https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96848
Bug ID: 96848
Summary: Inherited conditionally explicit constructors via
using declaration do not enforce explicitness if
dependent on template parameter
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: northon_patrick3 at yahoo dot ca
Target Milestone: ---
Example: https://godbolt.org/z/4x9r7e
```cpp
#include <iostream>
#include <type_traits>
struct E {};
struct F {};
struct G {};
template <typename From_, typename To_>
constexpr bool isValidImplicitConvert = false;
template <>
constexpr bool isValidImplicitConvert<E, G> = true;
template <typename T_>
struct A
{
template <typename OT_>
explicit(!isValidImplicitConvert<OT_, T_>) constexpr A(const OT_ &) {}
//explicit(isValidImplicitConvert<E, T_>) constexpr A(E) {}
//explicit(isValidImplicitConvert<F, T_>) constexpr A(F) {}
};
template <typename T_>
struct B : public A<T_>
{
using A<T_>::A;
};
int main(int, char **)
{
std::cout << std::is_convertible_v<E, A<G>> << '\n';
std::cout << std::is_convertible_v<F, A<G>> << '\n';
std::cout << std::is_convertible_v<E, B<G>> << '\n';
std::cout << std::is_convertible_v<F, B<G>> << '\n';
return 0;
}
```
Output:
```
1
0
1
1
```
Expected output:
```
1
0
1
0
```
When inheriting constructors from a base class via a using declaration, if said
constructors are conditionally explicit and the condition is dependent on a
deduced template parameter, the explicit state is ignored.
Clang give the expected output, however I am not sure who is correct.
