Auto merge of #24209 - nikomatsakis:refactor-unification, r=nrc

I'm on a quest to slowly refactor a lot of the inference code. A first step for that is moving the "pure data structures" out so as to simplify what's left. This PR moves `snapshot_vec`, `graph`, and `unify` into their own crate (`librustc_data_structures`). They can then be unit-tested, benchmarked, etc more easily. As a benefit, I improved the performance of unification slightly on the benchmark I added vs the original code.

r? @nrc 

12 files changed, 75 insertions, 1043 deletions

diff --git a/src/librustc/lib.rs b/src/librustc/lib.rs
index a4bb17bc354..ab5c4e76966 100644
--- a/src/librustc/lib.rs
+++ b/src/librustc/lib.rs
@@ -54,6 +54,7 @@ extern crate graphviz;
 extern crate libc;
 extern crate rustc_llvm;
 extern crate rustc_back;
+extern crate rustc_data_structures;
 extern crate serialize;
 extern crate rbml;
 extern crate collections;
@@ -103,7 +104,6 @@ pub mod middle {
     pub mod entry;
     pub mod expr_use_visitor;
     pub mod fast_reject;
-    pub mod graph;
     pub mod intrinsicck;
     pub mod infer;
     pub mod lang_items;
@@ -141,7 +141,6 @@ pub mod util {
     pub mod common;
     pub mod ppaux;
     pub mod nodemap;
-    pub mod snapshot_vec;
     pub mod lev_distance;
 }
 
diff --git a/src/librustc/middle/cfg/construct.rs b/src/librustc/middle/cfg/construct.rs
index cbc2ef1535e..359a1a486c9 100644
--- a/src/librustc/middle/cfg/construct.rs
+++ b/src/librustc/middle/cfg/construct.rs
@@ -8,9 +8,9 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use rustc_data_structures::graph;
 use middle::cfg::*;
 use middle::def;
-use middle::graph;
 use middle::pat_util;
 use middle::region::CodeExtent;
 use middle::ty;
diff --git a/src/librustc/middle/cfg/mod.rs b/src/librustc/middle/cfg/mod.rs
index ad4fdcd7b83..3ca221c9630 100644
--- a/src/librustc/middle/cfg/mod.rs
+++ b/src/librustc/middle/cfg/mod.rs
@@ -11,7 +11,7 @@
 //! Module that constructs a control-flow graph representing an item.
 //! Uses `Graph` as the underlying representation.
 
-use middle::graph;
+use rustc_data_structures::graph;
 use middle::ty;
 use syntax::ast;
 
@@ -24,7 +24,7 @@ pub struct CFG {
     pub exit: CFGIndex,
 }
 
-#[derive(Copy, Clone, PartialEq)]
+#[derive(Copy, Clone, Debug, PartialEq)]
 pub enum CFGNodeData {
     AST(ast::NodeId),
     Entry,
@@ -43,6 +43,7 @@ impl CFGNodeData {
     }
 }
 
+#[derive(Debug)]
 pub struct CFGEdgeData {
     pub exiting_scopes: Vec<ast::NodeId>
 }
diff --git a/src/librustc/middle/dataflow.rs b/src/librustc/middle/dataflow.rs
index 41b4495c5f0..1d5d4f72fc2 100644
--- a/src/librustc/middle/dataflow.rs
+++ b/src/librustc/middle/dataflow.rs
@@ -576,10 +576,9 @@ impl<'a, 'b, 'tcx, O:DataFlowOperator> PropagationContext<'a, 'b, 'tcx, O> {
                                                pred_bits: &[usize],
                                                cfg: &cfg::CFG,
                                                cfgidx: CFGIndex) {
-        cfg.graph.each_outgoing_edge(cfgidx, |_e_idx, edge| {
+        for (_, edge) in cfg.graph.outgoing_edges(cfgidx) {
             self.propagate_bits_into_entry_set_for(pred_bits, edge);
-            true
-        });
+        }
     }
 
     fn propagate_bits_into_entry_set_for(&mut self,
diff --git a/src/librustc/middle/graph.rs b/src/librustc/middle/graph.rs
deleted file mode 100644
index a9ac61b49ec..00000000000
--- a/src/librustc/middle/graph.rs
+++ /dev/null
@@ -1,484 +0,0 @@
-// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-//! A graph module for use in dataflow, region resolution, and elsewhere.
-//!
-//! # Interface details
-//!
-//! You customize the graph by specifying a "node data" type `N` and an
-//! "edge data" type `E`. You can then later gain access (mutable or
-//! immutable) to these "user-data" bits. Currently, you can only add
-//! nodes or edges to the graph. You cannot remove or modify them once
-//! added. This could be changed if we have a need.
-//!
-//! # Implementation details
-//!
-//! The main tricky thing about this code is the way that edges are
-//! stored. The edges are stored in a central array, but they are also
-//! threaded onto two linked lists for each node, one for incoming edges
-//! and one for outgoing edges. Note that every edge is a member of some
-//! incoming list and some outgoing list.  Basically you can load the
-//! first index of the linked list from the node data structures (the
-//! field `first_edge`) and then, for each edge, load the next index from
-//! the field `next_edge`). Each of those fields is an array that should
-//! be indexed by the direction (see the type `Direction`).
-
-#![allow(dead_code)] // still WIP
-
-use std::fmt::{Formatter, Error, Debug};
-use std::usize;
-use std::collections::BitSet;
-
-pub struct Graph<N,E> {
-    nodes: Vec<Node<N>> ,
-    edges: Vec<Edge<E>> ,
-}
-
-pub struct Node<N> {
-    first_edge: [EdgeIndex; 2], // see module comment
-    pub data: N,
-}
-
-pub struct Edge<E> {
-    next_edge: [EdgeIndex; 2], // see module comment
-    source: NodeIndex,
-    target: NodeIndex,
-    pub data: E,
-}
-
-impl<E: Debug> Debug for Edge<E> {
-    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
-        write!(f, "Edge {{ next_edge: [{:?}, {:?}], source: {:?}, target: {:?}, data: {:?} }}",
-               self.next_edge[0], self.next_edge[1], self.source,
-               self.target, self.data)
-    }
-}
-
-#[derive(Clone, Copy, PartialEq, Debug)]
-pub struct NodeIndex(pub usize);
-#[allow(non_upper_case_globals)]
-pub const InvalidNodeIndex: NodeIndex = NodeIndex(usize::MAX);
-
-#[derive(Copy, Clone, PartialEq, Debug)]
-pub struct EdgeIndex(pub usize);
-#[allow(non_upper_case_globals)]
-pub const InvalidEdgeIndex: EdgeIndex = EdgeIndex(usize::MAX);
-
-// Use a private field here to guarantee no more instances are created:
-#[derive(Copy, Clone, Debug)]
-pub struct Direction { repr: usize }
-#[allow(non_upper_case_globals)]
-pub const Outgoing: Direction = Direction { repr: 0 };
-#[allow(non_upper_case_globals)]
-pub const Incoming: Direction = Direction { repr: 1 };
-
-impl NodeIndex {
-    fn get(&self) -> usize { let NodeIndex(v) = *self; v }
-    /// Returns unique id (unique with respect to the graph holding associated node).
-    pub fn node_id(&self) -> usize { self.get() }
-}
-
-impl EdgeIndex {
-    fn get(&self) -> usize { let EdgeIndex(v) = *self; v }
-    /// Returns unique id (unique with respect to the graph holding associated edge).
-    pub fn edge_id(&self) -> usize { self.get() }
-}
-
-impl<N,E> Graph<N,E> {
-    pub fn new() -> Graph<N,E> {
-        Graph {
-            nodes: Vec::new(),
-            edges: Vec::new(),
-        }
-    }
-
-    pub fn with_capacity(num_nodes: usize,
-                         num_edges: usize) -> Graph<N,E> {
-        Graph {
-            nodes: Vec::with_capacity(num_nodes),
-            edges: Vec::with_capacity(num_edges),
-        }
-    }
-
-    ///////////////////////////////////////////////////////////////////////////
-    // Simple accessors
-
-    #[inline]
-    pub fn all_nodes<'a>(&'a self) -> &'a [Node<N>] {
-        &self.nodes
-    }
-
-    #[inline]
-    pub fn all_edges<'a>(&'a self) -> &'a [Edge<E>] {
-        &self.edges
-    }
-
-    ///////////////////////////////////////////////////////////////////////////
-    // Node construction
-
-    pub fn next_node_index(&self) -> NodeIndex {
-        NodeIndex(self.nodes.len())
-    }
-
-    pub fn add_node(&mut self, data: N) -> NodeIndex {
-        let idx = self.next_node_index();
-        self.nodes.push(Node {
-            first_edge: [InvalidEdgeIndex, InvalidEdgeIndex],
-            data: data
-        });
-        idx
-    }
-
-    pub fn mut_node_data<'a>(&'a mut self, idx: NodeIndex) -> &'a mut N {
-        &mut self.nodes[idx.get()].data
-    }
-
-    pub fn node_data<'a>(&'a self, idx: NodeIndex) -> &'a N {
-        &self.nodes[idx.get()].data
-    }
-
-    pub fn node<'a>(&'a self, idx: NodeIndex) -> &'a Node<N> {
-        &self.nodes[idx.get()]
-    }
-
-    ///////////////////////////////////////////////////////////////////////////
-    // Edge construction and queries
-
-    pub fn next_edge_index(&self) -> EdgeIndex {
-        EdgeIndex(self.edges.len())
-    }
-
-    pub fn add_edge(&mut self,
-                    source: NodeIndex,
-                    target: NodeIndex,
-                    data: E) -> EdgeIndex {
-        let idx = self.next_edge_index();
-
-        // read current first of the list of edges from each node
-        let source_first = self.nodes[source.get()]
-                                     .first_edge[Outgoing.repr];
-        let target_first = self.nodes[target.get()]
-                                     .first_edge[Incoming.repr];
-
-        // create the new edge, with the previous firsts from each node
-        // as the next pointers
-        self.edges.push(Edge {
-            next_edge: [source_first, target_first],
-            source: source,
-            target: target,
-            data: data
-        });
-
-        // adjust the firsts for each node target be the next object.
-        self.nodes[source.get()].first_edge[Outgoing.repr] = idx;
-        self.nodes[target.get()].first_edge[Incoming.repr] = idx;
-
-        return idx;
-    }
-
-    pub fn mut_edge_data<'a>(&'a mut self, idx: EdgeIndex) -> &'a mut E {
-        &mut self.edges[idx.get()].data
-    }
-
-    pub fn edge_data<'a>(&'a self, idx: EdgeIndex) -> &'a E {
-        &self.edges[idx.get()].data
-    }
-
-    pub fn edge<'a>(&'a self, idx: EdgeIndex) -> &'a Edge<E> {
-        &self.edges[idx.get()]
-    }
-
-    pub fn first_adjacent(&self, node: NodeIndex, dir: Direction) -> EdgeIndex {
-        //! Accesses the index of the first edge adjacent to `node`.
-        //! This is useful if you wish to modify the graph while walking
-        //! the linked list of edges.
-
-        self.nodes[node.get()].first_edge[dir.repr]
-    }
-
-    pub fn next_adjacent(&self, edge: EdgeIndex, dir: Direction) -> EdgeIndex {
-        //! Accesses the next edge in a given direction.
-        //! This is useful if you wish to modify the graph while walking
-        //! the linked list of edges.
-
-        self.edges[edge.get()].next_edge[dir.repr]
-    }
-
-    ///////////////////////////////////////////////////////////////////////////
-    // Iterating over nodes, edges
-
-    pub fn each_node<'a, F>(&'a self, mut f: F) -> bool where
-        F: FnMut(NodeIndex, &'a Node<N>) -> bool,
-    {
-        //! Iterates over all edges defined in the graph.
-        self.nodes.iter().enumerate().all(|(i, node)| f(NodeIndex(i), node))
-    }
-
-    pub fn each_edge<'a, F>(&'a self, mut f: F) -> bool where
-        F: FnMut(EdgeIndex, &'a Edge<E>) -> bool,
-    {
-        //! Iterates over all edges defined in the graph
-        self.edges.iter().enumerate().all(|(i, edge)| f(EdgeIndex(i), edge))
-    }
-
-    pub fn each_outgoing_edge<'a, F>(&'a self, source: NodeIndex, f: F) -> bool where
-        F: FnMut(EdgeIndex, &'a Edge<E>) -> bool,
-    {
-        //! Iterates over all outgoing edges from the node `from`
-
-        self.each_adjacent_edge(source, Outgoing, f)
-    }
-
-    pub fn each_incoming_edge<'a, F>(&'a self, target: NodeIndex, f: F) -> bool where
-        F: FnMut(EdgeIndex, &'a Edge<E>) -> bool,
-    {
-        //! Iterates over all incoming edges to the node `target`
-
-        self.each_adjacent_edge(target, Incoming, f)
-    }
-
-    pub fn each_adjacent_edge<'a, F>(&'a self,
-                                     node: NodeIndex,
-                                     dir: Direction,
-                                     mut f: F)
-                                     -> bool where
-        F: FnMut(EdgeIndex, &'a Edge<E>) -> bool,
-    {
-        //! Iterates over all edges adjacent to the node `node`
-        //! in the direction `dir` (either `Outgoing` or `Incoming)
-
-        let mut edge_idx = self.first_adjacent(node, dir);
-        while edge_idx != InvalidEdgeIndex {
-            let edge = &self.edges[edge_idx.get()];
-            if !f(edge_idx, edge) {
-                return false;
-            }
-            edge_idx = edge.next_edge[dir.repr];
-        }
-        return true;
-    }
-
-    ///////////////////////////////////////////////////////////////////////////
-    // Fixed-point iteration
-    //
-    // A common use for graphs in our compiler is to perform
-    // fixed-point iteration. In this case, each edge represents a
-    // constraint, and the nodes themselves are associated with
-    // variables or other bitsets. This method facilitates such a
-    // computation.
-
-    pub fn iterate_until_fixed_point<'a, F>(&'a self, mut op: F) where
-        F: FnMut(usize, EdgeIndex, &'a Edge<E>) -> bool,
-    {
-        let mut iteration = 0;
-        let mut changed = true;
-        while changed {
-            changed = false;
-            iteration += 1;
-            for (i, edge) in self.edges.iter().enumerate() {
-                changed |= op(iteration, EdgeIndex(i), edge);
-            }
-        }
-    }
-
-    pub fn depth_traverse<'a>(&'a self, start: NodeIndex) -> DepthFirstTraversal<'a, N, E>  {
-        DepthFirstTraversal {
-            graph: self,
-            stack: vec![start],
-            visited: BitSet::new()
-        }
-    }
-}
-
-pub struct DepthFirstTraversal<'g, N:'g, E:'g> {
-    graph: &'g Graph<N, E>,
-    stack: Vec<NodeIndex>,
-    visited: BitSet
-}
-
-impl<'g, N, E> Iterator for DepthFirstTraversal<'g, N, E> {
-    type Item = &'g N;
-
-    fn next(&mut self) -> Option<&'g N> {
-        while let Some(idx) = self.stack.pop() {
-            if !self.visited.insert(idx.node_id()) {
-                continue;
-            }
-            self.graph.each_outgoing_edge(idx, |_, e| -> bool {
-                if !self.visited.contains(&e.target().node_id()) {
-                    self.stack.push(e.target());
-                }
-                true
-            });
-
-            return Some(self.graph.node_data(idx));
-        }
-
-        return None;
-    }
-}
-
-pub fn each_edge_index<F>(max_edge_index: EdgeIndex, mut f: F) where
-    F: FnMut(EdgeIndex) -> bool,
-{
-    let mut i = 0;
-    let n = max_edge_index.get();
-    while i < n {
-        if !f(EdgeIndex(i)) {
-            return;
-        }
-        i += 1;
-    }
-}
-
-impl<E> Edge<E> {
-    pub fn source(&self) -> NodeIndex {
-        self.source
-    }
-
-    pub fn target(&self) -> NodeIndex {
-        self.target
-    }
-}
-
-#[cfg(test)]
-mod test {
-    use middle::graph::*;
-    use std::fmt::Debug;
-
-    type TestNode = Node<&'static str>;
-    type TestEdge = Edge<&'static str>;
-    type TestGraph = Graph<&'static str, &'static str>;
-
-    fn create_graph() -> TestGraph {
-        let mut graph = Graph::new();
-
-        // Create a simple graph
-        //
-        //    A -+> B --> C
-        //       |  |     ^
-        //       |  v     |
-        //       F  D --> E
-
-        let a = graph.add_node("A");
-        let b = graph.add_node("B");
-        let c = graph.add_node("C");
-        let d = graph.add_node("D");
-        let e = graph.add_node("E");
-        let f = graph.add_node("F");
-
-        graph.add_edge(a, b, "AB");
-        graph.add_edge(b, c, "BC");
-        graph.add_edge(b, d, "BD");
-        graph.add_edge(d, e, "DE");
-        graph.add_edge(e, c, "EC");
-        graph.add_edge(f, b, "FB");
-
-        return graph;
-    }
-
-    #[test]
-    fn each_node() {
-        let graph = create_graph();
-        let expected = ["A", "B", "C", "D", "E", "F"];
-        graph.each_node(|idx, node| {
-            assert_eq!(&expected[idx.get()], graph.node_data(idx));
-            assert_eq!(expected[idx.get()], node.data);
-            true
-        });
-    }
-
-    #[test]
-    fn each_edge() {
-        let graph = create_graph();
-        let expected = ["AB", "BC", "BD", "DE", "EC", "FB"];
-        graph.each_edge(|idx, edge| {
-            assert_eq!(&expected[idx.get()], graph.edge_data(idx));
-            assert_eq!(expected[idx.get()], edge.data);
-            true
-        });
-    }
-
-    fn test_adjacent_edges<N:PartialEq+Debug,E:PartialEq+Debug>(graph: &Graph<N,E>,
-                                      start_index: NodeIndex,
-                                      start_data: N,
-                                      expected_incoming: &[(E,N)],
-                                      expected_outgoing: &[(E,N)]) {
-        assert!(graph.node_data(start_index) == &start_data);
-
-        let mut counter = 0;
-        graph.each_incoming_edge(start_index, |edge_index, edge| {
-            assert!(graph.edge_data(edge_index) == &edge.data);
-            assert!(counter < expected_incoming.len());
-            debug!("counter={:?} expected={:?} edge_index={:?} edge={:?}",
-                   counter, expected_incoming[counter], edge_index, edge);
-            match expected_incoming[counter] {
-                (ref e, ref n) => {
-                    assert!(e == &edge.data);
-                    assert!(n == graph.node_data(edge.source));
-                    assert!(start_index == edge.target);
-                }
-            }
-            counter += 1;
-            true
-        });
-        assert_eq!(counter, expected_incoming.len());
-
-        let mut counter = 0;
-        graph.each_outgoing_edge(start_index, |edge_index, edge| {
-            assert!(graph.edge_data(edge_index) == &edge.data);
-            assert!(counter < expected_outgoing.len());
-            debug!("counter={:?} expected={:?} edge_index={:?} edge={:?}",
-                   counter, expected_outgoing[counter], edge_index, edge);
-            match expected_outgoing[counter] {
-                (ref e, ref n) => {
-                    assert!(e == &edge.data);
-                    assert!(start_index == edge.source);
-                    assert!(n == graph.node_data(edge.target));
-                }
-            }
-            counter += 1;
-            true
-        });
-        assert_eq!(counter, expected_outgoing.len());
-    }
-
-    #[test]
-    fn each_adjacent_from_a() {
-        let graph = create_graph();
-        test_adjacent_edges(&graph, NodeIndex(0), "A",
-                            &[],
-                            &[("AB", "B")]);
-    }
-
-    #[test]
-    fn each_adjacent_from_b() {
-        let graph = create_graph();
-        test_adjacent_edges(&graph, NodeIndex(1), "B",
-                            &[("FB", "F"), ("AB", "A"),],
-                            &[("BD", "D"), ("BC", "C"),]);
-    }
-
-    #[test]
-    fn each_adjacent_from_c() {
-        let graph = create_graph();
-        test_adjacent_edges(&graph, NodeIndex(2), "C",
-                            &[("EC", "E"), ("BC", "B")],
-                            &[]);
-    }
-
-    #[test]
-    fn each_adjacent_from_d() {
-        let graph = create_graph();
-        test_adjacent_edges(&graph, NodeIndex(3), "D",
-                            &[("BD", "B")],
-                            &[("DE", "E")]);
-    }
-}
diff --git a/src/librustc/middle/infer/freshen.rs b/src/librustc/middle/infer/freshen.rs
index 29f74d12ea3..d93d13beec8 100644
--- a/src/librustc/middle/infer/freshen.rs
+++ b/src/librustc/middle/infer/freshen.rs
@@ -37,7 +37,7 @@ use middle::ty_fold::TypeFolder;
 use std::collections::hash_map::{self, Entry};
 
 use super::InferCtxt;
-use super::unify::ToType;
+use super::unify_key::ToType;
 
 pub struct TypeFreshener<'a, 'tcx:'a> {
     infcx: &'a InferCtxt<'a, 'tcx>,
diff --git a/src/librustc/middle/infer/mod.rs b/src/librustc/middle/infer/mod.rs
index 0f62b440bf3..b0921a266f3 100644
--- a/src/librustc/middle/infer/mod.rs
+++ b/src/librustc/middle/infer/mod.rs
@@ -29,6 +29,7 @@ use middle::ty::replace_late_bound_regions;
 use middle::ty::{self, Ty};
 use middle::ty_fold::{TypeFolder, TypeFoldable};
 use middle::ty_relate::{Relate, RelateResult, TypeRelation};
+use rustc_data_structures::unify::{self, UnificationTable};
 use std::cell::{RefCell};
 use std::fmt;
 use std::rc::Rc;
@@ -41,8 +42,8 @@ use util::ppaux::{Repr, UserString};
 
 use self::combine::CombineFields;
 use self::region_inference::{RegionVarBindings, RegionSnapshot};
-use self::unify::{ToType, UnificationTable};
 use self::error_reporting::ErrorReporting;
+use self::unify_key::ToType;
 
 pub mod bivariate;
 pub mod combine;
@@ -57,7 +58,7 @@ pub mod resolve;
 mod freshen;
 pub mod sub;
 pub mod type_variable;
-pub mod unify;
+pub mod unify_key;
 
 pub type Bound<T> = Option<T>;
 pub type UnitResult<'tcx> = RelateResult<'tcx, ()>; // "unify result"
diff --git a/src/librustc/middle/infer/region_inference/mod.rs b/src/librustc/middle/infer/region_inference/mod.rs
index c6be97e6dbe..e76468131e0 100644
--- a/src/librustc/middle/infer/region_inference/mod.rs
+++ b/src/librustc/middle/infer/region_inference/mod.rs
@@ -20,14 +20,13 @@ use self::Classification::*;
 
 use super::{RegionVariableOrigin, SubregionOrigin, TypeTrace, MiscVariable};
 
+use rustc_data_structures::graph::{self, Direction, NodeIndex};
 use middle::region;
 use middle::ty::{self, Ty};
 use middle::ty::{BoundRegion, FreeRegion, Region, RegionVid};
 use middle::ty::{ReEmpty, ReStatic, ReInfer, ReFree, ReEarlyBound};
 use middle::ty::{ReLateBound, ReScope, ReVar, ReSkolemized, BrFresh};
 use middle::ty_relate::RelateResult;
-use middle::graph;
-use middle::graph::{Direction, NodeIndex};
 use util::common::indenter;
 use util::nodemap::{FnvHashMap, FnvHashSet};
 use util::ppaux::{Repr, UserString};
@@ -1325,10 +1324,8 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
         let num_vars = self.num_vars();
 
         let constraints = self.constraints.borrow();
-        let num_edges = constraints.len();
 
-        let mut graph = graph::Graph::with_capacity(num_vars as usize + 1,
-                                                    num_edges);
+        let mut graph = graph::Graph::new();
 
         for _ in 0..num_vars {
             graph.add_node(());
@@ -1370,10 +1367,10 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
         // not contained by an upper-bound.
         let (mut lower_bounds, lower_dup) =
             self.collect_concrete_regions(graph, var_data, node_idx,
-                                          graph::Incoming, dup_vec);
+                                          graph::INCOMING, dup_vec);
         let (mut upper_bounds, upper_dup) =
             self.collect_concrete_regions(graph, var_data, node_idx,
-                                          graph::Outgoing, dup_vec);
+                                          graph::OUTGOING, dup_vec);
 
         if lower_dup || upper_dup {
             return;
@@ -1433,7 +1430,7 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
         // that have no intersection.
         let (upper_bounds, dup_found) =
             self.collect_concrete_regions(graph, var_data, node_idx,
-                                          graph::Outgoing, dup_vec);
+                                          graph::OUTGOING, dup_vec);
 
         if dup_found {
             return;
@@ -1508,8 +1505,8 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
             // figure out the direction from which this node takes its
             // values, and search for concrete regions etc in that direction
             let dir = match classification {
-                Expanding => graph::Incoming,
-                Contracting => graph::Outgoing,
+                Expanding => graph::INCOMING,
+                Contracting => graph::OUTGOING,
             };
 
             process_edges(self, &mut state, graph, node_idx, dir);
@@ -1519,14 +1516,14 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
         return (result, dup_found);
 
         fn process_edges<'a, 'tcx>(this: &RegionVarBindings<'a, 'tcx>,
-                         state: &mut WalkState<'tcx>,
-                         graph: &RegionGraph,
-                         source_vid: RegionVid,
-                         dir: Direction) {
+                                   state: &mut WalkState<'tcx>,
+                                   graph: &RegionGraph,
+                                   source_vid: RegionVid,
+                                   dir: Direction) {
             debug!("process_edges(source_vid={:?}, dir={:?})", source_vid, dir);
 
             let source_node_index = NodeIndex(source_vid.index as usize);
-            graph.each_adjacent_edge(source_node_index, dir, |_, edge| {
+            for (_, edge) in graph.adjacent_edges(source_node_index, dir) {
                 match edge.data {
                     ConstrainVarSubVar(from_vid, to_vid) => {
                         let opp_vid =
@@ -1544,8 +1541,7 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
                         });
                     }
                 }
-                true
-            });
+            }
         }
     }
 
diff --git a/src/librustc/middle/infer/type_variable.rs b/src/librustc/middle/infer/type_variable.rs
index 03612a6c1ae..b3e3e016d85 100644
--- a/src/librustc/middle/infer/type_variable.rs
+++ b/src/librustc/middle/infer/type_variable.rs
@@ -17,7 +17,7 @@ use std::cmp::min;
 use std::marker::PhantomData;
 use std::mem;
 use std::u32;
-use util::snapshot_vec as sv;
+use rustc_data_structures::snapshot_vec as sv;
 
 pub struct TypeVariableTable<'tcx> {
     values: sv::SnapshotVec<Delegate<'tcx>>,
@@ -65,7 +65,7 @@ impl RelationDir {
 
 impl<'tcx> TypeVariableTable<'tcx> {
     pub fn new() -> TypeVariableTable<'tcx> {
-        TypeVariableTable { values: sv::SnapshotVec::new(Delegate(PhantomData)) }
+        TypeVariableTable { values: sv::SnapshotVec::new() }
     }
 
     fn relations<'a>(&'a mut self, a: ty::TyVid) -> &'a mut Vec<Relation> {
@@ -201,9 +201,7 @@ impl<'tcx> sv::SnapshotVecDelegate for Delegate<'tcx> {
     type Value = TypeVariableData<'tcx>;
     type Undo = UndoEntry;
 
-    fn reverse(&mut self,
-               values: &mut Vec<TypeVariableData<'tcx>>,
-               action: UndoEntry) {
+    fn reverse(values: &mut Vec<TypeVariableData<'tcx>>, action: UndoEntry) {
         match action {
             SpecifyVar(vid, relations) => {
                 values[vid.index as usize].value = Bounded(relations);
diff --git a/src/librustc/middle/infer/unify.rs b/src/librustc/middle/infer/unify.rs
deleted file mode 100644
index 4bbced1d75c..00000000000
--- a/src/librustc/middle/infer/unify.rs
+++ /dev/null
@@ -1,340 +0,0 @@
-// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-pub use self::VarValue::*;
-
-use std::marker;
-
-use middle::ty::{IntVarValue};
-use middle::ty::{self, Ty};
-use std::fmt::Debug;
-use std::marker::PhantomData;
-use syntax::ast;
-use util::snapshot_vec as sv;
-
-/// This trait is implemented by any type that can serve as a type
-/// variable. We call such variables *unification keys*. For example,
-/// this trait is implemented by `IntVid`, which represents integral
-/// variables.
-///
-/// Each key type has an associated value type `V`. For example, for
-/// `IntVid`, this is `Option<IntVarValue>`, representing some
-/// (possibly not yet known) sort of integer.
-///
-/// Implementations of this trait are at the end of this file.
-pub trait UnifyKey : Clone + Debug + PartialEq {
-    type Value : UnifyValue;
-
-    fn index(&self) -> u32;
-
-    fn from_index(u: u32) -> Self;
-
-    fn tag(k: Option<Self>) -> &'static str;
-}
-
-/// Trait for valid types that a type variable can be set to. Note that
-/// this is typically not the end type that the value will take on, but
-/// rather an `Option` wrapper (where `None` represents a variable
-/// whose value is not yet set).
-///
-/// Implementations of this trait are at the end of this file.
-pub trait UnifyValue : Clone + PartialEq + Debug {
-}
-
-/// Value of a unification key. We implement Tarjan's union-find
-/// algorithm: when two keys are unified, one of them is converted
-/// into a "redirect" pointing at the other. These redirects form a
-/// DAG: the roots of the DAG (nodes that are not redirected) are each
-/// associated with a value of type `V` and a rank. The rank is used
-/// to keep the DAG relatively balanced, which helps keep the running
-/// time of the algorithm under control. For more information, see
-/// <http://en.wikipedia.org/wiki/Disjoint-set_data_structure>.
-#[derive(PartialEq,Clone,Debug)]
-pub enum VarValue<K:UnifyKey> {
-    Redirect(K),
-    Root(K::Value, usize),
-}
-
-/// Table of unification keys and their values.
-pub struct UnificationTable<K:UnifyKey> {
-    /// Indicates the current value of each key.
-    values: sv::SnapshotVec<Delegate<K>>,
-}
-
-/// At any time, users may snapshot a unification table.  The changes
-/// made during the snapshot may either be *committed* or *rolled back*.
-pub struct Snapshot<K:UnifyKey> {
-    // Link snapshot to the key type `K` of the table.
-    marker: marker::PhantomData<K>,
-    snapshot: sv::Snapshot,
-}
-
-/// Internal type used to represent the result of a `get()` operation.
-/// Conveys the current root and value of the key.
-pub struct Node<K:UnifyKey> {
-    pub key: K,
-    pub value: K::Value,
-    pub rank: usize,
-}
-
-#[derive(Copy, Clone)]
-pub struct Delegate<K>(PhantomData<K>);
-
-// We can't use V:LatticeValue, much as I would like to,
-// because frequently the pattern is that V=Option<U> for some
-// other type parameter U, and we have no way to say
-// Option<U>:LatticeValue.
-
-impl<K:UnifyKey> UnificationTable<K> {
-    pub fn new() -> UnificationTable<K> {
-        UnificationTable {
-            values: sv::SnapshotVec::new(Delegate(PhantomData)),
-        }
-    }
-
-    /// Starts a new snapshot. Each snapshot must be either
-    /// rolled back or committed in a "LIFO" (stack) order.
-    pub fn snapshot(&mut self) -> Snapshot<K> {
-        Snapshot { marker: marker::PhantomData::<K>,
-                   snapshot: self.values.start_snapshot() }
-    }
-
-    /// Reverses all changes since the last snapshot. Also
-    /// removes any keys that have been created since then.
-    pub fn rollback_to(&mut self, snapshot: Snapshot<K>) {
-        debug!("{}: rollback_to()", UnifyKey::tag(None::<K>));
-        self.values.rollback_to(snapshot.snapshot);
-    }
-
-    /// Commits all changes since the last snapshot. Of course, they
-    /// can still be undone if there is a snapshot further out.
-    pub fn commit(&mut self, snapshot: Snapshot<K>) {
-        debug!("{}: commit()", UnifyKey::tag(None::<K>));
-        self.values.commit(snapshot.snapshot);
-    }
-
-    pub fn new_key(&mut self, value: K::Value) -> K {
-        let index = self.values.push(Root(value, 0));
-        let k = UnifyKey::from_index(index as u32);
-        debug!("{}: created new key: {:?}",
-               UnifyKey::tag(None::<K>),
-               k);
-        k
-    }
-
-    /// Find the root node for `vid`. This uses the standard
-    /// union-find algorithm with path compression:
-    /// <http://en.wikipedia.org/wiki/Disjoint-set_data_structure>.
-    ///
-    /// NB. This is a building-block operation and you would probably
-    /// prefer to call `probe` below.
-    fn get(&mut self, vid: K) -> Node<K> {
-        let index = vid.index() as usize;
-        let value = (*self.values.get(index)).clone();
-        match value {
-            Redirect(redirect) => {
-                let node: Node<K> = self.get(redirect.clone());
-                if node.key != redirect {
-                    // Path compression
-                    self.values.set(index, Redirect(node.key.clone()));
-                }
-                node
-            }
-            Root(value, rank) => {
-                Node { key: vid, value: value, rank: rank }
-            }
-        }
-    }
-
-    fn is_root(&self, key: &K) -> bool {
-        let index = key.index() as usize;
-        match *self.values.get(index) {
-            Redirect(..) => false,
-            Root(..) => true,
-        }
-    }
-
-    /// Sets the value for `vid` to `new_value`. `vid` MUST be a root
-    /// node! This is an internal operation used to impl other things.
-    fn set(&mut self, key: K, new_value: VarValue<K>) {
-        assert!(self.is_root(&key));
-
-        debug!("Updating variable {:?} to {:?}",
-               key, new_value);
-
-        let index = key.index() as usize;
-        self.values.set(index, new_value);
-    }
-
-    /// Either redirects `node_a` to `node_b` or vice versa, depending
-    /// on the relative rank. The value associated with the new root
-    /// will be `new_value`.
-    ///
-    /// NB: This is the "union" operation of "union-find". It is
-    /// really more of a building block. If the values associated with
-    /// your key are non-trivial, you would probably prefer to call
-    /// `unify_var_var` below.
-    fn unify(&mut self, node_a: &Node<K>, node_b: &Node<K>, new_value: K::Value) {
-        debug!("unify(node_a(id={:?}, rank={:?}), node_b(id={:?}, rank={:?}))",
-               node_a.key,
-               node_a.rank,
-               node_b.key,
-               node_b.rank);
-
-        let (new_root, new_rank) = if node_a.rank > node_b.rank {
-            // a has greater rank, so a should become b's parent,
-            // i.e., b should redirect to a.
-            self.set(node_b.key.clone(), Redirect(node_a.key.clone()));
-            (node_a.key.clone(), node_a.rank)
-        } else if node_a.rank < node_b.rank {
-            // b has greater rank, so a should redirect to b.
-            self.set(node_a.key.clone(), Redirect(node_b.key.clone()));
-            (node_b.key.clone(), node_b.rank)
-        } else {
-            // If equal, redirect one to the other and increment the
-            // other's rank.
-            assert_eq!(node_a.rank, node_b.rank);
-            self.set(node_b.key.clone(), Redirect(node_a.key.clone()));
-            (node_a.key.clone(), node_a.rank + 1)
-        };
-
-        self.set(new_root, Root(new_value, new_rank));
-    }
-}
-
-impl<K:UnifyKey> sv::SnapshotVecDelegate for Delegate<K> {
-    type Value = VarValue<K>;
-    type Undo = ();
-
-    fn reverse(&mut self, _: &mut Vec<VarValue<K>>, _: ()) {
-        panic!("Nothing to reverse");
-    }
-}
-
-///////////////////////////////////////////////////////////////////////////
-// Code to handle keys which carry a value, like ints,
-// floats---anything that doesn't have a subtyping relationship we
-// need to worry about.
-
-impl<'tcx,K,V> UnificationTable<K>
-    where K: UnifyKey<Value=Option<V>>,
-          V: Clone+PartialEq,
-          Option<V>: UnifyValue,
-{
-    pub fn unify_var_var(&mut self,
-                         a_id: K,
-                         b_id: K)
-                         -> Result<(),(V,V)>
-    {
-        let node_a = self.get(a_id);
-        let node_b = self.get(b_id);
-        let a_id = node_a.key.clone();
-        let b_id = node_b.key.clone();
-
-        if a_id == b_id { return Ok(()); }
-
-        let combined = {
-            match (&node_a.value, &node_b.value) {
-                (&None, &None) => {
-                    None
-                }
-                (&Some(ref v), &None) | (&None, &Some(ref v)) => {
-                    Some(v.clone())
-                }
-                (&Some(ref v1), &Some(ref v2)) => {
-                    if *v1 != *v2 {
-                        return Err((v1.clone(), v2.clone()));
-                    }
-                    Some(v1.clone())
-                }
-            }
-        };
-
-        Ok(self.unify(&node_a, &node_b, combined))
-    }
-
-    /// Sets the value of the key `a_id` to `b`. Because simple keys do not have any subtyping
-    /// relationships, if `a_id` already has a value, it must be the same as `b`.
-    pub fn unify_var_value(&mut self,
-                           a_id: K,
-                           b: V)
-                           -> Result<(),(V,V)>
-    {
-        let node_a = self.get(a_id);
-        let a_id = node_a.key.clone();
-
-        match node_a.value {
-            None => {
-                self.set(a_id, Root(Some(b), node_a.rank));
-                Ok(())
-            }
-
-            Some(ref a_t) => {
-                if *a_t == b {
-                    Ok(())
-                } else {
-                    Err((a_t.clone(), b))
-                }
-            }
-        }
-    }
-
-    pub fn has_value(&mut self, id: K) -> bool {
-        self.get(id).value.is_some()
-    }
-
-    pub fn probe(&mut self, a_id: K) -> Option<V> {
-        self.get(a_id).value.clone()
-    }
-}
-
-///////////////////////////////////////////////////////////////////////////
-
-// Integral type keys
-
-pub trait ToType<'tcx> {
-    fn to_type(&self, tcx: &ty::ctxt<'tcx>) -> Ty<'tcx>;
-}
-
-impl UnifyKey for ty::IntVid {
-    type Value = Option<IntVarValue>;
-    fn index(&self) -> u32 { self.index }
-    fn from_index(i: u32) -> ty::IntVid { ty::IntVid { index: i } }
-    fn tag(_: Option<ty::IntVid>) -> &'static str { "IntVid" }
-}
-
-impl<'tcx> ToType<'tcx> for IntVarValue {
-    fn to_type(&self, tcx: &ty::ctxt<'tcx>) -> Ty<'tcx> {
-        match *self {
-            ty::IntType(i) => ty::mk_mach_int(tcx, i),
-            ty::UintType(i) => ty::mk_mach_uint(tcx, i),
-        }
-    }
-}
-
-impl UnifyValue for Option<IntVarValue> { }
-
-// Floating point type keys
-
-impl UnifyKey for ty::FloatVid {
-    type Value = Option<ast::FloatTy>;
-    fn index(&self) -> u32 { self.index }
-    fn from_index(i: u32) -> ty::FloatVid { ty::FloatVid { index: i } }
-    fn tag(_: Option<ty::FloatVid>) -> &'static str { "FloatVid" }
-}
-
-impl UnifyValue for Option<ast::FloatTy> {
-}
-
-impl<'tcx> ToType<'tcx> for ast::FloatTy {
-    fn to_type(&self, tcx: &ty::ctxt<'tcx>) -> Ty<'tcx> {
-        ty::mk_mach_float(tcx, *self)
-    }
-}
diff --git a/src/librustc/middle/infer/unify_key.rs b/src/librustc/middle/infer/unify_key.rs
new file mode 100644
index 00000000000..6b23e2c5029
--- /dev/null
+++ b/src/librustc/middle/infer/unify_key.rs
@@ -0,0 +1,48 @@
+// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use middle::ty::{self, IntVarValue, Ty};
+use rustc_data_structures::unify::UnifyKey;
+use syntax::ast;
+
+pub trait ToType<'tcx> {
+    fn to_type(&self, tcx: &ty::ctxt<'tcx>) -> Ty<'tcx>;
+}
+
+impl UnifyKey for ty::IntVid {
+    type Value = Option<IntVarValue>;
+    fn index(&self) -> u32 { self.index }
+    fn from_index(i: u32) -> ty::IntVid { ty::IntVid { index: i } }
+    fn tag(_: Option<ty::IntVid>) -> &'static str { "IntVid" }
+}
+
+impl<'tcx> ToType<'tcx> for IntVarValue {
+    fn to_type(&self, tcx: &ty::ctxt<'tcx>) -> Ty<'tcx> {
+        match *self {
+            ty::IntType(i) => ty::mk_mach_int(tcx, i),
+            ty::UintType(i) => ty::mk_mach_uint(tcx, i),
+        }
+    }
+}
+
+// Floating point type keys
+
+impl UnifyKey for ty::FloatVid {
+    type Value = Option<ast::FloatTy>;
+    fn index(&self) -> u32 { self.index }
+    fn from_index(i: u32) -> ty::FloatVid { ty::FloatVid { index: i } }
+    fn tag(_: Option<ty::FloatVid>) -> &'static str { "FloatVid" }
+}
+
+impl<'tcx> ToType<'tcx> for ast::FloatTy {
+    fn to_type(&self, tcx: &ty::ctxt<'tcx>) -> Ty<'tcx> {
+        ty::mk_mach_float(tcx, *self)
+    }
+}
diff --git a/src/librustc/util/snapshot_vec.rs b/src/librustc/util/snapshot_vec.rs
deleted file mode 100644
index d2e0b3aec2f..00000000000
--- a/src/librustc/util/snapshot_vec.rs
+++ /dev/null
@@ -1,186 +0,0 @@
-// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-//! A utility class for implementing "snapshottable" things; a snapshottable data structure permits
-//! you to take a snapshot (via `start_snapshot`) and then, after making some changes, elect either
-//! to rollback to the start of the snapshot or commit those changes.
-//!
-//! This vector is intended to be used as part of an abstraction, not serve as a complete
-//! abstraction on its own. As such, while it will roll back most changes on its own, it also
-//! supports a `get_mut` operation that gives you an arbitrary mutable pointer into the vector. To
-//! ensure that any changes you make this with this pointer are rolled back, you must invoke
-//! `record` to record any changes you make and also supplying a delegate capable of reversing
-//! those changes.
-use self::UndoLog::*;
-
-use std::mem;
-
-pub enum UndoLog<D:SnapshotVecDelegate> {
-    /// Indicates where a snapshot started.
-    OpenSnapshot,
-
-    /// Indicates a snapshot that has been committed.
-    CommittedSnapshot,
-
-    /// New variable with given index was created.
-    NewElem(usize),
-
-    /// Variable with given index was changed *from* the given value.
-    SetElem(usize, D::Value),
-
-    /// Extensible set of actions
-    Other(D::Undo)
-}
-
-pub struct SnapshotVec<D:SnapshotVecDelegate> {
-    values: Vec<D::Value>,
-    undo_log: Vec<UndoLog<D>>,
-    delegate: D
-}
-
-// Snapshots are tokens that should be created/consumed linearly.
-pub struct Snapshot {
-    // Length of the undo log at the time the snapshot was taken.
-    length: usize,
-}
-
-pub trait SnapshotVecDelegate {
-    type Value;
-    type Undo;
-
-    fn reverse(&mut self, values: &mut Vec<Self::Value>, action: Self::Undo);
-}
-
-impl<D:SnapshotVecDelegate> SnapshotVec<D> {
-    pub fn new(delegate: D) -> SnapshotVec<D> {
-        SnapshotVec {
-            values: Vec::new(),
-            undo_log: Vec::new(),
-            delegate: delegate
-        }
-    }
-
-    fn in_snapshot(&self) -> bool {
-        !self.undo_log.is_empty()
-    }
-
-    pub fn record(&mut self, action: D::Undo) {
-        if self.in_snapshot() {
-            self.undo_log.push(Other(action));
-        }
-    }
-
-    pub fn push(&mut self, elem: D::Value) -> usize {
-        let len = self.values.len();
-        self.values.push(elem);
-
-        if self.in_snapshot() {
-            self.undo_log.push(NewElem(len));
-        }
-
-        len
-    }
-
-    pub fn get<'a>(&'a self, index: usize) -> &'a D::Value {
-        &self.values[index]
-    }
-
-    /// Returns a mutable pointer into the vec; whatever changes you make here cannot be undone
-    /// automatically, so you should be sure call `record()` with some sort of suitable undo
-    /// action.
-    pub fn get_mut<'a>(&'a mut self, index: usize) -> &'a mut D::Value {
-        &mut self.values[index]
-    }
-
-    /// Updates the element at the given index. The old value will saved (and perhaps restored) if
-    /// a snapshot is active.
-    pub fn set(&mut self, index: usize, new_elem: D::Value) {
-        let old_elem = mem::replace(&mut self.values[index], new_elem);
-        if self.in_snapshot() {
-            self.undo_log.push(SetElem(index, old_elem));
-        }
-    }
-
-    pub fn start_snapshot(&mut self) -> Snapshot {
-        let length = self.undo_log.len();
-        self.undo_log.push(OpenSnapshot);
-        Snapshot { length: length }
-    }
-
-    pub fn actions_since_snapshot(&self,
-                                  snapshot: &Snapshot)
-                                  -> &[UndoLog<D>] {
-        &self.undo_log[snapshot.length..]
-    }
-
-    fn assert_open_snapshot(&self, snapshot: &Snapshot) {
-        // Or else there was a failure to follow a stack discipline:
-        assert!(self.undo_log.len() > snapshot.length);
-
-        // Invariant established by start_snapshot():
-        assert!(
-            match self.undo_log[snapshot.length] {
-                OpenSnapshot => true,
-                _ => false
-            });
-    }
-
-    pub fn rollback_to(&mut self, snapshot: Snapshot) {
-        debug!("rollback_to({})", snapshot.length);
-
-        self.assert_open_snapshot(&snapshot);
-
-        while self.undo_log.len() > snapshot.length + 1 {
-            match self.undo_log.pop().unwrap() {
-                OpenSnapshot => {
-                    // This indicates a failure to obey the stack discipline.
-                    panic!("Cannot rollback an uncommitted snapshot");
-                }
-
-                CommittedSnapshot => {
-                    // This occurs when there are nested snapshots and
-                    // the inner is committed but outer is rolled back.
-                }
-
-                NewElem(i) => {
-                    self.values.pop();
-                    assert!(self.values.len() == i);
-                }
-
-                SetElem(i, v) => {
-                    self.values[i] = v;
-                }
-
-                Other(u) => {
-                    self.delegate.reverse(&mut self.values, u);
-                }
-            }
-        }
-
-        let v = self.undo_log.pop().unwrap();
-        assert!(match v { OpenSnapshot => true, _ => false });
-        assert!(self.undo_log.len() == snapshot.length);
-    }
-
-    /// Commits all changes since the last snapshot. Of course, they
-    /// can still be undone if there is a snapshot further out.
-    pub fn commit(&mut self, snapshot: Snapshot) {
-        debug!("commit({})", snapshot.length);
-
-        self.assert_open_snapshot(&snapshot);
-
-        if snapshot.length == 0 {
-            // The root snapshot.
-            self.undo_log.truncate(0);
-        } else {
-            self.undo_log[snapshot.length] = CommittedSnapshot;
-        }
-    }
-}