Warning: "possible misuse of comma operator here [-Werror,-Wcomma]"

[claremacrae]

This is more of a question than a bug report, as I haven't managed to narrow down my configuration enough to give you a minimal repro.

The question is: is the comma operator in this code intentional, and if so, could a static cast be added to silence the warning?

In some of my builds, where I treat warnings as errors, I am getting this:

/Users/clare/Documents/develop/ApprovalTests/ApprovalTests.cpp.CMakeSamples/ut/include/boost/ut.hpp:210:9: error: possible misuse of comma operator here [-Werror,-Wcomma]
    ++pi, ++si;
        ^
/Users/clare/Documents/develop/ApprovalTests/ApprovalTests.cpp.CMakeSamples/ut/include/boost/ut.hpp:210:5: note: cast expression to void to silence warning
    ++pi, ++si;
    ^~~~
    static_cast<void>( )
1 error generated.

Specifications

• Version: bba087c
• Platform: macOS
• Subsystem:

/opt/local/bin/clang-mp-9.0 --version
clang version 9.0.1 
Target: x86_64-apple-darwin19.6.0
Thread model: posix
InstalledDir: /opt/local/libexec/llvm-9.0/bin