[PATCH] Disable -Wctor-dtor-privacy warnings for some standard types

[Jonathan Wakely]

These types are not constructible by design, so we never want warnings
for them, even with -Wsystem-headers.

	* include/experimental/type_traits (experimental::nonesuch): Use
	pragma to disable -Wctor-dtor-privacy warnings.
	* include/std/type_traits (__is_convertible_helper<From, To, false>)
	(__is_nt_convertible_helper<From, To, false>, __nonesuch): Likewise.

Tested x86_64-linux, committed to trunk.


-------------- next part --------------
commit bde783a93449ed52ffa301c338b23cd57df0cc77
Author: redi <redi@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Fri Jun 14 14:03:20 2019 +0000

    Disable -Wctor-dtor-privacy warnings for some standard types
    
            * include/experimental/type_traits (experimental::nonesuch): Use
            pragma to disable -Wctor-dtor-privacy warnings.
            * include/std/type_traits (__is_convertible_helper<From, To, false>)
            (__is_nt_convertible_helper<From, To, false>, __nonesuch): Likewise.
    
    git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@272289 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/libstdc++-v3/include/experimental/type_traits b/libstdc++-v3/include/experimental/type_traits
index 2403bd24223..464c8d2f4bf 100644
--- a/libstdc++-v3/include/experimental/type_traits
+++ b/libstdc++-v3/include/experimental/type_traits
@@ -227,6 +227,8 @@ inline namespace fundamentals_v2
 
 template<typename...> using void_t = void;
 
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wctor-dtor-privacy"
 struct __nonesuchbase {};
 struct nonesuch : private __nonesuchbase
 {
@@ -234,6 +236,7 @@ struct nonesuch : private __nonesuchbase
   nonesuch(nonesuch const&) = delete;
   void operator=(nonesuch const&) = delete;
 };
+#pragma GCC diagnostic pop
 
 template<template<typename...> class _Op, typename... _Args>
   using is_detected
diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index e53d3c8d535..7d4deb156a1 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -1448,6 +1448,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       typedef typename is_void<_To>::type type;
     };
 
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wctor-dtor-privacy"
   template<typename _From, typename _To>
     class __is_convertible_helper<_From, _To, false>
     {
@@ -1466,7 +1468,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     public:
       typedef decltype(__test<_From, _To>(0)) type;
     };
-
+#pragma GCC diagnostic pop
 
   /// is_convertible
   template<typename _From, typename _To>
@@ -1481,6 +1483,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     : is_void<_To>
     { };
 
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wctor-dtor-privacy"
   template<typename _From, typename _To>
     class __is_nt_convertible_helper<_From, _To, false>
     {
@@ -1499,6 +1503,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     public:
       using type = decltype(__test<_From, _To>(0));
     };
+#pragma GCC diagnostic pop
 
   // is_nothrow_convertible for C++11
   template<typename _From, typename _To>
@@ -2894,12 +2899,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
              __call_is_nothrow_<_Fn, _Args...>>::type
     { };
 
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wctor-dtor-privacy"
   struct __nonesuchbase {};
   struct __nonesuch : private __nonesuchbase {
     ~__nonesuch() = delete;
     __nonesuch(__nonesuch const&) = delete;
     void operator=(__nonesuch const&) = delete;
   };
+#pragma GCC diagnostic pop
 
 #if __cplusplus >= 201703L
 # define __cpp_lib_is_invocable 201703