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pack-bitmap-write.c: gracefully fail to write non-closed bitmaps

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The set of objects covered by a bitmap must be closed under
reachability, since it must be the case that there is a valid bit
position assigned for every possible reachable object (otherwise the
bitmaps would be incomplete).

Pack bitmaps are never written from 'git repack' unless repacking
all-into-one, and so we never write non-closed bitmaps (except in the
case of partial clones where we aren't guaranteed to have all objects).

But multi-pack bitmaps change this, since it isn't known whether the
set of objects in the MIDX is closed under reachability until walking
them. Plumb through a bit that is set when a reachable object isn't
found.

As soon as a reachable object isn't found in the set of objects to
include in the bitmap, bitmap_writer_build() knows that the set is not
closed, and so it now fails gracefully.

A test is added in t0410 to trigger a bitmap write without full
reachability closure by removing local copies of some reachable objects
from a promisor remote.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Taylor Blau
2021-08-24 12:15:54 -04:00
committed by Junio C Hamano
parent fa95666a40
commit 3ba3d0621b
4 changed files with 64 additions and 26 deletions
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3
builtin/pack-objects.c
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@ -1256,7 +1256,8 @@ static void write_pack_file(void)
bitmap_writer_show_progress(progress);
bitmap_writer_select_commits(indexed_commits, indexed_commits_nr, -1);
bitmap_writer_build(&to_pack);
if (bitmap_writer_build(&to_pack) < 0)
die(_("failed to write bitmap index"));
bitmap_writer_finish(written_list, nr_written,
tmpname.buf, write_bitmap_options);
write_bitmap_index = 0;