libstdc++: Define operator<=> for std::stack and std::queue

Some more C++20 changes from P1614R2, "The Mothership has Landed".

	* include/bits/stl_queue.h (queue): Define operator<=> for C++20.
	* include/bits/stl_stack.h (stack): Likewise.
	* testsuite/23_containers/queue/cmp_c++20.cc: New test.
	* testsuite/23_containers/stack/cmp_c++20.cc: New test.

5 files changed, 151 insertions, 0 deletions

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index f7e0022..fde5ac1 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,5 +1,10 @@
 2020-04-19  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/bits/stl_queue.h (queue): Define operator<=> for C++20.
+	* include/bits/stl_stack.h (stack): Likewise.
+	* testsuite/23_containers/queue/cmp_c++20.cc: New test.
+	* testsuite/23_containers/stack/cmp_c++20.cc: New test.
+
 	* include/bits/unordered_map.h (unordered_map, unordered_multimap):
 	Remove redundant operator!= for C++20.
 	* include/bits/unordered_set.h (unordered_set, unordered_multiset):
diff --git a/libstdc++-v3/include/bits/stl_queue.h b/libstdc++-v3/include/bits/stl_queue.h
index d2b2705..8635d42 100644
--- a/libstdc++-v3/include/bits/stl_queue.h
+++ b/libstdc++-v3/include/bits/stl_queue.h
@@ -114,6 +114,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	friend bool
 	operator<(const queue<_Tp1, _Seq1>&, const queue<_Tp1, _Seq1>&);
 
+#if __cpp_lib_three_way_comparison
+      template<typename _Tp1, three_way_comparable _Seq1>
+	friend compare_three_way_result_t<_Seq1>
+	operator<=>(const queue<_Tp1, _Seq1>&, const queue<_Tp1, _Seq1>&);
+#endif
+
 #if __cplusplus >= 201103L
       template<typename _Alloc>
 	using _Uses = typename
@@ -380,6 +386,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     operator>=(const queue<_Tp, _Seq>& __x, const queue<_Tp, _Seq>& __y)
     { return !(__x < __y); }
 
+#if __cpp_lib_three_way_comparison
+  template<typename _Tp, three_way_comparable _Seq>
+    inline compare_three_way_result_t<_Seq>
+    operator<=>(const queue<_Tp, _Seq>& __x, const queue<_Tp, _Seq>& __y)
+    { return __x.c <=> __y.c; }
+#endif
+
 #if __cplusplus >= 201103L
   template<typename _Tp, typename _Seq>
     inline
diff --git a/libstdc++-v3/include/bits/stl_stack.h b/libstdc++-v3/include/bits/stl_stack.h
index 355966a..1ce98a9 100644
--- a/libstdc++-v3/include/bits/stl_stack.h
+++ b/libstdc++-v3/include/bits/stl_stack.h
@@ -116,6 +116,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	friend bool
 	operator<(const stack<_Tp1, _Seq1>&, const stack<_Tp1, _Seq1>&);
 
+#if __cpp_lib_three_way_comparison
+      template<typename _Tp1, three_way_comparable _Seq1>
+	friend compare_three_way_result_t<_Seq1>
+	operator<=>(const stack<_Tp1, _Seq1>&, const stack<_Tp1, _Seq1>&);
+#endif
+
 #if __cplusplus >= 201103L
       template<typename _Alloc>
 	using _Uses = typename
@@ -355,6 +361,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     operator>=(const stack<_Tp, _Seq>& __x, const stack<_Tp, _Seq>& __y)
     { return !(__x < __y); }
 
+#if __cpp_lib_three_way_comparison
+  template<typename _Tp, three_way_comparable _Seq>
+    inline compare_three_way_result_t<_Seq>
+    operator<=>(const stack<_Tp, _Seq>& __x, const stack<_Tp, _Seq>& __y)
+    { return __x.c <=> __y.c; }
+#endif
+
 #if __cplusplus >= 201103L
   template<typename _Tp, typename _Seq>
     inline
diff --git a/libstdc++-v3/testsuite/23_containers/queue/cmp_c++20.cc b/libstdc++-v3/testsuite/23_containers/queue/cmp_c++20.cc
new file mode 100644
index 0000000..5d0d4c97
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/queue/cmp_c++20.cc
@@ -0,0 +1,60 @@
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <queue>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  std::queue<int> c1{ {1, 2, 3} }, c2{ {1, 2, 3, 4} }, c3{ {1, 2, 4} };
+  VERIFY( c1 == c1 );
+  VERIFY( std::is_eq(c1 <=> c1) );
+  VERIFY( c1 < c2 );
+  VERIFY( std::is_lt(c1 <=> c2) );
+  VERIFY( c1 < c3 );
+  VERIFY( std::is_lt(c1 <=> c3) );
+  VERIFY( c2 < c3 );
+  VERIFY( std::is_lt(c2 <=> c3) );
+
+  static_assert( std::totally_ordered<std::queue<int>> );
+
+  static_assert( std::three_way_comparable<std::queue<int>,
+					   std::strong_ordering> );
+  static_assert( ! std::three_way_comparable<std::queue<float>,
+					     std::strong_ordering> );
+  static_assert( ! std::three_way_comparable<std::queue<float>,
+					     std::weak_ordering> );
+  static_assert( std::three_way_comparable<std::queue<float>,
+					   std::partial_ordering> );
+
+  struct E
+  {
+    bool operator==(E) { return true; }
+  };
+  static_assert( ! std::three_way_comparable<E> );
+  static_assert( ! std::three_way_comparable<std::queue<E>> );
+}
+
+int
+main()
+{
+  test01();
+}
diff --git a/libstdc++-v3/testsuite/23_containers/stack/cmp_c++20.cc b/libstdc++-v3/testsuite/23_containers/stack/cmp_c++20.cc
new file mode 100644
index 0000000..054e487
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/stack/cmp_c++20.cc
@@ -0,0 +1,60 @@
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <stack>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  std::stack<int> c1{ {1, 2, 3} }, c2{ {1, 2, 3, 4} }, c3{ {1, 2, 4} };
+  VERIFY( c1 == c1 );
+  VERIFY( std::is_eq(c1 <=> c1) );
+  VERIFY( c1 < c2 );
+  VERIFY( std::is_lt(c1 <=> c2) );
+  VERIFY( c1 < c3 );
+  VERIFY( std::is_lt(c1 <=> c3) );
+  VERIFY( c2 < c3 );
+  VERIFY( std::is_lt(c2 <=> c3) );
+
+  static_assert( std::totally_ordered<std::stack<int>> );
+
+  static_assert( std::three_way_comparable<std::stack<int>,
+					   std::strong_ordering> );
+  static_assert( ! std::three_way_comparable<std::stack<float>,
+					     std::strong_ordering> );
+  static_assert( ! std::three_way_comparable<std::stack<float>,
+					     std::weak_ordering> );
+  static_assert( std::three_way_comparable<std::stack<float>,
+					   std::partial_ordering> );
+
+  struct E
+  {
+    bool operator==(E) { return true; }
+  };
+  static_assert( ! std::three_way_comparable<E> );
+  static_assert( ! std::three_way_comparable<std::stack<E>> );
+}
+
+int
+main()
+{
+  test01();
+}