Subject: [PATCH 0/3] Fix REF_DELTA chain bug in 'git index-pack'

From: "Derrick Stolee via GitGitGadget" <[email-masked]>
Date: Wed, 23 Apr 2025 17:40:01 +0000

When fetching content from a remote, 'git index-pack' processes the packfile
content, storing a packfile appropriate for on-disk storage and a pack-index
helping to perform random-access into that packfile. To help with
compression, the packfile sent over the wire can use REF_DELTAs in addition
to OFS_DELTAs to refer to objects that are already known to exist in the
client's repository. REF_DELTAs can also refer to objects within the
packfile, though this is not typically done.

Because this inter-pack REF_DELTA is not a typical data shape, a latent bug
has been waiting that causes 'git index-pack' to die() even on legitimate
packfile content that it could resolve.

This series resolves this problem while also creating a test helper for
constructing packfiles with specific objects represented in specific types
of deltas and in a given order. This should make it easier to create test
cases like this in the future instead of updating t/lib-pack.sh through
other means.

Thanks, -Stolee

Derrick Stolee (3):
  test-tool: add pack-deltas helper
  t5309: create failing test for 'git index-pack'
  index-pack: allow revisiting REF_DELTA chains

 Makefile                     |   1 +
 builtin/index-pack.c         |  58 ++++++++-------
 t/helper/meson.build         |   1 +
 t/helper/test-pack-deltas.c  | 140 +++++++++++++++++++++++++++++++++++
 t/helper/test-tool.c         |   1 +
 t/helper/test-tool.h         |   1 +
 t/t5309-pack-delta-cycles.sh |  36 ++++++++-
 7 files changed, 210 insertions(+), 28 deletions(-)
 create mode 100644 t/helper/test-pack-deltas.c

base-commit: 4bbb303af69990ccd05fe3a2eb58a1ce036f8220
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1906%2Fderrickstolee%2Findex-pack-ref-deltas-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1906/derrickstolee/index-pack-ref-deltas-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1906
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