<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/64124>64124</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Clang falsely instantiates an object of a type with defaulted `operator==` despite its `requires false`
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          AMP999
      </td>
    </tr>
</table>

<pre>
    According to a discussion on [cpplang.slack.com](https://cpplang.slack.com/archives/C6K47F8TT/p1689107603335019?thread_ts=1689107603.335019&cid=C6K47F8TT) , apparently, there is a bug in clang which causes  the "PROBLEM" code (using `=default`) to be instantiated, despite its `requires false`.

> arthur-odwyer(@Quuxplusone):
> (attn 
> [@Nikolas Klauser](https://cpplang.slack.com/team/U02TVB7TMK2)
> )
> Where would we have to modify in the standard to get this to work as intended?
> https://godbolt.org/z/nc4Kv3TT6
> template<class T>
> struct S {
> Holder<T> h;
> 
> #if PROBLEM
>     friend bool operator==(const S& s, const S& t)
>       requires false = default;
> #else // NO PROBLEM
>     friend bool operator==(const S& s, const S& t)
> requires false { return s.h == t.h; }
> #endif
> };
> The "NO PROBLEM" code is quite properly never instantiated for any T, because it requires false; but the "PROBLEM" code (using =default) is instantiated, despite its requires false. Why does this happen, and can we make it not happen?

> Brian Bi:
> I think that might be a bug in Clang. [temp.inst]/5 says that a friend function definition isn't supposed to be instantiated until "it is referenced in a context that requires a function definition to exist or if the existence of the definition affects the semantics of the program".
</pre>
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