Hi

Renewing my patch to fix PR 56112 but for the insert methods, I totally 
change it, now works also with move-only key types.

I let you Jonathan find a better name than _ValueTypeEnforcer as usual :-)

libstdc++: [_Hashtable] Insert range of types convertible to value_type 
PR 56112

Fix insertion of range of types convertible to value_type. Fix also when 
this value_type
has a move-only key_type which also allow converted values to be moved.

libstdc++-v3/ChangeLog:

         PR libstdc++/56112
         * include/bits/hashtable_policy.h (_ValueTypeEnforcer): New.
         * include/bits/hashtable.h 
(_Hashtable<>::_M_insert_unique_aux): New.
         (_Hashtable<>::_M_insert(_Arg&&, const _NodeGenerator&, 
true_type)): Use latters.
         (_Hashtable<>::_M_insert(_Arg&&, const _NodeGenerator&, 
false_type)): Likewise.
         (_Hashtable(_InputIterator, _InputIterator, size_type, const 
_Hash&, const _Equal&,
         const allocator_type&, true_type)): Use this.insert range.
         (_Hashtable(_InputIterator, _InputIterator, size_type, const 
_Hash&, const _Equal&,
         const allocator_type&, false_type)): Use _M_insert.
         * testsuite/23_containers/unordered_map/cons/56112.cc: Check 
how many times conversion
         is done.
         (test02): New test case.
         * testsuite/23_containers/unordered_set/cons/56112.cc: New test.

Tested under Linux x86_64.

Ok to commit ?

François