[llvm-bugs] [Bug 36353] New: Can not derive from time_get_byname

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=36353

            Bug ID: 36353
           Summary: Can not derive from time_get_byname
           Product: libc++
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: jasonliu.development at gmail.com
                CC: llvm-bugs at lists.llvm.org, mclow.lists at gmail.com

I think this is a valid use case:

#include <locale>
typedef std::char_traits<wchar_t> It;
typedef std::istreambuf_iterator<wchar_t, It> Isit;
struct Mytime : public std::time_get_byname<wchar_t, Isit> {
    Mytime(const char *name, size_t refs)
        : std::time_get_byname<wchar_t, Isit>(name, refs) {}
    };

int main(){
const Mytime t("A",1);
}


When I compile this, I get a bunch of undefined symbols:

  "std::__1::time_get_byname<wchar_t, std::__1::istreambuf_iterator<wchar_t,
std::__1::char_traits<wchar_t> > >::do_date_order() const", referenced from:
      vtable for Mytime in bb-639bbe.o
  "std::__1::time_get_byname<wchar_t, std::__1::istreambuf_iterator<wchar_t,
std::__1::char_traits<wchar_t> > >::__X() const", referenced from:
      vtable for Mytime in bb-639bbe.o
  "std::__1::time_get_byname<wchar_t, std::__1::istreambuf_iterator<wchar_t,
std::__1::char_traits<wchar_t> > >::__c() const", referenced from:
      vtable for Mytime in bb-639bbe.o
  "std::__1::time_get_byname<wchar_t, std::__1::istreambuf_iterator<wchar_t,
std::__1::char_traits<wchar_t> > >::__r() const", referenced from:
      vtable for Mytime in bb-639bbe.o
  "std::__1::time_get_byname<wchar_t, std::__1::istreambuf_iterator<wchar_t,
std::__1::char_traits<wchar_t> > >::__x() const", referenced from:
      vtable for Mytime in bb-639bbe.o
  "std::__1::time_get_byname<wchar_t, std::__1::istreambuf_iterator<wchar_t,
std::__1::char_traits<wchar_t> > >::__am_pm() const", referenced from:
      vtable for Mytime in bb-639bbe.o
  "std::__1::time_get_byname<wchar_t, std::__1::istreambuf_iterator<wchar_t,
std::__1::char_traits<wchar_t> > >::__weeks() const", referenced from:
      vtable for Mytime in bb-639bbe.o
  "std::__1::time_get_byname<wchar_t, std::__1::istreambuf_iterator<wchar_t,
std::__1::char_traits<wchar_t> > >::__months() const", referenced from:
      vtable for Mytime in bb-639bbe.o
  "non-virtual thunk to std::__1::time_get_byname<wchar_t,
std::__1::istreambuf_iterator<wchar_t, std::__1::char_traits<wchar_t> >
>::__X() const", referenced from:
      vtable for Mytime in bb-639bbe.o
  "non-virtual thunk to std::__1::time_get_byname<wchar_t,
std::__1::istreambuf_iterator<wchar_t, std::__1::char_traits<wchar_t> >
>::__c() const", referenced from:
      vtable for Mytime in bb-639bbe.o
  "non-virtual thunk to std::__1::time_get_byname<wchar_t,
std::__1::istreambuf_iterator<wchar_t, std::__1::char_traits<wchar_t> >
>::__r() const", referenced from:
      vtable for Mytime in bb-639bbe.o
  "non-virtual thunk to std::__1::time_get_byname<wchar_t,
std::__1::istreambuf_iterator<wchar_t, std::__1::char_traits<wchar_t> >
>::__x() const", referenced from:
      vtable for Mytime in bb-639bbe.o
  "non-virtual thunk to std::__1::time_get_byname<wchar_t,
std::__1::istreambuf_iterator<wchar_t, std::__1::char_traits<wchar_t> >
>::__am_pm() const", referenced from:
      vtable for Mytime in bb-639bbe.o
  "non-virtual thunk to std::__1::time_get_byname<wchar_t,
std::__1::istreambuf_iterator<wchar_t, std::__1::char_traits<wchar_t> >
>::__weeks() const", referenced from:
      vtable for Mytime in bb-639bbe.o
  "non-virtual thunk to std::__1::time_get_byname<wchar_t,
std::__1::istreambuf_iterator<wchar_t, std::__1::char_traits<wchar_t> >
>::__months() const", referenced from:
      vtable for Mytime in bb-639bbe.o

When I look at the header and I saw those functions are marked as "always
inline" and "hidden", any reason why those functions are marked as hidden in
the library?

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