<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/119271>119271</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            clang fails deduction on array when adding const qualification
        </td>
    </tr>

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

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

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

<pre>
    To be honest, I'm not entirely sure that this is a clang bug (and @zygoloid can put me in my place quickly enough).

Here's an interesting example:

```cpp
using size_t = decltype(sizeof(0));

template <size_t N>
void f(const int* const (&)[N]);

template <class T>
void g(T const* const*);

int main() {
  int* pointers[3];
  f(pointers); // clang: error, gcc: ok

  g(pointers); // clang, gcc: ok

  const int* const (&h)[3] = pointers; // clang, gcc: ok
}
```

All three of these situations seem similar: we're taking an array of pointers to mutable `int` (no `const` anywhere) and trying to add `const` in two layers:

* `f` is trying to deduce a reference to an array of const pointers to const `int` (gcc is okay with this, clang fails deduction saying it cannot match `const int *` against `int*`)
* `g` is trying to deduce a pointer to const pointer to const `int` (which is similar, and both gcc and clang are fine with this)
* `h` is just directly binding the same reference that `f` would have, except not in a template deduction context (likewise similar, both gcc and clang are fine with this too)

At the very least, it seems like `f` and `h` should either both be valid or both be invalid. So I think it's either a clang bug (so I'm in the right spot) or a C++ bug (and I should be writing this issue in a different spot). 
</pre>
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