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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 - type traits considered non-constant in a constrained function template in a module."
href="https://bugs.llvm.org/show_bug.cgi?id=45249">45249</a>
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<th>Summary</th>
<td>type traits considered non-constant in a constrained function template in a module.
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>C2x
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>rbock@eudoxos.de
</td>
</tr>
<tr>
<th>CC</th>
<td>blitzrakete@gmail.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
</td>
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<p>
<div>
<pre>When used in a `requires` clause in a module, type traits are not considered
constexpr.
test.cpp
```
export module test;
import <type_traits>;
export template<typename T>
requires(std::is_integral_v<T>)
void do_something(const T&)
{
}
```
# clang++ -std=c++20 -stdlib=libc++ -fmodules -c -Xclang -emit-module-interface
-o test.pcm test.cpp
main.cpp
```
import test;
int main() {
do_something(7);
}
```
# clang++ -std=c++20 -stdlib=libc++ -fmodules -fimplicit-modules
-fimplicit-module-maps -fprebuilt-module-path=. main.cpp
Output:
```
In file included from main.cpp:1:
test.cpp:6:10: error: substitution into constraint expression resulted in a
non-constant expression
requires(std::is_integral_v<T>)
^~~~~~~~~~~~~~~~~~~~~
main.cpp:4:5: note: while checking constraint satisfaction for template
'do_something<int>' required here
do_something(7);
^~~~~~~~~~~~
main.cpp:4:5: note: in instantiation of function template specialization
'do_something<int>' requested here
test.cpp:6:10: note: subexpression not valid in a constant expression
requires(std::is_integral_v<T>)
^
main.cpp:4:5: error: no matching function for call to 'do_something'
do_something(7);
^~~~~~~~~~~~
test.cpp:7:6: note: candidate template ignored: failed template argument
deduction
void do_something(const T&)
^
2 errors generated.
```
# clang++ --version
clang version 11.0.0 (<a href="https://github.com/llvm/llvm-project.git">https://github.com/llvm/llvm-project.git</a>
70e4fb8a53984ff57b503cf13706c7e6683d650e)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/clang-trunk/bin</pre>
</div>
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