<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/129213>129213</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Clang 10 Incorrectly Accepts Invalid Enum Base Type Syntax enum class a : int b;
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang
      </td>
    </tr>

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

    <tr>
      <th>Reporter</th>
      <td>
          starbugs-qurong
      </td>
    </tr>
</table>

<pre>
    Clang 10 erroneously compiles code containing an invalid enum base type declaration (enum class a : int b;), while MSVC/GCC correctly reject it. This violates the C++ standard syntax rules.

For  the following code test.cpp:

```
template <typename T> 
void qux() {
    enum class a : int b; // Invalid syntax
}

int main() {
    qux<int>();
    return 0;
}
```
Compile with Clang 10:
clang++ -std=c++11 test.cpp
Expected Result:
Compilation fails with a syntax error (as in MSVC/GCC).

Actual Result:
Clang 10 compiles the code without errors.

Environment:
Compiler: Clang 10.0.0
Flags: -std=c++11

Compiler Explorer link: https://godbolt.org/z/P3sa4EKhd 
</pre>
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