<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/66152>66152</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            -Wthread-safety-reference doesn't warn when a reference to a guarded member is returned
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          pirama-arumuga-nainar
      </td>
    </tr>
</table>

<pre>
    `-Wthread-safety-reference` warns when a guarded member is returned by reference.

```
$ cat thread-safety.cpp 
#include <mutex>
#include <string>

extern void bar(std::string &s);

class C {
  private:
    std::mutex lock;
    std::string s __attribute__((guarded_by(lock)));

 public:
    std::string &foo() {
      bar(s); // warning emitted
 return s; // no warning
    }
};

$ clang++ -Wthread-safety -c thread-safety.cpp  -stdlib=libc++ -D_LIBCPP_ENABLE_THREAD_SAFETY_ANNOTATIONS 
thread-safety.cpp:13:11: warning: passing variable 's' by reference requires holding mutex 'lock' [-Wthread-safety-reference]
 bar(s);
          ^
1 warning generated.
```

While returning by reference is potentially a bug, it is not invalid.  Adding a `REQUIRES` annotation to this function is valid.
</pre>
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