libstdc++: Add deduction guides for std::packaged_task [PR105375]

This change was LWG 3117.

The test is copied from 20_util/function/cons/deduction.cc

libstdc++-v3/ChangeLog:

	PR libstdc++/105375
	* include/std/future (packaged_task): Add deduction guides.
	* testsuite/30_threads/packaged_task/cons/deduction.cc: New test.

libstdc++-v3/include/std/future

@@ -1622,6 +1622,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       }
     };
 
+  // _GLIBCXX_RESOLVE_LIB_DEFECTS
+  // 3117. Missing packaged_task deduction guides
+#if __cpp_deduction_guides >= 201606
+  template<typename _Res, typename... _ArgTypes>
+    packaged_task(_Res(*)(_ArgTypes...)) -> packaged_task<_Res(_ArgTypes...)>;
+
+  template<typename _Fun, typename _Signature = typename
+	   __function_guide_helper<decltype(&_Fun::operator())>::type>
+    packaged_task(_Fun) -> packaged_task<_Signature>;
+#endif
+
   /// swap
   template<typename _Res, typename... _ArgTypes>
     inline void

libstdc++-v3/testsuite/30_threads/packaged_task/cons/deduction.cc

@@ -0,0 +1,85 @@
+// // Copyright (C) 2017-2022 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++17 } }
+
+#include <future>
+
+template<typename T, typename U> struct require_same;
+template<typename T> struct require_same<T, T> { using type = void; };
+
+template<typename T, typename U>
+  typename require_same<T, U>::type
+  check_type(U&) { }
+
+void f0v();
+void f0vn() noexcept;
+int f0i();
+int f0in() noexcept;
+long f1l(int&);
+long f1ln(double*) noexcept;
+
+void
+test01()
+{
+  std::packaged_task task1{f0v};
+  check_type<std::packaged_task<void()>>(task1);
+
+  std::packaged_task task2{f0vn};
+  check_type<std::packaged_task<void()>>(task2);
+
+  std::packaged_task task3{f0i};
+  check_type<std::packaged_task<int()>>(task3);
+
+  std::packaged_task task4{f0in};
+  check_type<std::packaged_task<int()>>(task4);
+
+  std::packaged_task task5{f1l};
+  check_type<std::packaged_task<long(int&)>>(task5);
+
+  std::packaged_task task6{f1ln};
+  check_type<std::packaged_task<long(double*)>>(task6);
+
+  std::packaged_task task5a{std::move(task5)};
+  check_type<std::packaged_task<long(int&)>>(task5a);
+
+  std::packaged_task task6a{std::move(task6)};
+  check_type<std::packaged_task<long(double*)>>(task6a);
+}
+
+struct X {
+  int operator()(const short&, void*);
+};
+
+struct Y {
+  void operator()(int) const & noexcept;
+};
+
+void
+test02()
+{
+  X x;
+  std::packaged_task task1{x};
+  check_type<std::packaged_task<int(const short&, void*)>>(task1);
+
+  Y y;
+  std::packaged_task task2{y};
+  check_type<std::packaged_task<void(int)>>(task2);
+
+  std::packaged_task task3{[&x](float) -> X& { return x; }};
+  check_type<std::packaged_task<X&(float)>>(task3);
+}