intern the features

In a test on rust-lang#4810 (comment)
Before we got to 5000000 ticks in ~65 sec
After we got to 5000000 ticks in ~52 sec

src/cargo/core/interning.rs

@@ -22,9 +22,9 @@ impl InternedString {
  id_from_str.insert(str.to_string(), str_from_id.len() - 1);
  return InternedString { id: str_from_id.len() - 1 }
  }
-// pub fn to_inner(&self) -> String {
-// STRING_CASHE.read().unwrap().0[self.id].to_string()
-// }
+ pub fn to_inner(&self) -> String {
+ STRING_CASHE.read().unwrap().0[self.id].to_string()
+ }
 }
 
 impl fmt::Debug for InternedString {

src/cargo/core/resolver/mod.rs

@@ -332,7 +332,7 @@ struct Context {
  // switch to persistent hash maps if we can at some point or otherwise
  // make these much cheaper to clone in general.
  activations: Activations,
- resolve_features: HashMap<PackageId, HashSet<String>>,
+ resolve_features: HashMap<PackageId, HashSet<InternedString>>,
  links: HashMap<String, PackageId>,
 
  // These are two cheaply-cloneable lists (O(1) clone) which are effectively
@@ -371,7 +371,7 @@ pub fn resolve(summaries: &[(Summary, Method)],
  metadata: BTreeMap::new(),
  replacements: cx.resolve_replacements(),
  features: cx.resolve_features.iter().map(|(k, v)| {
- (k.clone(), v.clone())
+ (k.clone(), v.iter().map(|x| x.to_inner()).collect())
  }).collect(),
  unused_patches: Vec::new(),
  };
@@ -1318,8 +1318,8 @@ impl Context {
  let has_default_feature = summary.features().contains_key("default");
  Ok(match self.resolve_features.get(id) {
  Some(prev) => {
- features.iter().all(|f| prev.contains(f)) &&
- (!use_default || prev.contains("default") ||
+ features.iter().all(|f| prev.contains(&InternedString::new(f))) &&
+ (!use_default || prev.contains(&InternedString::new("default")) ||
  !has_default_feature)
  }
  None => features.is_empty() && (!use_default || !has_default_feature)
@@ -1434,9 +1434,7 @@ impl Context {
  let set = self.resolve_features.entry(pkgid.clone())
  .or_insert_with(HashSet::new);
  for feature in reqs.used {
- if !set.contains(feature) {
- set.insert(feature.to_string());
- }
+ set.insert(InternedString::new(feature));
  }
  }