Subject: [PATCH 2/2] shallow: handling fetch relative-deepen

From: "Samo Pogačnik via GitGitGadget" <[email-masked]>
Date: Tue, 09 Dec 2025 18:11:20 +0000

From: =?UTF-8?q?Samo=20Poga=C4=8Dnik?= <[email-masked]>

When a shallowed repository gets deepened beyond the beginning of a
merged branch, we may endup with some shallows, that are behind the
reachable ones. Added test 'fetching deepen beyond merged branch'
exposes that behaviour.

On the other hand, it seems that equivalent absolute depth driven
fetches result in all the correct shallows. That led to this proposal,
which unifies absolute and relative deepening in a way that the same
get_shallow_commits() call is used in both cases. The difference is
only that depth is adapted for relative deepening by measuring
equivalent depth of current local shallow commits in the current remote
repo. Thus a new function get_shallows_depth() has been added and the
function get_reachable_list() became redundant / removed.

The get_shallows_depth() function also shares the logic of the
get_shallow_commits() function, but it focuses on counting depth of
each existing shallow commit. The minimum result is stored as
'data->deepen_relative', which is set not to be zero for relative
deepening anyway. That way we can allways summ 'data->deepen_relative'
and 'depth' values, because 'data->deepen_relative' is always 0 in
absolute deepening.

Signed-off-by: Samo Pogačnik <[email-masked]>
---
 t/t5500-fetch-pack.sh |  24 +++++++
 upload-pack.c         | 142 +++++++++++++++++++++++-------------------
 2 files changed, 102 insertions(+), 64 deletions(-)

diff --git a/t/t5500-fetch-pack.sh b/t/t5500-fetch-pack.sh
index 2677cd5faa..d05c45e32b 100755
--- a/t/t5500-fetch-pack.sh
+++ b/t/t5500-fetch-pack.sh
@@ -955,6 +955,30 @@ test_expect_success 'fetching deepen' '
 	)
 '
 
+test_expect_success 'fetching deepen beyond merged branch' '
+	test_create_repo shallow-deepen-merged &&
+	(
+		cd shallow-deepen-merged &&
+		git commit --allow-empty -m one &&
+		git commit --allow-empty -m two &&
+		git commit --allow-empty -m three &&
+		git switch -c branch &&
+		git commit --allow-empty -m four &&
+		git commit --allow-empty -m five &&
+		git switch main &&
+		git merge --no-ff branch &&
+		cd - &&
+		git clone --bare --depth 3 "file://$(pwd)/shallow-deepen-merged" deepen.git &&
+		git -C deepen.git fetch origin --deepen=1 &&
+		echo "Shallow:" && cat deepen.git/shallow &&
+		git -C deepen.git rev-list --all >actual &&
+		echo "All rev-lis:" && cat actual &&
+		for commit in $(sed "/^$/d" deepen.git/shallow); do
+			test_grep "$commit" actual || exit 1
+		done
+	)
+'
+
 test_negotiation_algorithm_default () {
 	test_when_finished rm -rf clientv0 clientv2 &&
 	rm -rf server client &&
diff --git a/upload-pack.c b/upload-pack.c
index 2d2b70cbf2..ecd3e7f5ef 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -33,6 +33,7 @@
 #include "json-writer.h"
 #include "strmap.h"
 #include "promisor-remote.h"
+#include "tag.h"
 
 /* Remember to update object flag allocation in object.h */
 #define THEY_HAVE	(1u << 11)
@@ -704,54 +705,82 @@ error:
 	return -1;
 }
 
-static int get_reachable_list(struct upload_pack_data *data,
-			      struct object_array *reachable)
+define_commit_slab(commit_depth, int *);
+static void free_depth_in_slab(int **ptr)
 {
-	struct child_process cmd = CHILD_PROCESS_INIT;
-	int i;
-	struct object *o;
-	char namebuf[GIT_MAX_HEXSZ + 2]; /* ^ + hash + LF */
-	const unsigned hexsz = the_hash_algo->hexsz;
-	int ret;
-
-	if (do_reachable_revlist(&cmd, &data->shallows, reachable,
-				 data->allow_uor) < 0) {
-		ret = -1;
-		goto out;
-	}
-
-	while ((i = read_in_full(cmd.out, namebuf, hexsz + 1)) == hexsz + 1) {
-		struct object_id oid;
-		const char *p;
-
-		if (parse_oid_hex(namebuf, &oid, &p) || *p != '\n')
-			break;
-
-		o = lookup_object(the_repository, &oid);
-		if (o && o->type == OBJ_COMMIT) {
-			o->flags &= ~TMP_MARK;
+	FREE_AND_NULL(*ptr);
+}
+static void get_shallows_depth(struct upload_pack_data *data)
+{
+	size_t i = 0, j;
+	int cur_depth = 0, cur_depth_shallow = 0;
+	struct object_array stack = OBJECT_ARRAY_INIT;
+	struct commit *commit = NULL;
+	struct commit_graft *graft;
+	struct commit_depth depths;
+	struct object_array *heads = &data->want_obj;
+	struct object_array *shallows = &data->shallows;
+
+	init_commit_depth(&depths);
+	while (commit || i < heads->nr || stack.nr) {
+		struct commit_list *p;
+		if (!commit) {
+			if (i < heads->nr) {
+				int **depth_slot;
+				commit = (struct commit *)
+					deref_tag(the_repository,
+						  heads->objects[i++].item,
+						  NULL, 0);
+				if (!commit || commit->object.type != OBJ_COMMIT) {
+					commit = NULL;
+					continue;
+				}
+				depth_slot = commit_depth_at(&depths, commit);
+				if (!*depth_slot)
+					*depth_slot = xmalloc(sizeof(int));
+				**depth_slot = 0;
+				cur_depth = 0;
+			} else {
+				commit = (struct commit *)
+					object_array_pop(&stack);
+				cur_depth = **commit_depth_at(&depths, commit);
+			}
 		}
-	}
-	for (i = get_max_object_index(the_repository); 0 < i; i--) {
-		o = get_indexed_object(the_repository, i - 1);
-		if (o && o->type == OBJ_COMMIT &&
-		    (o->flags & TMP_MARK)) {
-			add_object_array(o, NULL, reachable);
-				o->flags &= ~TMP_MARK;
+		parse_commit_or_die(commit);
+		cur_depth++;
+		for (j = 0; j < shallows->nr; j++)
+			if (oideq(&commit->object.oid, &shallows->objects[j].item->oid))
+				if ((!cur_depth_shallow) || (cur_depth < cur_depth_shallow))
+					cur_depth_shallow = cur_depth;
+
+		if ((is_repository_shallow(the_repository) && !commit->parents &&
+		     (graft = lookup_commit_graft(the_repository, &commit->object.oid)) != NULL &&
+		     graft->nr_parent < 0)) {
+			commit = NULL;
+			continue;
+		}
+		for (p = commit->parents, commit = NULL; p; p = p->next) {
+			int **depth_slot = commit_depth_at(&depths, p->item);
+			if (!*depth_slot) {
+				*depth_slot = xmalloc(sizeof(int));
+				**depth_slot = cur_depth;
+			} else {
+				if (cur_depth >= **depth_slot)
+					continue;
+				**depth_slot = cur_depth;
+			}
+			if (p->next)
+				add_object_array(&p->item->object,
+						NULL, &stack);
+			else {
+				commit = p->item;
+				cur_depth = **commit_depth_at(&depths, commit);
+			}
 		}
 	}
-	close(cmd.out);
-
-	if (finish_command(&cmd)) {
-		ret = -1;
-		goto out;
-	}
-
-	ret = 0;
-
-out:
-	child_process_clear(&cmd);
-	return ret;
+	deep_clear_commit_depth(&depths, free_depth_in_slab);
+	object_array_clear(&stack);
+	data->deepen_relative = cur_depth_shallow;
 }
 
 static int has_unreachable(struct object_array *src, enum allow_uor allow_uor)
@@ -881,29 +910,14 @@ static void deepen(struct upload_pack_data *data, int depth)
 			struct object *object = data->shallows.objects[i].item;
 			object->flags |= NOT_SHALLOW;
 		}
-	} else if (data->deepen_relative) {
-		struct object_array reachable_shallows = OBJECT_ARRAY_INIT;
-		struct commit_list *result;
-
-		/*
-		 * Checking for reachable shallows requires that our refs be
-		 * marked with OUR_REF.
-		 */
-		refs_head_ref_namespaced(get_main_ref_store(the_repository),
-					 check_ref, data);
-		for_each_namespaced_ref_1(check_ref, data);
-
-		get_reachable_list(data, &reachable_shallows);
-		result = get_shallow_commits(&reachable_shallows,
-					     depth + 1,
-					     SHALLOW, NOT_SHALLOW);
-		send_shallow(data, result);
-		free_commit_list(result);
-		object_array_clear(&reachable_shallows);
 	} else {
 		struct commit_list *result;
 
-		result = get_shallow_commits(&data->want_obj, depth,
+		if (data->deepen_relative)
+			get_shallows_depth(data);
+
+		result = get_shallow_commits(&data->want_obj,
+					     data->deepen_relative + depth,
 					     SHALLOW, NOT_SHALLOW);
 		send_shallow(data, result);
 		free_commit_list(result);
-- 
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