[C++] Expression ExecuteScalarExpression execute empty args function with a wrong result

[ZhangHuiGui]

Describe the bug, including details regarding any error messages, version, and platform.

Problem

We have some arrow-builtin functions with no arguments support, like random/count_all/hash_count_all.

When we use call("random", {}, opts) and execute the expression with ExecuteScalarExpression(random_expr, cp::ExecBatch({}, 10)), the result only output one row. What we expected is 10 rows array.

 [
  0.5353881964857193
]

Reproduce

TEST(Expression, ExprWithNoArguments) {
   auto random_options = RandomOptions::FromSeed(/*seed=*/0);
   auto expr = call("random", {}, random_opts);
   ASSERT_OK_AND_ASSIGN(expr, expr.Bind(arrow::float64()));
  ASSERT_OK_AND_ASSIGN(auto out, ExecuteScalarExpression(
                                        expr, ExecBatch({}, 10)));
   std::cout << out.make_array()->ToString() << std::endl; // expect 10 rows but only get 1 row
}

Reason

The ExecuteScalarExpression internal code do some checks like below:

  bool all_scalar = true;
  for (size_t i = 0; i < arguments.size(); ++i) {
    ARROW_ASSIGN_OR_RAISE(
        arguments[i], ExecuteScalarExpression(call->arguments[i], input, exec_context));
    if (arguments[i].is_array()) {
      all_scalar = false;
    }
  }

The all_scalar will decide the output rows, if all_scalar is true, only output 1 row.
So we should consider the empty function arguments here? Or i missed some background here?

Component(s)

C++