[PATCH] sequencer: require trailing NL in footers

[Jonathan Tan <jonathantanmy@google.com>]

In commit 967dfd4 ("sequencer: use trailer's trailer layout",
2016-11-29), sequencer was taught to use the same mechanism as
interpret-trailers to determine the nature of the trailer of a commit
message (referred to as the "footer" in sequencer.c). However, the
requirement that a footer end in a newline character was inadvertently
removed. Restore that requirement.

While writing this commit, I noticed that if the "ignore_footer"
parameter in "has_conforming_footer" is greater than the distance
between the trailer start and sb->len, "has_conforming_footer" will
return an unexpected result. This does not occur in practice, because
"ignore_footer" is either zero or the return value of an invocation to
"ignore_non_trailer", which only skips empty lines and comment lines.
This commit contains a comment explaining this in the function's
documentation.

Reported-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
---

Thanks for the bug report. Here's a fix - I've verified this with the
way to reproduce provided in the original e-mail, and it seems to work
now.

The commit message of the referenced commit
(7b309aef0463340d3ad5449d1f605d14e10a4225) does not end in a newline,
which is probably why different behavior was observed with this commit
(as compared to others).

 sequencer.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/sequencer.c b/sequencer.c
index 77afecaeb..4cbe64b7f 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -151,6 +151,12 @@ static const char *get_todo_path(const struct replay_opts *opts)
  * Returns 1 for conforming footer
  * Returns 2 when sob exists within conforming footer
  * Returns 3 when sob exists within conforming footer as last entry
+ *
+ * A footer that does not end in a newline is considered non-conforming.
+ *
+ * ignore_footer, if not zero, should be the return value of an invocation to
+ * ignore_non_trailer. See the documentation of that function for more
+ * information.
  */
 static int has_conforming_footer(struct strbuf *sb, struct strbuf *sob,
 	int ignore_footer)
@@ -159,6 +165,11 @@ static int has_conforming_footer(struct strbuf *sb, struct strbuf *sob,
 	int i;
 	int found_sob = 0, found_sob_last = 0;
 
+	if (sb->len <= ignore_footer)
+		return 0;
+	if (sb->buf[sb->len - ignore_footer - 1] != '\n')
+		return 0;
+
 	trailer_info_get(&info, sb->buf);
 
 	if (info.trailer_start == info.trailer_end)
-- 
2.13.0.rc0.306.g87b477812d-goog