<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/63031>63031</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            False positive unused-lambda-capture with if constexpr
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          chrchr-github
      </td>
    </tr>
</table>

<pre>
    ~~~c++
#include <type_traits>
#include <vector>
#include <algorithm>

template<typename T>
bool f(int j, std::vector<int>& v) {
  const bool b = j > 0;

  std::for_each(v.begin(), v.end(), [b](auto& i) {  
    if constexpr (std::is_same_v<T, int>) {
      i += i ? 5 : 7;
    }
    else if (b)
    {
      i += 1;
    }
 });
  return b;
}

void g(std::vector<int>& w) {
 f<int>(0, w);
}
~~~
~~~
<source>:9:38: warning: lambda capture 'b' is not used [-Wunused-lambda-capture]
  std::for_each(v.begin(), v.end(), [b](auto& i) {      
 ^
<source>:22:5: note: in instantiation of function template specialization 'f<int>' requested here
    f<int>(0, w);
 ^
~~~
https://godbolt.org/z/4Ejczrv5n

The warning is correct on its face,  but not actionable.
</pre>
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