also check the iterator is not too long

src/librustc/lib.rs

@@ -43,6 +43,7 @@
 #![feature(nll)]
 #![feature(non_exhaustive)]
 #![feature(optin_builtin_traits)]
+#![feature(option_expect_none)]
 #![feature(range_is_empty)]
 #![feature(slice_patterns)]
 #![feature(specialization)]

src/librustc/mir/interpret/allocation.rs

@@ -356,6 +356,7 @@ impl<'tcx, Tag: Copy, Extra: AllocationExtra<Tag>> Allocation<Tag, Extra> {
         for dest in bytes {
             *dest = src.next().expect("iterator was shorter than it said it would be");
         }
+        src.next().expect_none("iterator was longer than it said it would be");
         Ok(())
     }