<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/154560>154560</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [flang] Missing diagnostic on `SIGN=` specifier being used on unformatted I/O
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            flang:frontend
      </td>
    </tr>

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

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

<pre>
    Consider the following code:
```
open(5, file='sign03.tmp', form="unformatted", sign='suppress')
end
```

The standard only allows the `SIGN=` specifier on formatted I/O as:
```
The SIGN= specifier is permitted only for a connection for formatted input/output.
```

This case should be diagnosed. 
</pre>
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