<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/122645>122645</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            clang 13 to trunk accepts implicit move of parameters in C++17 and not feature flag
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang
      </td>
    </tr>

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

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

<pre>
    The following code is not an error in clang but isn't valid to my knowledge.

```cpp
template <typename Pointer, typename F>
constexpr auto or_else(Pointer &&p, F &&f) -> remove_cvref_t<Pointer> {
    if (not p) {
 return FWD(f)( );
    }
    return std::move( p );  // not needed in clang 13+
}

std::unique_ptr<int> foo(std::unique_ptr<int> p) {
 return or_else(std::move(p), [] { return std::make_unique<int>(42); });
}
```

https://gcc.godbolt.org/z/TzWf6Eqov

The move on p isn't required as of clang-13 while compiled with `-std=c++17 -pedantic -pedantic-errors`.  The macro `__cpp_implicit_move` isn't defined either.
</pre>
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