ref-filter: refactor grab_objectname()

Prepares `grab_objectname()` for more generic usage.
This change will allow us to reuse `grab_objectname()` for
the `tree` and `parent` atoms in a following commit.

Mentored-by: Christian Couder <[email protected]>
Mentored-by: Heba Waly <[email protected]>
Signed-off-by: Hariom Verma <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: harry-hov

ref-filter.c

@@ -918,21 +918,27 @@ int verify_ref_format(struct ref_format *format)
 	return 0;
 }
 
-static int grab_objectname(const char *name, const struct object_id *oid,
+static const char *do_grab_objectname(const char *field, const struct object_id *oid,
+				      struct used_atom *atom)
+{
+	switch (atom->u.objectname.option) {
+	case O_FULL:
+		return oid_to_hex(oid);
+	case O_LENGTH:
+		return find_unique_abbrev(oid, atom->u.objectname.length);
+	case O_SHORT:
+		return find_unique_abbrev(oid, DEFAULT_ABBREV);
+	default:
+		BUG("unknown %%(%s) option", field);
+	}
+}
+
+static int grab_objectname(const char *name, const char *field, const struct object_id *oid,
 			   struct atom_value *v, struct used_atom *atom)
 {
-	if (starts_with(name, "objectname")) {
-		if (atom->u.objectname.option == O_SHORT) {
-			v->s = xstrdup(find_unique_abbrev(oid, DEFAULT_ABBREV));
-			return 1;
-		} else if (atom->u.objectname.option == O_FULL) {
-			v->s = xstrdup(oid_to_hex(oid));
-			return 1;
-		} else if (atom->u.objectname.option == O_LENGTH) {
-			v->s = xstrdup(find_unique_abbrev(oid, atom->u.objectname.length));
-			return 1;
-		} else
-			BUG("unknown %%(objectname) option");
+	if (starts_with(name, field)) {
+		v->s = xstrdup(do_grab_objectname(field, oid, atom));
+		return 1;
 	}
 	return 0;
 }
@@ -960,7 +966,7 @@ static void grab_common_values(struct atom_value *val, int deref, struct expand_
 		} else if (!strcmp(name, "deltabase"))
 			v->s = xstrdup(oid_to_hex(&oi->delta_base_oid));
 		else if (deref)
-			grab_objectname(name, &oi->oid, v, &used_atom[i]);
+			grab_objectname(name, "objectname", &oi->oid, v, &used_atom[i]);
 	}
 }
 
@@ -1740,7 +1746,7 @@ static int populate_value(struct ref_array_item *ref, struct strbuf *err)
 				v->s = xstrdup(buf + 1);
 			}
 			continue;
-		} else if (!deref && grab_objectname(name, &ref->objectname, v, atom)) {
+		} else if (!deref && grab_objectname(name, "objectname", &ref->objectname, v, atom)) {
 			continue;
 		} else if (!strcmp(name, "HEAD")) {
 			if (atom->u.head && !strcmp(ref->refname, atom->u.head))