list-objects-filter: implement filter tree:0

Teach list-objects the "tree:0" 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:0 - 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 considered only:commits as a name, but this is inaccurate because
it suggests that annotated tags are omitted, but actually they are
included.

The name "tree:0" allows later filtering based on depth, i.e. "tree:1"
would filter out all but the root tree and blobs. In order to avoid
confusion between 0 and capital O, the documentation was worded in a
somewhat round-about way that also hints at this future improvement to
the feature.

Signed-off-by: Matthew DeVore <matvore@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

3 files changed, 85 insertions, 0 deletions

diff --git a/t/t5317-pack-objects-filter-objects.sh b/t/t5317-pack-objects-filter-objects.sh
index 9839b48c1c..510d3537f6 100755
--- a/t/t5317-pack-objects-filter-objects.sh
+++ b/t/t5317-pack-objects-filter-objects.sh
@@ -72,6 +72,34 @@ 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:0' '
+	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:0 packfile has no blobs or trees' '
+	git -C r1 pack-objects --rev --stdout --filter=tree:0 >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:0' '
+	# We should get the tree specified directly but not its blobs or subtrees.
+	git -C r1 pack-objects --rev --stdout --filter=tree:0 >commitsonly.pack <<-EOF &&
+	HEAD:
+	EOF
+	git -C r1 index-pack ../commitsonly.pack &&
+	git -C r1 verify-pack -v ../commitsonly.pack >objs &&
+	awk "/tree|blob/{print \$1}" objs >trees_and_blobs &&
+	git -C r1 rev-parse HEAD: >expected &&
+	test_cmp expected 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 bbbe7537df..53fbf7db88 100755
--- a/t/t5616-partial-clone.sh
+++ b/t/t5616-partial-clone.sh
@@ -154,6 +154,48 @@ test_expect_success 'partial clone with transfer.fsckobjects=1 uses index-pack -
 	grep "git index-pack.*--fsck-objects" trace
 '
 
+test_expect_success 'use fsck before and after manually fetching a missing subtree' '
+	# push new commit so server has a subtree
+	mkdir src/dir &&
+	echo "in dir" >src/dir/file.txt &&
+	git -C src add dir/file.txt &&
+	git -C src commit -m "file in dir" &&
+	git -C src push -u srv master &&
+	SUBTREE=$(git -C src rev-parse HEAD:dir) &&
+
+	rm -rf dst &&
+	git clone --no-checkout --filter=tree:0 "file://$(pwd)/srv.bare" dst &&
+	git -C dst fsck &&
+
+	# Make sure we only have commits, and all trees and blobs are missing.
+	git -C dst rev-list --missing=allow-any --objects master \
+		>fetched_objects &&
+	awk -f print_1.awk fetched_objects |
+	xargs -n1 git -C dst cat-file -t >fetched_types &&
+
+	sort -u fetched_types >unique_types.observed &&
+	echo commit >unique_types.expected &&
+	test_cmp unique_types.expected unique_types.observed &&
+
+	# Auto-fetch a tree with cat-file.
+	git -C dst cat-file -p $SUBTREE >tree_contents &&
+	grep file.txt tree_contents &&
+
+	# fsck still works after an auto-fetch of a tree.
+	git -C dst fsck &&
+
+	# Auto-fetch all remaining trees and blobs with --missing=error
+	git -C dst rev-list --missing=error --objects master >fetched_objects &&
+	test_line_count = 70 fetched_objects &&
+
+	awk -f print_1.awk fetched_objects |
+	xargs -n1 git -C dst cat-file -t >fetched_types &&
+
+	sort -u fetched_types >unique_types.observed &&
+	printf "blob\ncommit\ntree\n" >unique_types.expected &&
+	test_cmp unique_types.expected unique_types.observed
+'
+
 test_expect_success 'partial clone fetches blobs pointed to by refs even if normally filtered out' '
 	rm -rf src dst &&
 	git init src &&
diff --git a/t/t6112-rev-list-filters-objects.sh b/t/t6112-rev-list-filters-objects.sh
index 0d4d43894b..2cbb81d3bb 100755
--- a/t/t6112-rev-list-filters-objects.sh
+++ b/t/t6112-rev-list-filters-objects.sh
@@ -230,6 +230,21 @@ test_expect_success 'rev-list W/ --missing=print and --missing=allow-any for tre
 	test_must_be_empty rev_list_err
 '
 
+# Test tree:0 filter.
+
+test_expect_success 'verify tree:0 includes trees in "filtered" output' '
+	git -C r3 rev-list --quiet --objects --filter-print-omitted \
+		--filter=tree:0 HEAD >revs &&
+
+	awk -f print_1.awk revs |
+	sed s/~// |
+	xargs -n1 git -C r3 cat-file -t >unsorted_filtered_types &&
+
+	sort -u unsorted_filtered_types >filtered_types &&
+	printf "blob\ntree\n" >expected &&
+	test_cmp expected filtered_types
+'
+
 # Delete some loose objects and use rev-list, but WITHOUT any filtering.
 # This models previously omitted objects that we did not receive.