<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/86833>86833</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            <algorithm>: `contains_subrange` should not use `std::cbegin` and `std::distance`
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          hewillk
      </td>
    </tr>
</table>

<pre>
    https://github.com/llvm/llvm-project/blob/c335accb07c0cfa4bd7f47edc94c9005692edfcc/libcxx/include/__algorithm/ranges_contains_subrange.h#L72-L80


...because they are based on the C++17 iterator model rather than the C++20 Ranges iterator model.
In addition, `__n2` is an integer type and may not accommodate `difference_type`.
I believe the above can be just simplified to: 

```cpp
if (ranges::distance(__range2) == 0)
  return true;
```


testcase:

```cpp
#include <ranges>
#include <algorithm>

static_assert(
 std::ranges::contains_subrange(
    std::views::iota(0, 5),
 std::views::iota(0, 5) | std::views::filter([](int i) { return true; }) )
);
```
https://godbolt.org/z/G6oMoM5Wz
</pre>
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