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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Undefined use of std::deque<const int> in std::assignable_from test"
href="https://bugs.llvm.org/show_bug.cgi?id=50716">50716</a>
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<th>Summary</th>
<td>Undefined use of std::deque<const int> in std::assignable_from test
</td>
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<th>Product</th>
<td>libc++
</td>
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<th>Version</th>
<td>12.0
</td>
</tr>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>All Bugs
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>zilla@kayari.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
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<pre>The tests for std::assignable_from use std::deque<const int> which is undefined
because it uses std::allocator<const int>. The Cpp17Allocator requirements say
the value type must be a non-const, non-volatile object type:
In file included from /home/jwakely/gcc/12/include/c++/12.0.0/deque:67,
from
std/concepts/concepts.lang/concept.assignable/assignable_from.compile.pass.cpp:17:
/home/jwakely/gcc/12/include/c++/12.0.0/bits/stl_deque.h: In instantiation of
'class std::deque<const int>':
/home/jwakely/gcc/12/include/c++/12.0.0/type_traits:3423:12: recursively
required by substitution of 'template<class _Tp1, class _Tp2> struct
std::__common_reference_impl<_Tp1&&, _Tp2&, 1, std::void_t<typename
std::__common_ref_impl<_Tp1&&, _Tp2&, void>::type> > [with _Tp1 = const
std::deque<int>; _Tp2 = const std::deque<const int>]'
/home/jwakely/gcc/12/include/c++/12.0.0/type_traits:3423:12: required from
'struct std::common_reference<const std::deque<int, std::allocator<int> >&,
const std::deque<const int, std::allocator<const int> >&>'
std/concepts/concepts.lang/concept.assignable/assignable_from.compile.pass.cpp:138:18:
required from 'constexpr bool CheckAssignableFromLvalues() [with T1 =
std::deque<int>; T2 = std::deque<const int>]'
std/concepts/concepts.lang/concept.assignable/assignable_from.compile.pass.cpp:147:44:
required from 'constexpr bool CheckAssignableFromLvaluesAndRvalues() [with T1
= std::deque<int>; T2 = std::deque<const int>]'
std/concepts/concepts.lang/concept.assignable/assignable_from.compile.pass.cpp:443:76:
required from here
/home/jwakely/gcc/12/include/c++/12.0.0/bits/stl_deque.h:778:66: error: static
assertion failed: std::deque must have a non-const, non-volatile value_type
778 | static_assert(is_same<typename remove_cv<_Tp>::type, _Tp>::value,
| ^~~~~
Implementations are not required to support that usage. Should that
non-portable test be guarded by a preprocessor check for _LIBCPP_VERSION or
similar?</pre>
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