Method add_node

consumer/src/tree.rs:190–216

(
            nodes: &mut HashMap<NodeId, NodeState>,
            pending_grafts: &mut HashMap<TreeId, NodeId>,
            changes: &mut Option<&mut InternalChanges>,
            parent_and_index: Op

        }

        fn add_node(
            nodes: &mut HashMap<NodeId, NodeState>,
            pending_grafts: &mut HashMap<TreeId, NodeId>,
            changes: &mut Option<&mut InternalChanges>,
            parent_and_index: Option<ParentAndIndex>,
            id: NodeId,
            data: NodeData,
        ) {
            if let Some(subtree_id) = data.tree_id() {
                if !data.children().is_empty() {
                    panic!(
                        "Node {:?} has both tree_id and children. \
                         A graft node's only child comes from its subtree.",
                        id.to_components().0
                    );
                }
                record_graft(pending_grafts, subtree_id, id);
            }
            let state = NodeState {
                parent_and_index,
                data,
            };
            nodes.insert(id, state);
            if let Some(changes) = changes {
                changes.added_node_ids.insert(id);
            }
        }

        for (local_node_id, node_data) in update.nodes {
            let node_id = map_id(local_node_id);