Function documents_dir 

pub fn documents_dir() -> Option<PathBuf>

The user’s Documents folder, where an application puts files the user made and wants to find again in a file manager: projects, exports, notes.

• Linux and other Unix systems: the XDG_DOCUMENTS_DIR line of user-dirs.dirs in the config root ($XDG_CONFIG_HOME when it is an absolute path, else $HOME/.config), which is where a desktop records the folder’s name in the user’s language, such as $HOME/Belgeler. A missing or unreadable file, a line that does not follow the format, and a line that names the home folder itself (the way that file turns a folder off) all give $HOME/Documents.
• macOS: $HOME/Documents.
• Windows: the Documents Known Folder, which the user can move to another drive; when the system does not answer, %USERPROFILE%\Documents.

None when there is no home folder to put it in. A HOME that is not an absolute path counts as missing, as it does for config_dir. The folder is not created and does not have to exist.