Re: [PATCH v2 11/11] ref-filter: introduce objectname_atom_parser()

[Eric Sunshine <sunshine@sunshineco.com>]

On Wed, Dec 16, 2015 at 10:30 AM, Karthik Nayak <karthik.188@gmail.com> wrote:
> Introduce objectname_atom_parser() which will parse the
> '%(objectname)' atom and store information into the 'used_atom'
> structure based on the modifiers used along with the atom.
>
> Helped-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
> Signed-off-by: Karthik Nayak <Karthik.188@gmail.com>
> ---
> diff --git a/ref-filter.c b/ref-filter.c
> @@ -43,6 +43,7 @@ static struct used_atom {
>                         enum { C_BARE, C_BODY, C_BODY_DEP, C_LINES, C_SIG, C_SUB } option;
>                         unsigned int no_lines;
>                 } contents;
> +               enum { O_FULL, O_SHORT } objectname;
>         } u;
>  } *used_atom;
> @@ -124,6 +125,21 @@ static void contents_atom_parser(struct used_atom *atom)
> +static void objectname_atom_parser(struct used_atom *atom)
> +{
> +       const char * buf;
> +
> +       if (match_atom_name(atom->str, "objectname", &buf))
> +               atom->u.objectname = O_FULL;
> +       if (!buf)
> +               return;

Let me make sure that I understand this correctly.

make_atom_name("objectname") will return true only for "objectname" or
"objectname:", and will return false for anything else, such as
"objectnamely" or "schmorf". Furthermore, the only way
objectname_atom_parser() can be called is when %(objectname) or
%(objectname:...) is seen, thus match_atom_name() *must* return true
here, which means the above conditional is misleading, suggesting that
it could somehow return false.

And, if match_atom_name() did return false here, then that indicates a
programming error: objectname_atom_parser() somehow got called for
something other than %(objectname) or %(objectname:...). This implies
that the code should instead be structured like this:

    if (!match_atom_name(..., "objectname", &buf)
        die("BUG: parsing non-'objectname'")
    if (!buf)
        atom->u.objectname = O_FULL;
    else if (!strcmp(buf, "short"))
        atom->u.objectname = O_SHORT;
    else
        die(_("unrecognized %%(objectname) argument: %s"), buf);

However, this can be simplified further by recognizing that, following
this patch series, match_atom_name() is *only* called by these new
parse functions[1], which means that, as a convenience,
match_atom_name() itself could become a void rather than boolean
function and die() if the expected atom name is not found. Thus, the
code would become:

    match_atom_name(...);
    if (!buf)
        ...
    else if (!strcmp(...))
        ...
    ...

By the way, the above commentary isn't specific to this patch and
%(objectname), but is in fact also relevant for all of the preceding
patches which introduce parse functions calling match_atom_name().

More below...

[1]: ...assuming you replace the unnecessary match_atom_name() in
populate_value() with starts_with() as suggested in my patch 7/11
review addendum[2].

[2]: http://article.gmane.org/gmane.comp.version-control.git/282700

> +
> +       if (!strcmp(buf, "short"))
> +               atom->u.objectname = O_SHORT;
> +       else
> +               die(_("unrecognized %%(objectname) argument: %s"), buf);
> +}
> +
> @@ -461,15 +477,16 @@ static void *get_obj(const unsigned char *sha1, struct object **obj, unsigned lo
>  static int grab_objectname(const char *name, const unsigned char *sha1,
> -                           struct atom_value *v)
> +                          struct atom_value *v, struct used_atom *atom)
>  {
> -       if (!strcmp(name, "objectname")) {
> -               v->s = xstrdup(sha1_to_hex(sha1));
> -               return 1;
> -       }
> -       if (!strcmp(name, "objectname:short")) {
> -               v->s = xstrdup(find_unique_abbrev(sha1, DEFAULT_ABBREV));
> -               return 1;
> +       if (starts_with(name, "objectname")) {
> +               if (atom->u.objectname == O_SHORT) {
> +                       v->s = xstrdup(find_unique_abbrev(sha1, DEFAULT_ABBREV));
> +                       return 1;
> +               } else if (atom->u.objectname == O_FULL) {
> +                       v->s = xstrdup(sha1_to_hex(sha1));
> +                       return 1;
> +               }

Since 'objectname' can only ever be O_SHORT or O_FULL wouldn't it be a
programming error if it ever falls through to this point after the
closing brace? Perhaps a die("BUG:...") would be appropriate?

>         }
>         return 0;
>  }
> @@ -493,7 +510,7 @@ static void grab_common_values(struct atom_value *val, int deref, struct object
>                         v->s = xstrfmt("%lu", sz);
>                 }
>                 else if (deref)
> -                       grab_objectname(name, obj->sha1, v);
> +                       grab_objectname(name, obj->sha1, v, &used_atom[i]);

This patch hunk is somehow corrupt and doesn't apply. Was there some
hand-editing involved, or were some earlier patches regenerated after
this patch was made or something?

>         }
>  }
>
> @@ -999,7 +1016,7 @@ static void populate_value(struct ref_array_item *ref)
>                                 v->s = xstrdup(buf + 1);
>                         }
>                         continue;
> -               } else if (!deref && grab_objectname(name, ref->objectname, v)) {
> +               } else if (!deref && grab_objectname(name, ref->objectname, v, atom)) {
>                         continue;
>                 } else if (!strcmp(name, "HEAD")) {
>                         const char *head;
> --
> 2.6.4