Merge branch 'tb/open-midx-bitmap-fallback'

Gracefully deal with a stale MIDX file that lists a packfile that
no longer exists.

* tb/open-midx-bitmap-fallback:
  pack-bitmap.c: gracefully degrade on failure to load MIDX'd pack

pack-bitmap.c

@@ -387,9 +387,11 @@ static int open_midx_bitmap_1(struct bitmap_index *bitmap_git,
 	}
 
 	for (i = 0; i < bitmap_git->midx->num_packs; i++) {
-		if (prepare_midx_pack(the_repository, bitmap_git->midx, i))
+		if (prepare_midx_pack(the_repository, bitmap_git->midx, i)) {
-			die(_("could not open pack %s"),
+			warning(_("could not open pack %s"),
 				bitmap_git->midx->pack_names[i]);
+			goto cleanup;
+		}
 	}
 
 	preferred = bitmap_git->midx->packs[midx_preferred_pack(bitmap_git)];

t/t5326-multi-pack-bitmaps.sh

@@ -478,4 +478,39 @@ test_expect_success 'git fsck correctly identifies good and bad bitmaps' '
 	grep "bitmap file '\''$packbitmap'\'' has invalid checksum" err
 '
 
+test_expect_success 'corrupt MIDX with bitmap causes fallback' '
+	git init corrupt-midx-bitmap &&
+	(
+		cd corrupt-midx-bitmap &&
+
+		test_commit first &&
+		git repack -d &&
+		test_commit second &&
+		git repack -d &&
+
+		git multi-pack-index write --bitmap &&
+		checksum=$(midx_checksum $objdir) &&
+		for f in $midx $midx-$checksum.bitmap
+		do
+			mv $f $f.bak || return 1
+		done &&
+
+		# pack everything together, invalidating the MIDX
+		git repack -ad &&
+		# then restore the now-stale MIDX
+		for f in $midx $midx-$checksum.bitmap
+		do
+			mv $f.bak $f || return 1
+		done &&
+
+		git rev-list --count --objects --use-bitmap-index HEAD >out 2>err &&
+		# should attempt opening the broken pack twice (once
+		# from the attempt to load it via the stale bitmap, and
+		# again when attempting to load it from the stale MIDX)
+		# before falling back to the non-MIDX case
+		test 2 -eq $(grep -c "could not open pack" err) &&
+		test 6 -eq $(cat out)
+	)
+'
+
 test_done