When passing the same packfile both as included and excluded via the
`--stdin-packs` option, then we will return an error because the
excluded packfile cannot be found. This is because we will only set the
`util` pointer for the included packfile list if it was found, so that
we later die when we notice that it's in fact not set for the excluded
packfile list.

Fix this bug by always setting the `util` pointer for both the included
and excluded list entries.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 builtin/pack-objects.c        |  8 +++-----
 t/t5331-pack-objects-stdin.sh | 26 ++++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index fdf3f440be..522eb4dd31 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -3366,11 +3366,9 @@ static void read_packs_list_from_stdin(void)
 	for (p = get_all_packs(the_repository); p; p = p->next) {
 		const char *pack_name = pack_basename(p);
 
-		item = string_list_lookup(&include_packs, pack_name);
-		if (!item)
-			item = string_list_lookup(&exclude_packs, pack_name);
-
-		if (item)
+		if ((item = string_list_lookup(&include_packs, pack_name)))
+			item->util = p;
+		if ((item = string_list_lookup(&exclude_packs, pack_name)))
 			item->util = p;
 	}
 
diff --git a/t/t5331-pack-objects-stdin.sh b/t/t5331-pack-objects-stdin.sh
index ab34cfc729..f389a78b38 100755
--- a/t/t5331-pack-objects-stdin.sh
+++ b/t/t5331-pack-objects-stdin.sh
@@ -7,6 +7,12 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
+packed_objects() {
+	git show-index <"$1" >tmp-object-list &&
+	cut -d' ' -f2 tmp-object-list &&
+	rm tmp-object-list
+ }
+
 test_expect_success 'pack-objects --stdin with duplicate packfile' '
 	test_when_finished "rm -fr repo" &&
 
@@ -26,4 +32,24 @@ test_expect_success 'pack-objects --stdin with duplicate packfile' '
 	)
 '
 
+test_expect_success 'pack-objects --stdin with same packfile excluded and included' '
+	test_when_finished "rm -fr repo" &&
+
+	git init repo &&
+	(
+		cd repo &&
+		test_commit "commit" &&
+		git repack -ad &&
+
+		(
+			basename .git/objects/pack/pack-*.pack &&
+			printf "^%s\n" "$(basename .git/objects/pack/pack-*.pack)"
+		) >packfiles &&
+
+		git pack-objects --stdin-packs generated-pack <packfiles &&
+		packed_objects generated-pack-*.idx >packed-objects &&
+		test_must_be_empty packed-objects
+	)
+'
+
 test_done
-- 
2.40.0