PR libstdc++/84535 constrain std::thread constructor

The standard requires that the std::thread constructor is constrained so
it can't be called with a first argument of type std::thread. The
current implementation only meets that requirement if the constructor is
called with one argument, by using deleted overloads. This uses an
enable_if constraint to enforce the requirement for any number of
arguments.

Also add a static assertion to give a more readable error for invalid
arguments that cannot be invoked. Also simplify _Invoker to reduce the
error cascade for ill-formed instantiations with non-invocable
arguments.

	PR libstdc++/84535
	* include/std/thread (thread::__not_same): New SFINAE helper.
	(thread::thread(_Callable&&, _Args&&...)): Add SFINAE constraint that
	first argument is not a std::thread. Add static assertion to check
	INVOKE expression is valid.
	(thread::thread(thread&), thread::thread(const thread&&)): Remove.
	(thread::_Invoke::_M_invoke, thread::_Invoke::operator()): Use
	__invoke_result for return types and remove exception specifications.
	* testsuite/30_threads/thread/cons/84535.cc: New.

From-SVN: r259893

libstdc++-v3/ChangeLog

 2018-05-03  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/84535
+	* include/std/thread (thread::__not_same): New SFINAE helper.
+	(thread::thread(_Callable&&, _Args&&...)): Add SFINAE constraint that
+	first argument is not a std::thread. Add static assertion to check
+	INVOKE expression is valid.
+	(thread::thread(thread&), thread::thread(const thread&&)): Remove.
+	(thread::_Invoke::_M_invoke, thread::_Invoke::operator()): Use
+	__invoke_result for return types and remove exception specifications.
+	* testsuite/30_threads/thread/cons/84535.cc: New.
+
 	* include/std/future (__async_result_of): Use __invoke_result instead
 	of result_of.
 

libstdc++-v3/include/std/thread

@@ -102,21 +102,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   private:
     id				_M_id;
 
-  public:
-    thread() noexcept = default;
     // _GLIBCXX_RESOLVE_LIB_DEFECTS
     // 2097.  packaged_task constructors should be constrained
-    thread(thread&) = delete;
-    thread(const thread&) = delete;
-    thread(const thread&&) = delete;
+    template<typename _Tp>
+      using __not_same = __not_<is_same<__remove_cvref_t<_Tp>, thread>>;
 
-    thread(thread&& __t) noexcept
-    { swap(__t); }
+  public:
+    thread() noexcept = default;
 
-    template<typename _Callable, typename... _Args>
+    template<typename _Callable, typename... _Args,
+	     typename = _Require<__not_same<_Callable>>>
       explicit
       thread(_Callable&& __f, _Args&&... __args)
       {
+	static_assert( __is_invocable<typename decay<_Callable>::type,
+				      typename decay<_Args>::type...>::value,
+	  "std::thread arguments must be invocable after conversion to rvalues"
+	  );
+
 #ifdef GTHR_ACTIVE_PROXY
 	// Create a reference to pthread_create, not just the gthr weak symbol.
 	auto __depend = reinterpret_cast<void(*)()>(&pthread_create);
@@ -135,6 +138,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	std::terminate();
     }
 
+    thread(const thread&) = delete;
+
+    thread(thread&& __t) noexcept
+    { swap(__t); }
+
     thread& operator=(const thread&) = delete;
 
     thread& operator=(thread&& __t) noexcept
@@ -222,29 +230,29 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       {
 	_Tuple _M_t;
 
-	template<size_t _Index>
-	  static __tuple_element_t<_Index, _Tuple>&&
-	  _S_declval();
+	template<typename>
+	  struct __result;
+	template<typename _Fn, typename... _Args>
+	  struct __result<tuple<_Fn, _Args...>>
+	  : __invoke_result<_Fn, _Args...>
+	  { };
 
 	template<size_t... _Ind>
-	  auto
+	  typename __result<_Tuple>::type
 	  _M_invoke(_Index_tuple<_Ind...>)
-	  noexcept(noexcept(std::__invoke(_S_declval<_Ind>()...)))
-	  -> decltype(std::__invoke(_S_declval<_Ind>()...))
 	  { return std::__invoke(std::get<_Ind>(std::move(_M_t))...); }
 
-	using _Indices
-	  = typename _Build_index_tuple<tuple_size<_Tuple>::value>::__type;
-
-	auto
+	typename __result<_Tuple>::type
 	operator()()
-	noexcept(noexcept(std::declval<_Invoker&>()._M_invoke(_Indices())))
-	-> decltype(std::declval<_Invoker&>()._M_invoke(_Indices()))
-	{ return _M_invoke(_Indices()); }
+	{
+	  using _Indices
+	    = typename _Build_index_tuple<tuple_size<_Tuple>::value>::__type;
+	  return _M_invoke(_Indices());
+	}
       };
 
     template<typename... _Tp>
-      using __decayed_tuple = tuple<typename std::decay<_Tp>::type...>;
+      using __decayed_tuple = tuple<typename decay<_Tp>::type...>;
 
   public:
     // Returns a call wrapper that stores

libstdc++-v3/testsuite/30_threads/thread/cons/84535.cc

+// { dg-do compile { target c++11 } }
+// { dg-require-cstdint "" }
+// { dg-require-gthreads "" }
+
+// Copyright (C) 2018 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/>.
+
+#include <thread>
+
+using std::is_constructible;
+using std::thread;
+
+// PR libstdc++/84535
+static_assert(!is_constructible<thread, thread, int>::value, "");
+static_assert(!is_constructible<thread, thread&, int>::value, "");
+static_assert(!is_constructible<thread, const thread&, int>::value, "");
+static_assert(!is_constructible<thread, const thread&&, int>::value, "");