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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - In certain cases `__VA_OPT__` incorectly expands to nothing when `-fms-compatibility` is present"
href="https://bugs.llvm.org/show_bug.cgi?id=51610">51610</a>
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<th>Summary</th>
<td>In certain cases `__VA_OPT__` incorectly expands to nothing when `-fms-compatibility` is present
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>12.0
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<th>Hardware</th>
<td>PC
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<th>OS</th>
<td>Linux
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>-New Bugs
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>blckcat@inbox.ru
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<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
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<pre>Clang with no flags successfully compiles following code:
#define CHECK_COMMA(...) CHECK_COMMA_(__VA_ARGS__,)
#define CHECK_COMMA_(x, ...) (__VA_OPT__(1) + 0)
static_assert(!CHECK_COMMA());
static_assert(CHECK_COMMA(,));
But if you add `-fms-compatibility`, the second assert fails.
This doesn't match the behavior of MSVC. MSVC v19.29 (VS16.11) with `/std:c++20
/Zc:preprocessor` compiles it successfully, and if you disable the
standard-conformant preprocessor the first assertion fails.</pre>
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