A fix for https://issues.dlang.org/show_bug.cgi?id=12929 prompted a discussion about C/C++ compatibility for anonymous structs/unions. After time had passed, it was discovered that the error caused by the original use case no longer occurred. Therefore, the issue was marked fixed, but the discussion about how to test for C/C++ compatibility remains unresolved. See https://github.com/dlang/dmd/pull/4107 for context.
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