[PATCH 6/6] default pack.indexDuplicates to false

[Jeff King <peff@peff.net>]

We should never see duplicate objects in packs, and it is
unknown what kind of complications such packs could create
during the repacking process. The previous commit introduced
a safety valve for checking packs coming into the repository
and being indexed by index-pack.

Let's turn the safety valve on by default. This helps
protect sites receiving packfiles from potentially malicious
strangers, and shouldn't affect normal use (and if it does,
it will have helped us identify a buggy packfile writer).
In a pinch, users can recover by turning off the option, or
by resorting to unpack-objects to explode the pack.

Note that this also turns the option on for packs we write
ourselves (e.g., via pack-objects, fast-import, or streaming
large blobs). We do not expect maliciously constructed
packfiles in these code paths, of course, but it can serve
as an extra check that we have no accidentally created a
buggy pack (and the check itself is cheap to perform).

Signed-off-by: Jeff King <peff@peff.net>
---
 pack-write.c                      | 1 -
 t/t5308-pack-detect-duplicates.sh | 9 ++++-----
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/pack-write.c b/pack-write.c
index da946a7..1e3c459 100644
--- a/pack-write.c
+++ b/pack-write.c
@@ -7,7 +7,6 @@ void reset_pack_idx_option(struct pack_idx_option *opts)
 	memset(opts, 0, sizeof(*opts));
 	opts->version = 2;
 	opts->off32_limit = 0x7fffffff;
-	opts->allow_duplicates = 1;
 }
 
 static int sha1_compare(const void *_a, const void *_b)
diff --git a/t/t5308-pack-detect-duplicates.sh b/t/t5308-pack-detect-duplicates.sh
index cb9b44e..e982095 100755
--- a/t/t5308-pack-detect-duplicates.sh
+++ b/t/t5308-pack-detect-duplicates.sh
@@ -37,10 +37,10 @@ test_expect_success 'index-pack will allow duplicate objects by default' '
 	git index-pack --stdin <no-dups.pack
 '
 
-test_expect_success 'index-pack will allow duplicate objects by default' '
+test_expect_success 'index-pack will allow duplicate objects if asked' '
 	clear_packs &&
 	create_pack dups.pack 100 &&
-	git index-pack --stdin <dups.pack
+	git -c pack.indexDuplicates=true index-pack --stdin <dups.pack
 '
 
 test_expect_success 'create batch-check test vectors' '
@@ -70,11 +70,10 @@ test_expect_success 'index-pack can reject packs with duplicates' '
 	test_cmp expect actual
 '
 
-test_expect_success 'index-pack can reject packs with duplicates' '
+test_expect_success 'index-pack rejects packs with duplicates by default' '
 	clear_packs &&
 	create_pack dups.pack 2 &&
-	test_must_fail \
-		git -c pack.indexDuplicates=0 index-pack --stdin <dups.pack &&
+	test_must_fail git index-pack --stdin <dups.pack &&
 	test_expect_code 1 git cat-file -e $LO_SHA1
 '
 
-- 
1.8.4.rc2.28.g6bb5f3f