https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114903
Bug ID: 114903
Summary: constraint of CTAD alias deduction guide is evaluated
on a wrong type
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: hokein.wu at gmail dot com
Target Milestone: ---
See the following example of nested templates:
```
#include <type_traits>
template <typename T>
struct Key {
Key(int);
};
class Forward {};
template <typename T>
constexpr bool C =
std::is_same<T, Forward>(); // changing `Forward` to `double` will make the
following static_assert passed.
template <typename Z>
struct Outer {
template <typename U>
struct Foo {
Foo(U);
U u;
};
template <typename V>
requires(C<Z>)
Foo(V) -> Foo<int>;
};
template <typename Y>
struct T {
template <typename Y2>
struct T2 {
template <typename K>
using AFoo = Outer<Y2>::template Foo<K>;
};
};
T<Forward>::T2<Forward>::AFoo a{1.0}; // the explict deduction guide should be
choosen, Foo<int>
static_assert(std::is_same<decltype(a), Outer<Forward>::Foo<int>>()); // expect
to be true!
```
The constraint `C` in the alias deduction guide should be true, as it is
evaluated on type `Forward`, but gcc seems to evaluate it on `double`.
