Further foundational stuff on ProjectionKind before I add it to AscribeUserType.

src/librustc/ty/context.rs

@@ -1888,6 +1888,24 @@ impl<'a, 'tcx> Lift<'tcx> for &'a List<CanonicalVarInfo> {
     }
 }
 
+impl<'a, 'tcx> Lift<'tcx> for &'a List<ProjectionKind<'a>> {
+    type Lifted = &'tcx List<ProjectionKind<'tcx>>;
+    fn lift_to_tcx<'b, 'gcx>(&self, tcx: TyCtxt<'b, 'gcx, 'tcx>) -> Option<Self::Lifted> {
+        if self.len() == 0 {
+            return Some(List::empty());
+        }
+        if tcx.interners.arena.in_arena(*self as *const _) {
+            return Some(unsafe { mem::transmute(*self) });
+        }
+        // Also try in the global tcx if we're not that.
+        if !tcx.is_global() {
+            self.lift_to_tcx(tcx.global_tcx())
+        } else {
+            None
+        }
+    }
+}
+
 pub mod tls {
     use super::{GlobalCtxt, TyCtxt};
 

src/librustc/ty/structural_impls.rs

@@ -13,6 +13,7 @@
 //! hand, though we've recently added some macros (e.g.,
 //! `BraceStructLiftImpl!`) to help with the tedium.
 
+use mir::ProjectionKind;
 use mir::interpret::ConstValue;
 use ty::{self, Lift, Ty, TyCtxt};
 use ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
@@ -628,6 +629,17 @@ impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<Ty<'tcx>> {
     }
 }
 
+impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<ProjectionKind<'tcx>> {
+    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
+        let v = self.iter().map(|t| t.fold_with(folder)).collect::<SmallVec<[_; 8]>>();
+        folder.tcx().intern_projs(&v)
+    }
+
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
+        self.iter().any(|t| t.visit_with(visitor))
+    }
+}
+
 impl<'tcx> TypeFoldable<'tcx> for ty::instance::Instance<'tcx> {
     fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
         use ty::InstanceDef::*;