partial-clone: avoid fetching when looking for objects

When using partial clone, find_non_local_tags() in builtin/fetch.c
checks each remote tag to see if its object also exists locally. There
is no expectation that the object exist locally, but this function
nevertheless triggers a lazy fetch if the object does not exist. This
can be extremely expensive when asking for a commit, as we are
completely removed from the context of the non-existent object and
thus supply no "haves" in the request.

6462d5e (fetch: remove fetch_if_missing=0, 2019-11-05) removed a
global variable that prevented these fetches in favor of a bitflag.
However, some object existence checks were not updated to use this flag.

Update find_non_local_tags() to use OBJECT_INFO_SKIP_FETCH_OBJECT in
addition to OBJECT_INFO_QUICK. The _QUICK option only prevents
repreparing the pack-file structures. We need to be extremely careful
about supplying _SKIP_FETCH_OBJECT when we expect an object to not exist
due to updated refs.

This resolves a broken test in t5616-partial-clone.sh.

Signed-off-by: Derrick Stolee <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: derrickstolee

builtin/fetch.c

@@ -335,6 +335,7 @@ static void find_non_local_tags(const struct ref *refs,
 	struct string_list_item *remote_ref_item;
 	const struct ref *ref;
 	struct refname_hash_entry *item = NULL;
+	const int quick_flags = OBJECT_INFO_QUICK | OBJECT_INFO_SKIP_FETCH_OBJECT;
 
 	refname_hash_init(&existing_refs);
 	refname_hash_init(&remote_refs);
@@ -353,10 +354,9 @@ static void find_non_local_tags(const struct ref *refs,
 		 */
 		if (ends_with(ref->name, "^{}")) {
 			if (item &&
-			    !has_object_file_with_flags(&ref->old_oid,
-							OBJECT_INFO_QUICK) &&
+			    !has_object_file_with_flags(&ref->old_oid, quick_flags) &&
 			    !oidset_contains(&fetch_oids, &ref->old_oid) &&
-			    !has_object_file_with_flags(&item->oid, OBJECT_INFO_QUICK) &&
+			    !has_object_file_with_flags(&item->oid, quick_flags) &&
 			    !oidset_contains(&fetch_oids, &item->oid))
 				clear_item(item);
 			item = NULL;
@@ -370,7 +370,7 @@ static void find_non_local_tags(const struct ref *refs,
 		 * fetch.
 		 */
 		if (item &&
-		    !has_object_file_with_flags(&item->oid, OBJECT_INFO_QUICK) &&
+		    !has_object_file_with_flags(&item->oid, quick_flags) &&
 		    !oidset_contains(&fetch_oids, &item->oid))
 			clear_item(item);
 
@@ -391,7 +391,7 @@ static void find_non_local_tags(const struct ref *refs,
 	 * checked to see if it needs fetching.
 	 */
 	if (item &&
-	    !has_object_file_with_flags(&item->oid, OBJECT_INFO_QUICK) &&
+	    !has_object_file_with_flags(&item->oid, quick_flags) &&
 	    !oidset_contains(&fetch_oids, &item->oid))
 		clear_item(item);
 

t/t5616-partial-clone.sh

@@ -390,7 +390,7 @@ test_expect_failure 'verify fetch succeeds when asking for new tags' '
 	git -C tag-test -c protocol.version=2 fetch --tags origin
 '
 
-test_expect_failure 'verify fetch downloads only one pack when updating refs' '
+test_expect_success 'verify fetch downloads only one pack when updating refs' '
 	git clone --filter=blob:none "file://$(pwd)/srv.bare" pack-test &&
 	ls pack-test/.git/objects/pack/*pack >pack-list &&
 	test_line_count = 2 pack-list &&