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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Question on backporting DR fixes"
href="https://bugs.llvm.org/show_bug.cgi?id=49991">49991</a>
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<th>Summary</th>
<td>Question on backporting DR fixes
</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>Other
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>C++17
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>cpp@daryl.haresign.com
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<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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<pre>I spent some time today investigating why Clang was rejecting the following
code in C++17 mode, but not C++20. MSVC and GCC both accept it in C++17.
#include <optional>
struct C {
C(C&) = default;
};
std::optional<C> o;
It seems <a href="https://wg21.link/cwg1331">https://wg21.link/cwg1331</a> was addressed by <a href="https://wg21.link/p641">https://wg21.link/p641</a>,
which was accepted into C++20.
Clang has the following commit which applies the change only in C++20 mode:
<a href="https://github.com/llvm/llvm-project/commit/9b2c5e7c44fd28c31f4a0b088d0bf71da4fddfa5">https://github.com/llvm/llvm-project/commit/9b2c5e7c44fd28c31f4a0b088d0bf71da4fddfa5</a>
Whereas GCC and MSVC seem to have applied it unconditionally.
Is there any policy for when defect fixes are applied in earlier standard
modes?</pre>
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