<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/66604>66604</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [clang] templated functions with non-public visibility invoked by templated using declarations fail to compile
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          8ightfold
      </td>
    </tr>
</table>

<pre>
    The following fails to compile on (to my knowledge) all versions of Clang, but works on GCC/MSVC.  It only affects templated functions invoked by template ``using`` declarations where the invocation depends on the ``using``s type.

Godbolt: https://godbolt.org/z/Gdq8q7WWc

```cpp
struct X {
private:
    template <typename>
    static constexpr int foo();

public:
    template <typename U>
    using bar = decltype(foo<U>());
};


using type = X::bar<float>;
```
```
<source>:8:26: error: 'foo' is a private member of 'X'
    using bar = decltype(foo<U>());
 ^~~~~~
<source>:12:17: note: in instantiation of template type alias 'bar' requested here
using type = X::bar<float>;
 ^
<source>:4:26: note: declared private here
    static constexpr int foo();
                         ^
1 error generated.
```
This affects bound member functions as well, and ``constexpr``ness has no affect.
I have confirmed this to be an issue as of ``clang version 16.0.2``, and affects all c++ standards.
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJykVcuS4yYU_Rq8udUqGdl6LLTwY9w1i6wyyfQWwZVEGoEakB1nkW9PIfyaiVOpZLzA4nHPPZwLB-ac7DRiTdZbst4v2OR7Y-tSdr1vjRKLxohz_aVHaI1S5iR1By2TyoE3wM0wSoVgNBBaegPDGd61OSkUHRJaAVMKjmidNNqBaWGnmO4I3UEzeTgZ--5C7OtuR-jhp59_3SUAnz0Yrc7A2ha5d-BxGBXzKKCdNPczktRH844CmvNtGkiekjydnNRd_ASBXDHLYsipR4vge5yD-TwKAkfUYuYQZv4G4cCfR0xIuifpJravRjRGeZJtoPd-dCTbEHog9NDFicTYjtDDH4QeXsVH-VF8_cof4yMwyVM-jnHEeTtxD29Aim0cGa08Mo8Beu4DwMM-s10gpdmAJPt0X-A885IDN9p5_H20ILWH1hhCS0Irkm0fWYxToyT_1wTwyzcpZmWgYRZItp_lDQsJLUOabDcvjtkeExb775LHNoIFgBntLZDJNg2zJNu1yjAf0G6BV9Wed7OdM5PlsyDZpiTZhuahQmitseGD0GKWogDpgMFFYBhwaNCGg0lo8UZo8YN7BbL-9Gf4PeW1pKEpAh9t5vKC1CC180x7GU-kae-FmLVhSjIX6AVlaAEWPyZ04TqEA_0_pAwcn9Jb3WS7sosXCMVNr3vK_3Di4J9-NyLLWCjoUKMNVz15WuYvfSjexRYaM2lxLeDdGZiDEyoVLIZpcbnRN4axq9E56JkDbS5wl3yfoWdHDBtqpR1QgA8ZvYEGgWmQzk0YMoTzEoGDnV0NDpZ5kib0wvhC4Eo3GCEndEvoNuimBbPCJQtRZ6LKKrbAeplXq6parvNi0dcFz0tcpiXNyoJWa85WmaAV50WKTVux1ULWNKVZWi0LStcVLRLK2jIv27bJq7wUWUVWKQ5MqkSp4xBMaTHTr_M8T1cLxRpUbvZ8Snk0ZRrs39Zh_UszdY6sUiWdd3cEL72aH4oYsd4_NeeT9D1oo1-iycBROtlIJf35mW-Ly037xqzDA_Pwviwmq-rv3Fb6fmoSbgZCD4Hg5e9ltOY35J7Qw7xfR-hh3vJfAQAA__-suxyM">