[LLVMbugs] [Bug 24137] New: std::make_shared will fail to compile for a const class with a default constructor

[bugzilla-daemon at llvm.org]

https://llvm.org/bugs/show_bug.cgi?id=24137

            Bug ID: 24137
           Summary: std::make_shared will fail to compile for a const
                    class with a default constructor
           Product: libc++
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: krasin at google.com
                CC: llvmbugs at cs.uiuc.edu, mclow.lists at gmail.com
    Classification: Unclassified

The following code will fail to compile:

#include <memory>

class Lala {
 public:
  Lala() = default;
  //Lala() {}                                                                   
  virtual ~Lala() = default;
};

int main(void) {
  const auto ptr = std::make_shared<const Lala>();
}

The error message is unsettling:

/usr/local/include/c++/v1/memory:2119:40: error: constructor for
'std::__1::__libcpp_compressed_pair_imp<std::__1::allocator<const Lala>, const
Lala, 1>' must explicitly initialize the const member '__second_'
    _LIBCPP_INLINE_VISIBILITY explicit __libcpp_compressed_pair_imp(_T1_param
__t1)
                                       ^
/usr/local/include/c++/v1/memory:2389:11: note: in instantiation of member
function 'std::__1::__libcpp_compressed_pair_imp<std::__1::allocator<const
Lala>, const Lala, 1>::__libcpp_compressed_pair_imp' requested here
        : base(_VSTD::forward<_T1_param>(__t1)) {}
          ^
/usr/local/include/c++/v1/memory:3771:12: note: in instantiation of member
function 'std::__1::__compressed_pair<std::__1::allocator<const Lala>, const
Lala>::__compressed_pair' requested here
        :  __data_(_VSTD::move(__a)) {}
           ^
/usr/local/include/c++/v1/memory:4366:26: note: in instantiation of member
function 'std::__1::__shared_ptr_emplace<const Lala, std::__1::allocator<const
Lala> >::__shared_ptr_emplace' requested here
    ::new(__hold2.get()) _CntrlBlk(__a2, _VSTD::forward<_Args>(__args)...);
                         ^
/usr/local/include/c++/v1/memory:4730:29: note: in instantiation of function
template specialization 'std::__1::shared_ptr<const Lala>::make_shared<>'
requested here
    return shared_ptr<_Tp>::make_shared(_VSTD::forward<_Args>(__args)...);
                            ^
/home/krasin/make_shared.cc:11:25: note: in instantiation of function template
specialization 'std::__1::make_shared<const Lala>' requested here
  const auto ptr = std::make_shared<const Lala>();
                        ^
/usr/local/include/c++/v1/memory:2107:9: note: '__second_' declared here
    _T2 __second_;
        ^
1 error generated.

I suspect this could be related to https://llvm.org/bugs/show_bug.cgi?id=21917,
but my feelings are that it's a different bug. Feel free to close this one, and
I will reopen 21917.

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