[committed] libstdc++: Swap expressions in noexcept-specifier of ranges::not_equal_to

[Jonathan Wakely]

Although this should never make a difference for sensible code, we
should really make the expression in the noexcept-specifier match the
expression in the function body.

libstdc++-v3/ChangeLog:

        * include/bits/ranges_cmp.h (not_equal_to): Make order of
        expressions in noexcept-specifier match the body.
        * testsuite/20_util/function_objects/range.cmp/not_equal_to.cc:
        Check noexcept.
---

Tested x86_64-linux. Pushed to trunk.

 libstdc++-v3/include/bits/ranges_cmp.h          |  2 +-
 .../function_objects/range.cmp/not_equal_to.cc  | 17 +++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/bits/ranges_cmp.h 
b/libstdc++-v3/include/bits/ranges_cmp.h
index 8425016288c..b1a33f48d02 100644
--- a/libstdc++-v3/include/bits/ranges_cmp.h
+++ b/libstdc++-v3/include/bits/ranges_cmp.h
@@ -99,7 +99,7 @@ namespace ranges
       requires equality_comparable_with<_Tp, _Up>
       constexpr bool
       operator()(_Tp&& __t, _Up&& __u) const
-      noexcept(noexcept(std::declval<_Up>() == std::declval<_Tp>()))
+      noexcept(noexcept(std::declval<_Tp>() == std::declval<_Up>()))
       { return !equal_to{}(std::forward<_Tp>(__t), std::forward<_Up>(__u)); }
 
     using is_transparent = __is_transparent;
diff --git 
a/libstdc++-v3/testsuite/20_util/function_objects/range.cmp/not_equal_to.cc 
b/libstdc++-v3/testsuite/20_util/function_objects/range.cmp/not_equal_to.cc
index 5b4f3cb32ff..1b5167f9783 100644
--- a/libstdc++-v3/testsuite/20_util/function_objects/range.cmp/not_equal_to.cc
+++ b/libstdc++-v3/testsuite/20_util/function_objects/range.cmp/not_equal_to.cc
@@ -68,9 +68,26 @@ test02()
   VERIFY( ! f(x, x) );
 }
 
+struct A
+{
+  bool operator==(const A&) const noexcept { return true; }
+  bool operator==(A&&) const { return true; }
+};
+
+void
+test03()
+{
+  const A a{};
+  static_assert( noexcept(a == a) );
+  static_assert( ! noexcept(a == A{}) );
+  static_assert( noexcept(std::ranges::not_equal_to{}(a, a)) );
+  static_assert( ! noexcept(std::ranges::not_equal_to{}(a, A{})) );
+}
+
 int
 main()
 {
   test01();
   test02();
+  test03();
 }
-- 
2.47.1