[PATCH 3/5] fast-export: avoid stripping encoding header if we cannot reencode

[Elijah Newren <newren@gmail.com>]

When fast-export encounters a commit with an 'encoding' header, it tries
to reencode in utf-8 and then drops the encoding header.  However, if it
fails to reencode in utf-8 because e.g. one of the characters in the
commit message was invalid in the old encoding, then we need to retain
the original encoding or otherwise we lose information needed to
understand all the other (valid) characters in the original commit
message.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 builtin/fast-export.c  |  7 +++++--
 t/t9350-fast-export.sh | 15 +++++++++++++++
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/builtin/fast-export.c b/builtin/fast-export.c
index 9e283482ef..7734a9f5a5 100644
--- a/builtin/fast-export.c
+++ b/builtin/fast-export.c
@@ -642,9 +642,12 @@ static void handle_commit(struct commit *commit, struct rev_info *rev,
 	printf("commit %s\nmark :%"PRIu32"\n", refname, last_idnum);
 	if (show_original_ids)
 		printf("original-oid %s\n", oid_to_hex(&commit->object.oid));
-	printf("%.*s\n%.*s\ndata %u\n%s",
+	printf("%.*s\n%.*s\n",
 	       (int)(author_end - author), author,
-	       (int)(committer_end - committer), committer,
+	       (int)(committer_end - committer), committer);
+	if (!reencoded && encoding)
+		printf("encoding %s\n", encoding);
+	printf("data %u\n%s",
 	       (unsigned)(reencoded
 			  ? strlen(reencoded) : message
 			  ? strlen(message) : 0),
diff --git a/t/t9350-fast-export.sh b/t/t9350-fast-export.sh
index 6c07f910eb..975c8c4014 100755
--- a/t/t9350-fast-export.sh
+++ b/t/t9350-fast-export.sh
@@ -110,6 +110,21 @@ test_expect_success 'iso-8859-7' '
 		 grep $(printf "\317\200") actual)
 '
 
+test_expect_success 'encoding preserved if reencoding fails' '
+
+	test_when_finished "git reset --hard HEAD~1" &&
+	test_when_finished "git config --unset i18n.commitencoding" &&
+	git config i18n.commitencoding iso-8859-7 &&
+	echo rosten >file &&
+	git commit -s -m "$(printf "Pi: \360; Invalid: \377")" file &&
+	git fast-export wer^..wer >iso-8859-7.fi &&
+	sed "s/wer/i18n-invalid/" iso-8859-7.fi |
+		(cd new &&
+		 git fast-import &&
+		 git cat-file commit i18n-invalid >actual &&
+		 grep ^encoding actual)
+'
+
 test_expect_success 'import/export-marks' '
 
 	git checkout -b marks master &&
-- 
2.21.0.779.g2f4b9c5032