@matheusbsbs / matheus-bagliano / commits / a72dfab8b8

pseudo-merge.c: ensure pseudo-merge groups are closed

When generating pseudo-merge bitmaps, it's possible that concurrent reference updates may reveal some pseudo-merge candidates which reach objects that are not contained in the bitmap's pack or pseudo-pack order (in the case of MIDX bitmaps). The latter case is relatively easy to demonstrate: if we generate a MIDX bitmap with only half of the repository packed, then the unpacked contents are not part of the MIDX's object order. If we happen to select one or more commit(s) from the unpacked portion of the repository for inclusion in a pseudo-merge, we'll get the following message when trying to generate its bitmap: $ git multi-pack-index write --bitmap [...] Selecting pseudo-merge commits: 100% (1/1), done. warning: Failed to write bitmap index. Packfile doesn't have full closure (object ... is missing) Building bitmaps: 50% (1/2), done. error: could not write multi-pack bitmap , and the attempted bitmap write will fail, leaving the repository without a current bitmap. Rectify this by ensuring that the commits which are pseudo-merge candidates can only be so if they appear somewhere in the packing order. This is sufficient, since we know that the original packing order is closed under reachability, so if a commit appears in that list as a potential pseudo-merge candidate, we know that everything reachable from it also appears in the list (and thus the candidate is a good one). Noticed-by: Jeff King <peff@peff.net> Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Taylor Blau committed Aug 15, 2024 at 13:31 UTC a72dfab8b8bcccee06d7bf53e5c0323e82a1765a

2 files changed +38

pseudo-merge.c

@@ -217,6 +217,8 @@ static int find_pseudo_merge_group_for_ref(const char *refname,

217 c = lookup_commit(the_repository, oid);

218 if (!c)

219 return 0;

220 + if (!packlist_find(writer->to_pack, oid))

221 + return 0;

222

223 has_bitmap = bitmap_writer_has_bitmapped_object_id(writer, oid);

224

t/t5333-pseudo-merge-bitmaps.sh

+36

@@ -410,4 +410,40 @@ test_expect_success 'empty pseudo-merge group' '

410 )

411 '

412

413 +test_expect_success 'pseudo-merge closure' '

414 + git init pseudo-merge-closure &&

415 + (

416 + cd pseudo-merge-closure &&

417 +

418 + test_commit A &&

419 + git repack -d &&

420 +

421 + test_commit B &&

422 +

423 + # Note that the contents of A is packed, but B is not. A

424 + # (and the objects reachable from it) are thus visible

425 + # to the MIDX, but the same is not true for B and its

426 + # objects.

427 + #

428 + # Ensure that we do not attempt to create a pseudo-merge

429 + # for B, depsite it matching the below pseudo-merge

430 + # group pattern, as doing so would result in a failure

431 + # to write a non-closed bitmap.

432 + git config bitmapPseudoMerge.test.pattern refs/ &&

433 + git config bitmapPseudoMerge.test.threshold now &&

434 +

435 + git multi-pack-index write --bitmap &&

436 +

437 + test-tool bitmap dump-pseudo-merges >pseudo-merges &&

438 + test_line_count = 1 pseudo-merges &&

439 +

440 + git rev-parse A >expect &&

441 +

442 + test-tool bitmap list-commits >actual &&

443 + test_cmp expect actual &&

444 + test-tool bitmap dump-pseudo-merge-commits 0 >actual &&

445 + test_cmp expect actual

446 + )

447 +'

448 +

449 test_done