<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/69801>69801</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            clang crash trying to use c++20 modules
        </td>
    </tr>

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

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

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

<pre>
    I just built clang from source (Oct 20, 2023) and tried a small program with a module, and I get this crash. There's a problem in the code (missing `std::` in front of `vector`), but of course it would be better to report whatever the problem is, instead of crashing.

File `buildsys.ccm`:
```c++
module;
#include <iostream>
export module buildsys;
```

File `main.cc`:
```c++
#include <vector>
import buildsys;
vector<int> nums;
```

This is my build script. 

File `build.sh`:
```sh

CXX=/Users/rob/Dev/llvm-project/build_phase1/bin/clang++
MACOS_SDK=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.0.sdk
CMD_START="$CXX -isysroot $MACOS_SDK -std=c++2b"

$CMD_START buildsys.ccm --precompile -fprebuilt-module-path=. -o buildsys.pcm
MF1="-fmodule-file=buildsys=buildsys.pcm"
$CMD_START -c main.cc $MF1 -o main.o
```

I'm running on a Intel MacBook Pro with macOS 14.0.

</pre>
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