<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/61763>61763</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [clang-16 regression] Friend declaration of a constrained friend class inside of a class template causes compile error
        </td>
    </tr>

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

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

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

<pre>
    
```c++
#include <concepts>

template <class = void>
struct Foo {
    template <std::same_as<void> Param>
    friend struct Bar;
};

template struct Foo<>;

template <std::same_as<void> Param>
struct Bar {
};
```

Clang-16 and further reject this program with the following error message:
```c++
<source>:11:11: error: type constraint differs in template redeclaration
template <std::same_as<void> Param>
 ^
<source>:5:15: note: previous template declaration is here
 template <std::same_as<void> Param>
              ^
1 error generated.
Compiler returned: 1
```
Clang versions 11-15 work as expected, though.
Compiler Explorer link: https://godbolt.org/z/erGavP1za.

GCC also had a similar bug at some point: [93467](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93467).
</pre>
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