https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86105
Bug ID: 86105
Summary: Conversion to ambiguous/inaccessible rvalue base is
valid in unevaluated context
Product: gcc
Version: 8.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: johelegp at gmail dot com
Target Milestone: ---
In the following snippet, the assertions fail although the `static_cast` is
ill-formed in non-unevaluated context. See https://godbolt.org/g/45VJvp, and a
related Clang report https://bugs.llvm.org/show_bug.cgi?id=37691.
```C++
#include <utility>
template <class To, class From>
constexpr bool is_static_castable(...)
{
return false;
};
template <
class To, class From,
class = decltype(static_cast<To>(std::declval<From>()))>
constexpr bool is_static_castable(int)
{
return true;
};
struct B {
};
struct D : B {
};
struct D2
: D
, B {
};
static_assert(!is_static_castable<B&&, D2&>(0), "");
struct D3 : private B {
};
static_assert(!is_static_castable<B&&, D3&>(0), "");
void f()
{
D2 d2;
(void)static_cast<B&&>(d2);
D3 d3;
(void)static_cast<B&&>(d3);
}
```
