[PATCH/RFC] sequencer.c: record revert/cherry-pick commit with trailer lines

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

When a commit is reverted (or cherry-picked with -x) we add an English
sentence recording that commit id in the new commit message. Make
these real trailer lines instead so that they are more friendly to
parsers (especially "git interpret-trailers").

A reverted commit will have a new trailer

    Revert: <commit-id>

Similarly a cherry-picked commit with -x will have

    Cherry-Pick: <commit-id>

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 I think standardizing how we record commit ids in the commit message
 is a good idea. Though to be honest this started because of my irk of
 an English string "cherry picked from..." that cannot be translated.
 It might as well be a computer language that happens to look like
 English.

 Documentation/git-cherry-pick.txt |  5 ++---
 sequencer.c                       | 20 ++++++--------------
 t/t3510-cherry-pick-sequence.sh   | 12 ++++++------
 t/t3511-cherry-pick-x.sh          | 26 +++++++++++++-------------
 4 files changed, 27 insertions(+), 36 deletions(-)

diff --git a/Documentation/git-cherry-pick.txt b/Documentation/git-cherry-pick.txt
index d35d771fc8..8ffbaed1a0 100644
--- a/Documentation/git-cherry-pick.txt
+++ b/Documentation/git-cherry-pick.txt
@@ -58,9 +58,8 @@ OPTIONS
 	message prior to committing.
 
 -x::
-	When recording the commit, append a line that says
-	"(cherry picked from commit ...)" to the original commit
-	message in order to indicate which commit this change was
+	When recording the commit, append "Cherry-Pick:" trailer line
+	recording the commit name which commit this change was
 	cherry-picked from.  This is done only for cherry
 	picks without conflicts.  Do not use this option if
 	you are cherry-picking from your private branch because
diff --git a/sequencer.c b/sequencer.c
index 9e1ab3a2a7..f7318f2862 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -36,7 +36,6 @@
 #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 ";
 
 GIT_PATH_FUNC(git_path_commit_editmsg, "COMMIT_EDITMSG")
 
@@ -1758,16 +1757,10 @@ static int do_pick_commit(enum todo_command command, struct commit *commit,
 		base_label = msg.label;
 		next = parent;
 		next_label = msg.parent_label;
-		strbuf_addstr(&msgbuf, "Revert \"");
-		strbuf_addstr(&msgbuf, msg.subject);
-		strbuf_addstr(&msgbuf, "\"\n\nThis reverts commit ");
-		strbuf_addstr(&msgbuf, oid_to_hex(&commit->object.oid));
-
-		if (commit->parents && commit->parents->next) {
-			strbuf_addstr(&msgbuf, ", reversing\nchanges made to ");
-			strbuf_addstr(&msgbuf, oid_to_hex(&parent->object.oid));
-		}
-		strbuf_addstr(&msgbuf, ".\n");
+		strbuf_addf(&msgbuf, "Revert \"%s\"\n\n", msg.subject);
+
+		strbuf_addf(&msgbuf, "Revert: %s\n",
+			    oid_to_hex(&commit->object.oid));
 	} else {
 		const char *p;
 
@@ -1784,9 +1777,8 @@ static int do_pick_commit(enum todo_command command, struct commit *commit,
 			strbuf_complete_line(&msgbuf);
 			if (!has_conforming_footer(&msgbuf, NULL, 0))
 				strbuf_addch(&msgbuf, '\n');
-			strbuf_addstr(&msgbuf, cherry_picked_prefix);
-			strbuf_addstr(&msgbuf, oid_to_hex(&commit->object.oid));
-			strbuf_addstr(&msgbuf, ")\n");
+			strbuf_addf(&msgbuf, "Cherry-Pick: %s\n",
+				    oid_to_hex(&commit->object.oid));
 		}
 		if (!is_fixup(command))
 			author = get_author(msg.message);
diff --git a/t/t3510-cherry-pick-sequence.sh b/t/t3510-cherry-pick-sequence.sh
index c84eeefdc9..89b6e7fc1e 100755
--- a/t/t3510-cherry-pick-sequence.sh
+++ b/t/t3510-cherry-pick-sequence.sh
@@ -390,10 +390,10 @@ test_expect_success '--continue respects opts' '
 	git cat-file commit HEAD~1 >picked_msg &&
 	git cat-file commit HEAD~2 >unrelatedpick_msg &&
 	git cat-file commit HEAD~3 >initial_msg &&
-	! grep "cherry picked from" initial_msg &&
-	grep "cherry picked from" unrelatedpick_msg &&
-	grep "cherry picked from" picked_msg &&
-	grep "cherry picked from" anotherpick_msg
+	! grep "Cherry-Pick:" initial_msg &&
+	grep "Cherry-Pick: " unrelatedpick_msg &&
+	grep "Cherry-Pick: " picked_msg &&
+	grep "Cherry-Pick: " anotherpick_msg
 '
 
 test_expect_success '--continue of single-pick respects -x' '
@@ -404,7 +404,7 @@ test_expect_success '--continue of single-pick respects -x' '
 	git cherry-pick --continue &&
 	test_path_is_missing .git/sequencer &&
 	git cat-file commit HEAD >msg &&
-	grep "cherry picked from" msg
+	grep "Cherry-Pick:" msg
 '
 
 test_expect_success '--continue respects -x in first commit in multi-pick' '
@@ -416,7 +416,7 @@ test_expect_success '--continue respects -x in first commit in multi-pick' '
 	test_path_is_missing .git/sequencer &&
 	git cat-file commit HEAD^ >msg &&
 	picked=$(git rev-parse --verify picked) &&
-	grep "cherry picked from.*$picked" msg
+	grep "Cherry-Pick: $picked" msg
 '
 
 test_expect_failure '--signoff is automatically propagated to resolved conflict' '
diff --git a/t/t3511-cherry-pick-x.sh b/t/t3511-cherry-pick-x.sh
index 9888bf34b9..db11dd2430 100755
--- a/t/t3511-cherry-pick-x.sh
+++ b/t/t3511-cherry-pick-x.sh
@@ -32,7 +32,7 @@ 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)
+Cherry-Pick: da39a3ee5e6b4b0d3255bfef95601890afd80709
 Tested-by: C.U. Thor <cuthor@example.com>"
 
 mesg_unclean="$mesg_one_line
@@ -81,7 +81,7 @@ test_expect_success 'cherry-pick -x inserts blank line after one line subject' '
 	cat <<-EOF >expect &&
 		$mesg_one_line
 
-		(cherry picked from commit $sha1)
+		Cherry-Pick: $sha1
 	EOF
 	git log -1 --pretty=format:%B >actual &&
 	test_cmp expect actual
@@ -129,7 +129,7 @@ test_expect_success 'cherry-pick -x inserts blank line when conforming footer no
 	cat <<-EOF >expect &&
 		$mesg_no_footer
 
-		(cherry picked from commit $sha1)
+		Cherry-Pick: $sha1
 	EOF
 	git log -1 --pretty=format:%B >actual &&
 	test_cmp expect actual
@@ -154,7 +154,7 @@ test_expect_success 'cherry-pick -x -s inserts blank line when conforming footer
 	cat <<-EOF >expect &&
 		$mesg_no_footer
 
-		(cherry picked from commit $sha1)
+		Cherry-Pick: $sha1
 		Signed-off-by: $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>
 	EOF
 	git log -1 --pretty=format:%B >actual &&
@@ -178,7 +178,7 @@ test_expect_success 'cherry-pick -x -s adds sob when last sob doesnt match commi
 	git cherry-pick -x -s mesg-with-footer &&
 	cat <<-EOF >expect &&
 		$mesg_with_footer
-		(cherry picked from commit $sha1)
+		Cherry-Pick: $sha1
 		Signed-off-by: $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>
 	EOF
 	git log -1 --pretty=format:%B >actual &&
@@ -201,7 +201,7 @@ test_expect_success 'cherry-pick -x -s adds sob even when trailing sob exists fo
 	git cherry-pick -x -s mesg-with-footer-sob &&
 	cat <<-EOF >expect &&
 		$mesg_with_footer_sob
-		(cherry picked from commit $sha1)
+		Cherry-Pick: $sha1
 		Signed-off-by: $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>
 	EOF
 	git log -1 --pretty=format:%B >actual &&
@@ -215,7 +215,7 @@ test_expect_success 'cherry-pick -x handles commits with no NL at end of message
 	git cherry-pick -x $sha1 &&
 	git log -1 --pretty=format:%B >actual &&
 
-	printf "\n(cherry picked from commit %s)\n" $sha1 >>msg &&
+	printf "\nCherry-Pick: %s\n" $sha1 >>msg &&
 	test_cmp msg actual
 '
 
@@ -226,7 +226,7 @@ test_expect_success 'cherry-pick -x handles commits with no footer and no NL at
 	git cherry-pick -x $sha1 &&
 	git log -1 --pretty=format:%B >actual &&
 
-	printf "\n\n(cherry picked from commit %s)\n" $sha1 >>msg &&
+	printf "\n\nCherry-Pick: %s\n" $sha1 >>msg &&
 	test_cmp msg actual
 '
 
@@ -252,19 +252,19 @@ test_expect_success 'cherry-pick -s handles commits with no footer and no NL at
 	test_cmp msg actual
 '
 
-test_expect_success 'cherry-pick -x treats "(cherry picked from..." line as part of footer' '
+test_expect_success 'cherry-pick -x treats "Cherry-Pick:" 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)
+		Cherry-Pick: $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' '
+test_expect_success 'cherry-pick -s treats "Cherry-Pick:" line as part of footer' '
 	pristine_detach initial &&
 	git cherry-pick -s mesg-with-cherry-footer &&
 	cat <<-EOF >expect &&
@@ -275,13 +275,13 @@ test_expect_success 'cherry-pick -s treats "(cherry picked from..." line as part
 	test_cmp expect actual
 '
 
-test_expect_success 'cherry-pick -x -s treats "(cherry picked from..." line as part of footer' '
+test_expect_success 'cherry-pick -x -s treats "Cherry-Pick:..." line as part of footer' '
 	pristine_detach initial &&
 	sha1=$(git rev-parse mesg-with-cherry-footer^0) &&
 	git cherry-pick -x -s mesg-with-cherry-footer &&
 	cat <<-EOF >expect &&
 		$mesg_with_cherry_footer
-		(cherry picked from commit $sha1)
+		Cherry-Pick: $sha1
 		Signed-off-by: $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>
 	EOF
 	git log -1 --pretty=format:%B >actual &&
-- 
2.19.1.1005.gac84295441