pack-revindex: ensure that on-disk reverse indexes are given precedence

When an on-disk reverse index exists, there is no need to generate one
in memory. In fact, doing so can be slow, and require large amounts of
the heap.

Let's make sure that we treat the on-disk reverse index with precedence
(i.e., that when it exists, we don't bother trying to generate an
equivalent one in memory) by teaching Git how to conditionally die()
when generating a reverse index in memory.

Then, add a test to ensure that when (a) an on-disk reverse index
exists, and (b) when setting GIT_TEST_REV_INDEX_DIE_IN_MEMORY, that we
do not die, implying that we read from the on-disk one.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/t/t5325-reverse-index.sh b/t/t5325-reverse-index.sh
index be452bb343..a344b18d7e 100755
--- a/t/t5325-reverse-index.sh
+++ b/t/t5325-reverse-index.sh
@@ -85,4 +85,13 @@ test_expect_success 'pack-objects respects pack.writeReverseIndex' '
 	test_path_is_file pack-1-*.rev
 '
 
+test_expect_success 'reverse index is not generated when available on disk' '
+	test_index_pack true &&
+	test_path_is_file $rev &&
+
+	git rev-parse HEAD >tip &&
+	GIT_TEST_REV_INDEX_DIE_IN_MEMORY=1 git cat-file \
+		--batch-check="%(objectsize:disk)" <tip
+'
+
 test_done