<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=http://email.email.llvm.org/c/eJylVMGO4zYM_RrnQsRw5E2cHHyYSVoUBYoWxaI9FrREx5qVJUOSk0m_vpTtZGZ22lMDBbIo6vGRfFLj1K3-1UK2fY4dQYgYxwADninbnjKx72IcQlY-ZeJHHtKgPefGXPrc-XMyvL7-NZ_Ju9ibTJRsEUUmDqAjaKu0xEgBYocRsl0hnQ0Reh16jLKDq44dKGpxNJEUSDfcYHLxo4zO8wHAb5jI_Vbsvmx-F2-kHpyu12vuBrLrENXC6iXKDU9BCpEcziKtlJOBpwEH8ulDFJsqrROwFwt9ph1A94OhnmyipC0cU9Kwz7PilBVPzOltTJaZLTxjoMWlep4_gH_JDMx5mXccIyuX_bv76TvLgngiry_MgVP9L_TFhfHnyj6OTIH45Ole3rcQn8Ldg2LUEnCMDtp_A7wkxHVW_vCI-pmPpzh6C5cP0d6H-lS97wTm-kEb8mt6HYzz5HO2sP3v1NVyh2jbl917wF9uMFrFHY3IYuM-uZbFlpq4iG5aSKdY250bTRLZHAJQShreO2A6QjB4N7iABlApTrK8U-fEWQ3JQ6ZeciD8pFjgMdkwBH22SUTA4vSY1CyOMz567Ckyg3gbCHq8QZOkITy15MlKAm6BdXY9t-BrlmR8hGvHu_B1zozAMsicLWNQ3zBeO1oZtbOZqDglwxzy97X6yV3pQn7BskslUtGmGkyXkfOw34BrCcdMPPNIl_k4OwSiPiRuZ-4-NI7dcQHBFBbIe84_HUa4orcJmhu9_vNxxdd3imtFhmugeDtfqbpUh_KAKxZf53z98x9PfKFXozf1R3mcmeLYLJpIz9AyrblnLyQjL3UII6X7vS0Polp1tdiVJNuqLPeCqmazVYftvmyxIFWJarunlcGGTKj5keFCW7rCBJGKvj2t_j8DXYtC8NjsN6Lkf97KEqmU-8NWNlWx2WdfCupRm8e7uvL1BNmM58CbRocY3jZnZRFNhJlh1NFQPb2PLJr44fViRd_fYLWaeNUTqX8AeIjftg>53927</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            P0641 not implemented as indicated
        </td>
    </tr>

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

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

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

<pre>
    On [the status page](https://clang.llvm.org/cxx_status.html#cxx20) it indicates that `const mismatch with defaulted copy constructor` aka [P0641R2](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0641r2.html) is implemented in Clang 8.
````
struct Base
{
    Base (Base &);

};

struct Derived : Base
{
    Derived(const Derived &) = default;
};


static auto f(const Derived &v) -> Derived
{
    return v;
}

````
https://compiler-explorer.com/z/j36aanfj6

My understanding of this is that this code should compiler accept this code as the proposal added:
> in the case of a copy constructor or copy assignment operator, the parameter type may be "reference to non-const T", where T is the name of the member function's class.

However, when compiling this with trunk and C++20, this seems to give both a compilation error and a warning `-Wdefaulted-function-deleted`.
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJx1VE1v2zAM_TXOhYhhy83XwYc22TAMGDYMw3YcaJmO1cmSIclJs18_ynbSdt0CBbIo6vGRfFJl60v52UCyeggtgQ8YBg89HilZHRKxbUPofVLcJ-I9D6nRHFOtT11q3TEanp5-TmfSNnQ6EQVbRJaIHagAytRKYiAPocUAyTqT1vgAnfIdBtnCWYUWampw0IFqkLa_wOjiBhms4wOAvzCS-5Kt7_Kv4pnUjdP5fE5tT2bpQz2zegwy58lLIaLDUcRVbaXnqceeXPwQWb6J6wjsxEyfaXtQXa-pIxMpKQP7mDRs0yQ7JNk9c3oeo2ViCw_oaXbZPEwfwL9oBuY8z2uOkRTz_tX98JdlRjyQUyfmwKn-D312YfypsrcjYyA-ebiW9znEm3DXoBiUBByCheZfgKeIuEyKd7eob_k4CoMzcHoV7WWoN9X7S2C265Umt6SnXltHLmUL23_HrhZrRNM8rl8CfrrAYGruaEAWG_fJNiy22MRZdONC2pq13dpBR5FNIQClpP6lA8YjBL2zvfWoAeuakyyu1DlxVkP0kLGXHAjfKBZ4jDb0Xh1NFBGwOB1GNYv9hI8OOwrMIFx6gg4vUEVpCEcNOTKSgFtgrFlOLfiWRBnv4dzyLnybMiMwDDJlyxjUVYzXDEYGZU0iNpySZg7py1p9sGc6kZuxzFyJWLSxBuNl5DzML-Bawj4RDzziZd5PDp6o85HbkbsPlWV3nEEwhgVyjvOPhxHO6EyE5kYvf9yu-PJKcVmT5hrUvJ0u6rKod8UOF0EFTeV417kA4dVN5O5c35N6MThdvlbOkdkP1SyX-ELN05Lb-Ugy8FJ5P1C8-qtiJzaLttxWTUPrXdY0ayF2tNpUOYkMixzvKsxltdBYkfYlvz_cA0NnGCFiP1aHhSpFJnjk21wU_E8bWSAVcrtbyWqT5dvkLqMOlb49mAtXjpSq4eh5Uysf_PPmJBmiMRzj801srSs_fr_n120xRi5H5n8A33fK4Q">