The preceding commit has added a new object filter for git-rev-list(1)
which allows to filter objects by type. Implement the equivalent filter
for packfile bitmaps so that we can answer these queries fast.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 pack-bitmap.c                      | 29 ++++++++++++++++++++++++++---
 t/t6113-rev-list-bitmap-filters.sh | 25 ++++++++++++++++++++++++-
 2 files changed, 50 insertions(+), 4 deletions(-)

diff --git a/pack-bitmap.c b/pack-bitmap.c
index 3ed15431cd..e419f4206b 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -780,9 +780,6 @@ static void filter_bitmap_exclude_type(struct bitmap_index *bitmap_git,
 	eword_t mask;
 	uint32_t i;
 
-	if (type != OBJ_BLOB && type != OBJ_TREE)
-		BUG("filter_bitmap_exclude_type: unsupported type '%d'", type);
-
 	/*
 	 * The non-bitmap version of this filter never removes
 	 * objects which the other side specifically asked for,
@@ -912,6 +909,24 @@ static void filter_bitmap_tree_depth(struct bitmap_index *bitmap_git,
 				   OBJ_BLOB);
 }
 
+static void filter_bitmap_object_type(struct bitmap_index *bitmap_git,
+				      struct object_list *tip_objects,
+				      struct bitmap *to_filter,
+				      enum object_type object_type)
+{
+	if (object_type < OBJ_COMMIT || object_type > OBJ_TAG)
+		BUG("filter_bitmap_object_type given invalid object");
+
+	if (object_type != OBJ_TAG)
+		filter_bitmap_exclude_type(bitmap_git, tip_objects, to_filter, OBJ_TAG);
+	if (object_type != OBJ_COMMIT)
+		filter_bitmap_exclude_type(bitmap_git, tip_objects, to_filter, OBJ_COMMIT);
+	if (object_type != OBJ_TREE)
+		filter_bitmap_exclude_type(bitmap_git, tip_objects, to_filter, OBJ_TREE);
+	if (object_type != OBJ_BLOB)
+		filter_bitmap_exclude_type(bitmap_git, tip_objects, to_filter, OBJ_BLOB);
+}
+
 static int filter_bitmap(struct bitmap_index *bitmap_git,
 			 struct object_list *tip_objects,
 			 struct bitmap *to_filter,
@@ -944,6 +959,14 @@ static int filter_bitmap(struct bitmap_index *bitmap_git,
 		return 0;
 	}
 
+	if (filter->choice == LOFC_OBJECT_TYPE) {
+		if (bitmap_git)
+			filter_bitmap_object_type(bitmap_git, tip_objects,
+						  to_filter,
+						  filter->object_type);
+		return 0;
+	}
+
 	/* filter choice not handled */
 	return -1;
 }
diff --git a/t/t6113-rev-list-bitmap-filters.sh b/t/t6113-rev-list-bitmap-filters.sh
index 3f889949ca..fb66735ac8 100755
--- a/t/t6113-rev-list-bitmap-filters.sh
+++ b/t/t6113-rev-list-bitmap-filters.sh
@@ -10,7 +10,8 @@ test_expect_success 'set up bitmapped repo' '
 	test_commit much-larger-blob-one &&
 	git repack -adb &&
 	test_commit two &&
-	test_commit much-larger-blob-two
+	test_commit much-larger-blob-two &&
+	git tag tag
 '
 
 test_expect_success 'filters fallback to non-bitmap traversal' '
@@ -75,4 +76,26 @@ test_expect_success 'tree:1 filter' '
 	test_cmp expect actual
 '
 
+test_expect_success 'object:type filter' '
+	git rev-list --objects --filter=object:type=tag tag >expect &&
+	git rev-list --use-bitmap-index \
+		     --objects --filter=object:type=tag tag >actual &&
+	test_cmp expect actual &&
+
+	git rev-list --objects --filter=object:type=commit tag >expect &&
+	git rev-list --use-bitmap-index \
+		     --objects --filter=object:type=commit tag >actual &&
+	test_bitmap_traversal expect actual &&
+
+	git rev-list --objects --filter=object:type=tree tag >expect &&
+	git rev-list --use-bitmap-index \
+		     --objects --filter=object:type=tree tag >actual &&
+	test_bitmap_traversal expect actual &&
+
+	git rev-list --objects --filter=object:type=blob tag >expect &&
+	git rev-list --use-bitmap-index \
+		     --objects --filter=object:type=blob tag >actual &&
+	test_bitmap_traversal expect actual
+'
+
 test_done
-- 
2.31.1