rustc_mir: disallow non-monomorphic vtables.

src/librustc_mir/interpret/traits.rs

@@ -1,4 +1,4 @@
-use rustc::ty::{self, Ty, Instance};
+use rustc::ty::{self, Ty, Instance, TypeFoldable};
 use rustc::ty::layout::{Size, Align, LayoutOf};
 use rustc::mir::interpret::{Scalar, Pointer, InterpResult, PointerArithmetic,};
 
@@ -20,6 +20,11 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
         let (ty, poly_trait_ref) = self.tcx.erase_regions(&(ty, poly_trait_ref));
 
+        // All vtables must be monomorphic, bail out otherwise.
+        if ty.needs_subst() || poly_trait_ref.needs_subst() {
+            throw_inval!(TooGeneric);
+        }
+
         if let Some(&vtable) = self.vtables.get(&(ty, poly_trait_ref)) {
             // This means we guarantee that there are no duplicate vtables, we will
             // always use the same vtable for the same (Type, Trait) combination.