Rust uses WTF-8 on Windows for OsStr[ing] and Path[Buf]. It's zero-overhead to cast from &str to &OsStr/&Path to &[u8] (though converting WTF-8 to UTF-16 costs

Rust uses WTF-8 on Windows for OsStr[ing] and Path[Buf]. It's zero-overhead to cast from &str to &OsStr/&Path to &[u8] (though converting WTF-8 to UTF-16 costs an extra operation when performing a Win32 function call). However this doesn't solve the inability to round-trip "possibly-valid UTF-8/16" to "Unicode text" and back (though Python's surrogateescape might be one viable approach). Other libraries handle this even worse than Rust. On Linux (filenames are bytes), Qt is unable to open files with invalid UTF-8 names, while GTK can open them (but shows an "invalid encoding" message instead of the original filename), which I think is a good-enough approach.