https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90397
Bug ID: 90397
Summary: Incompatibility with clang-tidy on std::variant
Product: gcc
Version: 9.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: philip.salvaggio at mac dot com
Target Milestone: ---
Created attachment 46315
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46315&action=edit
Minimal example
Since upgrading to GCC 9.1.1, I am getting the following errors when running
clang-tidy (8.0.0) on this minimal example. Not sure whether this is a bug in
the libstdc++ headers or in clang, but it seems to be related to the noexcept
specifier on __get(). The code compiles fine with g++.
#include <variant>
int main() {
std::variant<int, double> v;
v = 5;
int i = std::get<int>(v);
return 0;
}
In order to reproduce from the zipped folder:
mkdir build && cd build
cmake ..
make
clang-tidy ../example.cpp
give the following errors for me.
[build]$ clang-tidy ../example.cpp
6 errors generated.
Error while processing /home/fedora/example/build/../example.cpp.
/usr/lib/gcc/x86_64-redhat-linux/9/../../../../include/c++/9/variant:266:10:
error: cannot cast 'const std::variant<int, double>' to its private base class
'std::__detail::__variant::_Variant_storage<true, int, double>'
[clang-diagnostic-error]
std::forward<_Variant>(__v)._M_u);
^
/usr/lib/gcc/x86_64-redhat-linux/9/../../../../include/c++/9/variant:1610:35:
note: in instantiation of function template specialization
'std::__detail::__variant::__get<0, const std::variant<int, double> &>'
requested here
return __detail::__variant::__get<_Np>(__v);
^
/usr/lib/gcc/x86_64-redhat-linux/9/../../../../include/c++/9/variant:1359:11:
note: in instantiation of function template specialization 'std::get<0, int,
double>' requested here
std::get<__index>(*this) = std::forward<_Tp>(__rhs);
^
/home/fedora/example/example.cpp:5:5: note: in instantiation of function
template specialization 'std::variant<int, double>::operator=<int>' requested
here
v = 5;
^
/usr/lib/gcc/x86_64-redhat-linux/9/../../../../include/c++/9/variant:1220:7:
note: constrained by private inheritance here
: private __detail::__variant::_Variant_base<_Types...>,
^
/usr/lib/gcc/x86_64-redhat-linux/9/../../../../include/c++/9/variant:266:10:
error: cannot cast 'std::variant<int, double>' to its private base class
'std::__detail::__variant::_Variant_storage<true, int, double>'
[clang-diagnostic-error]
std::forward<_Variant>(__v)._M_u);
^
/usr/lib/gcc/x86_64-redhat-linux/9/../../../../include/c++/9/variant:1588:35:
note: in instantiation of function template specialization
'std::__detail::__variant::__get<0, std::variant<int, double> &>' requested
here
return __detail::__variant::__get<_Np>(__v);
^
/usr/lib/gcc/x86_64-redhat-linux/9/../../../../include/c++/9/variant:1061:19:
note: in instantiation of function template specialization 'std::get<0, int,
double>' requested here
return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(__v);
^
/home/fedora/example/example.cpp:7:16: note: in instantiation of function
template specialization 'std::get<int, int, double>' requested here
int i = std::get<int>(v);
^
/usr/lib/gcc/x86_64-redhat-linux/9/../../../../include/c++/9/variant:1220:7:
note: constrained by private inheritance here
: private __detail::__variant::_Variant_base<_Types...>,
^
/usr/lib/gcc/x86_64-redhat-linux/9/../../../../include/c++/9/variant:266:38:
error: '_M_u' is a private member of
'std::__detail::__variant::_Variant_storage<true, int, double>'
[clang-diagnostic-error]
std::forward<_Variant>(__v)._M_u);
^
/usr/lib/gcc/x86_64-redhat-linux/9/../../../../include/c++/9/variant:1220:7:
note: constrained by private inheritance here
: private __detail::__variant::_Variant_base<_Types...>,
^
/usr/lib/gcc/x86_64-redhat-linux/9/../../../../include/c++/9/variant:453:34:
note: member is declared here
_Variadic_union<_Types...> _M_u;
^
/usr/lib/gcc/x86_64-redhat-linux/9/../../../../include/c++/9/variant:1359:31:
error: cannot assign to return value because function 'get<0, int, double>'
returns a const value [clang-diagnostic-error]
std::get<__index>(*this) = std::forward<_Tp>(__rhs);
^
/home/fedora/example/example.cpp:5:5: note: in instantiation of function
template specialization 'std::variant<int, double>::operator=<int>' requested
here
v = 5;
^
/usr/lib/gcc/x86_64-redhat-linux/9/../../../../include/c++/9/variant:134:15:
note: function 'get<0, int, double>' which returns const-qualified type 'const
variant_alternative_t<0UL, variant<int, double> > &' (aka 'const int &')
declared here
constexpr variant_alternative_t<_Np, variant<_Types...>> const&
^
/usr/lib/gcc/x86_64-redhat-linux/9/../../../../include/c++/9/variant:1559:55:
error: '__get' is missing exception specification 'noexcept'
[clang-diagnostic-error]
friend constexpr decltype(auto) __detail::__variant::__get(_Vp&& __v);
^
/home/fedora/example/example.cpp:4:29: note: in instantiation of template class
'std::variant<int, double>' requested here
std::variant<int, double> v;
^
/usr/lib/gcc/x86_64-redhat-linux/9/../../../../include/c++/9/variant:263:5:
note: previous declaration is here
__get(_Variant&& __v) noexcept
^
Found compiler error(s).
