Add extra methods to IndexVec and implement TypeFoldable for it

Adds `get`/`get_mut` accessors and `drain`/`drain_enumerated` iterators
to IndexVec.

Implements TypeFoldable for IndexVec.

src/librustc/ty/structural_impls.rs

@@ -12,6 +12,7 @@ use infer::type_variable;
 use ty::{self, Lift, Ty, TyCtxt};
 use ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
 use rustc_data_structures::accumulate_vec::AccumulateVec;
+use rustc_data_structures::indexed_vec::{IndexVec, Idx};
 
 use std::rc::Rc;
 use syntax::abi;
@@ -834,3 +835,13 @@ impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for ty::error::ExpectedFoun
         self.expected.visit_with(visitor) || self.found.visit_with(visitor)
     }
 }
+
+impl<'tcx, T: TypeFoldable<'tcx>, I: Idx> TypeFoldable<'tcx> for IndexVec<I, T> {
+    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
+        self.iter().map(|x| x.fold_with(folder)).collect()
+    }
+
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
+        self.iter().any(|t| t.visit_with(visitor))
+    }
+}

src/librustc_data_structures/indexed_vec.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use std::collections::range::RangeArgument;
 use std::fmt::Debug;
 use std::iter::{self, FromIterator};
 use std::slice;
@@ -145,6 +146,18 @@ impl<I: Idx, T> IndexVec<I, T> {
         self.raw.iter_mut().enumerate().map(IntoIdx { _marker: PhantomData })
     }
 
+    #[inline]
+    pub fn drain<'a, R: RangeArgument<usize>>(
+        &'a mut self, range: R) -> impl Iterator<Item=T> + 'a {
+        self.raw.drain(range)
+    }
+
+    #[inline]
+    pub fn drain_enumerated<'a, R: RangeArgument<usize>>(
+        &'a mut self, range: R) -> impl Iterator<Item=(I, T)> + 'a {
+        self.raw.drain(range).enumerate().map(IntoIdx { _marker: PhantomData })
+    }
+
     #[inline]
     pub fn last(&self) -> Option<I> {
         self.len().checked_sub(1).map(I::new)
@@ -164,6 +177,16 @@ impl<I: Idx, T> IndexVec<I, T> {
     pub fn truncate(&mut self, a: usize) {
         self.raw.truncate(a)
     }
+
+    #[inline]
+    pub fn get(&self, index: I) -> Option<&T> {
+        self.raw.get(index.index())
+    }
+
+    #[inline]
+    pub fn get_mut(&mut self, index: I) -> Option<&mut T> {
+        self.raw.get_mut(index.index())
+    }
 }
 
 impl<I: Idx, T> Index<I> for IndexVec<I, T> {

src/librustc_data_structures/lib.rs

@@ -38,6 +38,7 @@
 #![feature(associated_consts)]
 #![feature(unsize)]
 #![feature(i128_type)]
+#![feature(conservative_impl_trait)]
 
 #![cfg_attr(unix, feature(libc))]
 #![cfg_attr(test, feature(test))]