message: Updated comments in resolve.rs to reflect actual data strcture used.
diff: @@ -16,14 +16,14 @@ use std::fmt;
  /// for each package.
  pub struct Resolve {
  /// A graph, whose vertices are packages and edges are dependency specifications
  - /// from `Cargo.toml`. We need a `Vec` here because the same package
  + /// from `Cargo.toml`. We need a `HashSet` here because the same package
  /// might be present in both `[dependencies]` and `[build-dependencies]`.
  graph: Graph<PackageId, HashSet<Dependency>>,
  /// Replacements from the `[replace]` table.
  replacements: HashMap<PackageId, PackageId>,
  /// Inverted version of `replacements`.
  reverse_replacements: HashMap<PackageId, PackageId>,
  - /// An empty `HashSet` to avoid creating a new `HashSet` for every package
  + /// An empty `Vec` to avoid creating a new `Vec` for every package
  /// that does not have any features, and to avoid using `Option` to
  /// simplify the API.
  empty_features: Vec<InternedString>,
  