parse_date(): '@' prefix forces git-timestamp

The only place that the issue this series addresses was observed
where we read "cat-file commit" output and put it in GIT_AUTHOR_DATE
in order to replay a commit with an ancient timestamp.

With the previous patch alone, "git commit --date='20100917 +0900'"
can be misinterpreted to mean an ancient timestamp, not September in
year 2010.  Guard this codepath by requring an extra '@' in front of
the raw git timestamp on the parsing side. This of course needs to
be compensated by updating get_author_ident_from_commit and the code
for "git commit --amend" to prepend '@' to the string read from the
existing commit in the GIT_AUTHOR_DATE environment variable.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/t/t3400-rebase.sh b/t/t3400-rebase.sh
index 6eaecec..e26e14d 100755
--- a/t/t3400-rebase.sh
+++ b/t/t3400-rebase.sh
@@ -218,4 +218,27 @@ test_expect_success 'rebase -m can copy notes' '
 	test "a note" = "$(git notes show HEAD)"
 '
 
+test_expect_success 'rebase commit with an ancient timestamp' '
+	git reset --hard &&
+
+	>old.one && git add old.one && test_tick &&
+	git commit --date="@12345 +0400" -m "Old one" &&
+	>old.two && git add old.two && test_tick &&
+	git commit --date="@23456 +0500" -m "Old two" &&
+	>old.three && git add old.three && test_tick &&
+	git commit --date="@34567 +0600" -m "Old three" &&
+
+	git cat-file commit HEAD^^ >actual &&
+	grep "author .* 12345 +0400$" actual &&
+	git cat-file commit HEAD^ >actual &&
+	grep "author .* 23456 +0500$" actual &&
+	git cat-file commit HEAD >actual &&
+	grep "author .* 34567 +0600$" actual &&
+
+	git rebase --onto HEAD^^ HEAD^ &&
+
+	git cat-file commit HEAD >actual &&
+	grep "author .* 34567 +0600$" actual
+'
+
 test_done