Add intern table for List<ProjectionElem<'tcx, (), ()>>.

Also added alias `ProjectionKind<'tcx>` for `ProjectionElem<'tcx, (), ()>`.

src/librustc/mir/mod.rs

@@ -1944,6 +1944,10 @@ pub type PlaceProjection<'tcx> = Projection<'tcx, Place<'tcx>, Local, Ty<'tcx>>;
 /// and the index is a local.
 pub type PlaceElem<'tcx> = ProjectionElem<'tcx, Local, Ty<'tcx>>;
 
+/// Alias for projections as they appear in `UserTypeProjection`, where we
+/// need neither the `V` parameter for `Index` nor the `T` for `Field`.
+pub type ProjectionKind<'tcx> = ProjectionElem<'tcx, (), ()>;
+
 newtype_index! {
     pub struct Field {
         DEBUG_FORMAT = "field[{}]"
@@ -2531,6 +2535,10 @@ pub struct UserTypeProjection<'tcx> {
     pub projs: Vec<ProjectionElem<'tcx, (), ()>>,
 }
 
+impl<'tcx> Copy for ProjectionKind<'tcx> { }
+
+CloneTypeFoldableAndLiftImpls! { ProjectionKind<'tcx>, }
+
 impl<'tcx> TypeFoldable<'tcx> for UserTypeProjection<'tcx> {
     fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
         use mir::ProjectionElem::*;

src/librustc/ty/context.rs

@@ -31,7 +31,7 @@ use middle::cstore::EncodedMetadata;
 use middle::lang_items;
 use middle::resolve_lifetime::{self, ObjectLifetimeDefault};
 use middle::stability;
-use mir::{self, Mir, interpret};
+use mir::{self, Mir, interpret, ProjectionKind};
 use mir::interpret::Allocation;
 use ty::subst::{CanonicalUserSubsts, Kind, Substs, Subst};
 use ty::ReprOptions;
@@ -132,6 +132,7 @@ pub struct CtxtInterners<'tcx> {
     clauses: InternedSet<'tcx, List<Clause<'tcx>>>,
     goal: InternedSet<'tcx, GoalKind<'tcx>>,
     goal_list: InternedSet<'tcx, List<Goal<'tcx>>>,
+    projs: InternedSet<'tcx, List<ProjectionKind<'tcx>>>,
 }
 
 impl<'gcx: 'tcx, 'tcx> CtxtInterners<'tcx> {
@@ -149,6 +150,7 @@ impl<'gcx: 'tcx, 'tcx> CtxtInterners<'tcx> {
             clauses: Default::default(),
             goal: Default::default(),
             goal_list: Default::default(),
+            projs: Default::default(),
         }
     }
 
@@ -2294,6 +2296,13 @@ impl<'tcx: 'lcx, 'lcx> Borrow<[Kind<'lcx>]> for Interned<'tcx, Substs<'tcx>> {
     }
 }
 
+impl<'tcx: 'lcx, 'lcx> Borrow<[ProjectionKind<'lcx>]>
+    for Interned<'tcx, List<ProjectionKind<'tcx>>> {
+    fn borrow<'a>(&'a self) -> &'a [ProjectionKind<'lcx>] {
+        &self.0[..]
+    }
+}
+
 impl<'tcx> Borrow<RegionKind> for Interned<'tcx, RegionKind> {
     fn borrow<'a>(&'a self) -> &'a RegionKind {
         &self.0
@@ -2441,7 +2450,8 @@ slice_interners!(
     type_list: _intern_type_list(Ty),
     substs: _intern_substs(Kind),
     clauses: _intern_clauses(Clause),
-    goal_list: _intern_goals(Goal)
+    goal_list: _intern_goals(Goal),
+    projs: _intern_projs(ProjectionKind)
 );
 
 // This isn't a perfect fit: CanonicalVarInfo slices are always
@@ -2743,6 +2753,14 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         }
     }
 
+    pub fn intern_projs(self, ps: &[ProjectionKind<'tcx>]) -> &'tcx List<ProjectionKind<'tcx>> {
+        if ps.len() == 0 {
+            List::empty()
+        } else {
+            self._intern_projs(ps)
+        }
+    }
+
     pub fn intern_canonical_var_infos(self, ts: &[CanonicalVarInfo]) -> CanonicalVarInfos<'gcx> {
         if ts.len() == 0 {
             List::empty()