interpret-trailers: add an option to show only the trailers

In theory it's easy for any reader who wants to parse
trailers to do so. But there are a lot of subtle corner
cases around what counts as a trailer, when the trailer
block begins and ends, etc. Since interpret-trailers already
has our parsing logic, let's let callers ask it to just
output the trailers.

They still have to parse the "key: value" lines, but at
least they can ignore all of the other corner cases.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 14 insertions, 9 deletions

diff --git a/trailer.c b/trailer.c
index 9bcd54e..83225c6 100644
--- a/trailer.c
+++ b/trailer.c
@@ -163,13 +163,15 @@ static void print_tok_val(FILE *outfile, const char *tok, const char *val)
 		fprintf(outfile, "%s%c %s\n", tok, separators[0], val);
 }
 
-static void print_all(FILE *outfile, struct list_head *head, int trim_empty)
+static void print_all(FILE *outfile, struct list_head *head,
+		      const struct process_trailer_options *opts)
 {
 	struct list_head *pos;
 	struct trailer_item *item;
 	list_for_each(pos, head) {
 		item = list_entry(pos, struct trailer_item, list);
-		if (!trim_empty || strlen(item->value) > 0)
+		if ((!opts->trim_empty || strlen(item->value) > 0) &&
+		    (!opts->only_trailers || item->token))
 			print_tok_val(outfile, item->token, item->value);
 	}
 }
@@ -886,7 +888,8 @@ static int ends_with_blank_line(const char *buf, size_t len)
 
 static int process_input_file(FILE *outfile,
 			      const char *str,
-			      struct list_head *head)
+			      struct list_head *head,
+			      const struct process_trailer_options *opts)
 {
 	struct trailer_info info;
 	struct strbuf tok = STRBUF_INIT;
@@ -896,9 +899,10 @@ static int process_input_file(FILE *outfile,
 	trailer_info_get(&info, str);
 
 	/* Print lines before the trailers as is */
-	fwrite(str, 1, info.trailer_start - str, outfile);
+	if (!opts->only_trailers)
+		fwrite(str, 1, info.trailer_start - str, outfile);
 
-	if (!info.blank_line_before_trailer)
+	if (!opts->only_trailers && !info.blank_line_before_trailer)
 		fprintf(outfile, "\n");
 
 	for (i = 0; i < info.trailer_nr; i++) {
@@ -913,7 +917,7 @@ static int process_input_file(FILE *outfile,
 			add_trailer_item(head,
 					 strbuf_detach(&tok, NULL),
 					 strbuf_detach(&val, NULL));
-		} else {
+		} else if (!opts->only_trailers) {
 			strbuf_addstr(&val, trailer);
 			strbuf_strip_suffix(&val, "\n");
 			add_trailer_item(head,
@@ -985,18 +989,19 @@ void process_trailers(const char *file,
 		outfile = create_in_place_tempfile(file);
 
 	/* Print the lines before the trailers */
-	trailer_end = process_input_file(outfile, sb.buf, &head);
+	trailer_end = process_input_file(outfile, sb.buf, &head, opts);
 
 	process_command_line_args(&arg_head, trailers);
 
 	process_trailers_lists(&head, &arg_head);
 
-	print_all(outfile, &head, opts->trim_empty);
+	print_all(outfile, &head, opts);
 
 	free_all(&head);
 
 	/* Print the lines after the trailers as is */
-	fwrite(sb.buf + trailer_end, 1, sb.len - trailer_end, outfile);
+	if (!opts->only_trailers)
+		fwrite(sb.buf + trailer_end, 1, sb.len - trailer_end, outfile);
 
 	if (opts->in_place)
 		if (rename_tempfile(&trailers_tempfile, file))