<table border="1" cellspacing="0" cellpadding="8">

    <tr>

        <th>Issue</th>

        <td>

            <a href=https://github.com/llvm/llvm-project/issues/61329>61329</a>

        </td>

    </tr>

    <tr>

        <th>Summary</th>

        <td>

            Using import and #include causes redeclaration errors

        </td>

    </tr>

    <tr>

      <th>Labels</th>

      <td>

            new issue

      </td>

    </tr>

    <tr>

      <th>Assignees</th>

      <td>

      </td>

    </tr>

    <tr>

      <th>Reporter</th>

      <td>

          rnikander

      </td>

    </tr>

</table>

<pre>

    I'm new to C++20 modules, so I don't know if this is supposed to work or not. It seems like a C++ file that uses modules and traditional #includes can get errors.

Here is a minimal example, using a recent HEAD (Clang 17). 

build.sh (obviously needs to be adjusted a bit for your environment)

```text

CLANG_DIR=/Users/rob/Dev/llvm-project/build

CXX=${CLANG_DIR}/bin/clang++

# Need on my macOS system

ISYS="-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.1.sdk"

$CXX $ISYS -std=c++2b foo.ccm --precompile -o foo.pcm 

$CXX $ISYS -std=c++2b main.cc -fprebuilt-module-path=. foo.pcm -o final.out

```

foo.ccm:

```c++

module;

#include <iostream>

export module foo;

export void foo_func() {

    std::cout << "in foo_func\n";

}

```

main.cc:

```c++

import foo;

#include <iostream>

int main(int argc, char *argv[])

{

 std::cout << "Test\n";

    return 0;

}

```

Leads to these errors:

```text

In file included from main.cc:3:

In file included from /Users/rob/Dev/llvm-project/build/bin/../include/c++/v1/iostream:43:

In file included from /Users/rob/Dev/llvm-project/build/bin/../include/c++/v1/ios:221:

In file included from /Users/rob/Dev/llvm-project/build/bin/../include/c++/v1/__locale:18:

In file included from /Users/rob/Dev/llvm-project/build/bin/../include/c++/v1/mutex:191:

In file included from /Users/rob/Dev/llvm-project/build/bin/../include/c++/v1/__memory/shared_ptr.h:30:

In file included from /Users/rob/Dev/llvm-project/build/bin/../include/c++/v1/__memory/uninitialized_algorithms.h:13:

In file included from /Users/rob/Dev/llvm-project/build/bin/../include/c++/v1/__algorithm/copy.h:12:

In file included from /Users/rob/Dev/llvm-project/build/bin/../include/c++/v1/__algorithm/copy_move_common.h:14:

In file included from /Users/rob/Dev/llvm-project/build/bin/../include/c++/v1/__algorithm/unwrap_range.h:19:

In file included from /Users/rob/Dev/llvm-project/build/bin/../include/c++/v1/__utility/pair.h:13:

/Users/rob/Dev/llvm-project/build/bin/../include/c++/v1/__compare/synth_three_way.h:28:45: error: redeclaration of '__synth_three_way' with a different type: 'const std::__1::(lambda at /Users/rob/Dev/llvm-project/build/bin/../include/c++/v1/__compare/synth_three_way.h:29:3)' vs 'const std::__1::(lambda at /Users/rob/Dev/llvm-project/build/bin/../include/c++/v1/__compare/synth_three_way.h:29:3)'

_LIBCPP_HIDE_FROM_ABI inline constexpr auto __synth_three_way =

 ^

/Users/rob/Dev/llvm-project/build/bin/../include/c++/v1/__compare/synth_three_way.h:28:45: note: previous definition is here

_LIBCPP_HIDE_FROM_ABI inline constexpr auto __synth_three_way =

 ^