sequencer.c: recognize "(cherry picked from ..." as part of s-o-b footer

When 'cherry-pick -s' is used to append a signed-off-by line to a cherry
picked commit, it does not currently detect the "(cherry picked from..."
that may have been appended by a previous 'cherry-pick -x' as part of the
s-o-b footer and it will insert a blank line before appending a new s-o-b.

Let's detect "(cherry picked from...)" as part of the footer so that we
will produce this:

   Signed-off-by: A U Thor <author@example.com>
   (cherry picked from da39a3ee5e6b4b0d3255bfef95601890afd80709)
   Signed-off-by: C O Mmitter <committer@example.com>

instead of this:

   Signed-off-by: A U Thor <author@example.com>
   (cherry picked from da39a3ee5e6b4b0d3255bfef95601890afd80709)

   Signed-off-by: C O Mmitter <committer@example.com>

[with improvements from Jonathan Nieder]

Signed-off-by: Brandon Casey <bcasey@nvidia.com>
Acked-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sequencer.c

@@ -18,6 +18,7 @@
 #define GIT_REFLOG_ACTION "GIT_REFLOG_ACTION"
 
 const char sign_off_header[] = "Signed-off-by: ";
+static const char cherry_picked_prefix[] = "(cherry picked from commit ";
 
 static void remove_sequencer_state(void)
 {
@@ -492,7 +493,7 @@ static int do_pick_commit(struct commit *commit, struct replay_opts *opts)
 		}
 
 		if (opts->record_origin) {
-			strbuf_addstr(&msgbuf, "(cherry picked from commit ");
+			strbuf_addstr(&msgbuf, cherry_picked_prefix);
 			strbuf_addstr(&msgbuf, sha1_to_hex(commit->object.sha1));
 			strbuf_addstr(&msgbuf, ")\n");
 		}
@@ -1017,16 +1018,44 @@ int sequencer_pick_revisions(struct replay_opts *opts)
 	return pick_commits(todo_list, opts);
 }
 
-static int ends_rfc2822_footer(struct strbuf *sb, int ignore_footer)
+static int is_rfc2822_line(const char *buf, int len)
 {
-	char ch, prev;
-	int i, j, k;
+	int i;
+
+	for (i = 0; i < len; i++) {
+		int ch = buf[i];
+		if (ch == ':')
+			return 1;
+		if (!isalnum(ch) && ch != '-')
+			break;
+	}
+
+	return 0;
+}
+
+static int is_cherry_picked_from_line(const char *buf, int len)
+{
+	/*
+	 * We only care that it looks roughly like (cherry picked from ...)
+	 */
+	return len > strlen(cherry_picked_prefix) + 1 &&
+		!prefixcmp(buf, cherry_picked_prefix) && buf[len - 1] == ')';
+}
+
+static int has_conforming_footer(struct strbuf *sb, int ignore_footer)
+{
+	char prev;
+	int i, k;
 	int len = sb->len - ignore_footer;
 	const char *buf = sb->buf;
 
+	/* footer must end with newline */
+	if (!len || buf[len - 1] != '\n')
+		return 0;
+
 	prev = '\0';
 	for (i = len - 1; i > 0; i--) {
-		ch = buf[i];
+		char ch = buf[i];
 		if (prev == '\n' && ch == '\n') /* paragraph break */
 			break;
 		prev = ch;
@@ -1041,15 +1070,9 @@ static int ends_rfc2822_footer(struct strbuf *sb, int ignore_footer)
 			; /* do nothing */
 		k++;
 
-		for (j = 0; i + j < len; j++) {
-			ch = buf[i + j];
-			if (ch == ':')
-				break;
-			if (isalnum(ch) ||
-			    (ch == '-'))
-				continue;
+		if (!is_rfc2822_line(buf + i, k - i - 1) &&
+		    !is_cherry_picked_from_line(buf + i, k - i - 1))
 			return 0;
-		}
 	}
 	return 1;
 }
@@ -1066,7 +1089,7 @@ void append_signoff(struct strbuf *msgbuf, int ignore_footer)
 	for (i = msgbuf->len - 1 - ignore_footer; i > 0 && msgbuf->buf[i - 1] != '\n'; i--)
 		; /* do nothing */
 	if (prefixcmp(msgbuf->buf + i, sob.buf)) {
-		if (!i || !ends_rfc2822_footer(msgbuf, ignore_footer))
+		if (!i || !has_conforming_footer(msgbuf, ignore_footer))
 			strbuf_splice(msgbuf, msgbuf->len - ignore_footer, 0, "\n", 1);
 		strbuf_splice(msgbuf, msgbuf->len - ignore_footer, 0, sob.buf, sob.len);
 	}

t/t3511-cherry-pick-x.sh

@@ -32,6 +32,10 @@ Signed-off-by: $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>"
 mesg_with_footer_sob="$mesg_with_footer
 Signed-off-by: $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>"
 
+mesg_with_cherry_footer="$mesg_with_footer_sob
+(cherry picked from commit da39a3ee5e6b4b0d3255bfef95601890afd80709)
+Tested-by: C.U. Thor <cuthor@example.com>"
+
 
 test_expect_success setup '
 	git config advice.detachedhead false &&
@@ -47,6 +51,8 @@ test_expect_success setup '
 	test_commit "$mesg_with_footer" foo b mesg-with-footer &&
 	git reset --hard initial &&
 	test_commit "$mesg_with_footer_sob" foo b mesg-with-footer-sob &&
+	git reset --hard initial &&
+	test_commit "$mesg_with_cherry_footer" foo b mesg-with-cherry-footer &&
 	pristine_detach initial &&
 	test_commit conflicting unrelated
 '
@@ -98,6 +104,19 @@ test_expect_success 'cherry-pick -s adds sob when last sob doesnt match committe
 	test_cmp expect actual
 '
 
+test_expect_success 'cherry-pick -x -s adds sob when last sob doesnt match committer' '
+	pristine_detach initial &&
+	sha1=`git rev-parse mesg-with-footer^0` &&
+	git cherry-pick -x -s mesg-with-footer &&
+	cat <<-EOF >expect &&
+		$mesg_with_footer
+		(cherry picked from commit $sha1)
+		Signed-off-by: $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>
+	EOF
+	git log -1 --pretty=format:%B >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'cherry-pick -s refrains from adding duplicate trailing sob' '
 	pristine_detach initial &&
 	git cherry-pick -s mesg-with-footer-sob &&
@@ -108,4 +127,40 @@ test_expect_success 'cherry-pick -s refrains from adding duplicate trailing sob'
 	test_cmp expect actual
 '
 
+test_expect_success 'cherry-pick -x -s adds sob even when trailing sob exists for committer' '
+	pristine_detach initial &&
+	sha1=`git rev-parse mesg-with-footer-sob^0` &&
+	git cherry-pick -x -s mesg-with-footer-sob &&
+	cat <<-EOF >expect &&
+		$mesg_with_footer_sob
+		(cherry picked from commit $sha1)
+		Signed-off-by: $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>
+	EOF
+	git log -1 --pretty=format:%B >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'cherry-pick -x treats "(cherry picked from..." line as part of footer' '
+	pristine_detach initial &&
+	sha1=`git rev-parse mesg-with-cherry-footer^0` &&
+	git cherry-pick -x mesg-with-cherry-footer &&
+	cat <<-EOF >expect &&
+		$mesg_with_cherry_footer
+		(cherry picked from commit $sha1)
+	EOF
+	git log -1 --pretty=format:%B >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'cherry-pick -s treats "(cherry picked from..." line as part of footer' '
+	pristine_detach initial &&
+	git cherry-pick -s mesg-with-cherry-footer &&
+	cat <<-EOF >expect &&
+		$mesg_with_cherry_footer
+		Signed-off-by: $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>
+	EOF
+	git log -1 --pretty=format:%B >actual &&
+	test_cmp expect actual
+'
+
 test_done