merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/t/t5308-pack-detect-duplicates.sh

@@ -0,0 +1,77 @@
+#!/bin/sh
+
+test_description='handling of duplicate objects in incoming packfiles'
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-pack.sh
+
+if ! test_have_prereq SHA1
+then
+       skip_all='not using SHA-1 for objects'
+       test_done
+fi
+
+# The sha1s we have in our pack. It's important that these have the same
+# starting byte, so that they end up in the same fanout section of the index.
+# That lets us make sure we are exercising the binary search with both sets.
+LO_SHA1=e68fe8129b546b101aee9510c5328e7f21ca1d18
+HI_SHA1=e69de29bb2d1d6434b8b29ae775ad8c2e48c5391
+
+# And here's a "missing sha1" which will produce failed lookups. It must also
+# be in the same fanout section, and should be between the two (so that during
+# our binary search, we are sure to end up looking at one or the other of the
+# duplicate runs).
+MISSING_SHA1='e69d000000000000000000000000000000000000'
+
+# git will never intentionally create packfiles with
+# duplicate objects, so we have to construct them by hand.
+#
+# $1 is the name of the packfile to create
+#
+# $2 is the number of times to duplicate each object
+create_pack () {
+	pack_header "$((2 * $2))" >"$1" &&
+	for i in $(test_seq 1 "$2"); do
+		pack_obj $LO_SHA1 &&
+		pack_obj $HI_SHA1
+	done >>"$1" &&
+	pack_trailer "$1"
+}
+
+# double-check that create_pack actually works
+test_expect_success 'pack with no duplicates' '
+	create_pack no-dups.pack 1 &&
+	git index-pack --stdin <no-dups.pack
+'
+
+test_expect_success 'index-pack will allow duplicate objects by default' '
+	clear_packs &&
+	create_pack dups.pack 100 &&
+	git index-pack --stdin <dups.pack
+'
+
+test_expect_success 'create batch-check test vectors' '
+	cat >input <<-EOF &&
+	$LO_SHA1
+	$HI_SHA1
+	$MISSING_SHA1
+	EOF
+	cat >expect <<-EOF
+	$LO_SHA1 blob 2
+	$HI_SHA1 blob 0
+	$MISSING_SHA1 missing
+	EOF
+'
+
+test_expect_success 'lookup in duplicated pack' '
+	git cat-file --batch-check <input >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'index-pack can reject packs with duplicates' '
+	clear_packs &&
+	create_pack dups.pack 2 &&
+	test_must_fail git index-pack --strict --stdin <dups.pack &&
+	test_expect_code 1 git cat-file -e $LO_SHA1
+'
+
+test_done