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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Clang frontend failed on parsing concept with packed parameters"
href="https://bugs.llvm.org/show_bug.cgi?id=45770">45770</a>
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<th>Summary</th>
<td>Clang frontend failed on parsing concept with packed parameters
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>10.0
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>release blocker
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>C++2a
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>luohaothu@live.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>Created <span class=""><a href="attachment.cgi?id=23431" name="attach_23431" title="Clang generated bug description files">attachment 23431</a> <a href="attachment.cgi?id=23431&action=edit" title="Clang generated bug description files">[details]</a></span>
Clang generated bug description files
Clang frontend failed on parsing following minimized case:
template <typename T, typename U>
concept C1 = false;
template <typename T, typename ... Args>
concept C2 = sizeof...(Args) == 1 && C1<T, Args>;
template <typename T> requires C2<T, int>
void f(T t) {}
int main() {
f(1);
return 0;
}
Steps to Reproduce:
Compile this snippet with command:
clang++-10 -std=c++20 main.cpp -o main
will cause the frontend to crash.
Expected Results:
It's obvious to find that code line `concept C2 = sizeof...(Args) == 1 && C1<T,
Args>;` doesn't correctly unpacked the parameter pack, which should be
corrected to:
concept C2 = sizeof...(Args) == 1 && (... && C1<T, Args>);
which will then compile correctly. It seems that the frontend has some defects
preventing itself from handling such syntax error.
Additional Information:
The environment tested is WSL1 on Windows 10 2004 with Ubuntu-18.04, and the
clang version is 10.0.0-++20200412073436+50d7e5d5e7d-1~exp1~20200412054917.132.
I've also tested on the Compiler Explorer website with clang 10 & clang (trunk)
which all give the same result. G++ (trunk) can handle the error correctly.</pre>
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