t5309: create failing test for 'git index-pack'

This new test demonstrates some behavior where a valid packfile is being rejected by the Git client due to the order in which it is resolving REF_DELTAs. The thin packfile has a REF_DELTA chain A->B->C where C is not included in the packfile. However, the client repository contains both C and B already. Thus, 'git index-pack' is able to resolve A before resolving B. When resolving B, it then attempts to resolve any other REF_DELTAs that are pointing to B as a base. This "revisits" A and complains as if there is a cycle, but it did not actually detect a cycle. A fix will arrive in the next change. Signed-off-by: Derrick Stolee <stolee@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Derrick Stolee committed Apr 28, 2025 at 20:24 UTC fd7fd7afc975a42dd60c96f57b83f2a4fc7e58c0
1 file changed +24
t/t5309-pack-delta-cycles.sh
+24
@@ -75,4 +75,28 @@ test_expect_success 'failover to a duplicate object in the same pack' '
75 test_must_fail git index-pack --fix-thin --stdin <recoverable.pack
76 '
77
78 +test_expect_failure 'index-pack works with thin pack A->B->C with B on disk' '
79 + git init server &&
80 + (
81 + cd server &&
82 + test_commit_bulk 4
83 + ) &&
84 +
85 + A=$(git -C server rev-parse HEAD^{tree}) &&
86 + B=$(git -C server rev-parse HEAD~1^{tree}) &&
87 + C=$(git -C server rev-parse HEAD~2^{tree}) &&
88 + git -C server reset --hard HEAD~1 &&
89 +
90 + test-tool -C server pack-deltas --num-objects=2 >thin.pack <<-EOF &&
91 + REF_DELTA $A $B
92 + REF_DELTA $B $C
93 + EOF
94 +
95 + git clone "file://$(pwd)/server" client &&
96 + (
97 + cd client &&
98 + git index-pack --fix-thin --stdin <../thin.pack
99 + )
100 +'
101 +
102 test_done