Hello!

With Git 2.51 we moved 'git-fetch(1)' and 'git-receive-pack(1)' to use
batched updates while doing reference updates. This provided a nice perf
boost since both commands will now use a single transaction for
reference updates. This removes the overhead of using individual
transaction per reference update and also avoids unnecessary
auto-compaction between reference updates in the reftable backend.

However, in the files-backend it does introduce two bugs when used on a
case-insensitive filesystem [1]:

1. When fetching references such as:

   - refs/heads/foo
   - refs/heads/Foo

Earlier we would simply overwrite the first reference with the second
and continue. Since Git 2.51 we simply abort stating a conflict.

This is resolved in the first commit by marking such conflicts as
REF_TRANSACTION_ERROR_CREATE_EXISTS. This allows batched updates to
reject the particular update, while applying the rest.

2. When fetching references such as:

  - refs/heads/foo
  - refs/heads/Foo/bar

Earlier we would apply the first, while the second would fail due to
conflict. Since Git 2.51, the lock files for both would be created, but
the 'commit' phase would abruptly end leaving the lock files.

The second commit fixes this by ensuring that on case-insensitive
filesystems we lowercase the refnames for availability check to ensure
F/D are caught and reported to the user.

Sorry for the long wait on this, with the OSSE and Git mini summit last
week, I didn't get as much computer time as I needed to test this.

- Karthik

[1]: https://lore.kernel.org/all/YQXPR01MB3046197EF39296549EE6DD669A33A@YQXPR01MB3046.CANPRD01.PROD.OUTLOOK.COM/ (local)

Signed-off-by: Karthik Nayak <redacted>
---
 builtin/fetch.c       | 21 ++++++++++++++++++---
 refs/files-backend.c  | 21 +++++++++++++++++++--
 t/t1400-update-ref.sh | 24 ++++++++++++++++++++++++
 t/t5510-fetch.sh      | 42 +++++++++++++++++++++++++++++++++++++++++-
 4 files changed, 102 insertions(+), 6 deletions(-)

Karthik Nayak (2):
      refs/files: use correct error type when locking fails
      refs/files: handle F/D conflicts in case-insensitive FS



base-commit: c44beea485f0f2feaf460e2ac87fdd5608d63cf0
change-id: 20250822-587-git-fetch-1-fails-fetches-on-case-insensitive-repositories-0a187c7ac41e

Thanks
- Karthik