reftable/writer: ensure valid range for log's update_index

Each reftable addition has an associated update_index. While writing
refs, the update_index is verified to be within the range of the
reftable writer, i.e. `writer.min_update_index <= ref.update_index` and
`writer.max_update_index => ref.update_index`.

The corresponding check for reflogs in `reftable_writer_add_log` is
however missing. Add a similar check, but only check for the upper
limit. This is because reflogs are treated a bit differently than refs.
Each reflog entry in reftable has an associated update_index and we also
allow expiring entries in the middle, which is done by simply writing a
new reflog entry with the same update_index. This means, writing reflog
entries with update_index lesser than the writer's update_index is an
expected scenario.

Add a new unit test to check for the limits and fix some of the existing
tests, which were setting arbitrary values for the update_index by
ensuring they stay within the now checked limits.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/t/unit-tests/t-reftable-stack.c b/t/unit-tests/t-reftable-stack.c
index 72f6747064..52b81475c3 100644
--- a/t/unit-tests/t-reftable-stack.c
+++ b/t/unit-tests/t-reftable-stack.c
@@ -770,8 +770,12 @@ static void t_reftable_stack_tombstone(void)
 		}
 
 		logs[i].refname = xstrdup(buf);
-		/* update_index is part of the key. */
-		logs[i].update_index = 42;
+		/*
+		 * update_index is part of the key so should be constant.
+		 * The value itself should be less than the writer's upper
+		 * limit.
+		 */
+		logs[i].update_index = 1;
 		if (i % 2 == 0) {
 			logs[i].value_type = REFTABLE_LOG_UPDATE;
 			t_reftable_set_hash(logs[i].value.update.new_hash, i,