[PATCH v2 1/2] trailer: ignore first line of message

[Christian Couder <christian.couder@gmail.com>]

When looking for the start of the trailers in the message
we are passed, we should ignore the first line of the message.

The reason is that if we are passed a patch or commit message
then the first line should be the patch title.
If we are passed only trailers we can expect that they start
with an empty line that can be ignored too.

This way we can properly process commit messages that have
only one line with something that looks like a trailer, for
example like "area of code: change we made".
---
 t/t7513-interpret-trailers.sh | 15 ++++++++++++++-
 trailer.c                     |  4 +++-
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/t/t7513-interpret-trailers.sh b/t/t7513-interpret-trailers.sh
index bd0ab46..9577b4e 100755
--- a/t/t7513-interpret-trailers.sh
+++ b/t/t7513-interpret-trailers.sh
@@ -93,12 +93,25 @@ test_expect_success 'with config option on the command line' '
 		Acked-by: Johan
 		Reviewed-by: Peff
 	EOF
-	echo "Acked-by: Johan" |
+	{ echo; echo "Acked-by: Johan"; } |
 	git -c "trailer.Acked-by.ifexists=addifdifferent" interpret-trailers \
 		--trailer "Reviewed-by: Peff" --trailer "Acked-by: Johan" >actual &&
 	test_cmp expected actual
 '
 
+test_expect_success 'with only a title in the message' '
+	cat >expected <<-\EOF &&
+		area: change
+
+		Reviewed-by: Peff
+		Acked-by: Johan
+	EOF
+	echo "area: change" |
+	git interpret-trailers --trailer "Reviewed-by: Peff" \
+		--trailer "Acked-by: Johan" >actual &&
+	test_cmp expected actual
+'
+
 test_expect_success 'with config setup' '
 	git config trailer.ack.key "Acked-by: " &&
 	cat >expected <<-\EOF &&
diff --git a/trailer.c b/trailer.c
index 4b14a56..b808868 100644
--- a/trailer.c
+++ b/trailer.c
@@ -740,8 +740,10 @@ static int find_trailer_start(struct strbuf **lines, int count)
 	/*
 	 * Get the start of the trailers by looking starting from the end
 	 * for a line with only spaces before lines with one separator.
+	 * The first line must not be analyzed as the others as it
+	 * should be either the message title or a blank line.
 	 */
-	for (start = count - 1; start >= 0; start--) {
+	for (start = count - 1; start >= 1; start--) {
 		if (lines[start]->buf[0] == comment_line_char)
 			continue;
 		if (contains_only_spaces(lines[start]->buf)) {
-- 
2.5.0.401.g009ef9b.dirty