[gcc r9-8832] libstdc++: Make variant_npos conversions explicit [PR 96766]

[Jonathan Wakely]

https://gcc.gnu.org/g:9def04578cca8a0850e835eb095d9ff60097f691

commit r9-8832-g9def04578cca8a0850e835eb095d9ff60097f691
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Aug 24 16:10:07 2020 +0100

    libstdc++: Make variant_npos conversions explicit [PR 96766]
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/96766
            * include/std/variant (_Variant_storage): Replace implicit
            conversions from size_t to __index_type with explicit casts.
    
    (cherry picked from commit 074436cf8cdd2a9ce75cadd36deb8301f00e55b9)

Diff:
---
 libstdc++-v3/include/std/variant | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index e1882b36700..91fec0baab6 100644
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -372,12 +372,16 @@ namespace __variant
   template<typename... _Types>
     struct _Variant_storage<false, _Types...>
     {
-      constexpr _Variant_storage() : _M_index(variant_npos) { }
+      constexpr
+      _Variant_storage()
+      : _M_index(static_cast<__index_type>(variant_npos))
+      { }
 
       template<size_t _Np, typename... _Args>
-	constexpr _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
+	constexpr
+	_Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
 	: _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
-	_M_index(_Np)
+	_M_index{_Np}
 	{ }
 
       constexpr void _M_reset_impl()
@@ -395,7 +399,7 @@ namespace __variant
       void _M_reset()
       {
 	_M_reset_impl();
-	_M_index = variant_npos;
+	_M_index = static_cast<__index_type>(variant_npos);
       }
 
       ~_Variant_storage()
@@ -424,16 +428,20 @@ namespace __variant
   template<typename... _Types>
     struct _Variant_storage<true, _Types...>
     {
-      constexpr _Variant_storage() : _M_index(variant_npos) { }
+      constexpr
+      _Variant_storage()
+      : _M_index(static_cast<__index_type>(variant_npos))
+      { }
 
       template<size_t _Np, typename... _Args>
-	constexpr _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
+	constexpr
+	_Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
 	: _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
-	_M_index(_Np)
+	_M_index{_Np}
 	{ }
 
       void _M_reset()
-      { _M_index = variant_npos; }
+      { _M_index = static_cast<__index_type>(variant_npos); }
 
       void*
       _M_storage() const
@@ -447,7 +455,7 @@ namespace __variant
       {
 	if constexpr (__never_valueless<_Types...>())
 	  return true;
-	return this->_M_index != __index_type(variant_npos);
+	return this->_M_index != static_cast<__index_type>(variant_npos);
       }
 
       _Variadic_union<_Types...> _M_u;