| Issue |
52956
|
| Summary |
clang-13 fails to compile libstdc++'s std::variant<std::vector<int>>: error: attempt to use a deleted function
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
trofi
|
Initially I observed the error as a `mold-1.0.0` build failure on `clang-13` which uses gcc-12's `libstdc++`. Here is a one line reproducer:
```c++
#include <variant>
#include <vector>
std::variant<std::vector<long> > v;
```
`gcc-12` builds it fine, `clang-13` fails:
```
$ /tmp/gcc-12/bin/c++ -std=c++20 -c tapi.cc
$ /tmp/clang-13/bin/c++ -std=c++20 -c tapi.cc
/<<NIX>>/gcc-12.0.0/include/c++/12.0.0/variant:460:2: error: attempt to use a deleted function
_Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
^
/<<NIX>>/gcc-12.0.0/include/c++/12.0.0/variant:747:4: note: in instantiation of function template specialization 'std::__detail::__variant::_Variant_storage<false, std::vector<long>>::_Variant_storage<0UL>' requested here
: _Base(__i, std::forward<_Args>(__args)...)
^
/<<NIX>>/gcc-12.0.0/include/c++/12.0.0/variant:742:9: note: in instantiation of function template specialization 'std::__detail::__variant::_Variant_base<std::vector<long>>::_Variant_base<0UL>' requested here
: _Variant_base(in_place_index<0>) { }
^
/<<NIX>>/gcc-12.0.0/include/c++/12.0.0/variant:1403:7: note: in instantiation of member function 'std::__detail::__variant::_Variant_base<std::vector<long>>::_Variant_base' requested here
variant() = default;
^
tapi.cc:13:34: note: in defaulted default constructor for 'std::variant<std::vector<long>>' first required here
std::variant<std::vector<long> > v;
^
/<<NIX>>/gcc-12.0.0/include/c++/12.0.0/variant:401:7: note: explicitly defaulted function was implicitly deleted here
~_Variadic_union() = default;
^
/<<NIX>>/gcc-12.0.0/include/c++/12.0.0/variant:409:30: note: destructor of '_Variadic_union<std::vector<long>>' is implicitly deleted because variant field '_M_first' has a non-trivial destructor
_Uninitialized<_First> _M_first;
^
/<<NIX>>/gcc-12.0.0/include/c++/12.0.0/variant:480:7: error: attempt to use a deleted function
~_Variant_storage()
^
/<<NIX>>/gcc-12.0.0/include/c++/12.0.0/variant:558:20: note: in instantiation of member function 'std::__detail::__variant::_Variant_storage<false, std::vector<long>>::~_Variant_storage' requested here
using _Base::_Base;
^
/<<NIX>>/gcc-12.0.0/include/c++/12.0.0/variant:742:9: note: in instantiation of function template specialization 'std::__detail::__variant::_Variant_base<std::vector<long>>::_Variant_base<0UL>' requested here
: _Variant_base(in_place_index<0>) { }
^
/<<NIX>>/gcc-12.0.0/include/c++/12.0.0/variant:1403:7: note: in instantiation of member function 'std::__detail::__variant::_Variant_base<std::vector<long>>::_Variant_base' requested here
variant() = default;
^
tapi.cc:13:34: note: in defaulted default constructor for 'std::variant<std::vector<long>>' first required here
std::variant<std::vector<long> > v;
^
/<<NIX>>/gcc-12.0.0/include/c++/12.0.0/variant:401:7: note: explicitly defaulted function was implicitly deleted here
~_Variadic_union() = default;
^
/<<NIX>>/gcc-12.0.0/include/c++/12.0.0/variant:409:30: note: destructor of '_Variadic_union<std::vector<long>>' is implicitly deleted because variant field '_M_first' has a non-trivial destructor
_Uninitialized<_First> _M_first;
^
2 errors generated.
```
I attempted to shrink down preprocessed file to extract compiler difference. My result:
```c++
struct _Vector_base {
~_Vector_base();
};
template <typename> union _Variadic_union {
~_Variadic_union() requires(!__has_trivial_destructor(_Variadic_union));
_Vector_base _M_first;
};
struct _Variant_storage {
_Variant_storage();
_Variadic_union<int> _M_u;
};
struct _Variant_storage v;
```
`gcc` / `clang` handling difference:
```
$ /tmp/gcc-12/bin/c++ -std=c++20 -c tapi.cc.cc
$ /tmp/clang-13/bin/c++ -std=c++20 -c tapi.cc.cc
tapi.cc.cc:6:32: error: incomplete type '_Variadic_union<int>' used in type trait _expression_
~_Variadic_union() requires(!__has_trivial_destructor(_Variadic_union));
^
tapi.cc.cc:11:24: note: in instantiation of template class '_Variadic_union<int>' requested here
_Variadic_union<int> _M_u;
^
tapi.cc.cc:5:27: note: definition of '_Variadic_union<int>' is not complete until the closing '}'
template <typename> union _Variadic_union {
^
tapi.cc.cc:13:25: error: attempt to use a deleted function
struct _Variant_storage v;
^
tapi.cc.cc:11:24: note: destructor of '_Variant_storage' is implicitly deleted because field '_M_u' has a deleted destructor
_Variadic_union<int> _M_u;
^
tapi.cc.cc:7:16: note: destructor of '_Variadic_union<int>' is implicitly deleted because variant field '_M_first' has a non-trivial destructor
_Vector_base _M_first;
^
2 errors generated.
```
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