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diff --git a/third_party/rust/petgraph/src/visit/traversal.rs b/third_party/rust/petgraph/src/visit/traversal.rs
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+++ b/third_party/rust/petgraph/src/visit/traversal.rs
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+use super::{GraphRef, IntoNodeIdentifiers, Reversed};
+use super::{IntoNeighbors, IntoNeighborsDirected, VisitMap, Visitable};
+use crate::Incoming;
+use std::collections::VecDeque;
+
+/// Visit nodes of a graph in a depth-first-search (DFS) emitting nodes in
+/// preorder (when they are first discovered).
+///
+/// The traversal starts at a given node and only traverses nodes reachable
+/// from it.
+///
+/// `Dfs` is not recursive.
+///
+/// `Dfs` does not itself borrow the graph, and because of this you can run
+/// a traversal over a graph while still retaining mutable access to it, if you
+/// use it like the following example:
+///
+/// ```
+/// use petgraph::Graph;
+/// use petgraph::visit::Dfs;
+///
+/// let mut graph = Graph::<_,()>::new();
+/// let a = graph.add_node(0);
+///
+/// let mut dfs = Dfs::new(&graph, a);
+/// while let Some(nx) = dfs.next(&graph) {
+///     // we can access `graph` mutably here still
+///     graph[nx] += 1;
+/// }
+///
+/// assert_eq!(graph[a], 1);
+/// ```
+///
+/// **Note:** The algorithm may not behave correctly if nodes are removed
+/// during iteration. It may not necessarily visit added nodes or edges.
+#[derive(Clone, Debug)]
+pub struct Dfs<N, VM> {
+    /// The stack of nodes to visit
+    pub stack: Vec<N>,
+    /// The map of discovered nodes
+    pub discovered: VM,
+}
+
+impl<N, VM> Default for Dfs<N, VM>
+where
+    VM: Default,
+{
+    fn default() -> Self {
+        Dfs {
+            stack: Vec::new(),
+            discovered: VM::default(),
+        }
+    }
+}
+
+impl<N, VM> Dfs<N, VM>
+where
+    N: Copy + PartialEq,
+    VM: VisitMap<N>,
+{
+    /// Create a new **Dfs**, using the graph's visitor map, and put **start**
+    /// in the stack of nodes to visit.
+    pub fn new<G>(graph: G, start: N) -> Self
+    where
+        G: GraphRef + Visitable<NodeId = N, Map = VM>,
+    {
+        let mut dfs = Dfs::empty(graph);
+        dfs.move_to(start);
+        dfs
+    }
+
+    /// Create a `Dfs` from a vector and a visit map
+    pub fn from_parts(stack: Vec<N>, discovered: VM) -> Self {
+        Dfs { stack, discovered }
+    }
+
+    /// Clear the visit state
+    pub fn reset<G>(&mut self, graph: G)
+    where
+        G: GraphRef + Visitable<NodeId = N, Map = VM>,
+    {
+        graph.reset_map(&mut self.discovered);
+        self.stack.clear();
+    }
+
+    /// Create a new **Dfs** using the graph's visitor map, and no stack.
+    pub fn empty<G>(graph: G) -> Self
+    where
+        G: GraphRef + Visitable<NodeId = N, Map = VM>,
+    {
+        Dfs {
+            stack: Vec::new(),
+            discovered: graph.visit_map(),
+        }
+    }
+
+    /// Keep the discovered map, but clear the visit stack and restart
+    /// the dfs from a particular node.
+    pub fn move_to(&mut self, start: N) {
+        self.stack.clear();
+        self.stack.push(start);
+    }
+
+    /// Return the next node in the dfs, or **None** if the traversal is done.
+    pub fn next<G>(&mut self, graph: G) -> Option<N>
+    where
+        G: IntoNeighbors<NodeId = N>,
+    {
+        while let Some(node) = self.stack.pop() {
+            if self.discovered.visit(node) {
+                for succ in graph.neighbors(node) {
+                    if !self.discovered.is_visited(&succ) {
+                        self.stack.push(succ);
+                    }
+                }
+                return Some(node);
+            }
+        }
+        None
+    }
+}
+
+/// Visit nodes in a depth-first-search (DFS) emitting nodes in postorder
+/// (each node after all its descendants have been emitted).
+///
+/// `DfsPostOrder` is not recursive.
+///
+/// The traversal starts at a given node and only traverses nodes reachable
+/// from it.
+#[derive(Clone, Debug)]
+pub struct DfsPostOrder<N, VM> {
+    /// The stack of nodes to visit
+    pub stack: Vec<N>,
+    /// The map of discovered nodes
+    pub discovered: VM,
+    /// The map of finished nodes
+    pub finished: VM,
+}
+
+impl<N, VM> Default for DfsPostOrder<N, VM>
+where
+    VM: Default,
+{
+    fn default() -> Self {
+        DfsPostOrder {
+            stack: Vec::new(),
+            discovered: VM::default(),
+            finished: VM::default(),
+        }
+    }
+}
+
+impl<N, VM> DfsPostOrder<N, VM>
+where
+    N: Copy + PartialEq,
+    VM: VisitMap<N>,
+{
+    /// Create a new `DfsPostOrder` using the graph's visitor map, and put
+    /// `start` in the stack of nodes to visit.
+    pub fn new<G>(graph: G, start: N) -> Self
+    where
+        G: GraphRef + Visitable<NodeId = N, Map = VM>,
+    {
+        let mut dfs = Self::empty(graph);
+        dfs.move_to(start);
+        dfs
+    }
+
+    /// Create a new `DfsPostOrder` using the graph's visitor map, and no stack.
+    pub fn empty<G>(graph: G) -> Self
+    where
+        G: GraphRef + Visitable<NodeId = N, Map = VM>,
+    {
+        DfsPostOrder {
+            stack: Vec::new(),
+            discovered: graph.visit_map(),
+            finished: graph.visit_map(),
+        }
+    }
+
+    /// Clear the visit state
+    pub fn reset<G>(&mut self, graph: G)
+    where
+        G: GraphRef + Visitable<NodeId = N, Map = VM>,
+    {
+        graph.reset_map(&mut self.discovered);
+        graph.reset_map(&mut self.finished);
+        self.stack.clear();
+    }
+
+    /// Keep the discovered and finished map, but clear the visit stack and restart
+    /// the dfs from a particular node.
+    pub fn move_to(&mut self, start: N) {
+        self.stack.clear();
+        self.stack.push(start);
+    }
+
+    /// Return the next node in the traversal, or `None` if the traversal is done.
+    pub fn next<G>(&mut self, graph: G) -> Option<N>
+    where
+        G: IntoNeighbors<NodeId = N>,
+    {
+        while let Some(&nx) = self.stack.last() {
+            if self.discovered.visit(nx) {
+                // First time visiting `nx`: Push neighbors, don't pop `nx`
+                for succ in graph.neighbors(nx) {
+                    if !self.discovered.is_visited(&succ) {
+                        self.stack.push(succ);
+                    }
+                }
+            } else {
+                self.stack.pop();
+                if self.finished.visit(nx) {
+                    // Second time: All reachable nodes must have been finished
+                    return Some(nx);
+                }
+            }
+        }
+        None
+    }
+}
+
+/// A breadth first search (BFS) of a graph.
+///
+/// The traversal starts at a given node and only traverses nodes reachable
+/// from it.
+///
+/// `Bfs` is not recursive.
+///
+/// `Bfs` does not itself borrow the graph, and because of this you can run
+/// a traversal over a graph while still retaining mutable access to it, if you
+/// use it like the following example:
+///
+/// ```
+/// use petgraph::Graph;
+/// use petgraph::visit::Bfs;
+///
+/// let mut graph = Graph::<_,()>::new();
+/// let a = graph.add_node(0);
+///
+/// let mut bfs = Bfs::new(&graph, a);
+/// while let Some(nx) = bfs.next(&graph) {
+///     // we can access `graph` mutably here still
+///     graph[nx] += 1;
+/// }
+///
+/// assert_eq!(graph[a], 1);
+/// ```
+///
+/// **Note:** The algorithm may not behave correctly if nodes are removed
+/// during iteration. It may not necessarily visit added nodes or edges.
+#[derive(Clone)]
+pub struct Bfs<N, VM> {
+    /// The queue of nodes to visit
+    pub stack: VecDeque<N>,
+    /// The map of discovered nodes
+    pub discovered: VM,
+}
+
+impl<N, VM> Default for Bfs<N, VM>
+where
+    VM: Default,
+{
+    fn default() -> Self {
+        Bfs {
+            stack: VecDeque::new(),
+            discovered: VM::default(),
+        }
+    }
+}
+
+impl<N, VM> Bfs<N, VM>
+where
+    N: Copy + PartialEq,
+    VM: VisitMap<N>,
+{
+    /// Create a new **Bfs**, using the graph's visitor map, and put **start**
+    /// in the stack of nodes to visit.
+    pub fn new<G>(graph: G, start: N) -> Self
+    where
+        G: GraphRef + Visitable<NodeId = N, Map = VM>,
+    {
+        let mut discovered = graph.visit_map();
+        discovered.visit(start);
+        let mut stack = VecDeque::new();
+        stack.push_front(start);
+        Bfs { stack, discovered }
+    }
+
+    /// Return the next node in the bfs, or **None** if the traversal is done.
+    pub fn next<G>(&mut self, graph: G) -> Option<N>
+    where
+        G: IntoNeighbors<NodeId = N>,
+    {
+        if let Some(node) = self.stack.pop_front() {
+            for succ in graph.neighbors(node) {
+                if self.discovered.visit(succ) {
+                    self.stack.push_back(succ);
+                }
+            }
+
+            return Some(node);
+        }
+        None
+    }
+}
+
+/// A topological order traversal for a graph.
+///
+/// **Note** that `Topo` only visits nodes that are not part of cycles,
+/// i.e. nodes in a true DAG. Use other visitors like `DfsPostOrder` or
+/// algorithms like kosaraju_scc to handle graphs with possible cycles.
+#[derive(Clone)]
+pub struct Topo<N, VM> {
+    tovisit: Vec<N>,
+    ordered: VM,
+}
+
+impl<N, VM> Default for Topo<N, VM>
+where
+    VM: Default,
+{
+    fn default() -> Self {
+        Topo {
+            tovisit: Vec::new(),
+            ordered: VM::default(),
+        }
+    }
+}
+
+impl<N, VM> Topo<N, VM>
+where
+    N: Copy + PartialEq,
+    VM: VisitMap<N>,
+{
+    /// Create a new `Topo`, using the graph's visitor map, and put all
+    /// initial nodes in the to visit list.
+    pub fn new<G>(graph: G) -> Self
+    where
+        G: IntoNodeIdentifiers + IntoNeighborsDirected + Visitable<NodeId = N, Map = VM>,
+    {
+        let mut topo = Self::empty(graph);
+        topo.extend_with_initials(graph);
+        topo
+    }
+
+    fn extend_with_initials<G>(&mut self, g: G)
+    where
+        G: IntoNodeIdentifiers + IntoNeighborsDirected<NodeId = N>,
+    {
+        // find all initial nodes (nodes without incoming edges)
+        self.tovisit.extend(
+            g.node_identifiers()
+                .filter(move |&a| g.neighbors_directed(a, Incoming).next().is_none()),
+        );
+    }
+
+    /* Private until it has a use */
+    /// Create a new `Topo`, using the graph's visitor map with *no* starting
+    /// index specified.
+    fn empty<G>(graph: G) -> Self
+    where
+        G: GraphRef + Visitable<NodeId = N, Map = VM>,
+    {
+        Topo {
+            ordered: graph.visit_map(),
+            tovisit: Vec::new(),
+        }
+    }
+
+    /// Clear visited state, and put all initial nodes in the to visit list.
+    pub fn reset<G>(&mut self, graph: G)
+    where
+        G: IntoNodeIdentifiers + IntoNeighborsDirected + Visitable<NodeId = N, Map = VM>,
+    {
+        graph.reset_map(&mut self.ordered);
+        self.tovisit.clear();
+        self.extend_with_initials(graph);
+    }
+
+    /// Return the next node in the current topological order traversal, or
+    /// `None` if the traversal is at the end.
+    ///
+    /// *Note:* The graph may not have a complete topological order, and the only
+    /// way to know is to run the whole traversal and make sure it visits every node.
+    pub fn next<G>(&mut self, g: G) -> Option<N>
+    where
+        G: IntoNeighborsDirected + Visitable<NodeId = N, Map = VM>,
+    {
+        // Take an unvisited element and find which of its neighbors are next
+        while let Some(nix) = self.tovisit.pop() {
+            if self.ordered.is_visited(&nix) {
+                continue;
+            }
+            self.ordered.visit(nix);
+            for neigh in g.neighbors(nix) {
+                // Look at each neighbor, and those that only have incoming edges
+                // from the already ordered list, they are the next to visit.
+                if Reversed(g)
+                    .neighbors(neigh)
+                    .all(|b| self.ordered.is_visited(&b))
+                {
+                    self.tovisit.push(neigh);
+                }
+            }
+            return Some(nix);
+        }
+        None
+    }
+}
+
+/// A walker is a traversal state, but where part of the traversal
+/// information is supplied manually to each next call.
+///
+/// This for example allows graph traversals that don't hold a borrow of the
+/// graph they are traversing.
+pub trait Walker<Context> {
+    type Item;
+    /// Advance to the next item
+    fn walk_next(&mut self, context: Context) -> Option<Self::Item>;
+
+    /// Create an iterator out of the walker and given `context`.
+    fn iter(self, context: Context) -> WalkerIter<Self, Context>
+    where
+        Self: Sized,
+        Context: Clone,
+    {
+        WalkerIter {
+            walker: self,
+            context,
+        }
+    }
+}
+
+/// A walker and its context wrapped into an iterator.
+#[derive(Clone, Debug)]
+pub struct WalkerIter<W, C> {
+    walker: W,
+    context: C,
+}
+
+impl<W, C> WalkerIter<W, C>
+where
+    W: Walker<C>,
+    C: Clone,
+{
+    pub fn context(&self) -> C {
+        self.context.clone()
+    }
+
+    pub fn inner_ref(&self) -> &W {
+        &self.walker
+    }
+
+    pub fn inner_mut(&mut self) -> &mut W {
+        &mut self.walker
+    }
+}
+
+impl<W, C> Iterator for WalkerIter<W, C>
+where
+    W: Walker<C>,
+    C: Clone,
+{
+    type Item = W::Item;
+    fn next(&mut self) -> Option<Self::Item> {
+        self.walker.walk_next(self.context.clone())
+    }
+}
+
+impl<'a, C, W: ?Sized> Walker<C> for &'a mut W
+where
+    W: Walker<C>,
+{
+    type Item = W::Item;
+    fn walk_next(&mut self, context: C) -> Option<Self::Item> {
+        (**self).walk_next(context)
+    }
+}
+
+impl<G> Walker<G> for Dfs<G::NodeId, G::Map>
+where
+    G: IntoNeighbors + Visitable,
+{
+    type Item = G::NodeId;
+    fn walk_next(&mut self, context: G) -> Option<Self::Item> {
+        self.next(context)
+    }
+}
+
+impl<G> Walker<G> for DfsPostOrder<G::NodeId, G::Map>
+where
+    G: IntoNeighbors + Visitable,
+{
+    type Item = G::NodeId;
+    fn walk_next(&mut self, context: G) -> Option<Self::Item> {
+        self.next(context)
+    }
+}
+
+impl<G> Walker<G> for Bfs<G::NodeId, G::Map>
+where
+    G: IntoNeighbors + Visitable,
+{
+    type Item = G::NodeId;
+    fn walk_next(&mut self, context: G) -> Option<Self::Item> {
+        self.next(context)
+    }
+}
+
+impl<G> Walker<G> for Topo<G::NodeId, G::Map>
+where
+    G: IntoNeighborsDirected + Visitable,
+{
+    type Item = G::NodeId;
+    fn walk_next(&mut self, context: G) -> Option<Self::Item> {
+        self.next(context)
+    }
+}