ref-filter: allow porcelain to translate messages in the output

Introduce setup_ref_filter_porcelain_msg() so that the messages used in
the atom %(upstream:track) can be translated if needed. By default, keep
the messages untranslated, which is the right behavior for plumbing
commands. This is needed as we port branch.c to use ref-filter's
printing API's.

Written-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

ref-filter.c

@@ -16,6 +16,27 @@
 #include "trailer.h"
 #include "wt-status.h"
 
+static struct ref_msg {
+	const char *gone;
+	const char *ahead;
+	const char *behind;
+	const char *ahead_behind;
+} msgs = {
+	 /* Untranslated plumbing messages: */
+	"gone",
+	"ahead %d",
+	"behind %d",
+	"ahead %d, behind %d"
+};
+
+void setup_ref_filter_porcelain_msg(void)
+{
+	msgs.gone = _("gone");
+	msgs.ahead = _("ahead %d");
+	msgs.behind = _("behind %d");
+	msgs.ahead_behind = _("ahead %d, behind %d");
+}
+
 typedef enum { FIELD_STR, FIELD_ULONG, FIELD_TIME } cmp_type;
 typedef enum { COMPARE_EQUAL, COMPARE_UNEQUAL, COMPARE_NONE } cmp_status;
 
@@ -1181,15 +1202,15 @@ static void fill_remote_ref_details(struct used_atom *atom, const char *refname,
 	else if (atom->u.remote_ref.option == RR_TRACK) {
 		if (stat_tracking_info(branch, &num_ours,
 				       &num_theirs, NULL)) {
-			*s = xstrdup("gone");
+			*s = xstrdup(msgs.gone);
 		} else if (!num_ours && !num_theirs)
 			*s = "";
 		else if (!num_ours)
-			*s = xstrfmt("behind %d", num_theirs);
+			*s = xstrfmt(msgs.behind, num_theirs);
 		else if (!num_theirs)
-			*s = xstrfmt("ahead %d", num_ours);
+			*s = xstrfmt(msgs.ahead, num_ours);
 		else
-			*s = xstrfmt("ahead %d, behind %d",
+			*s = xstrfmt(msgs.ahead_behind,
 				     num_ours, num_theirs);
 		if (!atom->u.remote_ref.nobracket && *s[0]) {
 			const char *to_free = *s;

ref-filter.h

@@ -113,5 +113,7 @@ struct ref_sorting *ref_default_sorting(void);
 int parse_opt_merge_filter(const struct option *opt, const char *arg, int unset);
 /*  Get the current HEAD's description */
 char *get_head_description(void);
+/*  Set up translated strings in the output. */
+void setup_ref_filter_porcelain_msg(void);
 
 #endif /*  REF_FILTER_H  */