pub fn collect_relations(env: &BuildEnvironment) -> BTreeMap<String, Relation>Expand description
Every document’s [parent, prev, next], from a pre-order walk of the
toctree graph rooted at env.root_doc.
Port of BuildEnvironment.collect_relations
(environment/__init__.py:778-795) over traverse_toctree. prev/
next are the flattened document order, so the first child of a
document has that document as its prev — Sphinx’s chain is linear, not
sibling-scoped.