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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 - Rejects valid code with requires clause referring to function parameter when called from variadic function"
href="https://bugs.llvm.org/show_bug.cgi?id=44670">44670</a>
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<th>Summary</th>
<td>Rejects valid code with requires clause referring to function parameter when called from variadic function
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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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>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</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
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<th>Reporter</th>
<td>david@doublewise.net
</td>
</tr>
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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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<p>
<div>
<pre>The following code
```
struct s {};
constexpr bool f(s) {
return true;
}
template<typename T>
bool a(T t) requires(f(t)) {
return true;
}
template<typename... Args>
bool b(Args ... args) {
(..., a(args));
return true;
}
//bool x = a(s());
bool y = b(s());
```
when compiled against 8d6884a15e86419c51ba456f8b6f5223696800a1 with the command
`clang++ -std=c++2a -o /dev/null -c main.cpp` should compile with no errors.
Instead, it outputs
```
main.cpp:14:8: error: no matching function for call to 'a'
(..., a(args));
^
main.cpp:19:10: note: in instantiation of function template specialization
'b<s>' requested here
bool y = b(s());
^
main.cpp:8:6: note: candidate function not viable: constraints not satisfied
bool a(T t) requires(f(t)) {
^
main.cpp:8:24: note: because substituted constraint expression is ill-formed:
reference to local variable 't' declared in enclosing function 'a<s>'
bool a(T t) requires(f(t)) {
^
1 error generated.
```
Uncommenting the direct call to `a` (the variable `x`) causes clang to accept
the code.</pre>
</div>
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