[PATCH v2 5/5] list-objects-filter: implement filter tree:none

[Matthew DeVore <matvore@google.com>]

Teach list-objects the "tree:none" filter which allows for filtering
out all tree and blob objects (unless other objects are explicitly
specified by the user). The purpose of this patch is to allow smaller
partial clones.

The name of this filter - tree:none - does not explicitly specify that
it also filters out all blobs, but this should not cause much confusion
because blobs are not at all useful without the trees that refer to
them.

I also consider only:commits as a name, but this is inaccurate because
it suggests that annotated tags are omitted, but actually they are
included.

Signed-off-by: Matthew DeVore <matvore@google.com>
---
 Documentation/rev-list-options.txt     |  2 ++
 list-objects-filter-options.c          |  4 +++
 list-objects-filter-options.h          |  1 +
 list-objects-filter.c                  | 49 +++++++++++++++++++-------
 t/t5317-pack-objects-filter-objects.sh | 27 ++++++++++++++
 t/t5616-partial-clone.sh               | 27 ++++++++++++++
 t/t6112-rev-list-filters-objects.sh    | 13 +++++++
 7 files changed, 110 insertions(+), 13 deletions(-)

diff --git a/Documentation/rev-list-options.txt b/Documentation/rev-list-options.txt
index 7b273635d..68b4b9552 100644
--- a/Documentation/rev-list-options.txt
+++ b/Documentation/rev-list-options.txt
@@ -743,6 +743,8 @@ specification contained in <path>.
 	A debug option to help with future "partial clone" development.
 	This option specifies how missing objects are handled.
 +
+The form '--filter=tree:none' omits all blobs and trees.
++
 The form '--missing=error' requests that rev-list stop with an error if
 a missing object is encountered.  This is the default action.
 +
diff --git a/list-objects-filter-options.c b/list-objects-filter-options.c
index c0e2bd6a0..523cb00a0 100644
--- a/list-objects-filter-options.c
+++ b/list-objects-filter-options.c
@@ -50,6 +50,10 @@ static int gently_parse_list_objects_filter(
 			return 0;
 		}
 
+	} else if (!strcmp(arg, "tree:none")) {
+		filter_options->choice = LOFC_TREE_NONE;
+		return 0;
+
 	} else if (skip_prefix(arg, "sparse:oid=", &v0)) {
 		struct object_context oc;
 		struct object_id sparse_oid;
diff --git a/list-objects-filter-options.h b/list-objects-filter-options.h
index 0000a61f8..af64e5c66 100644
--- a/list-objects-filter-options.h
+++ b/list-objects-filter-options.h
@@ -10,6 +10,7 @@ enum list_objects_filter_choice {
 	LOFC_DISABLED = 0,
 	LOFC_BLOB_NONE,
 	LOFC_BLOB_LIMIT,
+	LOFC_TREE_NONE,
 	LOFC_SPARSE_OID,
 	LOFC_SPARSE_PATH,
 	LOFC__COUNT /* must be last */
diff --git a/list-objects-filter.c b/list-objects-filter.c
index a0ba78b20..22c894093 100644
--- a/list-objects-filter.c
+++ b/list-objects-filter.c
@@ -26,38 +26,45 @@
 #define FILTER_SHOWN_BUT_REVISIT (1<<21)
 
 /*
- * A filter for list-objects to omit ALL blobs from the traversal.
- * And to OPTIONALLY collect a list of the omitted OIDs.
+ * A filter for list-objects to omit ALL blobs from the traversal, and possibly
+ * trees as well.
+ * Can OPTIONALLY collect a list of the omitted OIDs.
  */
-struct filter_blobs_none_data {
+struct filter_none_of_type_data {
+	/* blobs are always omitted */
+	unsigned omit_trees : 1;
 	struct oidset *omits;
 };
 
-static enum list_objects_filter_result filter_blobs_none(
+static enum list_objects_filter_result filter_none_of_type(
 	enum list_objects_filter_situation filter_situation,
 	struct object *obj,
 	const char *pathname,
 	const char *filename,
 	void *filter_data_)
 {
-	struct filter_blobs_none_data *filter_data = filter_data_;
+	struct filter_none_of_type_data *filter_data = filter_data_;
 
 	switch (filter_situation) {
 	default:
 		die("unknown filter_situation");
 		return LOFR_ZERO;
 
-	case LOFS_BEGIN_TREE:
-		assert(obj->type == OBJ_TREE);
-		/* always include all tree objects */
-		return LOFR_MARK_SEEN | LOFR_DO_SHOW;
-
 	case LOFS_END_TREE:
 		assert(obj->type == OBJ_TREE);
 		return LOFR_ZERO;
 
+	case LOFS_BEGIN_TREE:
+		assert(obj->type == OBJ_TREE);
+		if (!filter_data->omit_trees)
+			return LOFR_MARK_SEEN | LOFR_DO_SHOW;
+
+		/*
+		 * Fallthrough to insert into omitted list for trees as well as
+		 * blobs.
+		 */
+		/* fallthrough */
 	case LOFS_BLOB:
-		assert(obj->type == OBJ_BLOB);
 		assert((obj->flags & SEEN) == 0);
 
 		if (filter_data->omits)
@@ -72,10 +79,25 @@ static void *filter_blobs_none__init(
 	filter_object_fn *filter_fn,
 	filter_free_fn *filter_free_fn)
 {
-	struct filter_blobs_none_data *d = xcalloc(1, sizeof(*d));
+	struct filter_none_of_type_data *d = xcalloc(1, sizeof(*d));
+	d->omits = omitted;
+
+	*filter_fn = filter_none_of_type;
+	*filter_free_fn = free;
+	return d;
+}
+
+static void* filter_tree_none__init(
+	struct oidset *omitted,
+	struct list_objects_filter_options *filter_options,
+	filter_object_fn *filter_fn,
+	filter_free_fn *filter_free_fn)
+{
+	struct filter_none_of_type_data *d = xcalloc(1, sizeof(*d));
+	d->omit_trees = 1;
 	d->omits = omitted;
 
-	*filter_fn = filter_blobs_none;
+	*filter_fn = filter_none_of_type;
 	*filter_free_fn = free;
 	return d;
 }
@@ -374,6 +396,7 @@ static filter_init_fn s_filters[] = {
 	NULL,
 	filter_blobs_none__init,
 	filter_blobs_limit__init,
+	filter_tree_none__init,
 	filter_sparse_oid__init,
 	filter_sparse_path__init,
 };
diff --git a/t/t5317-pack-objects-filter-objects.sh b/t/t5317-pack-objects-filter-objects.sh
index 5e35f33bf..28a8c916a 100755
--- a/t/t5317-pack-objects-filter-objects.sh
+++ b/t/t5317-pack-objects-filter-objects.sh
@@ -72,6 +72,33 @@ test_expect_success 'get an error for missing tree object' '
 	grep -q "bad tree object" bad_tree
 '
 
+test_expect_success 'setup for tests of tree:none' '
+	mkdir r1/subtree &&
+	echo "This is a file in a subtree" > r1/subtree/file &&
+	git -C r1 add subtree/file &&
+	git -C r1 commit -m subtree
+'
+
+test_expect_success 'verify tree:none packfile has no blobs or trees' '
+	git -C r1 pack-objects --rev --stdout --filter=tree:none >commitsonly.pack <<-EOF &&
+	HEAD
+	EOF
+	git -C r1 index-pack ../commitsonly.pack &&
+	git -C r1 verify-pack -v ../commitsonly.pack >objs &&
+	! grep -E "tree|blob" objs
+'
+
+test_expect_success 'grab tree directly when using tree:none' '
+	# We should get the tree specified directly but not its blobs or subtrees.
+	git -C r1 pack-objects --rev --stdout --filter=tree:none >commitsonly.pack <<-EOF &&
+	HEAD:
+	EOF
+	git -C r1 index-pack ../commitsonly.pack &&
+	git -C r1 verify-pack -v ../commitsonly.pack >objs &&
+	grep -E "tree|blob" objs >trees_and_blobs &&
+	test_line_count = 1 trees_and_blobs
+'
+
 # Test blob:limit=<n>[kmg] filter.
 # We boundary test around the size parameter.  The filter is strictly less than
 # the value, so size 500 and 1000 should have the same results, but 1001 should
diff --git a/t/t5616-partial-clone.sh b/t/t5616-partial-clone.sh
index bbbe7537d..4fc068716 100755
--- a/t/t5616-partial-clone.sh
+++ b/t/t5616-partial-clone.sh
@@ -170,6 +170,33 @@ test_expect_success 'partial clone fetches blobs pointed to by refs even if norm
 	git -C dst fsck
 '
 
+test_expect_success 'can use tree:none to filter partial clone' '
+	rm -rf dst &&
+	git clone --no-checkout --filter=tree:none "file://$(pwd)/srv.bare" dst &&
+	git -C dst rev-list master --missing=allow-any --objects >fetched_objects &&
+	cat fetched_objects \
+		| awk -f print_1.awk \
+		| xargs -n1 git -C dst cat-file -t >fetched_types &&
+	sort fetched_types -u >unique_types.observed &&
+	echo commit > unique_types.expected &&
+	test_cmp unique_types.observed unique_types.expected
+'
+
+test_expect_success 'show missing tree objects with --missing=print' '
+	git -C dst rev-list master --missing=print --quiet --objects >missing_objs &&
+	sed "s/?//" missing_objs \
+		| xargs -n1 git -C srv.bare cat-file -t \
+		>missing_types &&
+	sort -u missing_types >missing_types.uniq &&
+	echo tree >expected &&
+	test_cmp missing_types.uniq expected
+'
+
+test_expect_success 'do not complain when a missing tree cannot be parsed' '
+	git -C dst rev-list master --missing=print --quiet --objects 2>rev_list_err >&2 &&
+	! grep -q "Could not read " rev_list_err
+'
+
 . "$TEST_DIRECTORY"/lib-httpd.sh
 start_httpd
 
diff --git a/t/t6112-rev-list-filters-objects.sh b/t/t6112-rev-list-filters-objects.sh
index 0a37dd5f9..ecdf6b4c3 100755
--- a/t/t6112-rev-list-filters-objects.sh
+++ b/t/t6112-rev-list-filters-objects.sh
@@ -196,6 +196,19 @@ test_expect_success 'verify sparse:oid=oid-ish omits top-level files' '
 	test_cmp observed expected
 '
 
+# Test tree:none filter.
+
+test_expect_success 'verify tree:none includes trees in "filtered" output' '
+	git -C r3 rev-list HEAD --quiet --objects --filter-print-omitted --filter=tree:none \
+		| awk -f print_1.awk \
+		| sed s/~// \
+		| xargs -n1 git -C r3 cat-file -t \
+		| sort -u >filtered_types &&
+	printf "blob\ntree\n" > expected &&
+	test_cmp filtered_types expected
+'
+
+
 # Delete some loose objects and use rev-list, but WITHOUT any filtering.
 # This models previously omitted objects that we did not receive.
 
-- 
2.18.0.597.ga71716f1ad-goog