<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/77995>77995</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [c++20][modules] '#pragma once' doesn't work with files included in global module fragment
        </td>
    </tr>

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

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

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

<pre>
    This isn't quite the same reproducer as #38554 or #58532 and the issue still exists in 17.0.6.

When using `#pragma once`, included files in the global module fragment hide the visibility of everything declared in them when the module is imported before a normal `#include`. This error disappears (and the example works) if _either_ the `#pragma once`s are turned into normal include guards, _or_ the `import c;` and `#include "a.hpp"` are swapped in the importing translation unit (d.cpp).

```cpp
// a.hpp
#pragma once
using a = int;
```

```cpp
// b.hpp
#pragma once
a b;
```

```cpp
// c.cpp
module;
#include "b.hpp"
export module c;
export using foo = a;
```

```
// d.cpp
import c;
#include "a.hpp"
a d;
foo f;
```

compile with:
```
clang++ -std=c++20 -x c++-module -fmodule-output=c.pcm -o c.o -c ./c.cpp
clang++ -std=c++20 -fmodule-file=c=c.pcm -c -o d.o d.cpp
```

error:
```
d.cpp:4:1: error: missing '#include "a.hpp"'; 'a' must be declared before it is used
    4 | a d;
      | ^
/.../a.hpp:2:7: note: declaration here is not visible
    2 | using a = int;
      |       ^
1 error generated.
```
</pre>
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