From c46c984f42bceca671b6d186a814881e0700b662 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E6=A0=BC=E6=A1=91?=
 <33797740+boenfu@users.noreply.github.com>
Date: Wed, 6 Apr 2022 02:15:50 +0800
Subject: [PATCH] fix(NODE-4133): array field NestedPaths return type (#3184)

---
 src/mongo_types.ts                                    | 2 +-
 test/types/community/collection/filterQuery.test-d.ts | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/mongo_types.ts b/src/mongo_types.ts
index 83bf11ad6a..fbbb2a475c 100644
--- a/src/mongo_types.ts
+++ b/src/mongo_types.ts
@@ -496,7 +496,7 @@ export type NestedPaths<Type> = Type extends
   | { _bsontype: string }
   ? []
   : Type extends ReadonlyArray<infer ArrayType>
-  ? [number, ...NestedPaths<ArrayType>]
+  ? [] | [number, ...NestedPaths<ArrayType>]
   : Type extends Map<string, any>
   ? [string]
   : // eslint-disable-next-line @typescript-eslint/ban-types
diff --git a/test/types/community/collection/filterQuery.test-d.ts b/test/types/community/collection/filterQuery.test-d.ts
index 53c83f586f..2f4d7f7e53 100644
--- a/test/types/community/collection/filterQuery.test-d.ts
+++ b/test/types/community/collection/filterQuery.test-d.ts
@@ -204,6 +204,14 @@ expectNotType<Filter<PetModel>>({ 'playmates.0.name': 123 });
 expectNotType<Filter<PetModel>>({ 'laps.foo': 'string' });
 expectNotType<Filter<PetModel>>({ 'treats.0': 123 });
 
+/// it should not accept wrong types for nested document array fields
+expectError<Filter<PetModel>>({
+  treats: {
+    $elemMatch: true
+  }
+});
+expectError<Filter<PetModel>>({ treats: 123 });
+
 // Nested arrays aren't checked
 expectNotType<Filter<PetModel>>({ 'meta.deep.nestedArray.0': 'not a number' });