Re: [RFC 3/4] ref-filter: change parsing function error handling

["Martin Ågren" <martin.agren@gmail.com>]

On 13 March 2018 at 11:16, Olga Telezhnaya <olyatelezhnaya@gmail.com> wrote:
> Continue removing any printing from ref-filter formatting logic,
> so that it could be more general.
>
> Change the signature of parse_ref_filter_atom() by changing return value,
> adding previous return value to function parameter and also adding
> strbuf parameter for error message.

I think the current return value is always non-negative. Maybe it would
be easier to leave the return value as-is, except return negative on
error? Unless I am missing something?

>
> Signed-off-by: Olga Telezhnaia <olyatelezhnaya@gmail.com>
> ---
>  ref-filter.c | 45 ++++++++++++++++++++++++++++++++-------------
>  1 file changed, 32 insertions(+), 13 deletions(-)
>
> diff --git a/ref-filter.c b/ref-filter.c
> index 07bedc636398c..e146215bf1e64 100644
> --- a/ref-filter.c
> +++ b/ref-filter.c
> @@ -397,7 +397,8 @@ struct atom_value {
>   * Used to parse format string and sort specifiers
>   */
>  static int parse_ref_filter_atom(const struct ref_format *format,
> -                                const char *atom, const char *ep)
> +                                const char *atom, const char *ep, int *res,
> +                                struct strbuf *err)
>  {
>         const char *sp;
>         const char *arg;
> @@ -406,14 +407,18 @@ static int parse_ref_filter_atom(const struct ref_format *format,
>         sp = atom;
>         if (*sp == '*' && sp < ep)
>                 sp++; /* deref */
> -       if (ep <= sp)
> -               die(_("malformed field name: %.*s"), (int)(ep-atom), atom);
> +       if (ep <= sp) {
> +               strbuf_addf(err, _("malformed field name: %.*s"), (int)(ep-atom), atom);
> +               return -1;
> +       }
>
>         /* Do we have the atom already used elsewhere? */
>         for (i = 0; i < used_atom_cnt; i++) {
>                 int len = strlen(used_atom[i].name);
> -               if (len == ep - atom && !memcmp(used_atom[i].name, atom, len))
> -                       return i;
> +               if (len == ep - atom && !memcmp(used_atom[i].name, atom, len)) {
> +                       *res = i;
> +                       return 0;
> +               }
>         }

If you did so, this hunk above would not need to be changed ...

> @@ -458,7 +465,8 @@ static int parse_ref_filter_atom(const struct ref_format *format,
>                 need_tagged = 1;
>         if (!strcmp(valid_atom[i].name, "symref"))
>                 need_symref = 1;
> -       return at;
> +       *res = at;
> +       return 0;
>  }

... nor this one above ...

>                 if (!ep)
>                         return error(_("malformed format string %s"), sp);
>                 /* sp points at "%(" and ep points at the closing ")" */
> -               at = parse_ref_filter_atom(format, sp + 2, ep);
> +               if (parse_ref_filter_atom(format, sp + 2, ep, &at, &err))
> +                       die("%s", err.buf);

And this would be more like "if (at < 0) die(...)".

>         for (cp = format->format; *cp && (sp = find_next(cp)); cp = ep + 1) {
>                 struct atom_value *atomv;
> +               struct strbuf err = STRBUF_INIT;
> +               int pos;
>
>                 ep = strchr(sp, ')');
>                 if (cp < sp)
>                         append_literal(cp, sp, &state);
> -               get_ref_atom_value(info,
> -                                  parse_ref_filter_atom(format, sp + 2, ep),
> -                                  &atomv);
> +               if (parse_ref_filter_atom(format, sp + 2, ep, &pos, &err))
> +                       return -1;
> +               get_ref_atom_value(info, pos, &atomv);
>                 if (atomv->handler(atomv, &state, error_buf))
>                         return -1;
> +               strbuf_release(&err);

This looks leaky: if we get an error, we've got something in the buffer
but we do not release it because we return early. Stepping back a bit, I
wonder why we do not do anything at all with "err". Stepping back a bit
more :-) I wonder if you could get rid of "err" and pass "error_buf" to
parse_ref_filter_atom() instead. Our caller would like to have access to
the error string?

This ties back to my comment on the first patch -- "return negative if
and only if you add some error string to the buffer" might be a useful
rule?

Martin