Describe the bug

I was investigating a libcxx failure on test std\input.output\filesystems\fs.op.funcs\fs.op.absolute\absolute.pass.cpp.
It fails because of a dubious test case that involves calling fs::absolute("", ec).
Interestingly, libstdc++, libc++, and MSVC STL all handle this differently.

Code

https://godbolt.org/z/MK97zP3jT

#include <filesystem>
#include <iostream>

namespace fs = std::filesystem;

int main()
{
    const fs::path cwd = fs::current_path();
    std::error_code ec{};

    std::cout << "CWD is " << cwd << std::endl;

    const fs::path ret = fs::absolute("", ec);

    std::cout << ret << '\t' << ec << std::endl;
}

Output

Command-line test case

See Godbolt link.

Expected behavior

• I think that returning an empty path() is fine; it's probably the desired behavior, unlike libc++.
  • However, since it's an 'erroneous' case, we may consider changing the implementation such that ec is set with an appropriate error code.
• If no implementation change is made, it should suffice to just document the reason of the test failure and move on.

STL version

Microsoft (R) C/C++ Optimizing Compiler Version 19.50.35725 for x64

Additional context