<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/129747>129747</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            c++23 std::ranges::copy_n advances InputIterator one more time than necessary
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

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

    <tr>
      <th>Reporter</th>
      <td>
          Be3y4uu-K0T
      </td>
    </tr>
</table>

<pre>
    Repeated error, but for copy_n from ranges. [(old resolved bug)](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50119)

Test program ([godbolt](https://godbolt.org/z/h6cbjqPT7)):
```c++
#include <iostream>
#include <sstream>
#include <vector>
#include <iterator>

int main()
{
    std::istringstream s("1 2 3 4 5");
    std::vector<int> v;
    std::ranges::copy_n(std::istream_iterator<int>(s), 2, std::back_inserter(v));
 std::ranges::copy_n(std::istream_iterator<int>(s), 2, back_inserter(v));

 std::ranges::copy(v, std::ostream_iterator<int>(std::cout, " "));
 std::cout << '\n';
}
```

Run:
`clang++ -std=c++23 index.cc -o index && ./index`

Actual output:
`1 2 4 5`

Expected output:
`1 2 3 4`

Environment:
```
% clang++ -v
Homebrew clang version 18.1.8
Target: arm64-apple-darwin24.3.0
Thread model: posix
InstalledDir: /opt/homebrew/bin
```
</pre>
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