[PATCH] Deprecate std::__is_nullptr_t type trait

[Jonathan Wakely]

This non-standard extension is redundant and unused by the library.

        * include/std/type_traits (__is_nullptr_t): Add deprecated attribute.

We support std::is_null_pointer so don't need a non-standard trait
that does the same thing.

Tested x86_64-linux, committed to trunk.


commit 8068073ad959c806a925b6c031965f6db6b70c90
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Wed Aug 14 12:26:24 2019 +0100

    Deprecate std::__is_nullptr_t type trait
    
    This non-standard extension is redundant and unused by the library.
    
            * include/std/type_traits (__is_nullptr_t): Add deprecated 
attribute.

diff --git a/libstdc++-v3/include/std/type_traits 
b/libstdc++-v3/include/std/type_traits
index b31c26ab381..d3f853d4ce2 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -597,11 +597,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     : public __is_null_pointer_helper<typename remove_cv<_Tp>::type>::type
     { };
 
-  /// __is_nullptr_t (extension).
+  /// __is_nullptr_t (deprecated extension).
   template<typename _Tp>
     struct __is_nullptr_t
     : public is_null_pointer<_Tp>
-    { };
+    { } _GLIBCXX_DEPRECATED;
 
   // Composite type categories.