Merge branch 'jt/pack-objects-prefetch-in-batch'

While packing many objects in a repository with a promissor remote,
lazily fetching missing objects from the promissor remote one by
one may be inefficient---the code now attempts to fetch all the
missing objects in batch (obviously this won't work for a lazy
clone that lazily fetches tree objects as you cannot even enumerate
what blobs are missing until you learn which trees are missing).

* jt/pack-objects-prefetch-in-batch:
  pack-objects: prefetch objects to be packed
  pack-objects: refactor to oid_object_info_extended

builtin/pack-objects.c

@@ -35,6 +35,7 @@
 #include "midx.h"
 #include "trace2.h"
 #include "shallow.h"
+#include "promisor-remote.h"
 
 #define IN_PACK(obj) oe_in_pack(&to_pack, obj)
 #define SIZE(obj) oe_size(&to_pack, obj)
@@ -1704,9 +1705,30 @@ static int can_reuse_delta(const struct object_id *base_oid,
 	return 0;
 }
 
-static void check_object(struct object_entry *entry)
+static void prefetch_to_pack(uint32_t object_index_start) {
+	struct oid_array to_fetch = OID_ARRAY_INIT;
+	uint32_t i;
+
+	for (i = object_index_start; i < to_pack.nr_objects; i++) {
+		struct object_entry *entry = to_pack.objects + i;
+
+		if (!oid_object_info_extended(the_repository,
+					      &entry->idx.oid,
+					      NULL,
+					      OBJECT_INFO_FOR_PREFETCH))
+			continue;
+		oid_array_append(&to_fetch, &entry->idx.oid);
+	}
+	promisor_remote_get_direct(the_repository,
+				   to_fetch.oid, to_fetch.nr);
+	oid_array_clear(&to_fetch);
+}
+
+static void check_object(struct object_entry *entry, uint32_t object_index)
 {
 	unsigned long canonical_size;
+	enum object_type type;
+	struct object_info oi = {.typep = &type, .sizep = &canonical_size};
 
 	if (IN_PACK(entry)) {
 		struct packed_git *p = IN_PACK(entry);
@@ -1840,8 +1862,18 @@ static void check_object(struct object_entry *entry)
 		unuse_pack(&w_curs);
 	}
 
-	oe_set_type(entry,
-		    oid_object_info(the_repository, &entry->idx.oid, &canonical_size));
+	if (oid_object_info_extended(the_repository, &entry->idx.oid, &oi,
+				     OBJECT_INFO_SKIP_FETCH_OBJECT | OBJECT_INFO_LOOKUP_REPLACE) < 0) {
+		if (has_promisor_remote()) {
+			prefetch_to_pack(object_index);
+			if (oid_object_info_extended(the_repository, &entry->idx.oid, &oi,
+						     OBJECT_INFO_SKIP_FETCH_OBJECT | OBJECT_INFO_LOOKUP_REPLACE) < 0)
+				type = -1;
+		} else {
+			type = -1;
+		}
+	}
+	oe_set_type(entry, type);
 	if (entry->type_valid) {
 		SET_SIZE(entry, canonical_size);
 	} else {
@@ -2061,7 +2093,7 @@ static void get_object_details(void)
 
 	for (i = 0; i < to_pack.nr_objects; i++) {
 		struct object_entry *entry = sorted_by_offset[i];
-		check_object(entry);
+		check_object(entry, i);
 		if (entry->type_valid &&
 		    oe_size_greater_than(&to_pack, entry, big_file_threshold))
 			entry->no_try_delta = 1;

t/t5300-pack-object.sh

@@ -497,4 +497,40 @@ test_expect_success 'make sure index-pack detects the SHA1 collision (large blob
 	)
 '
 
+test_expect_success 'prefetch objects' '
+	rm -rf server client &&
+
+	git init server &&
+	test_config -C server uploadpack.allowanysha1inwant 1 &&
+	test_config -C server uploadpack.allowfilter 1 &&
+	test_config -C server protocol.version 2 &&
+
+	echo one >server/one &&
+	git -C server add one &&
+	git -C server commit -m one &&
+	git -C server branch one_branch &&
+
+	echo two_a >server/two_a &&
+	echo two_b >server/two_b &&
+	git -C server add two_a two_b &&
+	git -C server commit -m two &&
+
+	echo three >server/three &&
+	git -C server add three &&
+	git -C server commit -m three &&
+	git -C server branch three_branch &&
+
+	# Clone, fetch "two" with blobs excluded, and re-push it. This requires
+	# the client to have the blobs of "two" - verify that these are
+	# prefetched in one batch.
+	git clone --filter=blob:none --single-branch -b one_branch \
+		"file://$(pwd)/server" client &&
+	test_config -C client protocol.version 2 &&
+	TWO=$(git -C server rev-parse three_branch^) &&
+	git -C client fetch --filter=blob:none origin "$TWO" &&
+	GIT_TRACE_PACKET=$(pwd)/trace git -C client push origin "$TWO":refs/heads/two_branch &&
+	grep "git> done" trace >donelines &&
+	test_line_count = 1 donelines
+'
+
 test_done