ref-filter: add objectsize to used_atom

When the support for "objectsize:disk" was bolted onto the
existing support for "objectsize", it didn't follow the
usual pattern for handling "atomtype:modifier", which reads
the <modifier> part just once while parsing the format
string, and store the parsed result in the union in the
used_atom structure, so that the string form of it does not
have to be parsed over and over at runtime (e.g. in
grab_common_values()).

Add a new member `objectsize` to the union `used_atom.u`,
so that we can separate the check of <modifier> from the
check of <atomtype>, this will bring scalability to atom
`%(objectsize)`.

Signed-off-by: ZheNing Hu <adlternative@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

ref-filter.c

@@ -146,6 +146,9 @@ static struct used_atom {
 			enum { O_FULL, O_LENGTH, O_SHORT } option;
 			unsigned int length;
 		} oid;
+		struct {
+			enum { O_SIZE, O_SIZE_DISK } option;
+		} objectsize;
 		struct email_option {
 			enum { EO_RAW, EO_TRIM, EO_LOCALPART } option;
 		} email_option;
@@ -269,11 +272,13 @@ static int objectsize_atom_parser(const struct ref_format *format, struct used_a
 				  const char *arg, struct strbuf *err)
 {
 	if (!arg) {
+		atom->u.objectsize.option = O_SIZE;
 		if (*atom->name == '*')
 			oi_deref.info.sizep = &oi_deref.size;
 		else
 			oi.info.sizep = &oi.size;
 	} else if (!strcmp(arg, "disk")) {
+		atom->u.objectsize.option = O_SIZE_DISK;
 		if (*atom->name == '*')
 			oi_deref.info.disk_sizep = &oi_deref.disk_size;
 		else
@@ -967,12 +972,14 @@ static void grab_common_values(struct atom_value *val, int deref, struct expand_
 			name++;
 		if (!strcmp(name, "objecttype"))
 			v->s = xstrdup(type_name(oi->type));
-		else if (!strcmp(name, "objectsize:disk")) {
-			v->value = oi->disk_size;
-			v->s = xstrfmt("%"PRIuMAX, (uintmax_t)oi->disk_size);
-		} else if (!strcmp(name, "objectsize")) {
-			v->value = oi->size;
-			v->s = xstrfmt("%"PRIuMAX , (uintmax_t)oi->size);
+		else if (starts_with(name, "objectsize")) {
+			if (used_atom[i].u.objectsize.option == O_SIZE_DISK) {
+				v->value = oi->disk_size;
+				v->s = xstrfmt("%"PRIuMAX, (uintmax_t)oi->disk_size);
+			} else if (used_atom[i].u.objectsize.option == O_SIZE) {
+				v->value = oi->size;
+				v->s = xstrfmt("%"PRIuMAX , (uintmax_t)oi->size);
+			}
 		} else if (!strcmp(name, "deltabase"))
 			v->s = xstrdup(oid_to_hex(&oi->delta_base_oid));
 		else if (deref)