[PATCH 3/3] fetch, remote: retain old OIDs when pruning refs

[Maciej Ciemborowicz <maciej.ciemborowicz@gmail.com>]

get_stale_heads() records the current value of each stale local ref in its
new_oid member. The pruning paths discard that value and request unconditional
deletion, so reference-transaction hooks receive a null old OID.

Carry the recorded values into the deletion transactions. This reuses data
collected while finding stale refs and therefore requires no additional ref
reads.

Signed-off-by: Maciej Ciemborowicz <maciej.ciemborowicz@gmail.com>
---
 builtin/fetch.c                  | 11 ++++++---
 builtin/remote.c                 | 30 +++++++++++++++++++----
 t/t1416-ref-transaction-hooks.sh | 42 ++++++++++++++++++++++++++++++++
 3 files changed, 75 insertions(+), 8 deletions(-)

diff --git a/builtin/fetch.c b/builtin/fetch.c
index d202147b21..a982d7541f 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -1452,14 +1452,18 @@ static int prune_refs(struct display_state *display_state,
 	struct ref *ref, *stale_refs = get_stale_heads(rs, ref_map);
 	struct strbuf err = STRBUF_INIT;
 	struct string_list refnames = STRING_LIST_INIT_NODUP;
+	struct oid_array old_oids = OID_ARRAY_INIT;
 
-	for (ref = stale_refs; ref; ref = ref->next)
+	for (ref = stale_refs; ref; ref = ref->next) {
 		string_list_append(&refnames, ref->name);
+		oid_array_append(&old_oids, &ref->new_oid);
+	}
 
 	if (!dry_run) {
 		if (transaction) {
 			for (ref = stale_refs; ref; ref = ref->next) {
-				result = ref_transaction_delete(transaction, ref->name, NULL,
+				result = ref_transaction_delete(transaction, ref->name,
+							&ref->new_oid,
 								NULL, 0, "fetch: prune", &err);
 				if (result)
 					goto cleanup;
@@ -1467,7 +1471,7 @@ static int prune_refs(struct display_state *display_state,
 		} else {
 			result = refs_delete_refs(get_main_ref_store(the_repository),
 						  "fetch: prune", &refnames,
-						  NULL, 0);
+						  &old_oids, 0);
 		}
 	}
 
@@ -1487,6 +1491,7 @@ static int prune_refs(struct display_state *display_state,
 
 cleanup:
 	string_list_clear(&refnames, 0);
+	oid_array_clear(&old_oids);
 	strbuf_release(&err);
 	free_refs(stale_refs);
 	return result;
diff --git a/builtin/remote.c b/builtin/remote.c
index 13d3cc52dd..7b0ad13342 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -17,6 +17,7 @@
 #include "refs.h"
 #include "refspec.h"
 #include "odb.h"
+#include "oid-array.h"
 #include "strvec.h"
 #include "commit-reach.h"
 #include "progress.h"
@@ -380,6 +381,11 @@ struct ref_states {
 	int queried;
 };
 
+struct stale_ref {
+	struct object_id oid;
+	char name[FLEX_ARRAY];
+};
+
 #define REF_STATES_INIT { \
 	.new_refs = STRING_LIST_INIT_DUP, \
 	.skipped = STRING_LIST_INIT_DUP, \
@@ -410,9 +416,13 @@ static int get_ref_states(const struct ref *remote_refs, struct ref_states *stat
 	}
 	stale_refs = get_stale_heads(&states->remote->fetch, fetch_map);
 	for (ref = stale_refs; ref; ref = ref->next) {
+		struct stale_ref *stale_ref;
 		struct string_list_item *item =
 			string_list_append(&states->stale, abbrev_branch(ref->name));
-		item->util = xstrdup(ref->name);
+
+		FLEX_ALLOC_STR(stale_ref, name, ref->name);
+		oidcpy(&stale_ref->oid, &ref->new_oid);
+		item->util = stale_ref;
 	}
 	free_refs(stale_refs);
 	free_refs(fetch_map);
@@ -1627,6 +1637,7 @@ static int prune_remote(const char *remote, int dry_run)
 	int result = 0;
 	struct ref_states states = REF_STATES_INIT;
 	struct string_list refs_to_prune = STRING_LIST_INIT_NODUP;
+	struct oid_array old_oids = OID_ARRAY_INIT;
 	struct string_list_item *item;
 
 	get_remote_ref_states(remote, &states, GET_REF_STATES);
@@ -1639,17 +1650,25 @@ static int prune_remote(const char *remote, int dry_run)
 	printf_ln(_("Pruning %s"), remote);
 	printf_ln(_("URL: %s"), states.remote->url.v[0]);
 
-	for_each_string_list_item(item, &states.stale)
-		string_list_append(&refs_to_prune, item->util);
+	for_each_string_list_item(item, &states.stale) {
+		struct stale_ref *stale_ref = item->util;
+		struct string_list_item *to_prune;
+
+		to_prune = string_list_append(&refs_to_prune, stale_ref->name);
+		to_prune->util = &stale_ref->oid;
+	}
 	string_list_sort(&refs_to_prune);
+	for_each_string_list_item(item, &refs_to_prune)
+		oid_array_append(&old_oids, item->util);
 
 	if (!dry_run)
 		result |= refs_delete_refs(get_main_ref_store(the_repository),
 					   "remote: prune", &refs_to_prune,
-					   NULL, 0);
+					   &old_oids, 0);
 
 	for_each_string_list_item(item, &states.stale) {
-		const char *refname = item->util;
+		struct stale_ref *stale_ref = item->util;
+		const char *refname = stale_ref->name;
 
 		if (dry_run)
 			printf_ln(_(" * [would prune] %s"),
@@ -1663,6 +1682,7 @@ static int prune_remote(const char *remote, int dry_run)
 				   stdout, " ", dry_run, &refs_to_prune);
 
 	string_list_clear(&refs_to_prune, 0);
+	oid_array_clear(&old_oids);
 	free_remote_ref_states(&states);
 	return result;
 }
diff --git a/t/t1416-ref-transaction-hooks.sh b/t/t1416-ref-transaction-hooks.sh
index 8d400cd7ac..39bdc1bc26 100755
--- a/t/t1416-ref-transaction-hooks.sh
+++ b/t/t1416-ref-transaction-hooks.sh
@@ -42,6 +42,48 @@ test_expect_success 'hook gets old values for batched branch/tag deletion' '
 	test_cmp expect actual
 '
 
+test_expect_success 'hook gets old values when pruning remote refs' '
+	test_create_repo empty.git --bare &&
+	test_create_repo prune &&
+	git -C prune remote add origin ../empty.git &&
+	test_commit -C prune one &&
+	one=$(git -C prune rev-parse HEAD) &&
+	test_commit -C prune two &&
+	two=$(git -C prune rev-parse HEAD) &&
+	git -C prune update-ref refs/remotes/origin/remote-prune-z "$one" &&
+	git -C prune update-ref refs/remotes/origin/remote-prune-a "$two" &&
+	git -C prune pack-refs --all &&
+	test_hook -C prune reference-transaction <<-\EOF &&
+		if test "$1" = committed
+		then
+			# Ignore backend-internal zero-to-zero records.
+			while read -r old new ref
+			do
+				case "$old" in
+				*[!0]*)
+					echo "$old $new $ref"
+					;;
+				esac
+			done >>actual
+		fi
+	EOF
+	(
+		cd prune &&
+		git remote prune origin &&
+		git update-ref refs/remotes/origin/fetch-prune "$one" &&
+		git fetch --prune origin &&
+		git update-ref refs/remotes/origin/atomic-prune "$one" &&
+		git fetch --atomic --prune origin &&
+		cat >expect <<-EOF &&
+			$two $ZERO_OID refs/remotes/origin/remote-prune-a
+			$one $ZERO_OID refs/remotes/origin/remote-prune-z
+			$one $ZERO_OID refs/remotes/origin/fetch-prune
+			$one $ZERO_OID refs/remotes/origin/atomic-prune
+		EOF
+		test_cmp expect actual
+	)
+'
+
 test_expect_success 'hook allows updating ref if successful' '
 	git reset --hard PRE &&
 	test_hook reference-transaction <<-\EOF &&
-- 
2.39.3 (Apple Git-146)