[committed] libstdc++: Add noexcept-specifier to std::reference_wrapper::operator()

[Jonathan Wakely via Gcc-patches]

Tested x86_64-linux, pushed to trunk.

-- >8 --

This isn't required by the standard, but there's an LWG issue suggesting
to add it.

Also use __invoke_result instead of result_of, to match the spec in
recent standards.

libstdc++-v3/ChangeLog:

        * include/bits/refwrap.h (reference_wrapper::operator()): Add
        noexcept-specifier and use __invoke_result instead of result_of.
        * testsuite/20_util/reference_wrapper/invoke-noexcept.cc: New test.
---
 libstdc++-v3/include/bits/refwrap.h               |  3 ++-
 .../20_util/reference_wrapper/invoke-noexcept.cc  | 15 +++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)
 create mode 100644 
libstdc++-v3/testsuite/20_util/reference_wrapper/invoke-noexcept.cc

diff --git a/libstdc++-v3/include/bits/refwrap.h 
b/libstdc++-v3/include/bits/refwrap.h
index 8016f87478e..976902bc7bc 100644
--- a/libstdc++-v3/include/bits/refwrap.h
+++ b/libstdc++-v3/include/bits/refwrap.h
@@ -348,8 +348,9 @@ _GLIBCXX_MEM_FN_TRAITS(&& noexcept, false_type, true_type)
 
       template<typename... _Args>
        _GLIBCXX20_CONSTEXPR
-       typename result_of<_Tp&(_Args&&...)>::type
+       typename __invoke_result<_Tp&, _Args...>::type
        operator()(_Args&&... __args) const
+       noexcept(__is_nothrow_invocable<_Tp&, _Args...>::value)
        {
 #if __cplusplus > 201703L
          if constexpr (is_object_v<type>)
diff --git 
a/libstdc++-v3/testsuite/20_util/reference_wrapper/invoke-noexcept.cc 
b/libstdc++-v3/testsuite/20_util/reference_wrapper/invoke-noexcept.cc
new file mode 100644
index 00000000000..91b5d097f08
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/reference_wrapper/invoke-noexcept.cc
@@ -0,0 +1,15 @@
+// { dg-do compile { target c++11 } }
+
+// C++11 20.8.3.4 reference_wrapper invocation [refwrap.invoke]
+
+#include <functional>
+
+struct F
+{
+  int operator()() noexcept(true) { return 1; }
+  int operator()() const noexcept(false) { return 2; }
+};
+
+F f;
+static_assert( noexcept(std::ref(f)()) );
+static_assert( ! noexcept(std::cref(f)()) );
-- 
2.37.2