When the "reserve" branch is satisfied, ranges::to directly passes the result of ranges::size(r) into the reserve call. However, given that the standard only guarantees that integer-class type can be explicitly converted to any integer-like type ([iterator.concept.winc] p6), this makes the call potentially ill-formed, since ranges::size(r) may return an integer-class type:

#include <ranges>
#include <vector>

int main() {
  auto r = std::ranges::subrange(std::views::iota(0ULL) | std::views::take(5), 5);
  auto v = r | std::ranges::to<std::vector<std::size_t>>(0); // cannot implicitly convert _Unsigned128 to size_t in MSVC-STL
}

We should do an explicit cast before calling reserve.