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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Assigning to non-active trivial union member is not accepted in constexpr context"
href="https://bugs.llvm.org/show_bug.cgi?id=48453">48453</a>
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<th>Summary</th>
<td>Assigning to non-active trivial union member is not accepted in constexpr context
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C++2a
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>m.cencora@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>blitzrakete@gmail.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<p>
<div>
<pre>Following program fails to compile in C++20 mode.
gcc accepts this code without any workarounds.
Even if following expression 'un.f2.f2 = true;' does not implicitly initialize
un.f2 (which I think it should according to language rules), then WORKAROUND1
should fix it, but it still doesn't work.
Passing -DWORKAROUND2 is needed to make this compile on clang.
#include <memory>
union Un
{
constexpr Un() {}
char f1;
union NestedUn
{
constexpr NestedUn() {}
int f1;
bool f2;
} f2;
};
constexpr bool test()
{
Un un;
#ifdef WORKAROUND1
un.f2 = {};
#elif WORKAROUND2
std::construct_at(&un.f2);
#endif
un.f2.f2 = true;
return un.f2.f2;
}
static_assert(test());</pre>
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