<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/54406>54406</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            clang does not properly convert the object in a member access expression
        </td>
    </tr>

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

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

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

<pre>
    Per [class.access.base]/6, this example is ill-formed:

```
struct A {
  int m;
} a;
struct B : A {};
int n = a.B::m;
```

... because the object expression `a` cannot be implicitly converted to `B` (because `B` is not a base class of `A`). Clang does not diagnose this and accepts the member access. This opens a hole in the protected member access rules:

```
struct C {
protected:
  int m;
};
struct D : private C {
  int get(C &c) { return c.D::m; }
};
```

This example is invalid for the same reason, but Clang accepts it. ([[class.protected]p1](https://eel.is/c++draft/class.protected#1), which normally would prevent `D` from accessing protected members on a `C` object that is not a `D` object, does not apply here because `m` as a member of the naming class `D` is private, not protected.)
</pre>
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