_to_lock_t() = default; };
+// struct adopt_lock_t { explicit adopt_lock_t() = default; };
+
+// This test checks for LWG 2510.
+
+#include <mutex>
+
+
+std::defer_lock_t f1() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+std::try_to_lock_t f2() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+std::adopt_lock_t f3() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+
+int main(int, char**) {
+    return 0;
+}
diff --git a/libcxx/test/std/thread/thread.mutex/thread.lock/types.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.lock/types.pass.cpp
index 84c39baafa6..c03ca4622aa 100644
--- a/libcxx/test/std/thread/thread.mutex/thread.lock/types.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.lock/types.pass.cpp
@@ -10,16 +10,15 @@
 
 // <mutex>
 
-// struct defer_lock_t {};
-// struct try_to_lock_t {};
-// struct adopt_lock_t {};
+// struct defer_lock_t { explicit defer_lock_t() = default; };
+// struct try_to_lock_t { explicit try_to_lock_t() = default; };
+// struct adopt_lock_t { explicit adopt_lock_t() = default; };
 //
 // constexpr defer_lock_t  defer_lock{};
 // constexpr try_to_lock_t try_to_lock{};
 // constexpr adopt_lock_t  adopt_lock{};
 
 #include <mutex>
-#include <type_traits>
 
 #include "test_macros.h"
 
@@ -33,5 +32,5 @@ int main(int, char**)
     T2 t2 = std::try_to_lock; ((void)t2);
     T3 t3 = std::adopt_lock; ((void)t3);
 
-  return 0;
+    return 0;
 }
diff --git a/libcxx/test/std/utilities/memory/allocator.tag/allocator_arg.fail.cpp b/libcxx/test/std/utilities/memory/allocator.tag/allocator_arg.fail.cpp
new file mode 100644
index 00000000000..2b8d09afaae
--- /dev/null
+++ b/libcxx/test/std/utilities/memory/allocator.tag/allocator_arg.fail.cpp
@@ -0,0 +1,25 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03
+
+// <memory>
+
+// struct allocator_arg_t { explicit allocator_arg_t() = default; };
+// const allocator_arg_t allocator_arg = allocator_arg_t();
+
+// This test checks for LWG 2510.
+
+#include <memory>
+
+
+std::allocator_arg_t f() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+
+int main(int, char**) {
+    return 0;
+}
diff --git a/libcxx/test/std/utilities/memory/allocator.tag/allocator_arg.pass.cpp b/libcxx/test/std/utilities/memory/allocator.tag/allocator_arg.pass.cpp
index 0253243319a..e22bec1e514 100644
--- a/libcxx/test/std/utilities/memory/allocator.tag/allocator_arg.pass.cpp
+++ b/libcxx/test/std/utilities/memory/allocator.tag/allocator_arg.pass.cpp
@@ -8,7 +8,7 @@
 
 // <memory>
 
-// struct allocator_arg_t { };
+// struct allocator_arg_t { explicit allocator_arg_t() = default; };
 // const allocator_arg_t allocator_arg = allocator_arg_t();
 
 #include <memory>
@@ -21,5 +21,5 @@ int main(int, char**)
 {
     test(std::allocator_arg);
 
-  return 0;
+    return 0;
 }
diff --git a/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/default.fail.cpp b/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/default.fail.cpp
new file mode 100644
index 00000000000..f25450af63b
--- /dev/null
+++ b/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/default.fail.cpp
@@ -0,0 +1,49 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03
+
+// <tuple>
+
+// template <class... Types> class tuple;
+
+// explicit(see-below) constexpr tuple();
+
+#include <tuple>
+
+
+struct Implicit {
+    Implicit() = default;
+};
+
+struct Explicit {
+    explicit Explicit() = default;
+};
+
+std::tuple<> test1() { return {}; }
+
+std::tuple<Implicit> test2() { return {}; }
+std::tuple<Explicit> test3() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+
+std::tuple<Implicit, Implicit> test4() { return {}; }
+std::tuple<Explicit, Implicit> test5() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+std::tuple<Implicit, Explicit> test6() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+std::tuple<Explicit, Explicit> test7() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+
+std::tuple<Implicit, Implicit, Implicit> test8() { return {}; }
+std::tuple<Implicit, Implicit, Explicit> test9() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+std::tuple<Implicit, Explicit, Implicit> test10() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+std::tuple<Implicit, Explicit, Explicit> test11() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+std::tuple<Explicit, Implicit, Implicit> test12() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+std::tuple<Explicit, Implicit, Explicit> test13() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+std::tuple<Explicit, Explicit, Implicit> test14() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+std::tuple<Explicit, Explicit, Explicit> test15() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+
+int main(int, char**) {
+    return 0;
+}
diff --git a/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/default.pass.cpp b/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/default.pass.cpp
index 46fd35ad4dd..9f855986257 100644
--- a/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/default.pass.cpp
+++ b/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/default.pass.cpp
@@ -10,7 +10,7 @@
 
 // template <class... Types> class tuple;
 
-// constexpr tuple();
+// explicit(see-below) constexpr tuple();
 
 // UNSUPPORTED: c++98, c++03
 
diff --git a/libcxx/test/std/utilities/utility/pairs/pair.piecewise/piecewise_construct.pass.cpp b/libcxx/test/std/utilities/utility/pairs/pair.piecewise/piecewise_construct.pass.cpp
index d70d060deb0..903aa935583 100644
--- a/libcxx/test/std/utilities/utility/pairs/pair.piecewise/piecewise_construct.pass.cpp
+++ b/libcxx/test/std/utilities/utility/pairs/pair.piecewise/piecewise_construct.pass.cpp
@@ -12,7 +12,7 @@
 
 // template <class T1, class T2> struct pair
 
-// struct piecewise_construct_t { };
+// struct piecewise_construct_t { explicit piecewise_construct_t() = default; };
 // constexpr piecewise_construct_t piecewise_construct = piecewise_construct_t();
 
 #include <utility>
diff --git a/libcxx/test/std/utilities/utility/pairs/pair.piecewise/piecewise_construct_t.fail.cpp b/libcxx/test/std/utilities/utility/pairs/pair.piecewise/piecewise_construct_t.fail.cpp
new file mode 100644
index 00000000000..90b3313eff1
--- /dev/null
+++ b/libcxx/test/std/utilities/utility/pairs/pair.piecewise/piecewise_construct_t.fail.cpp
@@ -0,0 +1,25 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03
+
+// <utility>
+
+// struct piecewise_construct_t { explicit piecewise_construct_t() = default; };
+// constexpr piecewise_construct_t piecewise_construct = piecewise_construct_t();
+
+// This test checks for LWG 2510.
+
+#include <utility>
+
+
+std::piecewise_construct_t f() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+
+int main(int, char**) {
+    return 0;
+}
diff --git a/libcxx/test/std/utilities/utility/pairs/pair.piecewise/piecewise_construct_t.pass.cpp b/libcxx/test/std/utilities/utility/pairs/pair.piecewise/piecewise_construct_t.pass.cpp
new file mode 100644
index 00000000000..0fdba067487
--- /dev/null
+++ b/libcxx/test/std/utilities/utility/pairs/pair.piecewise/piecewise_construct_t.pass.cpp
@@ -0,0 +1,24 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03
+
+// <utility>
+
+// struct piecewise_construct_t { explicit piecewise_construct_t() = default; };
+// constexpr piecewise_construct_t piecewise_construct = piecewise_construct_t();
+
+#include <utility>
+
+
+int main(int, char**) {
+    std::piecewise_construct_t x = std::piecewise_construct;
+    (void)x;
+
+    return 0;
+}
diff --git a/libcxx/test/std/utilities/utility/pairs/pairs.pair/default.explicit.fail.cpp b/libcxx/test/std/utilities/utility/pairs/pairs.pair/default.explicit.fail.cpp
new file mode 100644
index 00000000000..332fe33f41e
--- /dev/null
+++ b/libcxx/test/std/utilities/utility/pairs/pairs.pair/default.explicit.fail.cpp
@@ -0,0 +1,38 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03
+
+// <utility>
+
+// template <class T1, class T2> struct pair
+
+// explicit(see-below) constexpr pair();
+
+// This test checks the conditional explicitness of std::pair's default
+// constructor as introduced by the resolution of LWG 2510.
+
+#include <utility>
+
+
+struct ImplicitlyDefaultConstructible {
+    ImplicitlyDefaultConstructible() = default;
+};
+
+struct ExplicitlyDefaultConstructible {
+    explicit ExplicitlyDefaultConstructible() = default;
+};
+
+std::pair<ImplicitlyDefaultConstructible, ExplicitlyDefaultConstructible> test1() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+std::pair<ExplicitlyDefaultConstructible, ImplicitlyDefaultConstructible> test2() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+std::pair<ExplicitlyDefaultConstructible, ExplicitlyDefaultConstructible> test3() { return {}; } // expected-error 1 {{chosen constructor is explicit in copy-initialization}}
+std::pair<ImplicitlyDefaultConstructible, ImplicitlyDefaultConstructible> test4() { return {}; }
+
+int main(int, char**) {
+    return 0;
+}
diff --git a/libcxx/test/std/utilities/utility/pairs/pairs.pair/default.pass.cpp b/libcxx/test/std/utilities/utility/pairs/pairs.pair/default.pass.cpp
index de3730ef3cb..9c53cb8d14b 100644
--- a/libcxx/test/std/utilities/utility/pairs/pairs.pair/default.pass.cpp
+++ b/libcxx/test/std/utilities/utility/pairs/pairs.pair/default.pass.cpp
@@ -10,7 +10,7 @@
 
 // template <class T1, class T2> struct pair
 
-// constexpr pair();
+// explicit(see-below) constexpr pair();
 
 // This test doesn't pass due to a constexpr bug in GCC 4.9 that fails
 // to initialize any type without a user provided constructor in a constant