use fresh vars in place of _|_ when incorrect # of params supplied

src/rustc/middle/typeck.rs

@@ -2362,11 +2362,13 @@ fn check_expr_with_unifier(fcx: @fn_ctxt, expr: @ast::expr, unify: unifier,
                          } else {
                              "s were"
                          }]);
-            // HACK: build an arguments list with dummy arguments to
-            // check against
-            let dummy = {mode: ast::expl(ast::by_ref),
-                         ty: ty::mk_bot(fcx.ccx.tcx)};
-            arg_tys = vec::from_elem(supplied_arg_count, dummy);
+
+            // Just use fresh type variables for the types,
+            // since we don't know them.
+            arg_tys = vec::from_fn(supplied_arg_count) {|_i|
+                {mode: ast::expl(ast::by_ref),
+                 ty: next_ty_var(fcx)}
+            };
         }
 
         // Check the arguments.