Taylor Blau e3ffc236a8 midx: verify duplicate pack entries by OID and offset ...

A MIDX retains one entry per OID, while a non-strict pack index can
contain the same OID at several offsets. verify_midx_file() compares the
recorded offset with find_pack_entry_one(), which may return a different
member of that duplicate run and falsely report a valid MIDX as corrupt.

Check instead that the exact OID/offset pair exists anywhere in the
contiguous duplicate run in the source pack. That is the relevant
invariant: same-pack duplicates have no canonical representation, and
every matching physical copy is valid, including those recorded by
existing MIDXs.

This matches reader behavior. The OOFF chunk records the selected
(pack, offset), and midx_to_pack_pos() reconstructs its RIDX position
from that pair. If midx_pair_to_pack_pos() is given an unselected
duplicate offset, the lookup misses and its sole caller falls back from
partial reuse to normal packing. Readers therefore remain consistent
with whichever representation the MIDX records.

Write a MIDX over the existing duplicate-pack fixture, assert that its
selected offset differs from find_pack_entry_one(), and verify it. Then
run fsck as an application-level check.

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

2026-07-24 19:05:11 -07:00

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