Function reserved_path_component 

pub fn reserved_path_component(
    path: &[u8],
    leaf_symlink: bool,
) -> Option<ReservedPathComponent>

The first component of the repository-relative path that is reserved by reserved_tree_entry_name, if any. leaf_symlink says the last component is a symlink.

Components are split on both / and \. Empty and . components are skipped, so ./.heddle/x is a root .heddle.