midx.c: avoid cruft packs with non-zero `repack --batch-size`

Apply similar treatment with respect to cruft packs as in a few commits
ago to `repack` with a non-zero `--batch-size`.

Since the case of a non-zero `--batch-size` is handled separately (in
`fill_included_packs_batch()` instead of `fill_included_packs_all()`), a
separate fix must be applied for this case.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

midx.c

@@ -1946,6 +1946,8 @@ static int fill_included_packs_batch(struct repository *r,
 			continue;
 		if (!pack_kept_objects && p->pack_keep)
 			continue;
+		if (p->is_cruft)
+			continue;
 		if (open_pack_index(p) || !p->num_objects)
 			continue;
 

t/t5319-multi-pack-index.sh

@@ -807,6 +807,47 @@ test_expect_success 'repack (all) ignores cruft pack' '
 	)
 '
 
+test_expect_success 'repack (--batch-size) ignores cruft pack' '
+	git init repo &&
+	test_when_finished "rm -fr repo" &&
+	(
+		cd repo &&
+
+		test_commit_bulk 5 &&
+		test_commit --no-tag unreachable &&
+
+		git reset --hard HEAD^ &&
+		git reflog expire --all --expire=all &&
+		git repack --cruft -d &&
+
+		test_commit four &&
+
+		find $objdir/pack -type f -name "*.pack" | sort >before &&
+		git repack -d &&
+		find $objdir/pack -type f -name "*.pack" | sort >after &&
+
+		pack="$(comm -13 before after)" &&
+		test_file_size "$pack" >sz &&
+		# Set --batch-size to twice the size of the pack created
+		# in the previous step, since this is enough to
+		# accommodate it and the cruft pack.
+		#
+		# This means that the MIDX machinery *could* combine the
+		# new and cruft packs together.
+		#
+		# We ensure that it does not below.
+		batch="$((($(cat sz) * 2)))" &&
+
+		git multi-pack-index write &&
+
+		find $objdir/pack | sort >before &&
+		git multi-pack-index repack --batch-size=$batch &&
+		find $objdir/pack | sort >after &&
+
+		test_cmp before after
+	)
+'
+
 test_expect_success 'expire removes repacked packs' '
 	(
 		cd dup &&