<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/60890>60890</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [C++20] [Modules] definition with same mangled name as another definition
        </td>
    </tr>

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

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

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

<pre>
    Given the following valid set of files:

```cpp
export module a;
 
export template<typename T>
struct a {
        friend bool aa(a const & lhs) requires(true) {
                return static_cast<void>(lhs), true;
        }
};
```

```cpp
export module b;

import a;

struct b {
        a<int> m;
};
```

```cpp
export module c;

import a;

export struct c {
        void f() const {
                aa(m);
        }

        a<int> m;
};
```

```cpp
import a;
import b;
import c;

void d() {
        aa(c().m);
}
```

And compiling with

```shell
clang++ -std=c++20 -x c++-module --precompile -c a.cpp -o a.pcm
clang++ -std=c++20 -fmodule-file=a=a.pcm -x c++-module --precompile -c b.cpp -o b.pcm
clang++ -std=c++20 -fmodule-file=a=a.pcm -x c++-module --precompile -c c.cpp -o c.pcm
clang++ -std=c++20 -fmodule-file=a=a.pcm -fmodule-file=b=b.pcm -fmodule-file=c=c.pcm -c d.cpp -o /dev/null
```

Fails with

```
In file included from d.cpp:1:
a.cpp:5:14: error: definition with same mangled name '_ZW1a2aaRKS_1aIiE' as another definition
        friend bool aa(a const & lhs) requires(true) {
                    ^
a.cpp:5:14: note: previous definition is here
1 error generated.
```

Note that changing the order of importing `b` and `c` in `d.cpp` causes the issue to go away.

Tested with 70d78e035801a35c95c55384621724b0ef8ecb35, but has existed for much longer.
</pre>
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