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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [clang-cl] Implicit instantiation of template within its own definition inside noexcept of friend member function"
href="https://bugs.llvm.org/show_bug.cgi?id=47689">47689</a>
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<th>Summary</th>
<td>[clang-cl] Implicit instantiation of template within its own definition inside noexcept of friend member function
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>11.0
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<th>Hardware</th>
<td>PC
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<th>OS</th>
<td>Windows NT
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<th>Status</th>
<td>NEW
</td>
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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>C++
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>rixript@gmail.com
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<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<pre>Boost asio the following workaround:
<a href="https://github.com/chriskohlhoff/asio/blob/38fda8d/asio/include/asio/execution/blocking.hpp#L328-L336">https://github.com/chriskohlhoff/asio/blob/38fda8d/asio/include/asio/execution/blocking.hpp#L328-L336</a>
The first one for clang was fixed in 8c98c880. However there remains a
workaround for MSVC compiler.
The latest MSVC (19.27.29112) is able to handle both cases, but clang-cl is
able to handle only the second case.
Consider the following minified example:
template <typename T>
struct false_t {
static constexpr bool value = false;
};
template <int I = 0>
struct S {
using t = void;
friend void query() noexcept(false_t<S<>::t>::value) {}
};
MSVC is able to compile this:
C:\boost_test>cl /c test.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 19.27.29112 for x64
Copyright (C) Microsoft Corporation. All rights reserved.
test.cpp
However, clang-cl is unable to compile:
C:\boost_test>C:\llvm\llvm-11.0.0rc4\bin\clang-cl.exe /c
test.cpp
test.cpp(9,42): error: implicit instantiation of template 'S<0>' within its
own definition
friend void query() noexcept(false_t<S<>::t>::value) {}
^
1 error generated.</pre>
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