ref-filter: change parsing function error handling

Continue removing die() calls from ref-filter formatting logic,
so that it could be used by other commands.

Change the signature of parse_ref_filter_atom() by adding
strbuf parameter for error message.
The function returns the position in the used_atom[] array
(as before) for the given atom, or -1 to signal an error.
Upon failure, error message is appended to the strbuf.

Signed-off-by: Olga Telezhnaia <olyatelezhnaya@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

ref-filter.c

@@ -410,7 +410,8 @@ 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,
+				 struct strbuf *err)
 {
 	const char *sp;
 	const char *arg;
@@ -420,7 +421,8 @@ static int parse_ref_filter_atom(const struct ref_format *format,
 	if (*sp == '*' && sp < ep)
 		sp++; /* deref */
 	if (ep <= sp)
-		die(_("malformed field name: %.*s"), (int)(ep-atom), atom);
+		return strbuf_addf_ret(err, -1, _("malformed field name: %.*s"),
+				       (int)(ep-atom), atom);
 
 	/* Do we have the atom already used elsewhere? */
 	for (i = 0; i < used_atom_cnt; i++) {
@@ -446,7 +448,8 @@ static int parse_ref_filter_atom(const struct ref_format *format,
 	}
 
 	if (ARRAY_SIZE(valid_atom) <= i)
-		die(_("unknown field name: %.*s"), (int)(ep-atom), atom);
+		return strbuf_addf_ret(err, -1, _("unknown field name: %.*s"),
+				       (int)(ep-atom), atom);
 
 	/* Add it in, including the deref prefix */
 	at = used_atom_cnt;
@@ -728,17 +731,21 @@ int verify_ref_format(struct ref_format *format)
 
 	format->need_color_reset_at_eol = 0;
 	for (cp = format->format; *cp && (sp = find_next(cp)); ) {
+		struct strbuf err = STRBUF_INIT;
 		const char *color, *ep = strchr(sp, ')');
 		int at;
 
 		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);
+		at = parse_ref_filter_atom(format, sp + 2, ep, &err);
+		if (at < 0)
+			die("%s", err.buf);
 		cp = ep + 1;
 
 		if (skip_prefix(used_atom[at].name, "color:", &color))
 			format->need_color_reset_at_eol = !!strcmp(color, "reset");
+		strbuf_release(&err);
 	}
 	if (format->need_color_reset_at_eol && !want_color(format->use_color))
 		format->need_color_reset_at_eol = 0;
@@ -2157,13 +2164,17 @@ int format_ref_array_item(struct ref_array_item *info,
 
 	for (cp = format->format; *cp && (sp = find_next(cp)); cp = ep + 1) {
 		struct atom_value *atomv;
+		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);
+		pos = parse_ref_filter_atom(format, sp + 2, ep, error_buf);
+		if (pos < 0) {
+			pop_stack_element(&state.stack);
+			return -1;
+		}
+		get_ref_atom_value(info, pos, &atomv);
 		if (atomv->handler(atomv, &state, error_buf)) {
 			pop_stack_element(&state.stack);
 			return -1;
@@ -2222,7 +2233,12 @@ static int parse_sorting_atom(const char *atom)
 	 */
 	struct ref_format dummy = REF_FORMAT_INIT;
 	const char *end = atom + strlen(atom);
-	return parse_ref_filter_atom(&dummy, atom, end);
+	struct strbuf err = STRBUF_INIT;
+	int res = parse_ref_filter_atom(&dummy, atom, end, &err);
+	if (res < 0)
+		die("%s", err.buf);
+	strbuf_release(&err);
+	return res;
 }
 
 /*  If no sorting option is given, use refname to sort as default */