fix(types): make array paths optional in inferred type of array default returns undefined

Fix #12420

Author: vkarpov15

test/types/schema.test.ts

@@ -870,3 +870,15 @@ function gh12431() {
   type Example = InferSchemaType<typeof testSchema>;
   expectType<{ testDate?: Date, testDecimal?: Types.Decimal128 }>({} as Example);
 }
+
+function gh12420() {
+  const TestSchema = new Schema(
+    {
+      comments: { type: [String], default: () => undefined }
+    }
+  );
+
+  expectType<{
+    comments?: string[]
+  }>({} as InferSchemaType<typeof TestSchema>);
+}

types/inferschematype.d.ts

@@ -60,6 +60,12 @@ declare module 'mongoose' {
       : unknown;
 }
 
+type IsPathDefaultUndefined<PathType> = PathType extends { default: undefined } ?
+  true :
+  PathType extends { default: (...args: any[]) => undefined } ?
+    true :
+    false;
+
 /**
  * @summary Checks if a document path is required or optional.
  * @param {P} P Document path.
@@ -69,7 +75,7 @@ type IsPathRequired<P, TypeKey extends TypeKeyBaseType = DefaultTypeKey> =
   P extends { required: true | [true, string | undefined] } | ArrayConstructor | any[]
     ? true
     : P extends (Record<TypeKey, ArrayConstructor | any[]>)
-      ? P extends { default: undefined }
+      ? IsPathDefaultUndefined<P> extends true
         ? false
         : true
       : P extends (Record<TypeKey, any>)