https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121327
Bug ID: 121327
Summary: Not-matching concept fails to compile with error
"depends on itself"
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: b.stanimirov at abv dot bg
Target Milestone: ---
Consider the simple class:
```
template <typename T>
class id {
T m_id;
public:
constexpr id() : m_id() {}
constexpr bool operator==(const id& other) const = default;
template <std::equality_comparable_with<T> U>
constexpr bool operator==(const U& other) const {
return m_id == other;
}
};
```
Instantiating an `id<T>` works as expected with id-id and id-U comparisons. But
when inheriting from id as in:
```
struct user_id : public id<int> {};
```
When comparing user_id==user_id the inherited operator== is no longer an exact
match, so the compiler probes ==U, but instead of failing and trying the other
overload, it produces a gigantic wall or errors, essentially saying that
`equality_comparable_with` depends on itself.
Live compiler explorer demo: https://godbolt.org/z/W9Kfzoh69
I'm not sure whether this is a compiler but or one in libstdc++, as I get the
same error on clang with libstdc++, but not on msvc with msstl.
I haven't tried libc++ yet.
