<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/133515>133515</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            check_clang_tidy/FileCheck is not enforcing CHECK-MESSAGES in header files
        </td>
    </tr>

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

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

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

<pre>
    When trying to create a unit test for [this issue](https://github.com/llvm/llvm-project/issues/118009), I realized that check_clang_tidy / FileCheck is currently not handling the CHECK-MESSAGES lines from header files.

This can be reproduced with the following change:

```
--- a/clang-tools-extra/test/clang-tidy/checkers/readability/Inputs/duplicate-include/duplicate-include.h
+++ b/clang-tools-extra/test/clang-tidy/checkers/readability/Inputs/duplicate-include/duplicate-include.h
@@ -6,7 +6,7 @@ extern int g;
 extern int h;
 #include "duplicate-include2.h"
 extern int i;
-// CHECK-MESSAGES: :[[@LINE-2]]:1: warning: duplicate include
+// CHECK-MESSAGES: :[[@LINE-2]]:1: warning: foo include
After that change, run ninja check-clang-tools again. Result: all the tests continue to pass. I expect this test to fail since now the message is different.
```

Is this expected? How can we fix this?
</pre>
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