<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/115350>115350</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Name lookup of friend names is wrong on clang-cl
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          csimon-bambecksystems
      </td>
    </tr>
</table>

<pre>
    Names introduced as friends do not participate in name lookup [as explained here on cpprefererence](https://en.cppreference.com/w/cpp/language/namespace#Namespaces), so the problem with the following ill-formed code:

```
class foo {
  friend class bar;
  using baz = bar;  // Error! Name lookup does not find bar.
};
```

is the name `bar` has not been introduced for name-lookup purposes. MSVC acceps it (that's their problem) but weirdly, clang-cl accepts it and does not warn about a "microsoft extension." I can reproduce it on godbolt with either x86 msvc v19.latest or clang-cl 18.1.0 as the compiler. I know that clang-cl accepts some non-standard name lookup for class templates but this is not a class template, just a regular class. Fun story: I wrote a whole boatload of classes relying on this, uh, "idiom" that I thought I discovered, and I was feeling so good about myself. Then I confidently fed it to another compiler, just another clang with different configuration actually, and *sound of world crashing down.*
</pre>
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