[PATCH] PR libstdc++/79486 use lvalues in result_of expressions

[Jonathan Wakely]

This is a similar bug to the is_callable assertions I fixed in
shared_ptr the other day: it needs to use the correct value category
in the result_of type. This is also a regression, in code that has
been refactored on trunk.

        PR libstdc++/79486
        * include/std/future (__future_base::_Task_state::_M_run)
        (__future_base::_Task_state::_M_run_delayed): Use lvalue types in
        result_of expressions.
        * testsuite/30_threads/packaged_task/79486.cc: New.

Tested powerpc64le-linux, committed to trunk.



commit 10639bc87b988d5cdac07fc905fe4d8c800a6283
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Mon Feb 13 12:51:51 2017 +0000

    PR libstdc++/79486 use lvalues in result_of expressions
    
        PR libstdc++/79486
        * include/std/future (__future_base::_Task_state::_M_run)
        (__future_base::_Task_state::_M_run_delayed): Use lvalue types in
        result_of expressions.
        * testsuite/30_threads/packaged_task/79486.cc: New.

diff --git a/libstdc++-v3/include/std/future b/libstdc++-v3/include/std/future
index 6351d7e..cb53561 100644
--- a/libstdc++-v3/include/std/future
+++ b/libstdc++-v3/include/std/future
@@ -1416,7 +1416,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       virtual void
       _M_run(_Args&&... __args)
       {
-       auto __boundfn = [&] () -> typename result_of<_Fn(_Args&&...)>::type {
+       auto __boundfn = [&] () -> typename result_of<_Fn&(_Args&&...)>::type {
            return std::__invoke(_M_impl._M_fn, std::forward<_Args>(__args)...);
        };
        this->_M_set_result(_S_task_setter(this->_M_result, __boundfn));
@@ -1425,7 +1425,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       virtual void
       _M_run_delayed(_Args&&... __args, weak_ptr<_State_base> __self)
       {
-       auto __boundfn = [&] () -> typename result_of<_Fn(_Args&&...)>::type {
+       auto __boundfn = [&] () -> typename result_of<_Fn&(_Args&&...)>::type {
            return std::__invoke(_M_impl._M_fn, std::forward<_Args>(__args)...);
        };
        this->_M_set_delayed_result(_S_task_setter(this->_M_result, __boundfn),
diff --git a/libstdc++-v3/testsuite/30_threads/packaged_task/79486.cc 
b/libstdc++-v3/testsuite/30_threads/packaged_task/79486.cc
new file mode 100644
index 0000000..46b4f3d
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/packaged_task/79486.cc
@@ -0,0 +1,27 @@
+// Copyright (C) 2017 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-do compile { target c++11 } }
+
+#include <future>
+
+struct F {
+  void operator()() & { }
+  void operator()() && = delete; // PR libstdc++/79486
+};
+
+std::packaged_task<void()> t{F{}};