<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/57671>57671</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Missing C++20 modules imports in -ast-dump
        </td>
    </tr>

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

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

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

<pre>
    `test.cpp`:
```cpp
import std.core;

int i;
```
Running command `clang++ -std=c++20 -Xclang -ast-dump -fsyntax-only test.cpp` gives this result:
```
test.cpp:1:8: fatal error: module 'std.core' not found
import std.core;
~~~~~~~^~~
TranslationUnitDecl 0x5590c7227c58 <<invalid sloc>> <invalid sloc>
|-TypedefDecl 0x5590c72284e0 <<invalid sloc>> <invalid sloc> implicit __int128_t '__int128'
| `-BuiltinType 0x5590c7228220 '__int128'
|-TypedefDecl 0x5590c7228558 <<invalid sloc>> <invalid sloc> implicit __uint128_t 'unsigned __int128'
| `-BuiltinType 0x5590c7228240 'unsigned __int128'
|-TypedefDecl 0x5590c7228910 <<invalid sloc>> <invalid sloc> implicit __NSConstantString '__NSConstantString_tag'
| `-RecordType 0x5590c7228660 '__NSConstantString_tag'
|   `-CXXRecord 0x5590c72285b8 '__NSConstantString_tag'
|-TypedefDecl 0x5590c72289b8 <<invalid sloc>> <invalid sloc> implicit __builtin_ms_va_list 'char *'
| `-PointerType 0x5590c7228970 'char *'
|   `-BuiltinType 0x5590c7227d00 'char'
|-TypedefDecl 0x5590c7273260 <<invalid sloc>> <invalid sloc> implicit __builtin_va_list '__va_list_tag[1]'
| `-ConstantArrayType 0x5590c7273200 '__va_list_tag[1]' 1 
|   `-RecordType 0x5590c7228ac0 '__va_list_tag'
|     `-CXXRecord 0x5590c7228a18 '__va_list_tag'
`-VarDecl 0x5590c72732d8 <test.cpp:3:1, col:5> col:5 i 'int'
1 error generated.
```
There is no entry for `import` statement.

BTW Shouldn't ` -fsyntax-only` prevent from module lookup errors?

```bash
$ clang++ --version
clang version 16.0.0 (https://github.com/llvm/llvm-project.git ee761374f797a47919ec8f9f49f9b8b1b20573e8)
Target: x86_64-unknown-linux-gnu
Thread model: posix
```
</pre>
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