https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110904
Bug ID: 110904
Summary: __is_convertible incorrectly reports non-referenceable
function prototypes as convertible
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: nikolasklauser at berlin dot de
Target Milestone: ---
```
#include <utility>
using Function = void();
using ConstFunction = void() const;
static_assert((!std::is_convertible<ConstFunction, Function>::value), "");
static_assert((!std::is_convertible<ConstFunction, Function*>::value), ""); //
convertible
static_assert((!std::is_convertible<ConstFunction, Function&>::value), ""); //
convertible
static_assert((!std::is_convertible<ConstFunction, Function&&>::value), ""); //
convertible
static_assert((!std::is_convertible<Function*, ConstFunction>::value), "");
static_assert((!std::is_convertible<Function&, ConstFunction>::value), "");
static_assert((!std::is_convertible<ConstFunction, ConstFunction>::value), "");
static_assert((!std::is_convertible<ConstFunction, void>::value), "");
```
__is_convertible() claims that the cases marked above are convertible, but
AFAICT that shouldn't be true. According to the standard,
```
To test() {
return declval<From>();
}
```
has to be well formed, but that's never the case for `ConstFunction`.
