list-objects: implement object type filter

While it already is possible to filter objects by some criteria in
git-rev-list(1), it is not yet possible to filter out only a specific
type of objects. This makes some filters less useful. The `blob:limit`
filter for example filters blobs such that only those which are smaller
than the given limit are returned. But it is unfit to ask only for these
smallish blobs, given that git-rev-list(1) will continue to print tags,
commits and trees.

Now that we have the infrastructure in place to also filter tags and
commits, we can improve this situation by implementing a new filter
which selects objects based on their type. Above query can thus
trivially be implemented with the following command:

    $ git rev-list --objects --filter=object:type=blob \
        --filter=blob:limit=200

Furthermore, this filter allows to optimize for certain other cases: if
for example only tags or commits have been selected, there is no need to
walk down trees.

The new filter is not yet supported in bitmaps. This is going to be
implemented in a subsequent commit.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 76 insertions, 0 deletions

diff --git a/list-objects-filter.c b/list-objects-filter.c
index 0ebfa52..1c1ee3d 100644
--- a/list-objects-filter.c
+++ b/list-objects-filter.c
@@ -545,6 +545,81 @@ static void filter_sparse_oid__init(
 	filter->free_fn = filter_sparse_free;
 }
 
+/*
+ * A filter for list-objects to omit large blobs.
+ * And to OPTIONALLY collect a list of the omitted OIDs.
+ */
+struct filter_object_type_data {
+	enum object_type object_type;
+};
+
+static enum list_objects_filter_result filter_object_type(
+	struct repository *r,
+	enum list_objects_filter_situation filter_situation,
+	struct object *obj,
+	const char *pathname,
+	const char *filename,
+	struct oidset *omits,
+	void *filter_data_)
+{
+	struct filter_object_type_data *filter_data = filter_data_;
+
+	switch (filter_situation) {
+	default:
+		BUG("unknown filter_situation: %d", filter_situation);
+
+	case LOFS_TAG:
+		assert(obj->type == OBJ_TAG);
+		if (filter_data->object_type == OBJ_TAG)
+			return LOFR_MARK_SEEN | LOFR_DO_SHOW;
+		return LOFR_MARK_SEEN;
+
+	case LOFS_COMMIT:
+		assert(obj->type == OBJ_COMMIT);
+		if (filter_data->object_type == OBJ_COMMIT)
+			return LOFR_MARK_SEEN | LOFR_DO_SHOW;
+		return LOFR_MARK_SEEN;
+
+	case LOFS_BEGIN_TREE:
+		assert(obj->type == OBJ_TREE);
+
+		/*
+		 * If we only want to show commits or tags, then there is no
+		 * need to walk down trees.
+		 */
+		if (filter_data->object_type == OBJ_COMMIT ||
+		    filter_data->object_type == OBJ_TAG)
+			return LOFR_SKIP_TREE;
+
+		if (filter_data->object_type == OBJ_TREE)
+			return LOFR_MARK_SEEN | LOFR_DO_SHOW;
+
+		return LOFR_MARK_SEEN;
+
+	case LOFS_BLOB:
+		assert(obj->type == OBJ_BLOB);
+
+		if (filter_data->object_type == OBJ_BLOB)
+			return LOFR_MARK_SEEN | LOFR_DO_SHOW;
+		return LOFR_MARK_SEEN;
+
+	case LOFS_END_TREE:
+		return LOFR_ZERO;
+	}
+}
+
+static void filter_object_type__init(
+	struct list_objects_filter_options *filter_options,
+	struct filter *filter)
+{
+	struct filter_object_type_data *d = xcalloc(1, sizeof(*d));
+	d->object_type = filter_options->object_type;
+
+	filter->filter_data = d;
+	filter->filter_object_fn = filter_object_type;
+	filter->free_fn = free;
+}
+
 /* A filter which only shows objects shown by all sub-filters. */
 struct combine_filter_data {
 	struct subfilter *sub;
@@ -691,6 +766,7 @@ static filter_init_fn s_filters[] = {
 	filter_blobs_limit__init,
 	filter_trees_depth__init,
 	filter_sparse_oid__init,
+	filter_object_type__init,
 	filter_combine__init,
 };