trailer: clarify failure modes in parse_trailer

The parse_trailer function has a few modes of operation, all depending
on whether the separator is present in its input, and if yes, the
separator's position. Some of these modes are failure modes, and these
failure modes are handled differently depending on whether the trailer
line was sourced from a file or from a command-line argument.

Extract a function to find the separator, allowing the invokers of
parse_trailer to determine how to handle the failure modes instead of
making parse_trailer do it. In this function, also take in the list of
separators, so that we can distinguish between command line arguments
(which allow '=' as separator) and file input (which does not allow '='
as separator).

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

trailer.c

@@ -543,29 +543,37 @@ static int token_matches_item(const char *tok, struct arg_item *item, int tok_le
 	return item->conf.key ? !strncasecmp(tok, item->conf.key, tok_len) : 0;
 }
 
-static int parse_trailer(struct strbuf *tok, struct strbuf *val,
-			 const struct conf_info **conf, const char *trailer)
+/*
+ * Return the location of the first separator in line, or -1 if there is no
+ * separator.
+ */
+static int find_separator(const char *line, const char *separators)
+{
+	int loc = strcspn(line, separators);
+	if (!line[loc])
+		return -1;
+	return loc;
+}
+
+/*
+ * Obtain the token, value, and conf from the given trailer.
+ *
+ * separator_pos must not be 0, since the token cannot be an empty string.
+ *
+ * If separator_pos is -1, interpret the whole trailer as a token.
+ */
+static void parse_trailer(struct strbuf *tok, struct strbuf *val,
+			 const struct conf_info **conf, const char *trailer,
+			 int separator_pos)
 {
-	size_t len;
-	struct strbuf seps = STRBUF_INIT;
 	struct arg_item *item;
 	int tok_len;
 	struct list_head *pos;
 
-	strbuf_addstr(&seps, separators);
-	strbuf_addch(&seps, '=');
-	len = strcspn(trailer, seps.buf);
-	strbuf_release(&seps);
-	if (len == 0) {
-		int l = strlen(trailer);
-		while (l > 0 && isspace(trailer[l - 1]))
-			l--;
-		return error(_("empty trailer token in trailer '%.*s'"), l, trailer);
-	}
-	if (len < strlen(trailer)) {
-		strbuf_add(tok, trailer, len);
+	if (separator_pos != -1) {
+		strbuf_add(tok, trailer, separator_pos);
 		strbuf_trim(tok);
-		strbuf_addstr(val, trailer + len + 1);
+		strbuf_addstr(val, trailer + separator_pos + 1);
 		strbuf_trim(val);
 	} else {
 		strbuf_addstr(tok, trailer);
@@ -587,8 +595,6 @@ static int parse_trailer(struct strbuf *tok, struct strbuf *val,
 			break;
 		}
 	}
-
-	return 0;
 }
 
 static void add_trailer_item(struct list_head *head, char *tok, char *val)
@@ -619,6 +625,12 @@ static void process_command_line_args(struct list_head *arg_head,
 	const struct conf_info *conf;
 	struct list_head *pos;
 
+	/*
+	 * In command-line arguments, '=' is accepted (in addition to the
+	 * separators that are defined).
+	 */
+	char *cl_separators = xstrfmt("=%s", separators);
+
 	/* Add an arg item for each configured trailer with a command */
 	list_for_each(pos, &conf_head) {
 		item = list_entry(pos, struct arg_item, list);
@@ -631,7 +643,17 @@ static void process_command_line_args(struct list_head *arg_head,
 
 	/* Add an arg item for each trailer on the command line */
 	for_each_string_list_item(tr, trailers) {
-		if (!parse_trailer(&tok, &val, &conf, tr->string))
+		int separator_pos = find_separator(tr->string, cl_separators);
+		if (separator_pos == 0) {
+			struct strbuf sb = STRBUF_INIT;
+			strbuf_addstr(&sb, tr->string);
+			strbuf_trim(&sb);
+			error(_("empty trailer token in trailer '%.*s'"),
+			      (int) sb.len, sb.buf);
+			strbuf_release(&sb);
+		} else {
+			parse_trailer(&tok, &val, &conf, tr->string,
+				      separator_pos);
 			add_arg_item(arg_head,
 				     strbuf_detach(&tok, NULL),
 				     strbuf_detach(&val, NULL),
@@ -639,6 +661,9 @@ static void process_command_line_args(struct list_head *arg_head,
 		}
 	}
 
+	free(cl_separators);
+}
+
 static struct strbuf **read_input_file(const char *file)
 {
 	struct strbuf **lines;
@@ -775,12 +800,18 @@ static int process_input_file(FILE *outfile,
 
 	/* Parse trailer lines */
 	for (i = trailer_start; i < trailer_end; i++) {
-		if (lines[i]->buf[0] != comment_line_char &&
-		    !parse_trailer(&tok, &val, NULL, lines[i]->buf))
+		int separator_pos;
+		if (lines[i]->buf[0] == comment_line_char)
+			continue;
+		separator_pos = find_separator(lines[i]->buf, separators);
+		if (separator_pos >= 1) {
+			parse_trailer(&tok, &val, NULL, lines[i]->buf,
+				      separator_pos);
 			add_trailer_item(head,
 					 strbuf_detach(&tok, NULL),
 					 strbuf_detach(&val, NULL));
 		}
+	}
 
 	return trailer_end;
 }