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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Wunused-const-variable warns when variable template is used in body of uninstantiated function template"
href="https://bugs.llvm.org/show_bug.cgi?id=50533">50533</a>
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<th>Summary</th>
<td>Wunused-const-variable warns when variable template is used in body of uninstantiated function template
</td>
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<th>Product</th>
<td>clang
</td>
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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>
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<th>Status</th>
<td>NEW
</td>
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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>C++
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
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<th>Reporter</th>
<td>davidfromonline@gmail.com
</td>
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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>The following translation unit
```
namespace {
template<typename T>
constexpr bool false_ = false;
}
template<typename T>
void f() {
static_assert(false_<T>);
}
```
warns when compiled with `-Wunused-const-variable`:
```
<source>:4:16: warning: unused variable 'false_' [-Wunused-const-variable]
constexpr bool false_ = false;
^
1 warning generated.
Compiler returned: 0
```
even though the variable is clearly used.
See it live: <a href="https://godbolt.org/z/oYxMq1K6r">https://godbolt.org/z/oYxMq1K6r</a>
If an instantiation of `f` is visible, the warning goes away, but not all
instantiations are necessarily visible. The warning is also triggered with the
following slightly larger translation unit:
```
namespace {
template<typename T>
constexpr bool false_ = false;
}
template<typename T>
void f() {
static_assert(false_<T>);
}
template<typename T>
concept c = requires { f<T>(); };
static_assert(c<int>);
```
See it live: <a href="https://godbolt.org/z/f74G5Tx54">https://godbolt.org/z/f74G5Tx54</a></pre>
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