Call to consteval method from constexpr constructor makes constructor consteval.

[IViktorov]

#include <cstdint>
#include <print>



template <class T, std::size_t kSize>
struct Test {
    constexpr Test(const Test& t) noexcept: m_data{t.data()}, m_size{t.size()} {}
    constexpr Test(T (&data)[kSize]) noexcept: m_data{data}, m_size{kSize} {}

    constexpr T* data() const noexcept { return m_data; }
#ifdef NOCONSTEVAL
    constexpr static std::size_t size() noexcept { return kSize; }
#else
    consteval static std::size_t size() noexcept { return kSize; }
#endif

private:
    T* m_data;
    std::size_t m_size;
};



int main() {
    int arr[] = {1, 2, 3, 4, 5, 6};
    Test t1{arr};
    Test t{t1};
    std::println("arr[0] = {}, arr size = {}.", *t.data(), t.size());
}

With consteval size() method Test copy constructor becomes immediate function, but it should not.
Without consteval with constexpr size() everything goes as expected.
GCC doesn't have that problem with consteval methods, called in contructors.

https://godbolt.org/z/P157TafW8

[tbaederr]

CC @cor3ntin

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: None (IViktorov)

```C++ #include <cstdint> #include <print>

template <class T, std::size_t kSize>
struct Test {
constexpr Test(const Test& t) noexcept: m_data{t.data()}, m_size{t.size()} {}
constexpr Test(T (&data)[kSize]) noexcept: m_data{data}, m_size{kSize} {}

constexpr T* data() const noexcept { return m_data; }

#ifdef NOCONSTEVAL
constexpr static std::size_t size() noexcept { return kSize; }
#else
consteval static std::size_t size() noexcept { return kSize; }
#endif

private:
T* m_data;
std::size_t m_size;
};

int main() {
int arr[] = {1, 2, 3, 4, 5, 6};
Test t1{arr};
Test t{t1};
std::println("arr[0] = {}, arr size = {}.", *t.data(), t.size());
}

With `consteval size()` method `Test` copy constructor becomes immediate function, but it should not.
Without consteval with `constexpr size()` everything goes as expected.
GCC doesn't have that problem with consteval methods, called in contructors.

https://godbolt.org/z/P157TafW8
</details>

[cor3ntin]

Note that if the call to size doesn't try to read this, clang is perfectly happy
https://godbolt.org/z/171P8erfa

Maybe yet another instance of #63139 @shafik

[cor3ntin]

Fixed by #95474