Merging upstream version 1.72.1+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

5 files changed, 0 insertions, 4726 deletions

diff --git a/vendor/petgraph/src/graph_impl/frozen.rs b/vendor/petgraph/src/graph_impl/frozen.rs
deleted file mode 100644
index 1ba06d9d9..000000000
--- a/vendor/petgraph/src/graph_impl/frozen.rs
+++ /dev/null
@@ -1,96 +0,0 @@
-use std::ops::{Deref, Index, IndexMut};
-
-use super::Frozen;
-use crate::data::{DataMap, DataMapMut};
-use crate::graph::Graph;
-use crate::graph::{GraphIndex, IndexType};
-use crate::visit::{Data, GraphProp, IntoNeighborsDirected, IntoNodeIdentifiers, NodeIndexable};
-use crate::visit::{
-    GetAdjacencyMatrix, IntoEdges, IntoEdgesDirected, NodeCompactIndexable, NodeCount,
-};
-use crate::visit::{IntoEdgeReferences, IntoNeighbors, IntoNodeReferences, Visitable};
-use crate::{Direction, EdgeType};
-
-impl<'a, G> Frozen<'a, G> {
-    /// Create a new `Frozen` from a mutable reference to a graph.
-    pub fn new(gr: &'a mut G) -> Self {
-        Frozen(gr)
-    }
-}
-
-/// Deref allows transparent access to all shared reference (read-only)
-/// functionality in the underlying graph.
-impl<'a, G> Deref for Frozen<'a, G> {
-    type Target = G;
-    fn deref(&self) -> &G {
-        self.0
-    }
-}
-
-impl<'a, G, I> Index<I> for Frozen<'a, G>
-where
-    G: Index<I>,
-{
-    type Output = G::Output;
-    fn index(&self, i: I) -> &G::Output {
-        self.0.index(i)
-    }
-}
-
-impl<'a, G, I> IndexMut<I> for Frozen<'a, G>
-where
-    G: IndexMut<I>,
-{
-    fn index_mut(&mut self, i: I) -> &mut G::Output {
-        self.0.index_mut(i)
-    }
-}
-
-impl<'a, N, E, Ty, Ix> Frozen<'a, Graph<N, E, Ty, Ix>>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    /// Index the `Graph` by two indices, any combination of
-    /// node or edge indices is fine.
-    ///
-    /// **Panics** if the indices are equal or if they are out of bounds.
-    pub fn index_twice_mut<T, U>(
-        &mut self,
-        i: T,
-        j: U,
-    ) -> (
-        &mut <Graph<N, E, Ty, Ix> as Index<T>>::Output,
-        &mut <Graph<N, E, Ty, Ix> as Index<U>>::Output,
-    )
-    where
-        Graph<N, E, Ty, Ix>: IndexMut<T> + IndexMut<U>,
-        T: GraphIndex,
-        U: GraphIndex,
-    {
-        self.0.index_twice_mut(i, j)
-    }
-}
-
-macro_rules! access0 {
-    ($e:expr) => {
-        $e.0
-    };
-}
-
-Data! {delegate_impl [['a, G], G, Frozen<'a, G>, deref_twice]}
-DataMap! {delegate_impl [['a, G], G, Frozen<'a, G>, deref_twice]}
-DataMapMut! {delegate_impl [['a, G], G, Frozen<'a, G>, access0]}
-GetAdjacencyMatrix! {delegate_impl [['a, G], G, Frozen<'a, G>, deref_twice]}
-IntoEdgeReferences! {delegate_impl [['a, 'b, G], G, &'b Frozen<'a, G>, deref_twice]}
-IntoEdges! {delegate_impl [['a, 'b, G], G, &'b Frozen<'a, G>, deref_twice]}
-IntoEdgesDirected! {delegate_impl [['a, 'b, G], G, &'b Frozen<'a, G>, deref_twice]}
-IntoNeighbors! {delegate_impl [['a, 'b, G], G, &'b Frozen<'a, G>, deref_twice]}
-IntoNeighborsDirected! {delegate_impl [['a, 'b, G], G, &'b Frozen<'a, G>, deref_twice]}
-IntoNodeIdentifiers! {delegate_impl [['a, 'b, G], G, &'b Frozen<'a, G>, deref_twice]}
-IntoNodeReferences! {delegate_impl [['a, 'b, G], G, &'b Frozen<'a, G>, deref_twice]}
-NodeCompactIndexable! {delegate_impl [['a, G], G, Frozen<'a, G>, deref_twice]}
-NodeCount! {delegate_impl [['a, G], G, Frozen<'a, G>, deref_twice]}
-NodeIndexable! {delegate_impl [['a, G], G, Frozen<'a, G>, deref_twice]}
-GraphProp! {delegate_impl [['a, G], G, Frozen<'a, G>, deref_twice]}
-Visitable! {delegate_impl [['a, G], G, Frozen<'a, G>, deref_twice]}
diff --git a/vendor/petgraph/src/graph_impl/mod.rs b/vendor/petgraph/src/graph_impl/mod.rs
deleted file mode 100644
index 9fb43b3c4..000000000
--- a/vendor/petgraph/src/graph_impl/mod.rs
+++ /dev/null
@@ -1,2172 +0,0 @@
-use std::cmp;
-use std::fmt;
-use std::hash::Hash;
-use std::iter;
-use std::marker::PhantomData;
-use std::mem::size_of;
-use std::ops::{Index, IndexMut, Range};
-use std::slice;
-
-use crate::{Directed, Direction, EdgeType, Incoming, IntoWeightedEdge, Outgoing, Undirected};
-
-use crate::iter_format::{DebugMap, IterFormatExt, NoPretty};
-
-use crate::util::enumerate;
-use crate::visit::EdgeRef;
-use crate::visit::{IntoEdges, IntoEdgesDirected, IntoNodeReferences};
-
-#[cfg(feature = "serde-1")]
-mod serialization;
-
-/// The default integer type for graph indices.
-/// `u32` is the default to reduce the size of the graph's data and improve
-/// performance in the common case.
-///
-/// Used for node and edge indices in `Graph` and `StableGraph`, used
-/// for node indices in `Csr`.
-pub type DefaultIx = u32;
-
-/// Trait for the unsigned integer type used for node and edge indices.
-///
-/// Marked `unsafe` because: the trait must faithfully preserve
-/// and convert index values.
-pub unsafe trait IndexType: Copy + Default + Hash + Ord + fmt::Debug + 'static {
-    fn new(x: usize) -> Self;
-    fn index(&self) -> usize;
-    fn max() -> Self;
-}
-
-unsafe impl IndexType for usize {
-    #[inline(always)]
-    fn new(x: usize) -> Self {
-        x
-    }
-    #[inline(always)]
-    fn index(&self) -> Self {
-        *self
-    }
-    #[inline(always)]
-    fn max() -> Self {
-        ::std::usize::MAX
-    }
-}
-
-unsafe impl IndexType for u32 {
-    #[inline(always)]
-    fn new(x: usize) -> Self {
-        x as u32
-    }
-    #[inline(always)]
-    fn index(&self) -> usize {
-        *self as usize
-    }
-    #[inline(always)]
-    fn max() -> Self {
-        ::std::u32::MAX
-    }
-}
-
-unsafe impl IndexType for u16 {
-    #[inline(always)]
-    fn new(x: usize) -> Self {
-        x as u16
-    }
-    #[inline(always)]
-    fn index(&self) -> usize {
-        *self as usize
-    }
-    #[inline(always)]
-    fn max() -> Self {
-        ::std::u16::MAX
-    }
-}
-
-unsafe impl IndexType for u8 {
-    #[inline(always)]
-    fn new(x: usize) -> Self {
-        x as u8
-    }
-    #[inline(always)]
-    fn index(&self) -> usize {
-        *self as usize
-    }
-    #[inline(always)]
-    fn max() -> Self {
-        ::std::u8::MAX
-    }
-}
-
-/// Node identifier.
-#[derive(Copy, Clone, Default, PartialEq, PartialOrd, Eq, Ord, Hash)]
-pub struct NodeIndex<Ix = DefaultIx>(Ix);
-
-impl<Ix: IndexType> NodeIndex<Ix> {
-    #[inline]
-    pub fn new(x: usize) -> Self {
-        NodeIndex(IndexType::new(x))
-    }
-
-    #[inline]
-    pub fn index(self) -> usize {
-        self.0.index()
-    }
-
-    #[inline]
-    pub fn end() -> Self {
-        NodeIndex(IndexType::max())
-    }
-
-    fn _into_edge(self) -> EdgeIndex<Ix> {
-        EdgeIndex(self.0)
-    }
-}
-
-impl<Ix: IndexType> From<Ix> for NodeIndex<Ix> {
-    fn from(ix: Ix) -> Self {
-        NodeIndex(ix)
-    }
-}
-
-impl<Ix: fmt::Debug> fmt::Debug for NodeIndex<Ix> {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "NodeIndex({:?})", self.0)
-    }
-}
-
-/// Short version of `NodeIndex::new`
-pub fn node_index<Ix: IndexType>(index: usize) -> NodeIndex<Ix> {
-    NodeIndex::new(index)
-}
-
-/// Short version of `EdgeIndex::new`
-pub fn edge_index<Ix: IndexType>(index: usize) -> EdgeIndex<Ix> {
-    EdgeIndex::new(index)
-}
-
-/// Edge identifier.
-#[derive(Copy, Clone, Default, PartialEq, PartialOrd, Eq, Ord, Hash)]
-pub struct EdgeIndex<Ix = DefaultIx>(Ix);
-
-impl<Ix: IndexType> EdgeIndex<Ix> {
-    #[inline]
-    pub fn new(x: usize) -> Self {
-        EdgeIndex(IndexType::new(x))
-    }
-
-    #[inline]
-    pub fn index(self) -> usize {
-        self.0.index()
-    }
-
-    /// An invalid `EdgeIndex` used to denote absence of an edge, for example
-    /// to end an adjacency list.
-    #[inline]
-    pub fn end() -> Self {
-        EdgeIndex(IndexType::max())
-    }
-
-    fn _into_node(self) -> NodeIndex<Ix> {
-        NodeIndex(self.0)
-    }
-}
-
-impl<Ix: IndexType> From<Ix> for EdgeIndex<Ix> {
-    fn from(ix: Ix) -> Self {
-        EdgeIndex(ix)
-    }
-}
-
-impl<Ix: fmt::Debug> fmt::Debug for EdgeIndex<Ix> {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "EdgeIndex({:?})", self.0)
-    }
-}
-/*
- * FIXME: Use this impl again, when we don't need to add so many bounds
-impl<Ix: IndexType> fmt::Debug for EdgeIndex<Ix>
-{
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        try!(write!(f, "EdgeIndex("));
-        if *self == EdgeIndex::end() {
-            try!(write!(f, "End"));
-        } else {
-            try!(write!(f, "{}", self.index()));
-        }
-        write!(f, ")")
-    }
-}
-*/
-
-const DIRECTIONS: [Direction; 2] = [Outgoing, Incoming];
-
-/// The graph's node type.
-#[derive(Debug)]
-pub struct Node<N, Ix = DefaultIx> {
-    /// Associated node data.
-    pub weight: N,
-    /// Next edge in outgoing and incoming edge lists.
-    next: [EdgeIndex<Ix>; 2],
-}
-
-impl<E, Ix> Clone for Node<E, Ix>
-where
-    E: Clone,
-    Ix: Copy,
-{
-    clone_fields!(Node, weight, next,);
-}
-
-impl<N, Ix: IndexType> Node<N, Ix> {
-    /// Accessor for data structure internals: the first edge in the given direction.
-    pub fn next_edge(&self, dir: Direction) -> EdgeIndex<Ix> {
-        self.next[dir.index()]
-    }
-}
-
-/// The graph's edge type.
-#[derive(Debug)]
-pub struct Edge<E, Ix = DefaultIx> {
-    /// Associated edge data.
-    pub weight: E,
-    /// Next edge in outgoing and incoming edge lists.
-    next: [EdgeIndex<Ix>; 2],
-    /// Start and End node index
-    node: [NodeIndex<Ix>; 2],
-}
-
-impl<E, Ix> Clone for Edge<E, Ix>
-where
-    E: Clone,
-    Ix: Copy,
-{
-    clone_fields!(Edge, weight, next, node,);
-}
-
-impl<E, Ix: IndexType> Edge<E, Ix> {
-    /// Accessor for data structure internals: the next edge for the given direction.
-    pub fn next_edge(&self, dir: Direction) -> EdgeIndex<Ix> {
-        self.next[dir.index()]
-    }
-
-    /// Return the source node index.
-    pub fn source(&self) -> NodeIndex<Ix> {
-        self.node[0]
-    }
-
-    /// Return the target node index.
-    pub fn target(&self) -> NodeIndex<Ix> {
-        self.node[1]
-    }
-}
-
-/// `Graph<N, E, Ty, Ix>` is a graph datastructure using an adjacency list representation.
-///
-/// `Graph` is parameterized over:
-///
-/// - Associated data `N` for nodes and `E` for edges, called *weights*.
-///   The associated data can be of arbitrary type.
-/// - Edge type `Ty` that determines whether the graph edges are directed or undirected.
-/// - Index type `Ix`, which determines the maximum size of the graph.
-///
-/// The `Graph` is a regular Rust collection and is `Send` and `Sync` (as long
-/// as associated data `N` and `E` are).
-///
-/// The graph uses **O(|V| + |E|)** space, and allows fast node and edge insert,
-/// efficient graph search and graph algorithms.
-/// It implements **O(e')** edge lookup and edge and node removals, where **e'**
-/// is some local measure of edge count.
-/// Based on the graph datastructure used in rustc.
-///
-/// Here's an example of building a graph with directed edges, and below
-/// an illustration of how it could be rendered with graphviz (see
-/// [`Dot`](../dot/struct.Dot.html)):
-///
-/// ```
-/// use petgraph::Graph;
-///
-/// let mut deps = Graph::<&str, &str>::new();
-/// let pg = deps.add_node("petgraph");
-/// let fb = deps.add_node("fixedbitset");
-/// let qc = deps.add_node("quickcheck");
-/// let rand = deps.add_node("rand");
-/// let libc = deps.add_node("libc");
-/// deps.extend_with_edges(&[
-///     (pg, fb), (pg, qc),
-///     (qc, rand), (rand, libc), (qc, libc),
-/// ]);
-/// ```
-///
-/// ![graph-example](https://bluss.github.io/ndarray/images/graph-example.svg)
-///
-/// ### Graph Indices
-///
-/// The graph maintains indices for nodes and edges, and node and edge
-/// weights may be accessed mutably. Indices range in a compact interval, for
-/// example for *n* nodes indices are 0 to *n* - 1 inclusive.
-///
-/// `NodeIndex` and `EdgeIndex` are types that act as references to nodes and edges,
-/// but these are only stable across certain operations:
-///
-/// * **Removing nodes or edges may shift other indices.** Removing a node will
-/// force the last node to shift its index to take its place. Similarly,
-/// removing an edge shifts the index of the last edge.
-/// * Adding nodes or edges keeps indices stable.
-///
-/// The `Ix` parameter is `u32` by default. The goal is that you can ignore this parameter
-/// completely unless you need a very big graph -- then you can use `usize`.
-///
-/// * The fact that the node and edge indices in the graph each are numbered in compact
-/// intervals (from 0 to *n* - 1 for *n* nodes) simplifies some graph algorithms.
-///
-/// * You can select graph index integer type after the size of the graph. A smaller
-/// size may have better performance.
-///
-/// * Using indices allows mutation while traversing the graph, see `Dfs`,
-/// and `.neighbors(a).detach()`.
-///
-/// * You can create several graphs using the equal node indices but with
-/// differing weights or differing edges.
-///
-/// * Indices don't allow as much compile time checking as references.
-///
-pub struct Graph<N, E, Ty = Directed, Ix = DefaultIx> {
-    nodes: Vec<Node<N, Ix>>,
-    edges: Vec<Edge<E, Ix>>,
-    ty: PhantomData<Ty>,
-}
-
-/// A `Graph` with directed edges.
-///
-/// For example, an edge from *1* to *2* is distinct from an edge from *2* to
-/// *1*.
-pub type DiGraph<N, E, Ix = DefaultIx> = Graph<N, E, Directed, Ix>;
-
-/// A `Graph` with undirected edges.
-///
-/// For example, an edge between *1* and *2* is equivalent to an edge between
-/// *2* and *1*.
-pub type UnGraph<N, E, Ix = DefaultIx> = Graph<N, E, Undirected, Ix>;
-
-/// The resulting cloned graph has the same graph indices as `self`.
-impl<N, E, Ty, Ix: IndexType> Clone for Graph<N, E, Ty, Ix>
-where
-    N: Clone,
-    E: Clone,
-{
-    fn clone(&self) -> Self {
-        Graph {
-            nodes: self.nodes.clone(),
-            edges: self.edges.clone(),
-            ty: self.ty,
-        }
-    }
-
-    fn clone_from(&mut self, rhs: &Self) {
-        self.nodes.clone_from(&rhs.nodes);
-        self.edges.clone_from(&rhs.edges);
-        self.ty = rhs.ty;
-    }
-}
-
-impl<N, E, Ty, Ix> fmt::Debug for Graph<N, E, Ty, Ix>
-where
-    N: fmt::Debug,
-    E: fmt::Debug,
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        let etype = if self.is_directed() {
-            "Directed"
-        } else {
-            "Undirected"
-        };
-        let mut fmt_struct = f.debug_struct("Graph");
-        fmt_struct.field("Ty", &etype);
-        fmt_struct.field("node_count", &self.node_count());
-        fmt_struct.field("edge_count", &self.edge_count());
-        if self.edge_count() > 0 {
-            fmt_struct.field(
-                "edges",
-                &self
-                    .edges
-                    .iter()
-                    .map(|e| NoPretty((e.source().index(), e.target().index())))
-                    .format(", "),
-            );
-        }
-        // skip weights if they are ZST!
-        if size_of::<N>() != 0 {
-            fmt_struct.field(
-                "node weights",
-                &DebugMap(|| self.nodes.iter().map(|n| &n.weight).enumerate()),
-            );
-        }
-        if size_of::<E>() != 0 {
-            fmt_struct.field(
-                "edge weights",
-                &DebugMap(|| self.edges.iter().map(|n| &n.weight).enumerate()),
-            );
-        }
-        fmt_struct.finish()
-    }
-}
-
-enum Pair<T> {
-    Both(T, T),
-    One(T),
-    None,
-}
-
-use std::cmp::max;
-
-/// Get mutable references at index `a` and `b`.
-fn index_twice<T>(slc: &mut [T], a: usize, b: usize) -> Pair<&mut T> {
-    if max(a, b) >= slc.len() {
-        Pair::None
-    } else if a == b {
-        Pair::One(&mut slc[max(a, b)])
-    } else {
-        // safe because a, b are in bounds and distinct
-        unsafe {
-            let ar = &mut *(slc.get_unchecked_mut(a) as *mut _);
-            let br = &mut *(slc.get_unchecked_mut(b) as *mut _);
-            Pair::Both(ar, br)
-        }
-    }
-}
-
-impl<N, E> Graph<N, E, Directed> {
-    /// Create a new `Graph` with directed edges.
-    ///
-    /// This is a convenience method. Use `Graph::with_capacity` or `Graph::default` for
-    /// a constructor that is generic in all the type parameters of `Graph`.
-    pub fn new() -> Self {
-        Graph {
-            nodes: Vec::new(),
-            edges: Vec::new(),
-            ty: PhantomData,
-        }
-    }
-}
-
-impl<N, E> Graph<N, E, Undirected> {
-    /// Create a new `Graph` with undirected edges.
-    ///
-    /// This is a convenience method. Use `Graph::with_capacity` or `Graph::default` for
-    /// a constructor that is generic in all the type parameters of `Graph`.
-    pub fn new_undirected() -> Self {
-        Graph {
-            nodes: Vec::new(),
-            edges: Vec::new(),
-            ty: PhantomData,
-        }
-    }
-}
-
-impl<N, E, Ty, Ix> Graph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    /// Create a new `Graph` with estimated capacity.
-    pub fn with_capacity(nodes: usize, edges: usize) -> Self {
-        Graph {
-            nodes: Vec::with_capacity(nodes),
-            edges: Vec::with_capacity(edges),
-            ty: PhantomData,
-        }
-    }
-
-    /// Return the number of nodes (vertices) in the graph.
-    ///
-    /// Computes in **O(1)** time.
-    pub fn node_count(&self) -> usize {
-        self.nodes.len()
-    }
-
-    /// Return the number of edges in the graph.
-    ///
-    /// Computes in **O(1)** time.
-    pub fn edge_count(&self) -> usize {
-        self.edges.len()
-    }
-
-    /// Whether the graph has directed edges or not.
-    #[inline]
-    pub fn is_directed(&self) -> bool {
-        Ty::is_directed()
-    }
-
-    /// Add a node (also called vertex) with associated data `weight` to the graph.
-    ///
-    /// Computes in **O(1)** time.
-    ///
-    /// Return the index of the new node.
-    ///
-    /// **Panics** if the Graph is at the maximum number of nodes for its index
-    /// type (N/A if usize).
-    pub fn add_node(&mut self, weight: N) -> NodeIndex<Ix> {
-        let node = Node {
-            weight,
-            next: [EdgeIndex::end(), EdgeIndex::end()],
-        };
-        let node_idx = NodeIndex::new(self.nodes.len());
-        // check for max capacity, except if we use usize
-        assert!(<Ix as IndexType>::max().index() == !0 || NodeIndex::end() != node_idx);
-        self.nodes.push(node);
-        node_idx
-    }
-
-    /// Access the weight for node `a`.
-    ///
-    /// Also available with indexing syntax: `&graph[a]`.
-    pub fn node_weight(&self, a: NodeIndex<Ix>) -> Option<&N> {
-        self.nodes.get(a.index()).map(|n| &n.weight)
-    }
-
-    /// Access the weight for node `a`, mutably.
-    ///
-    /// Also available with indexing syntax: `&mut graph[a]`.
-    pub fn node_weight_mut(&mut self, a: NodeIndex<Ix>) -> Option<&mut N> {
-        self.nodes.get_mut(a.index()).map(|n| &mut n.weight)
-    }
-
-    /// Add an edge from `a` to `b` to the graph, with its associated
-    /// data `weight`.
-    ///
-    /// Return the index of the new edge.
-    ///
-    /// Computes in **O(1)** time.
-    ///
-    /// **Panics** if any of the nodes don't exist.<br>
-    /// **Panics** if the Graph is at the maximum number of edges for its index
-    /// type (N/A if usize).
-    ///
-    /// **Note:** `Graph` allows adding parallel (“duplicate”) edges. If you want
-    /// to avoid this, use [`.update_edge(a, b, weight)`](#method.update_edge) instead.
-    pub fn add_edge(&mut self, a: NodeIndex<Ix>, b: NodeIndex<Ix>, weight: E) -> EdgeIndex<Ix> {
-        let edge_idx = EdgeIndex::new(self.edges.len());
-        assert!(<Ix as IndexType>::max().index() == !0 || EdgeIndex::end() != edge_idx);
-        let mut edge = Edge {
-            weight,
-            node: [a, b],
-            next: [EdgeIndex::end(); 2],
-        };
-        match index_twice(&mut self.nodes, a.index(), b.index()) {
-            Pair::None => panic!("Graph::add_edge: node indices out of bounds"),
-            Pair::One(an) => {
-                edge.next = an.next;
-                an.next[0] = edge_idx;
-                an.next[1] = edge_idx;
-            }
-            Pair::Both(an, bn) => {
-                // a and b are different indices
-                edge.next = [an.next[0], bn.next[1]];
-                an.next[0] = edge_idx;
-                bn.next[1] = edge_idx;
-            }
-        }
-        self.edges.push(edge);
-        edge_idx
-    }
-
-    /// Add or update an edge from `a` to `b`.
-    /// If the edge already exists, its weight is updated.
-    ///
-    /// Return the index of the affected edge.
-    ///
-    /// Computes in **O(e')** time, where **e'** is the number of edges
-    /// connected to `a` (and `b`, if the graph edges are undirected).
-    ///
-    /// **Panics** if any of the nodes don't exist.
-    pub fn update_edge(&mut self, a: NodeIndex<Ix>, b: NodeIndex<Ix>, weight: E) -> EdgeIndex<Ix> {
-        if let Some(ix) = self.find_edge(a, b) {
-            if let Some(ed) = self.edge_weight_mut(ix) {
-                *ed = weight;
-                return ix;
-            }
-        }
-        self.add_edge(a, b, weight)
-    }
-
-    /// Access the weight for edge `e`.
-    ///
-    /// Also available with indexing syntax: `&graph[e]`.
-    pub fn edge_weight(&self, e: EdgeIndex<Ix>) -> Option<&E> {
-        self.edges.get(e.index()).map(|ed| &ed.weight)
-    }
-
-    /// Access the weight for edge `e`, mutably.
-    ///
-    /// Also available with indexing syntax: `&mut graph[e]`.
-    pub fn edge_weight_mut(&mut self, e: EdgeIndex<Ix>) -> Option<&mut E> {
-        self.edges.get_mut(e.index()).map(|ed| &mut ed.weight)
-    }
-
-    /// Access the source and target nodes for `e`.
-    pub fn edge_endpoints(&self, e: EdgeIndex<Ix>) -> Option<(NodeIndex<Ix>, NodeIndex<Ix>)> {
-        self.edges
-            .get(e.index())
-            .map(|ed| (ed.source(), ed.target()))
-    }
-
-    /// Remove `a` from the graph if it exists, and return its weight.
-    /// If it doesn't exist in the graph, return `None`.
-    ///
-    /// Apart from `a`, this invalidates the last node index in the graph
-    /// (that node will adopt the removed node index). Edge indices are
-    /// invalidated as they would be following the removal of each edge
-    /// with an endpoint in `a`.
-    ///
-    /// Computes in **O(e')** time, where **e'** is the number of affected
-    /// edges, including *n* calls to `.remove_edge()` where *n* is the number
-    /// of edges with an endpoint in `a`, and including the edges with an
-    /// endpoint in the displaced node.
-    pub fn remove_node(&mut self, a: NodeIndex<Ix>) -> Option<N> {
-        self.nodes.get(a.index())?;
-        for d in &DIRECTIONS {
-            let k = d.index();
-
-            // Remove all edges from and to this node.
-            loop {
-                let next = self.nodes[a.index()].next[k];
-                if next == EdgeIndex::end() {
-                    break;
-                }
-                let ret = self.remove_edge(next);
-                debug_assert!(ret.is_some());
-                let _ = ret;
-            }
-        }
-
-        // Use swap_remove -- only the swapped-in node is going to change
-        // NodeIndex<Ix>, so we only have to walk its edges and update them.
-
-        let node = self.nodes.swap_remove(a.index());
-
-        // Find the edge lists of the node that had to relocate.
-        // It may be that no node had to relocate, then we are done already.
-        let swap_edges = match self.nodes.get(a.index()) {
-            None => return Some(node.weight),
-            Some(ed) => ed.next,
-        };
-
-        // The swapped element's old index
-        let old_index = NodeIndex::new(self.nodes.len());
-        let new_index = a;
-
-        // Adjust the starts of the out edges, and ends of the in edges.
-        for &d in &DIRECTIONS {
-            let k = d.index();
-            let mut edges = edges_walker_mut(&mut self.edges, swap_edges[k], d);
-            while let Some(curedge) = edges.next_edge() {
-                debug_assert!(curedge.node[k] == old_index);
-                curedge.node[k] = new_index;
-            }
-        }
-        Some(node.weight)
-    }
-
-    /// For edge `e` with endpoints `edge_node`, replace links to it,
-    /// with links to `edge_next`.
-    fn change_edge_links(
-        &mut self,
-        edge_node: [NodeIndex<Ix>; 2],
-        e: EdgeIndex<Ix>,
-        edge_next: [EdgeIndex<Ix>; 2],
-    ) {
-        for &d in &DIRECTIONS {
-            let k = d.index();
-            let node = match self.nodes.get_mut(edge_node[k].index()) {
-                Some(r) => r,
-                None => {
-                    debug_assert!(
-                        false,
-                        "Edge's endpoint dir={:?} index={:?} not found",
-                        d, edge_node[k]
-                    );
-                    return;
-                }
-            };
-            let fst = node.next[k];
-            if fst == e {
-                //println!("Updating first edge 0 for node {}, set to {}", edge_node[0], edge_next[0]);
-                node.next[k] = edge_next[k];
-            } else {
-                let mut edges = edges_walker_mut(&mut self.edges, fst, d);
-                while let Some(curedge) = edges.next_edge() {
-                    if curedge.next[k] == e {
-                        curedge.next[k] = edge_next[k];
-                        break; // the edge can only be present once in the list.
-                    }
-                }
-            }
-        }
-    }
-
-    /// Remove an edge and return its edge weight, or `None` if it didn't exist.
-    ///
-    /// Apart from `e`, this invalidates the last edge index in the graph
-    /// (that edge will adopt the removed edge index).
-    ///
-    /// Computes in **O(e')** time, where **e'** is the size of four particular edge lists, for
-    /// the vertices of `e` and the vertices of another affected edge.
-    pub fn remove_edge(&mut self, e: EdgeIndex<Ix>) -> Option<E> {
-        // every edge is part of two lists,
-        // outgoing and incoming edges.
-        // Remove it from both
-        let (edge_node, edge_next) = match self.edges.get(e.index()) {
-            None => return None,
-            Some(x) => (x.node, x.next),
-        };
-        // Remove the edge from its in and out lists by replacing it with
-        // a link to the next in the list.
-        self.change_edge_links(edge_node, e, edge_next);
-        self.remove_edge_adjust_indices(e)
-    }
-
-    fn remove_edge_adjust_indices(&mut self, e: EdgeIndex<Ix>) -> Option<E> {
-        // swap_remove the edge -- only the removed edge
-        // and the edge swapped into place are affected and need updating
-        // indices.
-        let edge = self.edges.swap_remove(e.index());
-        let swap = match self.edges.get(e.index()) {
-            // no elment needed to be swapped.
-            None => return Some(edge.weight),
-            Some(ed) => ed.node,
-        };
-        let swapped_e = EdgeIndex::new(self.edges.len());
-
-        // Update the edge lists by replacing links to the old index by references to the new
-        // edge index.
-        self.change_edge_links(swap, swapped_e, [e, e]);
-        Some(edge.weight)
-    }
-
-    /// Return an iterator of all nodes with an edge starting from `a`.
-    ///
-    /// - `Directed`: Outgoing edges from `a`.
-    /// - `Undirected`: All edges from or to `a`.
-    ///
-    /// Produces an empty iterator if the node doesn't exist.<br>
-    /// Iterator element type is `NodeIndex<Ix>`.
-    ///
-    /// Use [`.neighbors(a).detach()`][1] to get a neighbor walker that does
-    /// not borrow from the graph.
-    ///
-    /// [1]: struct.Neighbors.html#method.detach
-    pub fn neighbors(&self, a: NodeIndex<Ix>) -> Neighbors<E, Ix> {
-        self.neighbors_directed(a, Outgoing)
-    }
-
-    /// Return an iterator of all neighbors that have an edge between them and
-    /// `a`, in the specified direction.
-    /// If the graph's edges are undirected, this is equivalent to *.neighbors(a)*.
-    ///
-    /// - `Directed`, `Outgoing`: All edges from `a`.
-    /// - `Directed`, `Incoming`: All edges to `a`.
-    /// - `Undirected`: All edges from or to `a`.
-    ///
-    /// Produces an empty iterator if the node doesn't exist.<br>
-    /// Iterator element type is `NodeIndex<Ix>`.
-    ///
-    /// For a `Directed` graph, neighbors are listed in reverse order of their
-    /// addition to the graph, so the most recently added edge's neighbor is
-    /// listed first. The order in an `Undirected` graph is arbitrary.
-    ///
-    /// Use [`.neighbors_directed(a, dir).detach()`][1] to get a neighbor walker that does
-    /// not borrow from the graph.
-    ///
-    /// [1]: struct.Neighbors.html#method.detach
-    pub fn neighbors_directed(&self, a: NodeIndex<Ix>, dir: Direction) -> Neighbors<E, Ix> {
-        let mut iter = self.neighbors_undirected(a);
-        if self.is_directed() {
-            let k = dir.index();
-            iter.next[1 - k] = EdgeIndex::end();
-            iter.skip_start = NodeIndex::end();
-        }
-        iter
-    }
-
-    /// Return an iterator of all neighbors that have an edge between them and
-    /// `a`, in either direction.
-    /// If the graph's edges are undirected, this is equivalent to *.neighbors(a)*.
-    ///
-    /// - `Directed` and `Undirected`: All edges from or to `a`.
-    ///
-    /// Produces an empty iterator if the node doesn't exist.<br>
-    /// Iterator element type is `NodeIndex<Ix>`.
-    ///
-    /// Use [`.neighbors_undirected(a).detach()`][1] to get a neighbor walker that does
-    /// not borrow from the graph.
-    ///
-    /// [1]: struct.Neighbors.html#method.detach
-    ///
-    pub fn neighbors_undirected(&self, a: NodeIndex<Ix>) -> Neighbors<E, Ix> {
-        Neighbors {
-            skip_start: a,
-            edges: &self.edges,
-            next: match self.nodes.get(a.index()) {
-                None => [EdgeIndex::end(), EdgeIndex::end()],
-                Some(n) => n.next,
-            },
-        }
-    }
-
-    /// Return an iterator of all edges of `a`.
-    ///
-    /// - `Directed`: Outgoing edges from `a`.
-    /// - `Undirected`: All edges connected to `a`.
-    ///
-    /// Produces an empty iterator if the node doesn't exist.<br>
-    /// Iterator element type is `EdgeReference<E, Ix>`.
-    pub fn edges(&self, a: NodeIndex<Ix>) -> Edges<E, Ty, Ix> {
-        self.edges_directed(a, Outgoing)
-    }
-
-    /// Return an iterator of all edges of `a`, in the specified direction.
-    ///
-    /// - `Directed`, `Outgoing`: All edges from `a`.
-    /// - `Directed`, `Incoming`: All edges to `a`.
-    /// - `Undirected`, `Outgoing`: All edges connected to `a`, with `a` being the source of each
-    ///   edge.
-    /// - `Undirected`, `Incoming`: All edges connected to `a`, with `a` being the target of each
-    ///   edge.
-    ///
-    /// Produces an empty iterator if the node `a` doesn't exist.<br>
-    /// Iterator element type is `EdgeReference<E, Ix>`.
-    pub fn edges_directed(&self, a: NodeIndex<Ix>, dir: Direction) -> Edges<E, Ty, Ix> {
-        Edges {
-            skip_start: a,
-            edges: &self.edges,
-            direction: dir,
-            next: match self.nodes.get(a.index()) {
-                None => [EdgeIndex::end(), EdgeIndex::end()],
-                Some(n) => n.next,
-            },
-            ty: PhantomData,
-        }
-    }
-
-    /// Return an iterator over all the edges connecting `a` and `b`.
-    ///
-    /// - `Directed`: Outgoing edges from `a`.
-    /// - `Undirected`: All edges connected to `a`.
-    ///
-    /// Iterator element type is `EdgeReference<E, Ix>`.
-    pub fn edges_connecting(
-        &self,
-        a: NodeIndex<Ix>,
-        b: NodeIndex<Ix>,
-    ) -> EdgesConnecting<E, Ty, Ix> {
-        EdgesConnecting {
-            target_node: b,
-            edges: self.edges_directed(a, Direction::Outgoing),
-            ty: PhantomData,
-        }
-    }
-
-    /// Lookup if there is an edge from `a` to `b`.
-    ///
-    /// Computes in **O(e')** time, where **e'** is the number of edges
-    /// connected to `a` (and `b`, if the graph edges are undirected).
-    pub fn contains_edge(&self, a: NodeIndex<Ix>, b: NodeIndex<Ix>) -> bool {
-        self.find_edge(a, b).is_some()
-    }
-
-    /// Lookup an edge from `a` to `b`.
-    ///
-    /// Computes in **O(e')** time, where **e'** is the number of edges
-    /// connected to `a` (and `b`, if the graph edges are undirected).
-    pub fn find_edge(&self, a: NodeIndex<Ix>, b: NodeIndex<Ix>) -> Option<EdgeIndex<Ix>> {
-        if !self.is_directed() {
-            self.find_edge_undirected(a, b).map(|(ix, _)| ix)
-        } else {
-            match self.nodes.get(a.index()) {
-                None => None,
-                Some(node) => self.find_edge_directed_from_node(node, b),
-            }
-        }
-    }
-
-    fn find_edge_directed_from_node(
-        &self,
-        node: &Node<N, Ix>,
-        b: NodeIndex<Ix>,
-    ) -> Option<EdgeIndex<Ix>> {
-        let mut edix = node.next[0];
-        while let Some(edge) = self.edges.get(edix.index()) {
-            if edge.node[1] == b {
-                return Some(edix);
-            }
-            edix = edge.next[0];
-        }
-        None
-    }
-
-    /// Lookup an edge between `a` and `b`, in either direction.
-    ///
-    /// If the graph is undirected, then this is equivalent to `.find_edge()`.
-    ///
-    /// Return the edge index and its directionality, with `Outgoing` meaning
-    /// from `a` to `b` and `Incoming` the reverse,
-    /// or `None` if the edge does not exist.
-    pub fn find_edge_undirected(
-        &self,
-        a: NodeIndex<Ix>,
-        b: NodeIndex<Ix>,
-    ) -> Option<(EdgeIndex<Ix>, Direction)> {
-        match self.nodes.get(a.index()) {
-            None => None,
-            Some(node) => self.find_edge_undirected_from_node(node, b),
-        }
-    }
-
-    fn find_edge_undirected_from_node(
-        &self,
-        node: &Node<N, Ix>,
-        b: NodeIndex<Ix>,
-    ) -> Option<(EdgeIndex<Ix>, Direction)> {
-        for &d in &DIRECTIONS {
-            let k = d.index();
-            let mut edix = node.next[k];
-            while let Some(edge) = self.edges.get(edix.index()) {
-                if edge.node[1 - k] == b {
-                    return Some((edix, d));
-                }
-                edix = edge.next[k];
-            }
-        }
-        None
-    }
-
-    /// Return an iterator over either the nodes without edges to them
-    /// (`Incoming`) or from them (`Outgoing`).
-    ///
-    /// An *internal* node has both incoming and outgoing edges.
-    /// The nodes in `.externals(Incoming)` are the source nodes and
-    /// `.externals(Outgoing)` are the sinks of the graph.
-    ///
-    /// For a graph with undirected edges, both the sinks and the sources are
-    /// just the nodes without edges.
-    ///
-    /// The whole iteration computes in **O(|V|)** time.
-    pub fn externals(&self, dir: Direction) -> Externals<N, Ty, Ix> {
-        Externals {
-            iter: self.nodes.iter().enumerate(),
-            dir,
-            ty: PhantomData,
-        }
-    }
-
-    /// Return an iterator over the node indices of the graph.
-    ///
-    /// For example, in a rare case where a graph algorithm were not applicable,
-    /// the following code will iterate through all nodes to find a
-    /// specific index:
-    ///
-    /// ```
-    /// # use petgraph::Graph;
-    /// # let mut g = Graph::<&str, i32>::new();
-    /// # g.add_node("book");
-    /// let index = g.node_indices().find(|i| g[*i] == "book").unwrap();
-    /// ```
-    pub fn node_indices(&self) -> NodeIndices<Ix> {
-        NodeIndices {
-            r: 0..self.node_count(),
-            ty: PhantomData,
-        }
-    }
-
-    /// Return an iterator yielding mutable access to all node weights.
-    ///
-    /// The order in which weights are yielded matches the order of their
-    /// node indices.
-    pub fn node_weights_mut(&mut self) -> NodeWeightsMut<N, Ix> {
-        NodeWeightsMut {
-            nodes: self.nodes.iter_mut(),
-        }
-    }
-
-    /// Return an iterator over the edge indices of the graph
-    pub fn edge_indices(&self) -> EdgeIndices<Ix> {
-        EdgeIndices {
-            r: 0..self.edge_count(),
-            ty: PhantomData,
-        }
-    }
-
-    /// Create an iterator over all edges, in indexed order.
-    ///
-    /// Iterator element type is `EdgeReference<E, Ix>`.
-    pub fn edge_references(&self) -> EdgeReferences<E, Ix> {
-        EdgeReferences {
-            iter: self.edges.iter().enumerate(),
-        }
-    }
-
-    /// Return an iterator yielding mutable access to all edge weights.
-    ///
-    /// The order in which weights are yielded matches the order of their
-    /// edge indices.
-    pub fn edge_weights_mut(&mut self) -> EdgeWeightsMut<E, Ix> {
-        EdgeWeightsMut {
-            edges: self.edges.iter_mut(),
-        }
-    }
-
-    // Remaining methods are of the more internal flavour, read-only access to
-    // the data structure's internals.
-
-    /// Access the internal node array.
-    pub fn raw_nodes(&self) -> &[Node<N, Ix>] {
-        &self.nodes
-    }
-
-    /// Access the internal edge array.
-    pub fn raw_edges(&self) -> &[Edge<E, Ix>] {
-        &self.edges
-    }
-
-    /// Convert the graph into a vector of Nodes and a vector of Edges
-    pub fn into_nodes_edges(self) -> (Vec<Node<N, Ix>>, Vec<Edge<E, Ix>>) {
-        (self.nodes, self.edges)
-    }
-
-    /// Accessor for data structure internals: the first edge in the given direction.
-    pub fn first_edge(&self, a: NodeIndex<Ix>, dir: Direction) -> Option<EdgeIndex<Ix>> {
-        match self.nodes.get(a.index()) {
-            None => None,
-            Some(node) => {
-                let edix = node.next[dir.index()];
-                if edix == EdgeIndex::end() {
-                    None
-                } else {
-                    Some(edix)
-                }
-            }
-        }
-    }
-
-    /// Accessor for data structure internals: the next edge for the given direction.
-    pub fn next_edge(&self, e: EdgeIndex<Ix>, dir: Direction) -> Option<EdgeIndex<Ix>> {
-        match self.edges.get(e.index()) {
-            None => None,
-            Some(node) => {
-                let edix = node.next[dir.index()];
-                if edix == EdgeIndex::end() {
-                    None
-                } else {
-                    Some(edix)
-                }
-            }
-        }
-    }
-
-    /// Index the `Graph` by two indices, any combination of
-    /// node or edge indices is fine.
-    ///
-    /// **Panics** if the indices are equal or if they are out of bounds.
-    ///
-    /// ```
-    /// use petgraph::{Graph, Incoming};
-    /// use petgraph::visit::Dfs;
-    ///
-    /// let mut gr = Graph::new();
-    /// let a = gr.add_node(0.);
-    /// let b = gr.add_node(0.);
-    /// let c = gr.add_node(0.);
-    /// gr.add_edge(a, b, 3.);
-    /// gr.add_edge(b, c, 2.);
-    /// gr.add_edge(c, b, 1.);
-    ///
-    /// // walk the graph and sum incoming edges into the node weight
-    /// let mut dfs = Dfs::new(&gr, a);
-    /// while let Some(node) = dfs.next(&gr) {
-    ///     // use a walker -- a detached neighbors iterator
-    ///     let mut edges = gr.neighbors_directed(node, Incoming).detach();
-    ///     while let Some(edge) = edges.next_edge(&gr) {
-    ///         let (nw, ew) = gr.index_twice_mut(node, edge);
-    ///         *nw += *ew;
-    ///     }
-    /// }
-    ///
-    /// // check the result
-    /// assert_eq!(gr[a], 0.);
-    /// assert_eq!(gr[b], 4.);
-    /// assert_eq!(gr[c], 2.);
-    /// ```
-    pub fn index_twice_mut<T, U>(
-        &mut self,
-        i: T,
-        j: U,
-    ) -> (
-        &mut <Self as Index<T>>::Output,
-        &mut <Self as Index<U>>::Output,
-    )
-    where
-        Self: IndexMut<T> + IndexMut<U>,
-        T: GraphIndex,
-        U: GraphIndex,
-    {
-        assert!(T::is_node_index() != U::is_node_index() || i.index() != j.index());
-
-        // Allow two mutable indexes here -- they are nonoverlapping
-        unsafe {
-            let self_mut = self as *mut _;
-            (
-                <Self as IndexMut<T>>::index_mut(&mut *self_mut, i),
-                <Self as IndexMut<U>>::index_mut(&mut *self_mut, j),
-            )
-        }
-    }
-
-    /// Reverse the direction of all edges
-    pub fn reverse(&mut self) {
-        // swap edge endpoints,
-        // edge incoming / outgoing lists,
-        // node incoming / outgoing lists
-        for edge in &mut self.edges {
-            edge.node.swap(0, 1);
-            edge.next.swap(0, 1);
-        }
-        for node in &mut self.nodes {
-            node.next.swap(0, 1);
-        }
-    }
-
-    /// Remove all nodes and edges
-    pub fn clear(&mut self) {
-        self.nodes.clear();
-        self.edges.clear();
-    }
-
-    /// Remove all edges
-    pub fn clear_edges(&mut self) {
-        self.edges.clear();
-        for node in &mut self.nodes {
-            node.next = [EdgeIndex::end(), EdgeIndex::end()];
-        }
-    }
-
-    /// Return the current node and edge capacity of the graph.
-    pub fn capacity(&self) -> (usize, usize) {
-        (self.nodes.capacity(), self.edges.capacity())
-    }
-
-    /// Reserves capacity for at least `additional` more nodes to be inserted in
-    /// the graph. Graph may reserve more space to avoid frequent reallocations.
-    ///
-    /// **Panics** if the new capacity overflows `usize`.
-    pub fn reserve_nodes(&mut self, additional: usize) {
-        self.nodes.reserve(additional);
-    }
-
-    /// Reserves capacity for at least `additional` more edges to be inserted in
-    /// the graph. Graph may reserve more space to avoid frequent reallocations.
-    ///
-    /// **Panics** if the new capacity overflows `usize`.
-    pub fn reserve_edges(&mut self, additional: usize) {
-        self.edges.reserve(additional);
-    }
-
-    /// Reserves the minimum capacity for exactly `additional` more nodes to be
-    /// inserted in the graph. Does nothing if the capacity is already
-    /// sufficient.
-    ///
-    /// Prefer `reserve_nodes` if future insertions are expected.
-    ///
-    /// **Panics** if the new capacity overflows `usize`.
-    pub fn reserve_exact_nodes(&mut self, additional: usize) {
-        self.nodes.reserve_exact(additional);
-    }
-
-    /// Reserves the minimum capacity for exactly `additional` more edges to be
-    /// inserted in the graph.
-    /// Does nothing if the capacity is already sufficient.
-    ///
-    /// Prefer `reserve_edges` if future insertions are expected.
-    ///
-    /// **Panics** if the new capacity overflows `usize`.
-    pub fn reserve_exact_edges(&mut self, additional: usize) {
-        self.edges.reserve_exact(additional);
-    }
-
-    /// Shrinks the capacity of the underlying nodes collection as much as possible.
-    pub fn shrink_to_fit_nodes(&mut self) {
-        self.nodes.shrink_to_fit();
-    }
-
-    /// Shrinks the capacity of the underlying edges collection as much as possible.
-    pub fn shrink_to_fit_edges(&mut self) {
-        self.edges.shrink_to_fit();
-    }
-
-    /// Shrinks the capacity of the graph as much as possible.
-    pub fn shrink_to_fit(&mut self) {
-        self.nodes.shrink_to_fit();
-        self.edges.shrink_to_fit();
-    }
-
-    /// Keep all nodes that return `true` from the `visit` closure,
-    /// remove the others.
-    ///
-    /// `visit` is provided a proxy reference to the graph, so that
-    /// the graph can be walked and associated data modified.
-    ///
-    /// The order nodes are visited is not specified.
-    pub fn retain_nodes<F>(&mut self, mut visit: F)
-    where
-        F: FnMut(Frozen<Self>, NodeIndex<Ix>) -> bool,
-    {
-        for index in self.node_indices().rev() {
-            if !visit(Frozen(self), index) {
-                let ret = self.remove_node(index);
-                debug_assert!(ret.is_some());
-                let _ = ret;
-            }
-        }
-    }
-
-    /// Keep all edges that return `true` from the `visit` closure,
-    /// remove the others.
-    ///
-    /// `visit` is provided a proxy reference to the graph, so that
-    /// the graph can be walked and associated data modified.
-    ///
-    /// The order edges are visited is not specified.
-    pub fn retain_edges<F>(&mut self, mut visit: F)
-    where
-        F: FnMut(Frozen<Self>, EdgeIndex<Ix>) -> bool,
-    {
-        for index in self.edge_indices().rev() {
-            if !visit(Frozen(self), index) {
-                let ret = self.remove_edge(index);
-                debug_assert!(ret.is_some());
-                let _ = ret;
-            }
-        }
-    }
-
-    /// Create a new `Graph` from an iterable of edges.
-    ///
-    /// Node weights `N` are set to default values.
-    /// Edge weights `E` may either be specified in the list,
-    /// or they are filled with default values.
-    ///
-    /// Nodes are inserted automatically to match the edges.
-    ///
-    /// ```
-    /// use petgraph::Graph;
-    ///
-    /// let gr = Graph::<(), i32>::from_edges(&[
-    ///     (0, 1), (0, 2), (0, 3),
-    ///     (1, 2), (1, 3),
-    ///     (2, 3),
-    /// ]);
-    /// ```
-    pub fn from_edges<I>(iterable: I) -> Self
-    where
-        I: IntoIterator,
-        I::Item: IntoWeightedEdge<E>,
-        <I::Item as IntoWeightedEdge<E>>::NodeId: Into<NodeIndex<Ix>>,
-        N: Default,
-    {
-        let mut g = Self::with_capacity(0, 0);
-        g.extend_with_edges(iterable);
-        g
-    }
-
-    /// Extend the graph from an iterable of edges.
-    ///
-    /// Node weights `N` are set to default values.
-    /// Edge weights `E` may either be specified in the list,
-    /// or they are filled with default values.
-    ///
-    /// Nodes are inserted automatically to match the edges.
-    pub fn extend_with_edges<I>(&mut self, iterable: I)
-    where
-        I: IntoIterator,
-        I::Item: IntoWeightedEdge<E>,
-        <I::Item as IntoWeightedEdge<E>>::NodeId: Into<NodeIndex<Ix>>,
-        N: Default,
-    {
-        let iter = iterable.into_iter();
-        let (low, _) = iter.size_hint();
-        self.edges.reserve(low);
-
-        for elt in iter {
-            let (source, target, weight) = elt.into_weighted_edge();
-            let (source, target) = (source.into(), target.into());
-            let nx = cmp::max(source, target);
-            while nx.index() >= self.node_count() {
-                self.add_node(N::default());
-            }
-            self.add_edge(source, target, weight);
-        }
-    }
-
-    /// Create a new `Graph` by mapping node and
-    /// edge weights to new values.
-    ///
-    /// The resulting graph has the same structure and the same
-    /// graph indices as `self`.
-    pub fn map<'a, F, G, N2, E2>(
-        &'a self,
-        mut node_map: F,
-        mut edge_map: G,
-    ) -> Graph<N2, E2, Ty, Ix>
-    where
-        F: FnMut(NodeIndex<Ix>, &'a N) -> N2,
-        G: FnMut(EdgeIndex<Ix>, &'a E) -> E2,
-    {
-        let mut g = Graph::with_capacity(self.node_count(), self.edge_count());
-        g.nodes.extend(enumerate(&self.nodes).map(|(i, node)| Node {
-            weight: node_map(NodeIndex::new(i), &node.weight),
-            next: node.next,
-        }));
-        g.edges.extend(enumerate(&self.edges).map(|(i, edge)| Edge {
-            weight: edge_map(EdgeIndex::new(i), &edge.weight),
-            next: edge.next,
-            node: edge.node,
-        }));
-        g
-    }
-
-    /// Create a new `Graph` by mapping nodes and edges.
-    /// A node or edge may be mapped to `None` to exclude it from
-    /// the resulting graph.
-    ///
-    /// Nodes are mapped first with the `node_map` closure, then
-    /// `edge_map` is called for the edges that have not had any endpoint
-    /// removed.
-    ///
-    /// The resulting graph has the structure of a subgraph of the original graph.
-    /// If no nodes are removed, the resulting graph has compatible node
-    /// indices; if neither nodes nor edges are removed, the result has
-    /// the same graph indices as `self`.
-    pub fn filter_map<'a, F, G, N2, E2>(
-        &'a self,
-        mut node_map: F,
-        mut edge_map: G,
-    ) -> Graph<N2, E2, Ty, Ix>
-    where
-        F: FnMut(NodeIndex<Ix>, &'a N) -> Option<N2>,
-        G: FnMut(EdgeIndex<Ix>, &'a E) -> Option<E2>,
-    {
-        let mut g = Graph::with_capacity(0, 0);
-        // mapping from old node index to new node index, end represents removed.
-        let mut node_index_map = vec![NodeIndex::end(); self.node_count()];
-        for (i, node) in enumerate(&self.nodes) {
-            if let Some(nw) = node_map(NodeIndex::new(i), &node.weight) {
-                node_index_map[i] = g.add_node(nw);
-            }
-        }
-        for (i, edge) in enumerate(&self.edges) {
-            // skip edge if any endpoint was removed
-            let source = node_index_map[edge.source().index()];
-            let target = node_index_map[edge.target().index()];
-            if source != NodeIndex::end() && target != NodeIndex::end() {
-                if let Some(ew) = edge_map(EdgeIndex::new(i), &edge.weight) {
-                    g.add_edge(source, target, ew);
-                }
-            }
-        }
-        g
-    }
-
-    /// Convert the graph into either undirected or directed. No edge adjustments
-    /// are done, so you may want to go over the result to remove or add edges.
-    ///
-    /// Computes in **O(1)** time.
-    pub fn into_edge_type<NewTy>(self) -> Graph<N, E, NewTy, Ix>
-    where
-        NewTy: EdgeType,
-    {
-        Graph {
-            nodes: self.nodes,
-            edges: self.edges,
-            ty: PhantomData,
-        }
-    }
-
-    //
-    // internal methods
-    //
-    #[cfg(feature = "serde-1")]
-    /// Fix up node and edge links after deserialization
-    fn link_edges(&mut self) -> Result<(), NodeIndex<Ix>> {
-        for (edge_index, edge) in enumerate(&mut self.edges) {
-            let a = edge.source();
-            let b = edge.target();
-            let edge_idx = EdgeIndex::new(edge_index);
-            match index_twice(&mut self.nodes, a.index(), b.index()) {
-                Pair::None => return Err(if a > b { a } else { b }),
-                Pair::One(an) => {
-                    edge.next = an.next;
-                    an.next[0] = edge_idx;
-                    an.next[1] = edge_idx;
-                }
-                Pair::Both(an, bn) => {
-                    // a and b are different indices
-                    edge.next = [an.next[0], bn.next[1]];
-                    an.next[0] = edge_idx;
-                    bn.next[1] = edge_idx;
-                }
-            }
-        }
-        Ok(())
-    }
-}
-
-/// An iterator over either the nodes without edges to them or from them.
-pub struct Externals<'a, N: 'a, Ty, Ix: IndexType = DefaultIx> {
-    iter: iter::Enumerate<slice::Iter<'a, Node<N, Ix>>>,
-    dir: Direction,
-    ty: PhantomData<Ty>,
-}
-
-impl<'a, N: 'a, Ty, Ix> Iterator for Externals<'a, N, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    type Item = NodeIndex<Ix>;
-    fn next(&mut self) -> Option<NodeIndex<Ix>> {
-        let k = self.dir.index();
-        loop {
-            match self.iter.next() {
-                None => return None,
-                Some((index, node)) => {
-                    if node.next[k] == EdgeIndex::end()
-                        && (Ty::is_directed() || node.next[1 - k] == EdgeIndex::end())
-                    {
-                        return Some(NodeIndex::new(index));
-                    } else {
-                        continue;
-                    }
-                }
-            }
-        }
-    }
-}
-
-/// Iterator over the neighbors of a node.
-///
-/// Iterator element type is `NodeIndex<Ix>`.
-///
-/// Created with [`.neighbors()`][1], [`.neighbors_directed()`][2] or
-/// [`.neighbors_undirected()`][3].
-///
-/// [1]: struct.Graph.html#method.neighbors
-/// [2]: struct.Graph.html#method.neighbors_directed
-/// [3]: struct.Graph.html#method.neighbors_undirected
-pub struct Neighbors<'a, E: 'a, Ix: 'a = DefaultIx> {
-    /// starting node to skip over
-    skip_start: NodeIndex<Ix>,
-    edges: &'a [Edge<E, Ix>],
-    next: [EdgeIndex<Ix>; 2],
-}
-
-impl<'a, E, Ix> Iterator for Neighbors<'a, E, Ix>
-where
-    Ix: IndexType,
-{
-    type Item = NodeIndex<Ix>;
-
-    fn next(&mut self) -> Option<NodeIndex<Ix>> {
-        // First any outgoing edges
-        match self.edges.get(self.next[0].index()) {
-            None => {}
-            Some(edge) => {
-                self.next[0] = edge.next[0];
-                return Some(edge.node[1]);
-            }
-        }
-        // Then incoming edges
-        // For an "undirected" iterator (traverse both incoming
-        // and outgoing edge lists), make sure we don't double
-        // count selfloops by skipping them in the incoming list.
-        while let Some(edge) = self.edges.get(self.next[1].index()) {
-            self.next[1] = edge.next[1];
-            if edge.node[0] != self.skip_start {
-                return Some(edge.node[0]);
-            }
-        }
-        None
-    }
-}
-
-impl<'a, E, Ix> Clone for Neighbors<'a, E, Ix>
-where
-    Ix: IndexType,
-{
-    clone_fields!(Neighbors, skip_start, edges, next,);
-}
-
-impl<'a, E, Ix> Neighbors<'a, E, Ix>
-where
-    Ix: IndexType,
-{
-    /// Return a “walker” object that can be used to step through the
-    /// neighbors and edges from the origin node.
-    ///
-    /// Note: The walker does not borrow from the graph, this is to allow mixing
-    /// edge walking with mutating the graph's weights.
-    pub fn detach(&self) -> WalkNeighbors<Ix> {
-        WalkNeighbors {
-            skip_start: self.skip_start,
-            next: self.next,
-        }
-    }
-}
-
-struct EdgesWalkerMut<'a, E: 'a, Ix: IndexType = DefaultIx> {
-    edges: &'a mut [Edge<E, Ix>],
-    next: EdgeIndex<Ix>,
-    dir: Direction,
-}
-
-fn edges_walker_mut<E, Ix>(
-    edges: &mut [Edge<E, Ix>],
-    next: EdgeIndex<Ix>,
-    dir: Direction,
-) -> EdgesWalkerMut<E, Ix>
-where
-    Ix: IndexType,
-{
-    EdgesWalkerMut { edges, next, dir }
-}
-
-impl<'a, E, Ix> EdgesWalkerMut<'a, E, Ix>
-where
-    Ix: IndexType,
-{
-    fn next_edge(&mut self) -> Option<&mut Edge<E, Ix>> {
-        self.next().map(|t| t.1)
-    }
-
-    fn next(&mut self) -> Option<(EdgeIndex<Ix>, &mut Edge<E, Ix>)> {
-        let this_index = self.next;
-        let k = self.dir.index();
-        match self.edges.get_mut(self.next.index()) {
-            None => None,
-            Some(edge) => {
-                self.next = edge.next[k];
-                Some((this_index, edge))
-            }
-        }
-    }
-}
-
-impl<'a, N, E, Ty, Ix> IntoEdges for &'a Graph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    type Edges = Edges<'a, E, Ty, Ix>;
-    fn edges(self, a: Self::NodeId) -> Self::Edges {
-        self.edges(a)
-    }
-}
-
-impl<'a, N, E, Ty, Ix> IntoEdgesDirected for &'a Graph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    type EdgesDirected = Edges<'a, E, Ty, Ix>;
-    fn edges_directed(self, a: Self::NodeId, dir: Direction) -> Self::EdgesDirected {
-        self.edges_directed(a, dir)
-    }
-}
-
-/// Iterator over the edges of from or to a node
-pub struct Edges<'a, E: 'a, Ty, Ix: 'a = DefaultIx>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    /// starting node to skip over
-    skip_start: NodeIndex<Ix>,
-    edges: &'a [Edge<E, Ix>],
-
-    /// Next edge to visit.
-    next: [EdgeIndex<Ix>; 2],
-
-    /// For directed graphs: the direction to iterate in
-    /// For undirected graphs: the direction of edges
-    direction: Direction,
-    ty: PhantomData<Ty>,
-}
-
-impl<'a, E, Ty, Ix> Iterator for Edges<'a, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    type Item = EdgeReference<'a, E, Ix>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        //      type        direction    |    iterate over    reverse
-        //                               |
-        //    Directed      Outgoing     |      outgoing        no
-        //    Directed      Incoming     |      incoming        no
-        //   Undirected     Outgoing     |        both       incoming
-        //   Undirected     Incoming     |        both       outgoing
-
-        // For iterate_over, "both" is represented as None.
-        // For reverse, "no" is represented as None.
-        let (iterate_over, reverse) = if Ty::is_directed() {
-            (Some(self.direction), None)
-        } else {
-            (None, Some(self.direction.opposite()))
-        };
-
-        if iterate_over.unwrap_or(Outgoing) == Outgoing {
-            let i = self.next[0].index();
-            if let Some(Edge { node, weight, next }) = self.edges.get(i) {
-                self.next[0] = next[0];
-                return Some(EdgeReference {
-                    index: edge_index(i),
-                    node: if reverse == Some(Outgoing) {
-                        swap_pair(*node)
-                    } else {
-                        *node
-                    },
-                    weight,
-                });
-            }
-        }
-
-        if iterate_over.unwrap_or(Incoming) == Incoming {
-            while let Some(Edge { node, weight, next }) = self.edges.get(self.next[1].index()) {
-                let edge_index = self.next[1];
-                self.next[1] = next[1];
-                // In any of the "both" situations, self-loops would be iterated over twice.
-                // Skip them here.
-                if iterate_over.is_none() && node[0] == self.skip_start {
-                    continue;
-                }
-
-                return Some(EdgeReference {
-                    index: edge_index,
-                    node: if reverse == Some(Incoming) {
-                        swap_pair(*node)
-                    } else {
-                        *node
-                    },
-                    weight,
-                });
-            }
-        }
-
-        None
-    }
-}
-
-/// Iterator over the multiple directed edges connecting a source node to a target node
-pub struct EdgesConnecting<'a, E: 'a, Ty, Ix: 'a = DefaultIx>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    target_node: NodeIndex<Ix>,
-    edges: Edges<'a, E, Ty, Ix>,
-    ty: PhantomData<Ty>,
-}
-
-impl<'a, E, Ty, Ix> Iterator for EdgesConnecting<'a, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    type Item = EdgeReference<'a, E, Ix>;
-
-    fn next(&mut self) -> Option<EdgeReference<'a, E, Ix>> {
-        while let Some(edge) = self.edges.next() {
-            if edge.node[1] == self.target_node {
-                return Some(edge);
-            }
-        }
-
-        None
-    }
-}
-
-fn swap_pair<T>(mut x: [T; 2]) -> [T; 2] {
-    x.swap(0, 1);
-    x
-}
-
-impl<'a, E, Ty, Ix> Clone for Edges<'a, E, Ty, Ix>
-where
-    Ix: IndexType,
-    Ty: EdgeType,
-{
-    fn clone(&self) -> Self {
-        Edges {
-            skip_start: self.skip_start,
-            edges: self.edges,
-            next: self.next,
-            direction: self.direction,
-            ty: self.ty,
-        }
-    }
-}
-
-/// Iterator yielding mutable access to all node weights.
-pub struct NodeWeightsMut<'a, N: 'a, Ix: IndexType = DefaultIx> {
-    nodes: ::std::slice::IterMut<'a, Node<N, Ix>>,
-}
-
-impl<'a, N, Ix> Iterator for NodeWeightsMut<'a, N, Ix>
-where
-    Ix: IndexType,
-{
-    type Item = &'a mut N;
-
-    fn next(&mut self) -> Option<&'a mut N> {
-        self.nodes.next().map(|node| &mut node.weight)
-    }
-
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        self.nodes.size_hint()
-    }
-}
-
-/// Iterator yielding mutable access to all edge weights.
-pub struct EdgeWeightsMut<'a, E: 'a, Ix: IndexType = DefaultIx> {
-    edges: ::std::slice::IterMut<'a, Edge<E, Ix>>,
-}
-
-impl<'a, E, Ix> Iterator for EdgeWeightsMut<'a, E, Ix>
-where
-    Ix: IndexType,
-{
-    type Item = &'a mut E;
-
-    fn next(&mut self) -> Option<&'a mut E> {
-        self.edges.next().map(|edge| &mut edge.weight)
-    }
-
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        self.edges.size_hint()
-    }
-}
-
-/// Index the `Graph` by `NodeIndex` to access node weights.
-///
-/// **Panics** if the node doesn't exist.
-impl<N, E, Ty, Ix> Index<NodeIndex<Ix>> for Graph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    type Output = N;
-    fn index(&self, index: NodeIndex<Ix>) -> &N {
-        &self.nodes[index.index()].weight
-    }
-}
-
-/// Index the `Graph` by `NodeIndex` to access node weights.
-///
-/// **Panics** if the node doesn't exist.
-impl<N, E, Ty, Ix> IndexMut<NodeIndex<Ix>> for Graph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    fn index_mut(&mut self, index: NodeIndex<Ix>) -> &mut N {
-        &mut self.nodes[index.index()].weight
-    }
-}
-
-/// Index the `Graph` by `EdgeIndex` to access edge weights.
-///
-/// **Panics** if the edge doesn't exist.
-impl<N, E, Ty, Ix> Index<EdgeIndex<Ix>> for Graph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    type Output = E;
-    fn index(&self, index: EdgeIndex<Ix>) -> &E {
-        &self.edges[index.index()].weight
-    }
-}
-
-/// Index the `Graph` by `EdgeIndex` to access edge weights.
-///
-/// **Panics** if the edge doesn't exist.
-impl<N, E, Ty, Ix> IndexMut<EdgeIndex<Ix>> for Graph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    fn index_mut(&mut self, index: EdgeIndex<Ix>) -> &mut E {
-        &mut self.edges[index.index()].weight
-    }
-}
-
-/// Create a new empty `Graph`.
-impl<N, E, Ty, Ix> Default for Graph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    fn default() -> Self {
-        Self::with_capacity(0, 0)
-    }
-}
-
-/// A  `GraphIndex` is a node or edge index.
-pub trait GraphIndex: Copy {
-    #[doc(hidden)]
-    fn index(&self) -> usize;
-    #[doc(hidden)]
-    fn is_node_index() -> bool;
-}
-
-impl<Ix: IndexType> GraphIndex for NodeIndex<Ix> {
-    #[inline]
-    fn index(&self) -> usize {
-        NodeIndex::index(*self)
-    }
-    #[inline]
-    fn is_node_index() -> bool {
-        true
-    }
-}
-
-impl<Ix: IndexType> GraphIndex for EdgeIndex<Ix> {
-    #[inline]
-    fn index(&self) -> usize {
-        EdgeIndex::index(*self)
-    }
-    #[inline]
-    fn is_node_index() -> bool {
-        false
-    }
-}
-
-/// A “walker” object that can be used to step through the edge list of a node.
-///
-/// Created with [`.detach()`](struct.Neighbors.html#method.detach).
-///
-/// The walker does not borrow from the graph, so it lets you step through
-/// neighbors or incident edges while also mutating graph weights, as
-/// in the following example:
-///
-/// ```
-/// use petgraph::{Graph, Incoming};
-/// use petgraph::visit::Dfs;
-///
-/// let mut gr = Graph::new();
-/// let a = gr.add_node(0.);
-/// let b = gr.add_node(0.);
-/// let c = gr.add_node(0.);
-/// gr.add_edge(a, b, 3.);
-/// gr.add_edge(b, c, 2.);
-/// gr.add_edge(c, b, 1.);
-///
-/// // step through the graph and sum incoming edges into the node weight
-/// let mut dfs = Dfs::new(&gr, a);
-/// while let Some(node) = dfs.next(&gr) {
-///     // use a detached neighbors walker
-///     let mut edges = gr.neighbors_directed(node, Incoming).detach();
-///     while let Some(edge) = edges.next_edge(&gr) {
-///         gr[node] += gr[edge];
-///     }
-/// }
-///
-/// // check the result
-/// assert_eq!(gr[a], 0.);
-/// assert_eq!(gr[b], 4.);
-/// assert_eq!(gr[c], 2.);
-/// ```
-pub struct WalkNeighbors<Ix> {
-    skip_start: NodeIndex<Ix>,
-    next: [EdgeIndex<Ix>; 2],
-}
-
-impl<Ix> Clone for WalkNeighbors<Ix>
-where
-    Ix: IndexType,
-{
-    fn clone(&self) -> Self {
-        WalkNeighbors {
-            skip_start: self.skip_start,
-            next: self.next,
-        }
-    }
-}
-
-impl<Ix: IndexType> WalkNeighbors<Ix> {
-    /// Step to the next edge and its endpoint node in the walk for graph `g`.
-    ///
-    /// The next node indices are always the others than the starting point
-    /// where the `WalkNeighbors` value was created.
-    /// For an `Outgoing` walk, the target nodes,
-    /// for an `Incoming` walk, the source nodes of the edge.
-    pub fn next<N, E, Ty: EdgeType>(
-        &mut self,
-        g: &Graph<N, E, Ty, Ix>,
-    ) -> Option<(EdgeIndex<Ix>, NodeIndex<Ix>)> {
-        // First any outgoing edges
-        match g.edges.get(self.next[0].index()) {
-            None => {}
-            Some(edge) => {
-                let ed = self.next[0];
-                self.next[0] = edge.next[0];
-                return Some((ed, edge.node[1]));
-            }
-        }
-        // Then incoming edges
-        // For an "undirected" iterator (traverse both incoming
-        // and outgoing edge lists), make sure we don't double
-        // count selfloops by skipping them in the incoming list.
-        while let Some(edge) = g.edges.get(self.next[1].index()) {
-            let ed = self.next[1];
-            self.next[1] = edge.next[1];
-            if edge.node[0] != self.skip_start {
-                return Some((ed, edge.node[0]));
-            }
-        }
-        None
-    }
-
-    pub fn next_node<N, E, Ty: EdgeType>(
-        &mut self,
-        g: &Graph<N, E, Ty, Ix>,
-    ) -> Option<NodeIndex<Ix>> {
-        self.next(g).map(|t| t.1)
-    }
-
-    pub fn next_edge<N, E, Ty: EdgeType>(
-        &mut self,
-        g: &Graph<N, E, Ty, Ix>,
-    ) -> Option<EdgeIndex<Ix>> {
-        self.next(g).map(|t| t.0)
-    }
-}
-
-/// Iterator over the node indices of a graph.
-#[derive(Clone, Debug)]
-pub struct NodeIndices<Ix = DefaultIx> {
-    r: Range<usize>,
-    ty: PhantomData<fn() -> Ix>,
-}
-
-impl<Ix: IndexType> Iterator for NodeIndices<Ix> {
-    type Item = NodeIndex<Ix>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        self.r.next().map(node_index)
-    }
-
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        self.r.size_hint()
-    }
-}
-
-impl<Ix: IndexType> DoubleEndedIterator for NodeIndices<Ix> {
-    fn next_back(&mut self) -> Option<Self::Item> {
-        self.r.next_back().map(node_index)
-    }
-}
-
-impl<Ix: IndexType> ExactSizeIterator for NodeIndices<Ix> {}
-
-/// Iterator over the edge indices of a graph.
-#[derive(Clone, Debug)]
-pub struct EdgeIndices<Ix = DefaultIx> {
-    r: Range<usize>,
-    ty: PhantomData<fn() -> Ix>,
-}
-
-impl<Ix: IndexType> Iterator for EdgeIndices<Ix> {
-    type Item = EdgeIndex<Ix>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        self.r.next().map(edge_index)
-    }
-
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        self.r.size_hint()
-    }
-}
-
-impl<Ix: IndexType> DoubleEndedIterator for EdgeIndices<Ix> {
-    fn next_back(&mut self) -> Option<Self::Item> {
-        self.r.next_back().map(edge_index)
-    }
-}
-
-impl<Ix: IndexType> ExactSizeIterator for EdgeIndices<Ix> {}
-
-/// Reference to a `Graph` edge.
-#[derive(Debug)]
-pub struct EdgeReference<'a, E: 'a, Ix = DefaultIx> {
-    index: EdgeIndex<Ix>,
-    node: [NodeIndex<Ix>; 2],
-    weight: &'a E,
-}
-
-impl<'a, E, Ix: IndexType> Clone for EdgeReference<'a, E, Ix> {
-    fn clone(&self) -> Self {
-        *self
-    }
-}
-
-impl<'a, E, Ix: IndexType> Copy for EdgeReference<'a, E, Ix> {}
-
-impl<'a, E, Ix: IndexType> PartialEq for EdgeReference<'a, E, Ix>
-where
-    E: PartialEq,
-{
-    fn eq(&self, rhs: &Self) -> bool {
-        self.index == rhs.index && self.weight == rhs.weight
-    }
-}
-
-impl<'a, N, E, Ty, Ix> IntoNodeReferences for &'a Graph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    type NodeRef = (NodeIndex<Ix>, &'a N);
-    type NodeReferences = NodeReferences<'a, N, Ix>;
-    fn node_references(self) -> Self::NodeReferences {
-        NodeReferences {
-            iter: self.nodes.iter().enumerate(),
-        }
-    }
-}
-
-/// Iterator over all nodes of a graph.
-pub struct NodeReferences<'a, N: 'a, Ix: IndexType = DefaultIx> {
-    iter: iter::Enumerate<slice::Iter<'a, Node<N, Ix>>>,
-}
-
-impl<'a, N, Ix> Iterator for NodeReferences<'a, N, Ix>
-where
-    Ix: IndexType,
-{
-    type Item = (NodeIndex<Ix>, &'a N);
-
-    fn next(&mut self) -> Option<Self::Item> {
-        self.iter
-            .next()
-            .map(|(i, node)| (node_index(i), &node.weight))
-    }
-
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        self.iter.size_hint()
-    }
-}
-
-impl<'a, N, Ix> DoubleEndedIterator for NodeReferences<'a, N, Ix>
-where
-    Ix: IndexType,
-{
-    fn next_back(&mut self) -> Option<Self::Item> {
-        self.iter
-            .next_back()
-            .map(|(i, node)| (node_index(i), &node.weight))
-    }
-}
-
-impl<'a, N, Ix> ExactSizeIterator for NodeReferences<'a, N, Ix> where Ix: IndexType {}
-
-impl<'a, Ix, E> EdgeReference<'a, E, Ix>
-where
-    Ix: IndexType,
-{
-    /// Access the edge’s weight.
-    ///
-    /// **NOTE** that this method offers a longer lifetime
-    /// than the trait (unfortunately they don't match yet).
-    pub fn weight(&self) -> &'a E {
-        self.weight
-    }
-}
-
-impl<'a, Ix, E> EdgeRef for EdgeReference<'a, E, Ix>
-where
-    Ix: IndexType,
-{
-    type NodeId = NodeIndex<Ix>;
-    type EdgeId = EdgeIndex<Ix>;
-    type Weight = E;
-
-    fn source(&self) -> Self::NodeId {
-        self.node[0]
-    }
-    fn target(&self) -> Self::NodeId {
-        self.node[1]
-    }
-    fn weight(&self) -> &E {
-        self.weight
-    }
-    fn id(&self) -> Self::EdgeId {
-        self.index
-    }
-}
-
-/// Iterator over all edges of a graph.
-pub struct EdgeReferences<'a, E: 'a, Ix: IndexType = DefaultIx> {
-    iter: iter::Enumerate<slice::Iter<'a, Edge<E, Ix>>>,
-}
-
-impl<'a, E, Ix> Iterator for EdgeReferences<'a, E, Ix>
-where
-    Ix: IndexType,
-{
-    type Item = EdgeReference<'a, E, Ix>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        self.iter.next().map(|(i, edge)| EdgeReference {
-            index: edge_index(i),
-            node: edge.node,
-            weight: &edge.weight,
-        })
-    }
-
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        self.iter.size_hint()
-    }
-}
-
-impl<'a, E, Ix> DoubleEndedIterator for EdgeReferences<'a, E, Ix>
-where
-    Ix: IndexType,
-{
-    fn next_back(&mut self) -> Option<Self::Item> {
-        self.iter.next_back().map(|(i, edge)| EdgeReference {
-            index: edge_index(i),
-            node: edge.node,
-            weight: &edge.weight,
-        })
-    }
-}
-
-impl<'a, E, Ix> ExactSizeIterator for EdgeReferences<'a, E, Ix> where Ix: IndexType {}
-
-mod frozen;
-#[cfg(feature = "stable_graph")]
-pub mod stable_graph;
-
-/// `Frozen` is a graph wrapper.
-///
-/// The `Frozen` only allows shared access (read-only) to the
-/// underlying graph `G`, but it allows mutable access to its
-/// node and edge weights.
-///
-/// This is used to ensure immutability of the graph's structure
-/// while permitting weights to be both read and written.
-///
-/// See indexing implementations and the traits `Data` and `DataMap`
-/// for read-write access to the graph's weights.
-pub struct Frozen<'a, G: 'a>(&'a mut G);
diff --git a/vendor/petgraph/src/graph_impl/serialization.rs b/vendor/petgraph/src/graph_impl/serialization.rs
deleted file mode 100644
index e108f3dd4..000000000
--- a/vendor/petgraph/src/graph_impl/serialization.rs
+++ /dev/null
@@ -1,345 +0,0 @@
-use serde::de::Error;
-
-use std::marker::PhantomData;
-
-use crate::prelude::*;
-
-use crate::graph::Node;
-use crate::graph::{Edge, IndexType};
-use crate::serde_utils::CollectSeqWithLength;
-use crate::serde_utils::MappedSequenceVisitor;
-use crate::serde_utils::{FromDeserialized, IntoSerializable};
-use crate::EdgeType;
-
-use super::{EdgeIndex, NodeIndex};
-use serde::{Deserialize, Deserializer, Serialize, Serializer};
-
-/// Serialization representation for Graph
-/// Keep in sync with deserialization and StableGraph
-///
-/// The serialization format is as follows, in Pseudorust:
-///
-/// Graph {
-///     nodes: [N],
-///     node_holes: [NodeIndex<Ix>],
-///     edge_property: EdgeProperty,
-///     edges: [Option<(NodeIndex<Ix>, NodeIndex<Ix>, E)>]
-/// }
-///
-/// The same format is used by both Graph and StableGraph.
-///
-/// For graph there are restrictions:
-/// node_holes is always empty and edges are always Some
-///
-/// A stable graph serialization that obeys these restrictions
-/// (effectively, it has no interior vacancies) can de deserialized
-/// as a graph.
-///
-/// Node indices are serialized as integers and are fixed size for
-/// binary formats, so the Ix parameter matters there.
-#[derive(Serialize)]
-#[serde(rename = "Graph")]
-#[serde(bound(serialize = "N: Serialize, E: Serialize, Ix: IndexType + Serialize"))]
-pub struct SerGraph<'a, N: 'a, E: 'a, Ix: 'a + IndexType> {
-    #[serde(serialize_with = "ser_graph_nodes")]
-    nodes: &'a [Node<N, Ix>],
-    node_holes: &'a [NodeIndex<Ix>],
-    edge_property: EdgeProperty,
-    #[serde(serialize_with = "ser_graph_edges")]
-    edges: &'a [Edge<E, Ix>],
-}
-
-// Deserialization representation for Graph
-// Keep in sync with serialization and StableGraph
-#[derive(Deserialize)]
-#[serde(rename = "Graph")]
-#[serde(bound(
-    deserialize = "N: Deserialize<'de>, E: Deserialize<'de>, Ix: IndexType + Deserialize<'de>"
-))]
-pub struct DeserGraph<N, E, Ix> {
-    #[serde(deserialize_with = "deser_graph_nodes")]
-    nodes: Vec<Node<N, Ix>>,
-    #[serde(deserialize_with = "deser_graph_node_holes")]
-    #[allow(unused)]
-    #[serde(default = "Vec::new")]
-    node_holes: Vec<NodeIndex<Ix>>,
-    edge_property: EdgeProperty,
-    #[serde(deserialize_with = "deser_graph_edges")]
-    edges: Vec<Edge<E, Ix>>,
-}
-
-impl<Ix> Serialize for NodeIndex<Ix>
-where
-    Ix: IndexType + Serialize,
-{
-    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
-    where
-        S: Serializer,
-    {
-        self.0.serialize(serializer)
-    }
-}
-
-impl<'de, Ix> Deserialize<'de> for NodeIndex<Ix>
-where
-    Ix: IndexType + Deserialize<'de>,
-{
-    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
-    where
-        D: Deserializer<'de>,
-    {
-        Ok(NodeIndex(Ix::deserialize(deserializer)?))
-    }
-}
-
-impl<Ix> Serialize for EdgeIndex<Ix>
-where
-    Ix: IndexType + Serialize,
-{
-    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
-    where
-        S: Serializer,
-    {
-        self.0.serialize(serializer)
-    }
-}
-
-impl<'de, Ix> Deserialize<'de> for EdgeIndex<Ix>
-where
-    Ix: IndexType + Deserialize<'de>,
-{
-    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
-    where
-        D: Deserializer<'de>,
-    {
-        Ok(EdgeIndex(Ix::deserialize(deserializer)?))
-    }
-}
-
-#[derive(Serialize, Deserialize)]
-#[serde(rename_all = "lowercase")]
-#[derive(Debug)]
-pub enum EdgeProperty {
-    Undirected,
-    Directed,
-}
-
-impl EdgeProperty {
-    pub fn is_directed(&self) -> bool {
-        match *self {
-            EdgeProperty::Directed => true,
-            EdgeProperty::Undirected => false,
-        }
-    }
-}
-
-impl<Ty> From<PhantomData<Ty>> for EdgeProperty
-where
-    Ty: EdgeType,
-{
-    fn from(_: PhantomData<Ty>) -> Self {
-        if Ty::is_directed() {
-            EdgeProperty::Directed
-        } else {
-            EdgeProperty::Undirected
-        }
-    }
-}
-
-impl<Ty> FromDeserialized for PhantomData<Ty>
-where
-    Ty: EdgeType,
-{
-    type Input = EdgeProperty;
-    fn from_deserialized<E2>(input: Self::Input) -> Result<Self, E2>
-    where
-        E2: Error,
-    {
-        if input.is_directed() != Ty::is_directed() {
-            Err(E2::custom(format_args!(
-                "graph edge property mismatch, \
-                 expected {:?}, found {:?}",
-                EdgeProperty::from(PhantomData::<Ty>),
-                input
-            )))
-        } else {
-            Ok(PhantomData)
-        }
-    }
-}
-
-fn ser_graph_nodes<S, N, Ix>(nodes: &&[Node<N, Ix>], serializer: S) -> Result<S::Ok, S::Error>
-where
-    S: Serializer,
-    N: Serialize,
-    Ix: Serialize + IndexType,
-{
-    serializer.collect_seq_exact(nodes.iter().map(|node| &node.weight))
-}
-
-fn ser_graph_edges<S, E, Ix>(edges: &&[Edge<E, Ix>], serializer: S) -> Result<S::Ok, S::Error>
-where
-    S: Serializer,
-    E: Serialize,
-    Ix: Serialize + IndexType,
-{
-    serializer.collect_seq_exact(
-        edges
-            .iter()
-            .map(|edge| Some((edge.source(), edge.target(), &edge.weight))),
-    )
-}
-
-fn deser_graph_nodes<'de, D, N, Ix>(deserializer: D) -> Result<Vec<Node<N, Ix>>, D::Error>
-where
-    D: Deserializer<'de>,
-    N: Deserialize<'de>,
-    Ix: IndexType + Deserialize<'de>,
-{
-    deserializer.deserialize_seq(MappedSequenceVisitor::new(|n| {
-        Ok(Node {
-            weight: n,
-            next: [EdgeIndex::end(); 2],
-        })
-    }))
-}
-
-fn deser_graph_node_holes<'de, D, Ix>(deserializer: D) -> Result<Vec<NodeIndex<Ix>>, D::Error>
-where
-    D: Deserializer<'de>,
-    Ix: IndexType + Deserialize<'de>,
-{
-    deserializer.deserialize_seq(
-        MappedSequenceVisitor::<NodeIndex<Ix>, NodeIndex<Ix>, _>::new(|_| {
-            Err("Graph can not have holes in the node set, found non-empty node_holes")
-        }),
-    )
-}
-
-fn deser_graph_edges<'de, D, N, Ix>(deserializer: D) -> Result<Vec<Edge<N, Ix>>, D::Error>
-where
-    D: Deserializer<'de>,
-    N: Deserialize<'de>,
-    Ix: IndexType + Deserialize<'de>,
-{
-    deserializer.deserialize_seq(MappedSequenceVisitor::<
-        Option<(NodeIndex<Ix>, NodeIndex<Ix>, N)>,
-        _,
-        _,
-    >::new(|x| {
-        if let Some((i, j, w)) = x {
-            Ok(Edge {
-                weight: w,
-                node: [i, j],
-                next: [EdgeIndex::end(); 2],
-            })
-        } else {
-            Err("Graph can not have holes in the edge set, found None, expected edge")
-        }
-    }))
-}
-
-impl<'a, N, E, Ty, Ix> IntoSerializable for &'a Graph<N, E, Ty, Ix>
-where
-    Ix: IndexType,
-    Ty: EdgeType,
-{
-    type Output = SerGraph<'a, N, E, Ix>;
-    fn into_serializable(self) -> Self::Output {
-        SerGraph {
-            nodes: &self.nodes,
-            node_holes: &[],
-            edges: &self.edges,
-            edge_property: EdgeProperty::from(PhantomData::<Ty>),
-        }
-    }
-}
-
-/// Requires crate feature `"serde-1"`
-impl<N, E, Ty, Ix> Serialize for Graph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType + Serialize,
-    N: Serialize,
-    E: Serialize,
-{
-    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
-    where
-        S: Serializer,
-    {
-        self.into_serializable().serialize(serializer)
-    }
-}
-
-pub fn invalid_node_err<E>(node_index: usize, len: usize) -> E
-where
-    E: Error,
-{
-    E::custom(format_args!(
-        "invalid value: node index `{}` does not exist in graph \
-         with node bound {}",
-        node_index, len
-    ))
-}
-
-pub fn invalid_length_err<Ix, E>(node_or_edge: &str, len: usize) -> E
-where
-    E: Error,
-    Ix: IndexType,
-{
-    E::custom(format_args!(
-        "invalid size: graph {} count {} exceeds index type maximum {}",
-        node_or_edge,
-        len,
-        <Ix as IndexType>::max().index()
-    ))
-}
-
-impl<'a, N, E, Ty, Ix> FromDeserialized for Graph<N, E, Ty, Ix>
-where
-    Ix: IndexType,
-    Ty: EdgeType,
-{
-    type Input = DeserGraph<N, E, Ix>;
-    fn from_deserialized<E2>(input: Self::Input) -> Result<Self, E2>
-    where
-        E2: Error,
-    {
-        let ty = PhantomData::<Ty>::from_deserialized(input.edge_property)?;
-        let nodes = input.nodes;
-        let edges = input.edges;
-        if nodes.len() >= <Ix as IndexType>::max().index() {
-            Err(invalid_length_err::<Ix, _>("node", nodes.len()))?
-        }
-
-        if edges.len() >= <Ix as IndexType>::max().index() {
-            Err(invalid_length_err::<Ix, _>("edge", edges.len()))?
-        }
-
-        let mut gr = Graph {
-            nodes: nodes,
-            edges: edges,
-            ty: ty,
-        };
-        let nc = gr.node_count();
-        gr.link_edges()
-            .map_err(|i| invalid_node_err(i.index(), nc))?;
-        Ok(gr)
-    }
-}
-
-/// Requires crate feature `"serde-1"`
-impl<'de, N, E, Ty, Ix> Deserialize<'de> for Graph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType + Deserialize<'de>,
-    N: Deserialize<'de>,
-    E: Deserialize<'de>,
-{
-    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
-    where
-        D: Deserializer<'de>,
-    {
-        Self::from_deserialized(DeserGraph::deserialize(deserializer)?)
-    }
-}
diff --git a/vendor/petgraph/src/graph_impl/stable_graph/mod.rs b/vendor/petgraph/src/graph_impl/stable_graph/mod.rs
deleted file mode 100644
index 142aaebed..000000000
--- a/vendor/petgraph/src/graph_impl/stable_graph/mod.rs
+++ /dev/null
@@ -1,1817 +0,0 @@
-//! `StableGraph` keeps indices stable across removals.
-//!
-//! Depends on `feature = "stable_graph"`.
-//!
-
-use std::cmp;
-use std::fmt;
-use std::iter;
-use std::marker::PhantomData;
-use std::mem::replace;
-use std::mem::size_of;
-use std::ops::{Index, IndexMut};
-use std::slice;
-
-use crate::{Directed, Direction, EdgeType, Graph, Incoming, Outgoing, Undirected};
-
-use crate::iter_format::{DebugMap, IterFormatExt, NoPretty};
-use crate::iter_utils::IterUtilsExt;
-
-use super::{index_twice, Edge, Frozen, Node, Pair, DIRECTIONS};
-use crate::visit::{
-    EdgeRef, IntoEdgeReferences, IntoEdges, IntoEdgesDirected, IntoNodeReferences, NodeIndexable,
-};
-use crate::IntoWeightedEdge;
-
-// reexport those things that are shared with Graph
-#[doc(no_inline)]
-pub use crate::graph::{
-    edge_index, node_index, DefaultIx, EdgeIndex, GraphIndex, IndexType, NodeIndex,
-};
-
-use crate::util::enumerate;
-
-#[cfg(feature = "serde-1")]
-mod serialization;
-
-/// `StableGraph<N, E, Ty, Ix>` is a graph datastructure using an adjacency
-/// list representation.
-///
-/// The graph **does not invalidate** any unrelated node or edge indices when
-/// items are removed.
-///
-/// `StableGraph` is parameterized over:
-///
-/// - Associated data `N` for nodes and `E` for edges, also called *weights*.
-///   The associated data can be of arbitrary type.
-/// - Edge type `Ty` that determines whether the graph edges are directed or undirected.
-/// - Index type `Ix`, which determines the maximum size of the graph.
-///
-/// The graph uses **O(|V| + |E|)** space, and allows fast node and edge insert
-/// and efficient graph search.
-///
-/// It implements **O(e')** edge lookup and edge and node removals, where **e'**
-/// is some local measure of edge count.
-///
-/// - Nodes and edges are each numbered in an interval from *0* to some number
-/// *m*, but *not all* indices in the range are valid, since gaps are formed
-/// by deletions.
-///
-/// - You can select graph index integer type after the size of the graph. A smaller
-/// size may have better performance.
-///
-/// - Using indices allows mutation while traversing the graph, see `Dfs`.
-///
-/// - The `StableGraph` is a regular rust collection and is `Send` and `Sync`
-/// (as long as associated data `N` and `E` are).
-///
-/// - Indices don't allow as much compile time checking as references.
-///
-/// Depends on crate feature `stable_graph` (default). *Stable Graph is still
-/// missing a few methods compared to Graph. You can contribute to help it
-/// achieve parity.*
-pub struct StableGraph<N, E, Ty = Directed, Ix = DefaultIx> {
-    g: Graph<Option<N>, Option<E>, Ty, Ix>,
-    node_count: usize,
-    edge_count: usize,
-
-    // node and edge free lists (both work the same way)
-    //
-    // free_node, if not NodeIndex::end(), points to a node index
-    // that is vacant (after a deletion).  The next item in the list is kept in
-    // that Node's Node.next[0] field. For Node, it's a node index stored
-    // in an EdgeIndex location, and the _into_edge()/_into_node() methods
-    // convert.
-    free_node: NodeIndex<Ix>,
-    free_edge: EdgeIndex<Ix>,
-}
-
-/// A `StableGraph` with directed edges.
-///
-/// For example, an edge from *1* to *2* is distinct from an edge from *2* to
-/// *1*.
-pub type StableDiGraph<N, E, Ix = DefaultIx> = StableGraph<N, E, Directed, Ix>;
-
-/// A `StableGraph` with undirected edges.
-///
-/// For example, an edge between *1* and *2* is equivalent to an edge between
-/// *2* and *1*.
-pub type StableUnGraph<N, E, Ix = DefaultIx> = StableGraph<N, E, Undirected, Ix>;
-
-impl<N, E, Ty, Ix> fmt::Debug for StableGraph<N, E, Ty, Ix>
-where
-    N: fmt::Debug,
-    E: fmt::Debug,
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        let etype = if self.is_directed() {
-            "Directed"
-        } else {
-            "Undirected"
-        };
-        let mut fmt_struct = f.debug_struct("StableGraph");
-        fmt_struct.field("Ty", &etype);
-        fmt_struct.field("node_count", &self.node_count);
-        fmt_struct.field("edge_count", &self.edge_count);
-        if self.g.edges.iter().any(|e| e.weight.is_some()) {
-            fmt_struct.field(
-                "edges",
-                &self
-                    .g
-                    .edges
-                    .iter()
-                    .filter(|e| e.weight.is_some())
-                    .map(|e| NoPretty((e.source().index(), e.target().index())))
-                    .format(", "),
-            );
-        }
-        // skip weights if they are ZST!
-        if size_of::<N>() != 0 {
-            fmt_struct.field(
-                "node weights",
-                &DebugMap(|| {
-                    self.g
-                        .nodes
-                        .iter()
-                        .map(|n| n.weight.as_ref())
-                        .enumerate()
-                        .filter_map(|(i, wo)| wo.map(move |w| (i, w)))
-                }),
-            );
-        }
-        if size_of::<E>() != 0 {
-            fmt_struct.field(
-                "edge weights",
-                &DebugMap(|| {
-                    self.g
-                        .edges
-                        .iter()
-                        .map(|n| n.weight.as_ref())
-                        .enumerate()
-                        .filter_map(|(i, wo)| wo.map(move |w| (i, w)))
-                }),
-            );
-        }
-        fmt_struct.field("free_node", &self.free_node);
-        fmt_struct.field("free_edge", &self.free_edge);
-        fmt_struct.finish()
-    }
-}
-
-impl<N, E> StableGraph<N, E, Directed> {
-    /// Create a new `StableGraph` with directed edges.
-    ///
-    /// This is a convenience method. See `StableGraph::with_capacity`
-    /// or `StableGraph::default` for a constructor that is generic in all the
-    /// type parameters of `StableGraph`.
-    pub fn new() -> Self {
-        Self::with_capacity(0, 0)
-    }
-}
-
-impl<N, E, Ty, Ix> StableGraph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    /// Create a new `StableGraph` with estimated capacity.
-    pub fn with_capacity(nodes: usize, edges: usize) -> Self {
-        StableGraph {
-            g: Graph::with_capacity(nodes, edges),
-            node_count: 0,
-            edge_count: 0,
-            free_node: NodeIndex::end(),
-            free_edge: EdgeIndex::end(),
-        }
-    }
-
-    /// Return the current node and edge capacity of the graph.
-    pub fn capacity(&self) -> (usize, usize) {
-        self.g.capacity()
-    }
-
-    /// Remove all nodes and edges
-    pub fn clear(&mut self) {
-        self.node_count = 0;
-        self.edge_count = 0;
-        self.free_node = NodeIndex::end();
-        self.free_edge = EdgeIndex::end();
-        self.g.clear();
-    }
-
-    /// Remove all edges
-    pub fn clear_edges(&mut self) {
-        self.edge_count = 0;
-        self.free_edge = EdgeIndex::end();
-        self.g.edges.clear();
-        // clear edges without touching the free list
-        for node in &mut self.g.nodes {
-            if node.weight.is_some() {
-                node.next = [EdgeIndex::end(), EdgeIndex::end()];
-            }
-        }
-    }
-
-    /// Return the number of nodes (vertices) in the graph.
-    ///
-    /// Computes in **O(1)** time.
-    pub fn node_count(&self) -> usize {
-        self.node_count
-    }
-
-    /// Return the number of edges in the graph.
-    ///
-    /// Computes in **O(1)** time.
-    pub fn edge_count(&self) -> usize {
-        self.edge_count
-    }
-
-    /// Whether the graph has directed edges or not.
-    #[inline]
-    pub fn is_directed(&self) -> bool {
-        Ty::is_directed()
-    }
-
-    /// Add a node (also called vertex) with associated data `weight` to the graph.
-    ///
-    /// Computes in **O(1)** time.
-    ///
-    /// Return the index of the new node.
-    ///
-    /// **Panics** if the `StableGraph` is at the maximum number of nodes for
-    /// its index type.
-    pub fn add_node(&mut self, weight: N) -> NodeIndex<Ix> {
-        let index = if self.free_node != NodeIndex::end() {
-            let node_idx = self.free_node;
-            let node_slot = &mut self.g.nodes[node_idx.index()];
-            let _old = replace(&mut node_slot.weight, Some(weight));
-            debug_assert!(_old.is_none());
-            self.free_node = node_slot.next[0]._into_node();
-            node_slot.next[0] = EdgeIndex::end();
-            node_idx
-        } else {
-            self.g.add_node(Some(weight))
-        };
-        self.node_count += 1;
-        index
-    }
-
-    /// free_node: Which free list to update for the vacancy
-    fn add_vacant_node(&mut self, free_node: &mut NodeIndex<Ix>) {
-        let node_idx = self.g.add_node(None);
-        // link the free list
-        let node_slot = &mut self.g.nodes[node_idx.index()];
-        node_slot.next[0] = free_node._into_edge();
-        *free_node = node_idx;
-    }
-
-    /// Remove `a` from the graph if it exists, and return its weight.
-    /// If it doesn't exist in the graph, return `None`.
-    ///
-    /// The node index `a` is invalidated, but none other.
-    /// Edge indices are invalidated as they would be following the removal of
-    /// each edge with an endpoint in `a`.
-    ///
-    /// Computes in **O(e')** time, where **e'** is the number of affected
-    /// edges, including *n* calls to `.remove_edge()` where *n* is the number
-    /// of edges with an endpoint in `a`.
-    pub fn remove_node(&mut self, a: NodeIndex<Ix>) -> Option<N> {
-        let node_weight = self.g.nodes.get_mut(a.index())?.weight.take()?;
-        for d in &DIRECTIONS {
-            let k = d.index();
-
-            // Remove all edges from and to this node.
-            loop {
-                let next = self.g.nodes[a.index()].next[k];
-                if next == EdgeIndex::end() {
-                    break;
-                }
-                let ret = self.remove_edge(next);
-                debug_assert!(ret.is_some());
-                let _ = ret;
-            }
-        }
-
-        let node_slot = &mut self.g.nodes[a.index()];
-        //let node_weight = replace(&mut self.g.nodes[a.index()].weight, Entry::Empty(self.free_node));
-        //self.g.nodes[a.index()].next = [EdgeIndex::end(), EdgeIndex::end()];
-        node_slot.next = [self.free_node._into_edge(), EdgeIndex::end()];
-        self.free_node = a;
-        self.node_count -= 1;
-
-        Some(node_weight)
-    }
-
-    pub fn contains_node(&self, a: NodeIndex<Ix>) -> bool {
-        self.get_node(a).is_some()
-    }
-
-    // Return the Node if it is not vacant (non-None weight)
-    fn get_node(&self, a: NodeIndex<Ix>) -> Option<&Node<Option<N>, Ix>> {
-        self.g
-            .nodes
-            .get(a.index())
-            .and_then(|node| node.weight.as_ref().map(move |_| node))
-    }
-
-    /// Add an edge from `a` to `b` to the graph, with its associated
-    /// data `weight`.
-    ///
-    /// Return the index of the new edge.
-    ///
-    /// Computes in **O(1)** time.
-    ///
-    /// **Panics** if any of the nodes don't exist.<br>
-    /// **Panics** if the `StableGraph` is at the maximum number of edges for
-    /// its index type.
-    ///
-    /// **Note:** `StableGraph` allows adding parallel (“duplicate”) edges.
-    pub fn add_edge(&mut self, a: NodeIndex<Ix>, b: NodeIndex<Ix>, weight: E) -> EdgeIndex<Ix> {
-        let edge_idx;
-        let mut new_edge = None::<Edge<_, _>>;
-        {
-            let edge: &mut Edge<_, _>;
-
-            if self.free_edge != EdgeIndex::end() {
-                edge_idx = self.free_edge;
-                edge = &mut self.g.edges[edge_idx.index()];
-                let _old = replace(&mut edge.weight, Some(weight));
-                debug_assert!(_old.is_none());
-                self.free_edge = edge.next[0];
-                edge.node = [a, b];
-            } else {
-                edge_idx = EdgeIndex::new(self.g.edges.len());
-                assert!(<Ix as IndexType>::max().index() == !0 || EdgeIndex::end() != edge_idx);
-                new_edge = Some(Edge {
-                    weight: Some(weight),
-                    node: [a, b],
-                    next: [EdgeIndex::end(); 2],
-                });
-                edge = new_edge.as_mut().unwrap();
-            }
-
-            let wrong_index = match index_twice(&mut self.g.nodes, a.index(), b.index()) {
-                Pair::None => Some(cmp::max(a.index(), b.index())),
-                Pair::One(an) => {
-                    if an.weight.is_none() {
-                        Some(a.index())
-                    } else {
-                        edge.next = an.next;
-                        an.next[0] = edge_idx;
-                        an.next[1] = edge_idx;
-                        None
-                    }
-                }
-                Pair::Both(an, bn) => {
-                    // a and b are different indices
-                    if an.weight.is_none() {
-                        Some(a.index())
-                    } else if bn.weight.is_none() {
-                        Some(b.index())
-                    } else {
-                        edge.next = [an.next[0], bn.next[1]];
-                        an.next[0] = edge_idx;
-                        bn.next[1] = edge_idx;
-                        None
-                    }
-                }
-            };
-            if let Some(i) = wrong_index {
-                panic!(
-                    "StableGraph::add_edge: node index {} is not a node in the graph",
-                    i
-                );
-            }
-            self.edge_count += 1;
-        }
-        if let Some(edge) = new_edge {
-            self.g.edges.push(edge);
-        }
-        edge_idx
-    }
-
-    /// free_edge: Which free list to update for the vacancy
-    fn add_vacant_edge(&mut self, free_edge: &mut EdgeIndex<Ix>) {
-        let edge_idx = EdgeIndex::new(self.g.edges.len());
-        debug_assert!(edge_idx != EdgeIndex::end());
-        let mut edge = Edge {
-            weight: None,
-            node: [NodeIndex::end(); 2],
-            next: [EdgeIndex::end(); 2],
-        };
-        edge.next[0] = *free_edge;
-        *free_edge = edge_idx;
-        self.g.edges.push(edge);
-    }
-
-    /// Add or update an edge from `a` to `b`.
-    /// If the edge already exists, its weight is updated.
-    ///
-    /// Return the index of the affected edge.
-    ///
-    /// Computes in **O(e')** time, where **e'** is the number of edges
-    /// connected to `a` (and `b`, if the graph edges are undirected).
-    ///
-    /// **Panics** if any of the nodes don't exist.
-    pub fn update_edge(&mut self, a: NodeIndex<Ix>, b: NodeIndex<Ix>, weight: E) -> EdgeIndex<Ix> {
-        if let Some(ix) = self.find_edge(a, b) {
-            self[ix] = weight;
-            return ix;
-        }
-        self.add_edge(a, b, weight)
-    }
-
-    /// Remove an edge and return its edge weight, or `None` if it didn't exist.
-    ///
-    /// Invalidates the edge index `e` but no other.
-    ///
-    /// Computes in **O(e')** time, where **e'** is the number of edges
-    /// connected to the same endpoints as `e`.
-    pub fn remove_edge(&mut self, e: EdgeIndex<Ix>) -> Option<E> {
-        // every edge is part of two lists,
-        // outgoing and incoming edges.
-        // Remove it from both
-        let (is_edge, edge_node, edge_next) = match self.g.edges.get(e.index()) {
-            None => return None,
-            Some(x) => (x.weight.is_some(), x.node, x.next),
-        };
-        if !is_edge {
-            return None;
-        }
-
-        // Remove the edge from its in and out lists by replacing it with
-        // a link to the next in the list.
-        self.g.change_edge_links(edge_node, e, edge_next);
-
-        // Clear the edge and put it in the free list
-        let edge = &mut self.g.edges[e.index()];
-        edge.next = [self.free_edge, EdgeIndex::end()];
-        edge.node = [NodeIndex::end(), NodeIndex::end()];
-        self.free_edge = e;
-        self.edge_count -= 1;
-        edge.weight.take()
-    }
-
-    /// Access the weight for node `a`.
-    ///
-    /// Also available with indexing syntax: `&graph[a]`.
-    pub fn node_weight(&self, a: NodeIndex<Ix>) -> Option<&N> {
-        match self.g.nodes.get(a.index()) {
-            Some(no) => no.weight.as_ref(),
-            None => None,
-        }
-    }
-
-    /// Access the weight for node `a`, mutably.
-    ///
-    /// Also available with indexing syntax: `&mut graph[a]`.
-    pub fn node_weight_mut(&mut self, a: NodeIndex<Ix>) -> Option<&mut N> {
-        match self.g.nodes.get_mut(a.index()) {
-            Some(no) => no.weight.as_mut(),
-            None => None,
-        }
-    }
-
-    /// Return an iterator yielding mutable access to all node weights.
-    ///
-    /// The order in which weights are yielded matches the order of their node
-    /// indices.
-    pub fn node_weights_mut(&mut self) -> impl Iterator<Item = &mut N> {
-        self.g
-            .node_weights_mut()
-            .flat_map(|maybe_node| maybe_node.iter_mut())
-    }
-
-    /// Return an iterator over the node indices of the graph
-    pub fn node_indices(&self) -> NodeIndices<N, Ix> {
-        NodeIndices {
-            iter: enumerate(self.raw_nodes()),
-        }
-    }
-
-    /// Access the weight for edge `e`.
-    ///
-    /// Also available with indexing syntax: `&graph[e]`.
-    pub fn edge_weight(&self, e: EdgeIndex<Ix>) -> Option<&E> {
-        match self.g.edges.get(e.index()) {
-            Some(ed) => ed.weight.as_ref(),
-            None => None,
-        }
-    }
-
-    /// Access the weight for edge `e`, mutably
-    ///
-    /// Also available with indexing syntax: `&mut graph[e]`.
-    pub fn edge_weight_mut(&mut self, e: EdgeIndex<Ix>) -> Option<&mut E> {
-        match self.g.edges.get_mut(e.index()) {
-            Some(ed) => ed.weight.as_mut(),
-            None => None,
-        }
-    }
-
-    /// Return an iterator yielding mutable access to all edge weights.
-    ///
-    /// The order in which weights are yielded matches the order of their edge
-    /// indices.
-    pub fn edge_weights_mut(&mut self) -> impl Iterator<Item = &mut E> {
-        self.g
-            .edge_weights_mut()
-            .flat_map(|maybe_edge| maybe_edge.iter_mut())
-    }
-
-    /// Access the source and target nodes for `e`.
-    pub fn edge_endpoints(&self, e: EdgeIndex<Ix>) -> Option<(NodeIndex<Ix>, NodeIndex<Ix>)> {
-        match self.g.edges.get(e.index()) {
-            Some(ed) if ed.weight.is_some() => Some((ed.source(), ed.target())),
-            _otherwise => None,
-        }
-    }
-
-    /// Return an iterator over the edge indices of the graph
-    pub fn edge_indices(&self) -> EdgeIndices<E, Ix> {
-        EdgeIndices {
-            iter: enumerate(self.raw_edges()),
-        }
-    }
-
-    /// Lookup if there is an edge from `a` to `b`.
-    ///
-    /// Computes in **O(e')** time, where **e'** is the number of edges
-    /// connected to `a` (and `b`, if the graph edges are undirected).
-    pub fn contains_edge(&self, a: NodeIndex<Ix>, b: NodeIndex<Ix>) -> bool {
-        self.find_edge(a, b).is_some()
-    }
-
-    /// Lookup an edge from `a` to `b`.
-    ///
-    /// Computes in **O(e')** time, where **e'** is the number of edges
-    /// connected to `a` (and `b`, if the graph edges are undirected).
-    pub fn find_edge(&self, a: NodeIndex<Ix>, b: NodeIndex<Ix>) -> Option<EdgeIndex<Ix>> {
-        if !self.is_directed() {
-            self.find_edge_undirected(a, b).map(|(ix, _)| ix)
-        } else {
-            match self.get_node(a) {
-                None => None,
-                Some(node) => self.g.find_edge_directed_from_node(node, b),
-            }
-        }
-    }
-
-    /// Lookup an edge between `a` and `b`, in either direction.
-    ///
-    /// If the graph is undirected, then this is equivalent to `.find_edge()`.
-    ///
-    /// Return the edge index and its directionality, with `Outgoing` meaning
-    /// from `a` to `b` and `Incoming` the reverse,
-    /// or `None` if the edge does not exist.
-    pub fn find_edge_undirected(
-        &self,
-        a: NodeIndex<Ix>,
-        b: NodeIndex<Ix>,
-    ) -> Option<(EdgeIndex<Ix>, Direction)> {
-        match self.get_node(a) {
-            None => None,
-            Some(node) => self.g.find_edge_undirected_from_node(node, b),
-        }
-    }
-
-    /// Return an iterator of all nodes with an edge starting from `a`.
-    ///
-    /// - `Directed`: Outgoing edges from `a`.
-    /// - `Undirected`: All edges connected to `a`.
-    ///
-    /// Produces an empty iterator if the node doesn't exist.<br>
-    /// Iterator element type is `NodeIndex<Ix>`.
-    ///
-    /// Use [`.neighbors(a).detach()`][1] to get a neighbor walker that does
-    /// not borrow from the graph.
-    ///
-    /// [1]: struct.Neighbors.html#method.detach
-    pub fn neighbors(&self, a: NodeIndex<Ix>) -> Neighbors<E, Ix> {
-        self.neighbors_directed(a, Outgoing)
-    }
-
-    /// Return an iterator of all neighbors that have an edge between them and `a`,
-    /// in the specified direction.
-    /// If the graph's edges are undirected, this is equivalent to *.neighbors(a)*.
-    ///
-    /// - `Directed`, `Outgoing`: All edges from `a`.
-    /// - `Directed`, `Incoming`: All edges to `a`.
-    /// - `Undirected`: All edges connected to `a`.
-    ///
-    /// Produces an empty iterator if the node doesn't exist.<br>
-    /// Iterator element type is `NodeIndex<Ix>`.
-    ///
-    /// Use [`.neighbors_directed(a, dir).detach()`][1] to get a neighbor walker that does
-    /// not borrow from the graph.
-    ///
-    /// [1]: struct.Neighbors.html#method.detach
-    pub fn neighbors_directed(&self, a: NodeIndex<Ix>, dir: Direction) -> Neighbors<E, Ix> {
-        let mut iter = self.neighbors_undirected(a);
-        if self.is_directed() {
-            let k = dir.index();
-            iter.next[1 - k] = EdgeIndex::end();
-            iter.skip_start = NodeIndex::end();
-        }
-        iter
-    }
-
-    /// Return an iterator of all neighbors that have an edge between them and `a`,
-    /// in either direction.
-    /// If the graph's edges are undirected, this is equivalent to *.neighbors(a)*.
-    ///
-    /// - `Directed` and `Undirected`: All edges connected to `a`.
-    ///
-    /// Produces an empty iterator if the node doesn't exist.<br>
-    /// Iterator element type is `NodeIndex<Ix>`.
-    ///
-    /// Use [`.neighbors_undirected(a).detach()`][1] to get a neighbor walker that does
-    /// not borrow from the graph.
-    ///
-    /// [1]: struct.Neighbors.html#method.detach
-    pub fn neighbors_undirected(&self, a: NodeIndex<Ix>) -> Neighbors<E, Ix> {
-        Neighbors {
-            skip_start: a,
-            edges: &self.g.edges,
-            next: match self.get_node(a) {
-                None => [EdgeIndex::end(), EdgeIndex::end()],
-                Some(n) => n.next,
-            },
-        }
-    }
-
-    /// Return an iterator of all edges of `a`.
-    ///
-    /// - `Directed`: Outgoing edges from `a`.
-    /// - `Undirected`: All edges connected to `a`.
-    ///
-    /// Produces an empty iterator if the node doesn't exist.<br>
-    /// Iterator element type is `EdgeReference<E, Ix>`.
-    pub fn edges(&self, a: NodeIndex<Ix>) -> Edges<E, Ty, Ix> {
-        self.edges_directed(a, Outgoing)
-    }
-
-    /// Return an iterator of all edges of `a`, in the specified direction.
-    ///
-    /// - `Directed`, `Outgoing`: All edges from `a`.
-    /// - `Directed`, `Incoming`: All edges to `a`.
-    /// - `Undirected`, `Outgoing`: All edges connected to `a`, with `a` being the source of each
-    ///   edge.
-    /// - `Undirected`, `Incoming`: All edges connected to `a`, with `a` being the target of each
-    ///   edge.
-    ///
-    /// Produces an empty iterator if the node `a` doesn't exist.<br>
-    /// Iterator element type is `EdgeReference<E, Ix>`.
-    pub fn edges_directed(&self, a: NodeIndex<Ix>, dir: Direction) -> Edges<E, Ty, Ix> {
-        Edges {
-            skip_start: a,
-            edges: &self.g.edges,
-            direction: dir,
-            next: match self.get_node(a) {
-                None => [EdgeIndex::end(), EdgeIndex::end()],
-                Some(n) => n.next,
-            },
-            ty: PhantomData,
-        }
-    }
-
-    /// Return an iterator over either the nodes without edges to them
-    /// (`Incoming`) or from them (`Outgoing`).
-    ///
-    /// An *internal* node has both incoming and outgoing edges.
-    /// The nodes in `.externals(Incoming)` are the source nodes and
-    /// `.externals(Outgoing)` are the sinks of the graph.
-    ///
-    /// For a graph with undirected edges, both the sinks and the sources are
-    /// just the nodes without edges.
-    ///
-    /// The whole iteration computes in **O(|V|)** time.
-    pub fn externals(&self, dir: Direction) -> Externals<N, Ty, Ix> {
-        Externals {
-            iter: self.raw_nodes().iter().enumerate(),
-            dir,
-            ty: PhantomData,
-        }
-    }
-
-    /// Index the `StableGraph` by two indices, any combination of
-    /// node or edge indices is fine.
-    ///
-    /// **Panics** if the indices are equal or if they are out of bounds.
-    pub fn index_twice_mut<T, U>(
-        &mut self,
-        i: T,
-        j: U,
-    ) -> (
-        &mut <Self as Index<T>>::Output,
-        &mut <Self as Index<U>>::Output,
-    )
-    where
-        Self: IndexMut<T> + IndexMut<U>,
-        T: GraphIndex,
-        U: GraphIndex,
-    {
-        assert!(T::is_node_index() != U::is_node_index() || i.index() != j.index());
-
-        // Allow two mutable indexes here -- they are nonoverlapping
-        unsafe {
-            let self_mut = self as *mut _;
-            (
-                <Self as IndexMut<T>>::index_mut(&mut *self_mut, i),
-                <Self as IndexMut<U>>::index_mut(&mut *self_mut, j),
-            )
-        }
-    }
-
-    /// Keep all nodes that return `true` from the `visit` closure,
-    /// remove the others.
-    ///
-    /// `visit` is provided a proxy reference to the graph, so that
-    /// the graph can be walked and associated data modified.
-    ///
-    /// The order nodes are visited is not specified.
-    ///
-    /// The node indices of the removed nodes are invalidated, but none other.
-    /// Edge indices are invalidated as they would be following the removal of
-    /// each edge with an endpoint in a removed node.
-    ///
-    /// Computes in **O(n + e')** time, where **n** is the number of node indices and
-    ///  **e'** is the number of affected edges, including *n* calls to `.remove_edge()`
-    /// where *n* is the number of edges with an endpoint in a removed node.
-    pub fn retain_nodes<F>(&mut self, mut visit: F)
-    where
-        F: FnMut(Frozen<Self>, NodeIndex<Ix>) -> bool,
-    {
-        for i in 0..self.node_bound() {
-            let ix = node_index(i);
-            if self.contains_node(ix) && !visit(Frozen(self), ix) {
-                self.remove_node(ix);
-            }
-        }
-        self.check_free_lists();
-    }
-
-    /// Keep all edges that return `true` from the `visit` closure,
-    /// remove the others.
-    ///
-    /// `visit` is provided a proxy reference to the graph, so that
-    /// the graph can be walked and associated data modified.
-    ///
-    /// The order edges are visited is not specified.
-    ///
-    /// The edge indices of the removed edes are invalidated, but none other.
-    ///
-    /// Computes in **O(e'')** time, **e'** is the number of affected edges,
-    /// including the calls to `.remove_edge()` for each removed edge.
-    pub fn retain_edges<F>(&mut self, mut visit: F)
-    where
-        F: FnMut(Frozen<Self>, EdgeIndex<Ix>) -> bool,
-    {
-        for i in 0..self.edge_bound() {
-            let ix = edge_index(i);
-            if self.edge_weight(ix).is_some() && !visit(Frozen(self), ix) {
-                self.remove_edge(ix);
-            }
-        }
-        self.check_free_lists();
-    }
-
-    /// Create a new `StableGraph` from an iterable of edges.
-    ///
-    /// Node weights `N` are set to default values.
-    /// Edge weights `E` may either be specified in the list,
-    /// or they are filled with default values.
-    ///
-    /// Nodes are inserted automatically to match the edges.
-    ///
-    /// ```
-    /// use petgraph::stable_graph::StableGraph;
-    ///
-    /// let gr = StableGraph::<(), i32>::from_edges(&[
-    ///     (0, 1), (0, 2), (0, 3),
-    ///     (1, 2), (1, 3),
-    ///     (2, 3),
-    /// ]);
-    /// ```
-    pub fn from_edges<I>(iterable: I) -> Self
-    where
-        I: IntoIterator,
-        I::Item: IntoWeightedEdge<E>,
-        <I::Item as IntoWeightedEdge<E>>::NodeId: Into<NodeIndex<Ix>>,
-        N: Default,
-    {
-        let mut g = Self::with_capacity(0, 0);
-        g.extend_with_edges(iterable);
-        g
-    }
-
-    /// Create a new `StableGraph` by mapping node and
-    /// edge weights to new values.
-    ///
-    /// The resulting graph has the same structure and the same
-    /// graph indices as `self`.
-    pub fn map<'a, F, G, N2, E2>(
-        &'a self,
-        mut node_map: F,
-        mut edge_map: G,
-    ) -> StableGraph<N2, E2, Ty, Ix>
-    where
-        F: FnMut(NodeIndex<Ix>, &'a N) -> N2,
-        G: FnMut(EdgeIndex<Ix>, &'a E) -> E2,
-    {
-        let g = self.g.map(
-            move |i, w| w.as_ref().map(|w| node_map(i, w)),
-            move |i, w| w.as_ref().map(|w| edge_map(i, w)),
-        );
-        StableGraph {
-            g,
-            node_count: self.node_count,
-            edge_count: self.edge_count,
-            free_node: self.free_node,
-            free_edge: self.free_edge,
-        }
-    }
-
-    /// Create a new `StableGraph` by mapping nodes and edges.
-    /// A node or edge may be mapped to `None` to exclude it from
-    /// the resulting graph.
-    ///
-    /// Nodes are mapped first with the `node_map` closure, then
-    /// `edge_map` is called for the edges that have not had any endpoint
-    /// removed.
-    ///
-    /// The resulting graph has the structure of a subgraph of the original graph.
-    /// Nodes and edges that are not removed maintain their old node or edge
-    /// indices.
-    pub fn filter_map<'a, F, G, N2, E2>(
-        &'a self,
-        mut node_map: F,
-        mut edge_map: G,
-    ) -> StableGraph<N2, E2, Ty, Ix>
-    where
-        F: FnMut(NodeIndex<Ix>, &'a N) -> Option<N2>,
-        G: FnMut(EdgeIndex<Ix>, &'a E) -> Option<E2>,
-    {
-        let node_bound = self.node_bound();
-        let edge_bound = self.edge_bound();
-        let mut result_g = StableGraph::with_capacity(node_bound, edge_bound);
-        // use separate free lists so that
-        // add_node / add_edge below do not reuse the tombstones
-        let mut free_node = NodeIndex::end();
-        let mut free_edge = EdgeIndex::end();
-
-        // the stable graph keeps the node map itself
-
-        for (i, node) in enumerate(self.raw_nodes()) {
-            if i >= node_bound {
-                break;
-            }
-            if let Some(node_weight) = node.weight.as_ref() {
-                if let Some(new_weight) = node_map(NodeIndex::new(i), node_weight) {
-                    result_g.add_node(new_weight);
-                    continue;
-                }
-            }
-            result_g.add_vacant_node(&mut free_node);
-        }
-        for (i, edge) in enumerate(self.raw_edges()) {
-            if i >= edge_bound {
-                break;
-            }
-            let source = edge.source();
-            let target = edge.target();
-            if let Some(edge_weight) = edge.weight.as_ref() {
-                if result_g.contains_node(source) && result_g.contains_node(target) {
-                    if let Some(new_weight) = edge_map(EdgeIndex::new(i), edge_weight) {
-                        result_g.add_edge(source, target, new_weight);
-                        continue;
-                    }
-                }
-            }
-            result_g.add_vacant_edge(&mut free_edge);
-        }
-        result_g.free_node = free_node;
-        result_g.free_edge = free_edge;
-        result_g.check_free_lists();
-        result_g
-    }
-
-    /// Extend the graph from an iterable of edges.
-    ///
-    /// Node weights `N` are set to default values.
-    /// Edge weights `E` may either be specified in the list,
-    /// or they are filled with default values.
-    ///
-    /// Nodes are inserted automatically to match the edges.
-    pub fn extend_with_edges<I>(&mut self, iterable: I)
-    where
-        I: IntoIterator,
-        I::Item: IntoWeightedEdge<E>,
-        <I::Item as IntoWeightedEdge<E>>::NodeId: Into<NodeIndex<Ix>>,
-        N: Default,
-    {
-        let iter = iterable.into_iter();
-
-        for elt in iter {
-            let (source, target, weight) = elt.into_weighted_edge();
-            let (source, target) = (source.into(), target.into());
-            let nx = cmp::max(source, target);
-            while nx.index() >= self.node_count() {
-                self.add_node(N::default());
-            }
-            self.add_edge(source, target, weight);
-        }
-    }
-
-    //
-    // internal methods
-    //
-    fn raw_nodes(&self) -> &[Node<Option<N>, Ix>] {
-        self.g.raw_nodes()
-    }
-
-    fn raw_edges(&self) -> &[Edge<Option<E>, Ix>] {
-        self.g.raw_edges()
-    }
-
-    fn edge_bound(&self) -> usize {
-        self.edge_references()
-            .next_back()
-            .map_or(0, |edge| edge.id().index() + 1)
-    }
-
-    #[cfg(feature = "serde-1")]
-    /// Fix up node and edge links after deserialization
-    fn link_edges(&mut self) -> Result<(), NodeIndex<Ix>> {
-        // set up free node list
-        self.node_count = 0;
-        self.edge_count = 0;
-        let mut free_node = NodeIndex::end();
-        for (node_index, node) in enumerate(&mut self.g.nodes) {
-            if node.weight.is_some() {
-                self.node_count += 1;
-            } else {
-                // free node
-                node.next = [free_node._into_edge(), EdgeIndex::end()];
-                free_node = NodeIndex::new(node_index);
-            }
-        }
-        self.free_node = free_node;
-
-        let mut free_edge = EdgeIndex::end();
-        for (edge_index, edge) in enumerate(&mut self.g.edges) {
-            if edge.weight.is_none() {
-                // free edge
-                edge.next = [free_edge, EdgeIndex::end()];
-                free_edge = EdgeIndex::new(edge_index);
-                continue;
-            }
-            let a = edge.source();
-            let b = edge.target();
-            let edge_idx = EdgeIndex::new(edge_index);
-            match index_twice(&mut self.g.nodes, a.index(), b.index()) {
-                Pair::None => return Err(if a > b { a } else { b }),
-                Pair::One(an) => {
-                    edge.next = an.next;
-                    an.next[0] = edge_idx;
-                    an.next[1] = edge_idx;
-                }
-                Pair::Both(an, bn) => {
-                    // a and b are different indices
-                    edge.next = [an.next[0], bn.next[1]];
-                    an.next[0] = edge_idx;
-                    bn.next[1] = edge_idx;
-                }
-            }
-            self.edge_count += 1;
-        }
-        self.free_edge = free_edge;
-        Ok(())
-    }
-
-    #[cfg(not(debug_assertions))]
-    fn check_free_lists(&self) {}
-    #[cfg(debug_assertions)]
-    // internal method to debug check the free lists (linked lists)
-    fn check_free_lists(&self) {
-        let mut free_node = self.free_node;
-        let mut free_node_len = 0;
-        while free_node != NodeIndex::end() {
-            if let Some(n) = self.g.nodes.get(free_node.index()) {
-                if n.weight.is_none() {
-                    free_node = n.next[0]._into_node();
-                    free_node_len += 1;
-                    continue;
-                }
-                debug_assert!(
-                    false,
-                    "Corrupt free list: pointing to existing {:?}",
-                    free_node.index()
-                );
-            }
-            debug_assert!(false, "Corrupt free list: missing {:?}", free_node.index());
-        }
-        debug_assert_eq!(self.node_count(), self.raw_nodes().len() - free_node_len);
-
-        let mut free_edge_len = 0;
-        let mut free_edge = self.free_edge;
-        while free_edge != EdgeIndex::end() {
-            if let Some(n) = self.g.edges.get(free_edge.index()) {
-                if n.weight.is_none() {
-                    free_edge = n.next[0];
-                    free_edge_len += 1;
-                    continue;
-                }
-                debug_assert!(
-                    false,
-                    "Corrupt free list: pointing to existing {:?}",
-                    free_node.index()
-                );
-            }
-            debug_assert!(false, "Corrupt free list: missing {:?}", free_edge.index());
-        }
-        debug_assert_eq!(self.edge_count(), self.raw_edges().len() - free_edge_len);
-    }
-}
-
-/// The resulting cloned graph has the same graph indices as `self`.
-impl<N, E, Ty, Ix: IndexType> Clone for StableGraph<N, E, Ty, Ix>
-where
-    N: Clone,
-    E: Clone,
-{
-    fn clone(&self) -> Self {
-        StableGraph {
-            g: self.g.clone(),
-            node_count: self.node_count,
-            edge_count: self.edge_count,
-            free_node: self.free_node,
-            free_edge: self.free_edge,
-        }
-    }
-
-    fn clone_from(&mut self, rhs: &Self) {
-        self.g.clone_from(&rhs.g);
-        self.node_count = rhs.node_count;
-        self.edge_count = rhs.edge_count;
-        self.free_node = rhs.free_node;
-        self.free_edge = rhs.free_edge;
-    }
-}
-
-/// Index the `StableGraph` by `NodeIndex` to access node weights.
-///
-/// **Panics** if the node doesn't exist.
-impl<N, E, Ty, Ix> Index<NodeIndex<Ix>> for StableGraph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    type Output = N;
-    fn index(&self, index: NodeIndex<Ix>) -> &N {
-        self.node_weight(index).unwrap()
-    }
-}
-
-/// Index the `StableGraph` by `NodeIndex` to access node weights.
-///
-/// **Panics** if the node doesn't exist.
-impl<N, E, Ty, Ix> IndexMut<NodeIndex<Ix>> for StableGraph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    fn index_mut(&mut self, index: NodeIndex<Ix>) -> &mut N {
-        self.node_weight_mut(index).unwrap()
-    }
-}
-
-/// Index the `StableGraph` by `EdgeIndex` to access edge weights.
-///
-/// **Panics** if the edge doesn't exist.
-impl<N, E, Ty, Ix> Index<EdgeIndex<Ix>> for StableGraph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    type Output = E;
-    fn index(&self, index: EdgeIndex<Ix>) -> &E {
-        self.edge_weight(index).unwrap()
-    }
-}
-
-/// Index the `StableGraph` by `EdgeIndex` to access edge weights.
-///
-/// **Panics** if the edge doesn't exist.
-impl<N, E, Ty, Ix> IndexMut<EdgeIndex<Ix>> for StableGraph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    fn index_mut(&mut self, index: EdgeIndex<Ix>) -> &mut E {
-        self.edge_weight_mut(index).unwrap()
-    }
-}
-
-/// Create a new empty `StableGraph`.
-impl<N, E, Ty, Ix> Default for StableGraph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    fn default() -> Self {
-        Self::with_capacity(0, 0)
-    }
-}
-
-/// Convert a `Graph` into a `StableGraph`
-///
-/// Computes in **O(|V| + |E|)** time.
-///
-/// The resulting graph has the same node and edge indices as
-/// the original graph.
-impl<N, E, Ty, Ix> From<Graph<N, E, Ty, Ix>> for StableGraph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    fn from(g: Graph<N, E, Ty, Ix>) -> Self {
-        let nodes = g.nodes.into_iter().map(|e| Node {
-            weight: Some(e.weight),
-            next: e.next,
-        });
-        let edges = g.edges.into_iter().map(|e| Edge {
-            weight: Some(e.weight),
-            node: e.node,
-            next: e.next,
-        });
-        StableGraph {
-            node_count: nodes.len(),
-            edge_count: edges.len(),
-            g: Graph {
-                edges: edges.collect(),
-                nodes: nodes.collect(),
-                ty: g.ty,
-            },
-            free_node: NodeIndex::end(),
-            free_edge: EdgeIndex::end(),
-        }
-    }
-}
-
-/// Convert a `StableGraph` into a `Graph`
-///
-/// Computes in **O(|V| + |E|)** time.
-///
-/// This translates the stable graph into a graph with node and edge indices in
-/// a compact interval without holes (like `Graph`s always are).
-///
-/// Only if the stable graph had no vacancies after deletions (if node bound was
-/// equal to node count, and the same for edges), would the resulting graph have
-/// the same node and edge indices as the input.
-impl<N, E, Ty, Ix> From<StableGraph<N, E, Ty, Ix>> for Graph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    fn from(graph: StableGraph<N, E, Ty, Ix>) -> Self {
-        let mut result_g = Graph::with_capacity(graph.node_count(), graph.edge_count());
-        // mapping from old node index to new node index
-        let mut node_index_map = vec![NodeIndex::end(); graph.node_bound()];
-
-        for (i, node) in enumerate(graph.g.nodes) {
-            if let Some(nw) = node.weight {
-                node_index_map[i] = result_g.add_node(nw);
-            }
-        }
-        for edge in graph.g.edges {
-            let source_index = edge.source().index();
-            let target_index = edge.target().index();
-            if let Some(ew) = edge.weight {
-                let source = node_index_map[source_index];
-                let target = node_index_map[target_index];
-                debug_assert!(source != NodeIndex::end());
-                debug_assert!(target != NodeIndex::end());
-                result_g.add_edge(source, target, ew);
-            }
-        }
-        result_g
-    }
-}
-
-impl<'a, N, E, Ty, Ix> IntoNodeReferences for &'a StableGraph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    type NodeRef = (NodeIndex<Ix>, &'a N);
-    type NodeReferences = NodeReferences<'a, N, Ix>;
-    fn node_references(self) -> Self::NodeReferences {
-        NodeReferences {
-            iter: enumerate(self.raw_nodes()),
-        }
-    }
-}
-
-/// Iterator over all nodes of a graph.
-pub struct NodeReferences<'a, N: 'a, Ix: IndexType = DefaultIx> {
-    iter: iter::Enumerate<slice::Iter<'a, Node<Option<N>, Ix>>>,
-}
-
-impl<'a, N, Ix> Iterator for NodeReferences<'a, N, Ix>
-where
-    Ix: IndexType,
-{
-    type Item = (NodeIndex<Ix>, &'a N);
-
-    fn next(&mut self) -> Option<Self::Item> {
-        self.iter
-            .ex_find_map(|(i, node)| node.weight.as_ref().map(move |w| (node_index(i), w)))
-    }
-
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        let (_, hi) = self.iter.size_hint();
-        (0, hi)
-    }
-}
-
-impl<'a, N, Ix> DoubleEndedIterator for NodeReferences<'a, N, Ix>
-where
-    Ix: IndexType,
-{
-    fn next_back(&mut self) -> Option<Self::Item> {
-        self.iter
-            .ex_rfind_map(|(i, node)| node.weight.as_ref().map(move |w| (node_index(i), w)))
-    }
-}
-
-/// Reference to a `StableGraph` edge.
-#[derive(Debug)]
-pub struct EdgeReference<'a, E: 'a, Ix = DefaultIx> {
-    index: EdgeIndex<Ix>,
-    node: [NodeIndex<Ix>; 2],
-    weight: &'a E,
-}
-
-impl<'a, E, Ix: IndexType> Clone for EdgeReference<'a, E, Ix> {
-    fn clone(&self) -> Self {
-        *self
-    }
-}
-
-impl<'a, E, Ix: IndexType> Copy for EdgeReference<'a, E, Ix> {}
-
-impl<'a, E, Ix: IndexType> PartialEq for EdgeReference<'a, E, Ix>
-where
-    E: PartialEq,
-{
-    fn eq(&self, rhs: &Self) -> bool {
-        self.index == rhs.index && self.weight == rhs.weight
-    }
-}
-
-impl<'a, Ix, E> EdgeReference<'a, E, Ix>
-where
-    Ix: IndexType,
-{
-    /// Access the edge’s weight.
-    ///
-    /// **NOTE** that this method offers a longer lifetime
-    /// than the trait (unfortunately they don't match yet).
-    pub fn weight(&self) -> &'a E {
-        self.weight
-    }
-}
-
-impl<'a, Ix, E> EdgeRef for EdgeReference<'a, E, Ix>
-where
-    Ix: IndexType,
-{
-    type NodeId = NodeIndex<Ix>;
-    type EdgeId = EdgeIndex<Ix>;
-    type Weight = E;
-
-    fn source(&self) -> Self::NodeId {
-        self.node[0]
-    }
-    fn target(&self) -> Self::NodeId {
-        self.node[1]
-    }
-    fn weight(&self) -> &E {
-        self.weight
-    }
-    fn id(&self) -> Self::EdgeId {
-        self.index
-    }
-}
-
-impl<'a, N, E, Ty, Ix> IntoEdges for &'a StableGraph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    type Edges = Edges<'a, E, Ty, Ix>;
-    fn edges(self, a: Self::NodeId) -> Self::Edges {
-        self.edges(a)
-    }
-}
-
-impl<'a, N, E, Ty, Ix> IntoEdgesDirected for &'a StableGraph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    type EdgesDirected = Edges<'a, E, Ty, Ix>;
-    fn edges_directed(self, a: Self::NodeId, dir: Direction) -> Self::EdgesDirected {
-        self.edges_directed(a, dir)
-    }
-}
-
-/// Iterator over the edges of from or to a node
-pub struct Edges<'a, E: 'a, Ty, Ix: 'a = DefaultIx>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    /// starting node to skip over
-    skip_start: NodeIndex<Ix>,
-    edges: &'a [Edge<Option<E>, Ix>],
-
-    /// Next edge to visit.
-    next: [EdgeIndex<Ix>; 2],
-
-    /// For directed graphs: the direction to iterate in
-    /// For undirected graphs: the direction of edges
-    direction: Direction,
-    ty: PhantomData<Ty>,
-}
-
-impl<'a, E, Ty, Ix> Iterator for Edges<'a, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    type Item = EdgeReference<'a, E, Ix>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        //      type        direction    |    iterate over    reverse
-        //                               |
-        //    Directed      Outgoing     |      outgoing        no
-        //    Directed      Incoming     |      incoming        no
-        //   Undirected     Outgoing     |        both       incoming
-        //   Undirected     Incoming     |        both       outgoing
-
-        // For iterate_over, "both" is represented as None.
-        // For reverse, "no" is represented as None.
-        let (iterate_over, reverse) = if Ty::is_directed() {
-            (Some(self.direction), None)
-        } else {
-            (None, Some(self.direction.opposite()))
-        };
-
-        if iterate_over.unwrap_or(Outgoing) == Outgoing {
-            let i = self.next[0].index();
-            if let Some(Edge {
-                node,
-                weight: Some(weight),
-                next,
-            }) = self.edges.get(i)
-            {
-                self.next[0] = next[0];
-                return Some(EdgeReference {
-                    index: edge_index(i),
-                    node: if reverse == Some(Outgoing) {
-                        swap_pair(*node)
-                    } else {
-                        *node
-                    },
-                    weight,
-                });
-            }
-        }
-
-        if iterate_over.unwrap_or(Incoming) == Incoming {
-            while let Some(Edge { node, weight, next }) = self.edges.get(self.next[1].index()) {
-                debug_assert!(weight.is_some());
-                let edge_index = self.next[1];
-                self.next[1] = next[1];
-                // In any of the "both" situations, self-loops would be iterated over twice.
-                // Skip them here.
-                if iterate_over.is_none() && node[0] == self.skip_start {
-                    continue;
-                }
-
-                return Some(EdgeReference {
-                    index: edge_index,
-                    node: if reverse == Some(Incoming) {
-                        swap_pair(*node)
-                    } else {
-                        *node
-                    },
-                    weight: weight.as_ref().unwrap(),
-                });
-            }
-        }
-
-        None
-    }
-}
-
-fn swap_pair<T>(mut x: [T; 2]) -> [T; 2] {
-    x.swap(0, 1);
-    x
-}
-
-impl<'a, N: 'a, E: 'a, Ty, Ix> IntoEdgeReferences for &'a StableGraph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    type EdgeRef = EdgeReference<'a, E, Ix>;
-    type EdgeReferences = EdgeReferences<'a, E, Ix>;
-
-    /// Create an iterator over all edges in the graph, in indexed order.
-    ///
-    /// Iterator element type is `EdgeReference<E, Ix>`.
-    fn edge_references(self) -> Self::EdgeReferences {
-        EdgeReferences {
-            iter: self.g.edges.iter().enumerate(),
-        }
-    }
-}
-
-/// Iterator over all edges of a graph.
-pub struct EdgeReferences<'a, E: 'a, Ix: 'a = DefaultIx> {
-    iter: iter::Enumerate<slice::Iter<'a, Edge<Option<E>, Ix>>>,
-}
-
-impl<'a, E, Ix> Iterator for EdgeReferences<'a, E, Ix>
-where
-    Ix: IndexType,
-{
-    type Item = EdgeReference<'a, E, Ix>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        self.iter.ex_find_map(|(i, edge)| {
-            edge.weight.as_ref().map(move |weight| EdgeReference {
-                index: edge_index(i),
-                node: edge.node,
-                weight,
-            })
-        })
-    }
-}
-
-impl<'a, E, Ix> DoubleEndedIterator for EdgeReferences<'a, E, Ix>
-where
-    Ix: IndexType,
-{
-    fn next_back(&mut self) -> Option<Self::Item> {
-        self.iter.ex_rfind_map(|(i, edge)| {
-            edge.weight.as_ref().map(move |weight| EdgeReference {
-                index: edge_index(i),
-                node: edge.node,
-                weight,
-            })
-        })
-    }
-}
-
-/// An iterator over either the nodes without edges to them or from them.
-pub struct Externals<'a, N: 'a, Ty, Ix: IndexType = DefaultIx> {
-    iter: iter::Enumerate<slice::Iter<'a, Node<Option<N>, Ix>>>,
-    dir: Direction,
-    ty: PhantomData<Ty>,
-}
-
-impl<'a, N: 'a, Ty, Ix> Iterator for Externals<'a, N, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    type Item = NodeIndex<Ix>;
-    fn next(&mut self) -> Option<NodeIndex<Ix>> {
-        let k = self.dir.index();
-        loop {
-            match self.iter.next() {
-                None => return None,
-                Some((index, node)) => {
-                    if node.weight.is_some()
-                        && node.next[k] == EdgeIndex::end()
-                        && (Ty::is_directed() || node.next[1 - k] == EdgeIndex::end())
-                    {
-                        return Some(NodeIndex::new(index));
-                    } else {
-                        continue;
-                    }
-                }
-            }
-        }
-    }
-}
-
-/// Iterator over the neighbors of a node.
-///
-/// Iterator element type is `NodeIndex`.
-pub struct Neighbors<'a, E: 'a, Ix: 'a = DefaultIx> {
-    /// starting node to skip over
-    skip_start: NodeIndex<Ix>,
-    edges: &'a [Edge<Option<E>, Ix>],
-    next: [EdgeIndex<Ix>; 2],
-}
-
-impl<'a, E, Ix> Neighbors<'a, E, Ix>
-where
-    Ix: IndexType,
-{
-    /// Return a “walker” object that can be used to step through the
-    /// neighbors and edges from the origin node.
-    ///
-    /// Note: The walker does not borrow from the graph, this is to allow mixing
-    /// edge walking with mutating the graph's weights.
-    pub fn detach(&self) -> WalkNeighbors<Ix> {
-        WalkNeighbors {
-            inner: super::WalkNeighbors {
-                skip_start: self.skip_start,
-                next: self.next,
-            },
-        }
-    }
-}
-
-impl<'a, E, Ix> Iterator for Neighbors<'a, E, Ix>
-where
-    Ix: IndexType,
-{
-    type Item = NodeIndex<Ix>;
-
-    fn next(&mut self) -> Option<NodeIndex<Ix>> {
-        // First any outgoing edges
-        match self.edges.get(self.next[0].index()) {
-            None => {}
-            Some(edge) => {
-                debug_assert!(edge.weight.is_some());
-                self.next[0] = edge.next[0];
-                return Some(edge.node[1]);
-            }
-        }
-        // Then incoming edges
-        // For an "undirected" iterator (traverse both incoming
-        // and outgoing edge lists), make sure we don't double
-        // count selfloops by skipping them in the incoming list.
-        while let Some(edge) = self.edges.get(self.next[1].index()) {
-            debug_assert!(edge.weight.is_some());
-            self.next[1] = edge.next[1];
-            if edge.node[0] != self.skip_start {
-                return Some(edge.node[0]);
-            }
-        }
-        None
-    }
-}
-
-/// A “walker” object that can be used to step through the edge list of a node.
-///
-/// See [*.detach()*](struct.Neighbors.html#method.detach) for more information.
-///
-/// The walker does not borrow from the graph, so it lets you step through
-/// neighbors or incident edges while also mutating graph weights, as
-/// in the following example:
-///
-/// ```
-/// use petgraph::visit::Dfs;
-/// use petgraph::Incoming;
-/// use petgraph::stable_graph::StableGraph;
-///
-/// let mut gr = StableGraph::new();
-/// let a = gr.add_node(0.);
-/// let b = gr.add_node(0.);
-/// let c = gr.add_node(0.);
-/// gr.add_edge(a, b, 3.);
-/// gr.add_edge(b, c, 2.);
-/// gr.add_edge(c, b, 1.);
-///
-/// // step through the graph and sum incoming edges into the node weight
-/// let mut dfs = Dfs::new(&gr, a);
-/// while let Some(node) = dfs.next(&gr) {
-///     // use a detached neighbors walker
-///     let mut edges = gr.neighbors_directed(node, Incoming).detach();
-///     while let Some(edge) = edges.next_edge(&gr) {
-///         gr[node] += gr[edge];
-///     }
-/// }
-///
-/// // check the result
-/// assert_eq!(gr[a], 0.);
-/// assert_eq!(gr[b], 4.);
-/// assert_eq!(gr[c], 2.);
-/// ```
-pub struct WalkNeighbors<Ix> {
-    inner: super::WalkNeighbors<Ix>,
-}
-
-impl<Ix: IndexType> Clone for WalkNeighbors<Ix> {
-    clone_fields!(WalkNeighbors, inner);
-}
-
-impl<Ix: IndexType> WalkNeighbors<Ix> {
-    /// Step to the next edge and its endpoint node in the walk for graph `g`.
-    ///
-    /// The next node indices are always the others than the starting point
-    /// where the `WalkNeighbors` value was created.
-    /// For an `Outgoing` walk, the target nodes,
-    /// for an `Incoming` walk, the source nodes of the edge.
-    pub fn next<N, E, Ty: EdgeType>(
-        &mut self,
-        g: &StableGraph<N, E, Ty, Ix>,
-    ) -> Option<(EdgeIndex<Ix>, NodeIndex<Ix>)> {
-        self.inner.next(&g.g)
-    }
-
-    pub fn next_node<N, E, Ty: EdgeType>(
-        &mut self,
-        g: &StableGraph<N, E, Ty, Ix>,
-    ) -> Option<NodeIndex<Ix>> {
-        self.next(g).map(|t| t.1)
-    }
-
-    pub fn next_edge<N, E, Ty: EdgeType>(
-        &mut self,
-        g: &StableGraph<N, E, Ty, Ix>,
-    ) -> Option<EdgeIndex<Ix>> {
-        self.next(g).map(|t| t.0)
-    }
-}
-
-/// Iterator over the node indices of a graph.
-pub struct NodeIndices<'a, N: 'a, Ix: 'a = DefaultIx> {
-    iter: iter::Enumerate<slice::Iter<'a, Node<Option<N>, Ix>>>,
-}
-
-impl<'a, N, Ix: IndexType> Iterator for NodeIndices<'a, N, Ix> {
-    type Item = NodeIndex<Ix>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        self.iter.ex_find_map(|(i, node)| {
-            if node.weight.is_some() {
-                Some(node_index(i))
-            } else {
-                None
-            }
-        })
-    }
-
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        let (_, hi) = self.iter.size_hint();
-        (0, hi)
-    }
-}
-
-impl<'a, N, Ix: IndexType> DoubleEndedIterator for NodeIndices<'a, N, Ix> {
-    fn next_back(&mut self) -> Option<Self::Item> {
-        self.iter.ex_rfind_map(|(i, node)| {
-            if node.weight.is_some() {
-                Some(node_index(i))
-            } else {
-                None
-            }
-        })
-    }
-}
-
-impl<N, E, Ty, Ix> NodeIndexable for StableGraph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType,
-{
-    /// Return an upper bound of the node indices in the graph
-    fn node_bound(&self) -> usize {
-        self.node_indices().next_back().map_or(0, |i| i.index() + 1)
-    }
-    fn to_index(&self, ix: NodeIndex<Ix>) -> usize {
-        ix.index()
-    }
-    fn from_index(&self, ix: usize) -> Self::NodeId {
-        NodeIndex::new(ix)
-    }
-}
-
-/// Iterator over the edge indices of a graph.
-pub struct EdgeIndices<'a, E: 'a, Ix: 'a = DefaultIx> {
-    iter: iter::Enumerate<slice::Iter<'a, Edge<Option<E>, Ix>>>,
-}
-
-impl<'a, E, Ix: IndexType> Iterator for EdgeIndices<'a, E, Ix> {
-    type Item = EdgeIndex<Ix>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        self.iter.ex_find_map(|(i, node)| {
-            if node.weight.is_some() {
-                Some(edge_index(i))
-            } else {
-                None
-            }
-        })
-    }
-
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        let (_, hi) = self.iter.size_hint();
-        (0, hi)
-    }
-}
-
-impl<'a, E, Ix: IndexType> DoubleEndedIterator for EdgeIndices<'a, E, Ix> {
-    fn next_back(&mut self) -> Option<Self::Item> {
-        self.iter.ex_rfind_map(|(i, node)| {
-            if node.weight.is_some() {
-                Some(edge_index(i))
-            } else {
-                None
-            }
-        })
-    }
-}
-
-#[test]
-fn stable_graph() {
-    let mut gr = StableGraph::<_, _>::with_capacity(0, 0);
-    let a = gr.add_node(0);
-    let b = gr.add_node(1);
-    let c = gr.add_node(2);
-    let _ed = gr.add_edge(a, b, 1);
-    println!("{:?}", gr);
-    gr.remove_node(b);
-    println!("{:?}", gr);
-    let d = gr.add_node(3);
-    println!("{:?}", gr);
-    gr.check_free_lists();
-    gr.remove_node(a);
-    gr.check_free_lists();
-    gr.remove_node(c);
-    gr.check_free_lists();
-    println!("{:?}", gr);
-    gr.add_edge(d, d, 2);
-    println!("{:?}", gr);
-
-    let e = gr.add_node(4);
-    gr.add_edge(d, e, 3);
-    println!("{:?}", gr);
-    for neigh in gr.neighbors(d) {
-        println!("edge {:?} -> {:?}", d, neigh);
-    }
-    gr.check_free_lists();
-}
-
-#[test]
-fn dfs() {
-    use crate::visit::Dfs;
-
-    let mut gr = StableGraph::<_, _>::with_capacity(0, 0);
-    let a = gr.add_node("a");
-    let b = gr.add_node("b");
-    let c = gr.add_node("c");
-    let d = gr.add_node("d");
-    gr.add_edge(a, b, 1);
-    gr.add_edge(a, c, 2);
-    gr.add_edge(b, c, 3);
-    gr.add_edge(b, d, 4);
-    gr.add_edge(c, d, 5);
-    gr.add_edge(d, b, 6);
-    gr.add_edge(c, b, 7);
-    println!("{:?}", gr);
-
-    let mut dfs = Dfs::new(&gr, a);
-    while let Some(next) = dfs.next(&gr) {
-        println!("dfs visit => {:?}, weight={:?}", next, &gr[next]);
-    }
-}
-
-#[test]
-fn test_retain_nodes() {
-    let mut gr = StableGraph::<_, _>::with_capacity(6, 6);
-    let a = gr.add_node("a");
-    let f = gr.add_node("f");
-    let b = gr.add_node("b");
-    let c = gr.add_node("c");
-    let d = gr.add_node("d");
-    let e = gr.add_node("e");
-    gr.add_edge(a, b, 1);
-    gr.add_edge(a, c, 2);
-    gr.add_edge(b, c, 3);
-    gr.add_edge(b, d, 4);
-    gr.add_edge(c, d, 5);
-    gr.add_edge(d, b, 6);
-    gr.add_edge(c, b, 7);
-    gr.add_edge(d, e, 8);
-    gr.remove_node(f);
-
-    assert_eq!(gr.node_count(), 5);
-    assert_eq!(gr.edge_count(), 8);
-    gr.retain_nodes(|frozen_gr, ix| frozen_gr[ix] >= "c");
-    assert_eq!(gr.node_count(), 3);
-    assert_eq!(gr.edge_count(), 2);
-
-    gr.check_free_lists();
-}
diff --git a/vendor/petgraph/src/graph_impl/stable_graph/serialization.rs b/vendor/petgraph/src/graph_impl/stable_graph/serialization.rs
deleted file mode 100644
index c24ca636b..000000000
--- a/vendor/petgraph/src/graph_impl/stable_graph/serialization.rs
+++ /dev/null
@@ -1,296 +0,0 @@
-use serde::de::Error;
-use serde::{Deserialize, Deserializer, Serialize, Serializer};
-
-use std::marker::PhantomData;
-
-use crate::prelude::*;
-
-use crate::graph::Node;
-use crate::graph::{Edge, IndexType};
-use crate::serde_utils::CollectSeqWithLength;
-use crate::serde_utils::MappedSequenceVisitor;
-use crate::serde_utils::{FromDeserialized, IntoSerializable};
-use crate::stable_graph::StableGraph;
-use crate::util::rev;
-use crate::visit::NodeIndexable;
-use crate::EdgeType;
-
-use super::super::serialization::{invalid_length_err, invalid_node_err, EdgeProperty};
-
-// Serialization representation for StableGraph
-// Keep in sync with deserialization and Graph
-#[derive(Serialize)]
-#[serde(rename = "Graph")]
-#[serde(bound(serialize = "N: Serialize, E: Serialize, Ix: IndexType + Serialize"))]
-pub struct SerStableGraph<'a, N: 'a, E: 'a, Ix: 'a + IndexType> {
-    nodes: Somes<&'a [Node<Option<N>, Ix>]>,
-    node_holes: Holes<&'a [Node<Option<N>, Ix>]>,
-    edge_property: EdgeProperty,
-    #[serde(serialize_with = "ser_stable_graph_edges")]
-    edges: &'a [Edge<Option<E>, Ix>],
-}
-
-// Deserialization representation for StableGraph
-// Keep in sync with serialization and Graph
-#[derive(Deserialize)]
-#[serde(rename = "Graph")]
-#[serde(bound(
-    deserialize = "N: Deserialize<'de>, E: Deserialize<'de>, Ix: IndexType + Deserialize<'de>"
-))]
-pub struct DeserStableGraph<N, E, Ix> {
-    #[serde(deserialize_with = "deser_stable_graph_nodes")]
-    nodes: Vec<Node<Option<N>, Ix>>,
-    #[serde(default = "Vec::new")]
-    node_holes: Vec<NodeIndex<Ix>>,
-    edge_property: EdgeProperty,
-    #[serde(deserialize_with = "deser_stable_graph_edges")]
-    edges: Vec<Edge<Option<E>, Ix>>,
-}
-
-/// `Somes` are the present node weights N, with known length.
-struct Somes<T>(usize, T);
-
-impl<'a, N, Ix> Serialize for Somes<&'a [Node<Option<N>, Ix>]>
-where
-    N: Serialize,
-{
-    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
-    where
-        S: Serializer,
-    {
-        serializer.collect_seq_with_length(
-            self.0,
-            self.1.iter().filter_map(|node| node.weight.as_ref()),
-        )
-    }
-}
-
-/// Holes are the node indices of vacancies, with known length
-struct Holes<T>(usize, T);
-
-impl<'a, N, Ix> Serialize for Holes<&'a [Node<Option<N>, Ix>]>
-where
-    Ix: Serialize + IndexType,
-{
-    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
-    where
-        S: Serializer,
-    {
-        serializer.collect_seq_with_length(
-            self.0,
-            self.1.iter().enumerate().filter_map(|(i, node)| {
-                if node.weight.is_none() {
-                    Some(NodeIndex::<Ix>::new(i))
-                } else {
-                    None
-                }
-            }),
-        )
-    }
-}
-
-fn ser_stable_graph_edges<S, E, Ix>(
-    edges: &&[Edge<Option<E>, Ix>],
-    serializer: S,
-) -> Result<S::Ok, S::Error>
-where
-    S: Serializer,
-    E: Serialize,
-    Ix: Serialize + IndexType,
-{
-    serializer.collect_seq_exact(edges.iter().map(|edge| {
-        edge.weight
-            .as_ref()
-            .map(|w| (edge.source(), edge.target(), w))
-    }))
-}
-
-fn deser_stable_graph_nodes<'de, D, N, Ix>(
-    deserializer: D,
-) -> Result<Vec<Node<Option<N>, Ix>>, D::Error>
-where
-    D: Deserializer<'de>,
-    N: Deserialize<'de>,
-    Ix: IndexType + Deserialize<'de>,
-{
-    deserializer.deserialize_seq(MappedSequenceVisitor::new(|n| {
-        Ok(Node {
-            weight: Some(n),
-            next: [EdgeIndex::end(); 2],
-        })
-    }))
-}
-
-fn deser_stable_graph_edges<'de, D, N, Ix>(
-    deserializer: D,
-) -> Result<Vec<Edge<Option<N>, Ix>>, D::Error>
-where
-    D: Deserializer<'de>,
-    N: Deserialize<'de>,
-    Ix: IndexType + Deserialize<'de>,
-{
-    deserializer.deserialize_seq(MappedSequenceVisitor::<
-        Option<(NodeIndex<Ix>, NodeIndex<Ix>, N)>,
-        _,
-        _,
-    >::new(|x| {
-        if let Some((i, j, w)) = x {
-            Ok(Edge {
-                weight: Some(w),
-                node: [i, j],
-                next: [EdgeIndex::end(); 2],
-            })
-        } else {
-            Ok(Edge {
-                weight: None,
-                node: [NodeIndex::end(); 2],
-                next: [EdgeIndex::end(); 2],
-            })
-        }
-    }))
-}
-
-impl<'a, N, E, Ty, Ix> IntoSerializable for &'a StableGraph<N, E, Ty, Ix>
-where
-    Ix: IndexType,
-    Ty: EdgeType,
-{
-    type Output = SerStableGraph<'a, N, E, Ix>;
-    fn into_serializable(self) -> Self::Output {
-        let nodes = &self.raw_nodes()[..self.node_bound()];
-        let node_count = self.node_count();
-        let hole_count = nodes.len() - node_count;
-        let edges = &self.raw_edges()[..self.edge_bound()];
-        SerStableGraph {
-            nodes: Somes(node_count, nodes),
-            node_holes: Holes(hole_count, nodes),
-            edges: edges,
-            edge_property: EdgeProperty::from(PhantomData::<Ty>),
-        }
-    }
-}
-
-/// Requires crate feature `"serde-1"`
-impl<N, E, Ty, Ix> Serialize for StableGraph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType + Serialize,
-    N: Serialize,
-    E: Serialize,
-{
-    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
-    where
-        S: Serializer,
-    {
-        self.into_serializable().serialize(serializer)
-    }
-}
-
-impl<'a, N, E, Ty, Ix> FromDeserialized for StableGraph<N, E, Ty, Ix>
-where
-    Ix: IndexType,
-    Ty: EdgeType,
-{
-    type Input = DeserStableGraph<N, E, Ix>;
-    fn from_deserialized<E2>(input: Self::Input) -> Result<Self, E2>
-    where
-        E2: Error,
-    {
-        let ty = PhantomData::<Ty>::from_deserialized(input.edge_property)?;
-        let mut nodes = input.nodes;
-        let node_holes = input.node_holes;
-        let edges = input.edges;
-        if edges.len() >= <Ix as IndexType>::max().index() {
-            Err(invalid_length_err::<Ix, _>("edge", edges.len()))?
-        }
-
-        // insert Nones for each hole
-        let mut offset = node_holes.len();
-        let node_bound = node_holes.len() + nodes.len();
-        for hole_pos in rev(node_holes) {
-            offset -= 1;
-            if hole_pos.index() >= node_bound {
-                Err(invalid_node_err(hole_pos.index(), node_bound))?;
-            }
-            let insert_pos = hole_pos.index() - offset;
-            nodes.insert(
-                insert_pos,
-                Node {
-                    weight: None,
-                    next: [EdgeIndex::end(); 2],
-                },
-            );
-        }
-
-        if nodes.len() >= <Ix as IndexType>::max().index() {
-            Err(invalid_length_err::<Ix, _>("node", nodes.len()))?
-        }
-
-        let node_bound = nodes.len();
-        let mut sgr = StableGraph {
-            g: Graph {
-                nodes: nodes,
-                edges: edges,
-                ty: ty,
-            },
-            node_count: 0,
-            edge_count: 0,
-            free_edge: EdgeIndex::end(),
-            free_node: NodeIndex::end(),
-        };
-        sgr.link_edges()
-            .map_err(|i| invalid_node_err(i.index(), node_bound))?;
-        Ok(sgr)
-    }
-}
-
-/// Requires crate feature `"serde-1"`
-impl<'de, N, E, Ty, Ix> Deserialize<'de> for StableGraph<N, E, Ty, Ix>
-where
-    Ty: EdgeType,
-    Ix: IndexType + Deserialize<'de>,
-    N: Deserialize<'de>,
-    E: Deserialize<'de>,
-{
-    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
-    where
-        D: Deserializer<'de>,
-    {
-        Self::from_deserialized(DeserStableGraph::deserialize(deserializer)?)
-    }
-}
-
-#[test]
-fn test_from_deserialized_with_holes() {
-    use crate::graph::node_index;
-    use crate::stable_graph::StableUnGraph;
-    use itertools::assert_equal;
-    use serde::de::value::Error as SerdeError;
-
-    let input = DeserStableGraph::<_, (), u32> {
-        nodes: vec![
-            Node {
-                weight: Some(1),
-                next: [EdgeIndex::end(); 2],
-            },
-            Node {
-                weight: Some(4),
-                next: [EdgeIndex::end(); 2],
-            },
-            Node {
-                weight: Some(5),
-                next: [EdgeIndex::end(); 2],
-            },
-        ],
-        node_holes: vec![node_index(0), node_index(2), node_index(3), node_index(6)],
-        edges: vec![],
-        edge_property: EdgeProperty::Undirected,
-    };
-    let graph = StableUnGraph::from_deserialized::<SerdeError>(input).unwrap();
-
-    assert_eq!(graph.node_count(), 3);
-    assert_equal(
-        graph.raw_nodes().iter().map(|n| n.weight.as_ref().cloned()),
-        vec![None, Some(1), None, None, Some(4), Some(5), None],
-    );
-}