<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/162846>162846</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            feature: Per-module -fmodules-decluse (-fmodules-decluse=<module_name>)
        </td>
    </tr>

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

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

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

<pre>
    I’m setting up Clang module maps for Qt and thought I’d use -fmodules-decluse to test my work. Unfortunately, enabling -fmodules-decluse results in quite a few errors of this kind:

```
While building module '_DarwinFoundation2' imported from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/stdio.h:61:
In file included from <module-includes>:1:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/nl_types.h:44:10: error: module _DarwinFoundation2 does not directly depend on a module exporting 'sys/cdefs.h', which is part of indirectly-used module cdefs
   44 | #include <sys/cdefs.h>
      |          ^
```

Which doesn't seem possible to work around.

As suggesteded in https://discourse.llvm.org/t/fmodules-decluse-resulting-in-errors-from-xcode-sdk/88267 a `-fmodules-decluse=<module_name>` might be a useful addition to the modules machinery.

Thanks!
</pre>
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