sequencer: reencode commit message for am/rebase --show-current-patch

The message file will be used as commit message for the
git-{am,rebase} --continue.

Signed-off-by: Doan Tran Cong Danh <congdanhqx@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sequencer.c

@@ -2972,7 +2972,8 @@ static int make_patch(struct repository *r,
 
 	strbuf_addf(&buf, "%s/message", get_dir(opts));
 	if (!file_exists(buf.buf)) {
-		const char *commit_buffer = get_commit_buffer(commit, NULL);
+		const char *encoding = get_commit_output_encoding();
+		const char *commit_buffer = logmsg_reencode(commit, NULL, encoding);
 		find_commit_subject(commit_buffer, &subject);
 		res |= write_message(subject, strlen(subject), buf.buf, 1);
 		unuse_commit_buffer(commit, commit_buffer);

t/t3434-rebase-i18n.sh

@@ -54,4 +54,31 @@ test_expect_failure 'rebase --rebase-merges update encoding eucJP to ISO-2022-JP
 	compare_msg eucJP.txt eucJP ISO-2022-JP
 '
 
+test_rebase_continue_update_encode () {
+	old=$1
+	new=$2
+	msgfile=$3
+	test_expect_success "rebase --continue update from $old to $new" '
+		(git rebase --abort || : abort current git-rebase failure) &&
+		git switch -c conflict-$old-$new one &&
+		echo for-conflict >two.t &&
+		git add two.t &&
+		git config i18n.commitencoding $old &&
+		git commit -F "$TEST_DIRECTORY/t3434/$msgfile" &&
+		git config i18n.commitencoding $new &&
+		test_must_fail git rebase -m master &&
+		test -f .git/rebase-merge/message &&
+		git stripspace <.git/rebase-merge/message >two.t &&
+		git add two.t &&
+		git rebase --continue &&
+		compare_msg $msgfile $old $new &&
+		: git-commit assume invalid utf-8 is latin1 &&
+		test_cmp expect two.t
+	'
+}
+
+test_rebase_continue_update_encode ISO-8859-1 UTF-8 ISO8859-1.txt
+test_rebase_continue_update_encode eucJP UTF-8 eucJP.txt
+test_rebase_continue_update_encode eucJP ISO-2022-JP eucJP.txt
+
 test_done

t/t3434/ISO8859-1.txt

@@ -0,0 +1,3 @@
+�����
+
+�b�d�fg