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refs: fix invalid old object IDs when migrating reflogs

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When migrating reflog entries between different storage formats we end
up with invalid old object IDs for the migrated entries: instead of
writing the old object ID of the to-be-migrated entry, we end up with
the all-zeroes object ID.

The root cause of this issue is that we don't know to use the old object
ID provided by the caller. Instead, we manually resolve the old object
ID by resolving the current value of its matching reference. But as that
reference does not yet exist in the target ref storage we always end up
resolving it to all-zeroes.

This issue got unnoticed as there is no user-facing command that would
even show the old object ID. While `git log -g` knows to show the new
object ID, we don't have any formatting directive to show the old object
ID.

Fix the bug by introducing a new flag `REF_LOG_USE_PROVIDED_OIDS`. If
set, backends are instructed to use the old and new object IDs provided
by the caller, without doing any manual resolving. Set this flag in
`ref_transaction_update_reflog()`.

Amend our tests in t1460-refs-migrate to use our test tool to read
reflog entries. This test tool prints out both old and new object ID of
each reflog entry, which fixes the test gap. Furthermore it also prints
the full identity used to write the reflog, which provides test coverage
for the previous commit in this patch series that fixed the identity for
migrated reflogs.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Patrick Steinhardt
2025-08-06 07:54:20 +02:00
committed by Junio C Hamano
parent 046c67325c
commit 465eff81de
6 changed files with 55 additions and 13 deletions
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9
refs.h
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@@ -760,13 +760,20 @@ struct ref_transaction *ref_store_transaction_begin(struct ref_store *refs,
*/
#define REF_SKIP_CREATE_REFLOG (1 << 12)
/*
* When writing a REF_LOG_ONLY record, use the old and new object IDs provided
* in the update instead of resolving the old object ID. The caller must also
* set both REF_HAVE_OLD and REF_HAVE_NEW.
*/
#define REF_LOG_USE_PROVIDED_OIDS (1 << 13)
/*
* Bitmask of all of the flags that are allowed to be passed in to
* ref_transaction_update() and friends:
*/
#define REF_TRANSACTION_UPDATE_ALLOWED_FLAGS \
(REF_NO_DEREF | REF_FORCE_CREATE_REFLOG | REF_SKIP_OID_VERIFICATION | \
REF_SKIP_REFNAME_VERIFICATION | REF_SKIP_CREATE_REFLOG)
REF_SKIP_REFNAME_VERIFICATION | REF_SKIP_CREATE_REFLOG | REF_LOG_USE_PROVIDED_OIDS)
/*
* Add a reference update to transaction. `new_oid` is the value that