[PATCH] commit -s: allow "(cherry picked " lines in sign-off section

@@ -528,6 +528,8 @@ static int ends_rfc2822_footer(struct strbuf *sb)
 		i++;
 
 	for (; i < len; i = k) {
+		static const char cherry_pick[] = "(cherry picked from commit ";
+
 		for (k = i; k < len && buf[k] != '\n'; k++)
 			; /* do nothing */
 		k++;

@@ -535,6 +537,20 @@ static int ends_rfc2822_footer(struct strbuf *sb)
 		if ((buf[k] == ' ' || buf[k] == '\t') && !first)
 			continue;
 
+		if (!first && buf[k] == '(' && k + strlen(cherry_pick) < len) {
+			/* Might be a cherry-pick notice. */
+			const char *p = buf + k;
+			if (!memcmp(p, cherry_pick, strlen(cherry_pick))) {
+				p = memchr(buf + k, '\n', len - k);
+				if (!p)
+					return 0;
+				if (p + 1 == buf + len)
+					return 1;
+				k = p - buf;
+				continue;
+			}
+		}
+
 		first = 0;
 
 		for (j = 0; i + j < len; j++) {

@@ -625,6 +641,10 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 		for (i = sb.len - 1; i > 0 && sb.buf[i - 1] != '\n'; i--)
 			; /* do nothing */
 		if (prefixcmp(sb.buf + i, sob.buf)) {
+			/*
+			 * Only insert an extra newline if the previous line
+			 * is not part of a Signed-off-by:/Acked-by:/etc chain.
+			 */
 			if (!i || !ends_rfc2822_footer(&sb))
 				strbuf_addch(&sb, '\n');
 			strbuf_addbuf(&sb, &sob);

@@ -0,0 +1,112 @@
+#!/bin/sh
+
+test_description='tests for the log messages cherry-pick produces
+
+  ----
+  +      cherry-pick of branch
+     +   signoff
+    +    basic
+  ++     mainline
+  +++    initial
+'
+. ./test-lib.sh
+
+prepare_commit () {
+	git checkout initial &&
+	test_commit "$1" &&
+	test_tick &&
+	git commit --amend --allow-empty-message -F "$1.message" &&
+	git tag -d "$1" &&
+	git tag "$1"
+}
+
+test_cmp_message () {
+	expect=$1 &&
+	shift &&
+	git log -1 --pretty=format:%B "$@" >actual &&
+	test_cmp "$expect" actual
+}
+
+cat >basic.message <<\EOF
+ A branch
+
+Here comes the lovely description of a change to pick up.
+Contributions come from many people:
+EOF
+
+{
+	cat basic.message
+	cat <<-\EOF
+
+	Signed-off-by: Foo <foo@example.com>
+	Signed-off-by: Bar <bar@example.com>
+	Tested-by: Baz <baz@example.com>
+	EOF
+} >signoff.message
+
+test_expect_success 'setup' '
+	test_commit initial &&
+	prepare_commit basic &&
+	prepare_commit signoff
+'
+
+test_expect_success 'cherry-pick preserves message' '
+	cat basic.message >expect &&
+	git checkout initial &&
+	git cherry-pick basic &&
+	test_cmp_message expect
+'
+
+test_expect_success 'cherry-pick -s adds signoff' '
+	{
+		cat basic.message &&
+		echo &&
+		echo "Signed-off-by: C O Mitter <committer@example.com>"
+	} >expect &&
+	git checkout initial &&
+	git cherry-pick -s basic &&
+	test_cmp_message expect HEAD
+'
+
+test_expect_success 'cherry-pick -s integrates into existing signoff chain' '
+	{
+		cat signoff.message &&
+		echo "Signed-off-by: C O Mitter <committer@example.com>"
+	} >expect &&
+	git checkout initial &&
+	git cherry-pick -s signoff &&
+	test_cmp_message expect HEAD
+'
+
+test_expect_success 'cherry-pick -x adds old commit id' '
+	{
+		cat basic.message &&
+		echo "(cherry picked from commit $(git rev-parse basic^0))"
+	} >expect &&
+	git checkout initial &&
+	git cherry-pick -x basic &&
+	test_cmp_message expect HEAD
+'
+
+test_expect_success 'cherry-pick -x integrates into signoff chain' '
+	{
+		cat signoff.message &&
+		echo "(cherry picked from commit $(git rev-parse signoff^0))"
+	} >expect &&
+	git checkout initial &&
+	git cherry-pick -x signoff &&
+	test_cmp_message expect HEAD
+'
+
+test_expect_success 'cherry-pick -x -s' '
+	{
+		cat signoff.message &&
+		echo "(cherry picked from commit $(git rev-parse signoff^0))"
+		echo "Signed-off-by: C O Mitter <committer@example.com>"
+	} >expect &&
+	git checkout initial &&
+	git cherry-pick -x -s signoff &&
+	test_cmp_message expect HEAD
+'
+
+test_done