remove hack cuz the bug is fixed by rust-itertools/itertools#835

Signed-off-by: Richard Chien <[email protected]>

src/expr/macro/src/gen.rs

@@ -61,15 +61,8 @@ impl FunctionAttr {
         }
         let args = self.args.iter().map(|ty| types::expand_type_wildcard(ty));
         let ret = types::expand_type_wildcard(&self.ret);
-        // multi_cartesian_product should emit an empty set if the input is empty.
-        let args_cartesian_product =
-            args.multi_cartesian_product()
-                .chain(match self.args.is_empty() {
-                    true => vec![vec![]],
-                    false => vec![],
-                });
         let mut attrs = Vec::new();
-        for (args, mut ret) in args_cartesian_product.cartesian_product(ret) {
+        for (args, mut ret) in args.multi_cartesian_product().cartesian_product(ret) {
             if ret == "auto" {
                 ret = types::min_compatible_type(&args);
             }