sparse annotation for error types?

[Jakub Kicinski]

Hi!

Recently we've been getting a steady stream of patches from Changzhong
to fix missing assignment to error variables before jumping to error
cases.

I wonder if for new code it'd make sense to add an annotation for a type
which has to be returned non-zero?

What I have in mind is the following common flow:

int do_a_thing(struct my_obj *obj, int param)
{
        int err;

        err = first_step(obj, 1);
        if (err)
                return err;

        if (some_check(obj)) {
                err = -EINVAL; /* need explicit error set! */
                goto err_undo_1s;
        }

        err = second_step(obj, param);
        if (err)
                goto err_undo_1s;

        err = third_step(obj, 0);
        if (err)
                goto err_undo_2s;

        return 0;

err_undo_2s:
        second_undo(obj);
err_undo_1s:
        first_undo(obj);
        return err;
}


The variable err should never be returned when it's equal to 0.
So if we annotate it, let's say as:

        int __nzret err;

could sparse then warn if we forgot to assign it after
"if (some_check(obj))"? 

Am I the only one who thinks this would be a good idea?