projection predicates can be copy

src/librustc/ty/mod.rs

@@ -995,7 +995,7 @@ pub type PolyTypeOutlivesPredicate<'tcx> = PolyOutlivesPredicate<Ty<'tcx>, ty::R
 /// equality between arbitrary types. Processing an instance of Form
 /// #2 eventually yields one of these `ProjectionPredicate`
 /// instances to normalize the LHS.
-#[derive(Clone, PartialEq, Eq, Hash)]
+#[derive(Copy, Clone, PartialEq, Eq, Hash)]
 pub struct ProjectionPredicate<'tcx> {
     pub projection_ty: ProjectionTy<'tcx>,
     pub ty: Ty<'tcx>,