[libcxx-commits] [libcxx] [libc++][filesystem] Report an error for canonical("") (PR #215031)

[Yordan Vásquez via libcxx-commits]

vyordan wrote:

@philnik777 

MSVC STL doesn't even error on `canonical("")` - its internal `_Canonical` helper returns success immediately for an empty input, so both `canonical("")` and `weakly_canonical("")` succeed there:
[filesystem#L3039-L3042](https://github.com/microsoft/STL/blob/1f932bc4246b31afc460a44372be09d50a21964a/stl/inc/filesystem#L3039-L3042)
[filesystem#L4109-L4120](https://github.com/microsoft/STL/blob/1f932bc4246b31afc460a44372be09d50a21964a/stl/inc/filesystem#L4109-L4120)

https://github.com/llvm/llvm-project/pull/215031