From 60c10242c5f74a012d7eebb89622552819f8f097 Mon Sep 17 00:00:00 2001
From: m-shaka <buddha0818@gmail.com>
Date: Tue, 2 Jul 2024 21:34:46 +0900
Subject: [PATCH] `Jsonify`: Convert `undefined` to `null` in union element of
 array (#901)

---
 source/jsonify.d.ts | 3 ++-
 test-d/jsonify.ts   | 6 ++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/source/jsonify.d.ts b/source/jsonify.d.ts
index ef5d726dc..a1954cd20 100644
--- a/source/jsonify.d.ts
+++ b/source/jsonify.d.ts
@@ -12,6 +12,7 @@ import type {UnknownArray} from './unknown-array';
 type NotJsonable = ((...arguments_: any[]) => any) | undefined | symbol;
 
 type NeverToNull<T> = IsNever<T> extends true ? null : T;
+type UndefinedToNull<T> = T extends undefined ? null : T;
 
 // Handles tuples and arrays
 type JsonifyList<T extends UnknownArray> = T extends readonly []
@@ -20,7 +21,7 @@ type JsonifyList<T extends UnknownArray> = T extends readonly []
 		? [NeverToNull<Jsonify<F>>, ...JsonifyList<R>]
 		: IsUnknown<T[number]> extends true
 			? []
-			: Array<T[number] extends NotJsonable ? null : Jsonify<T[number]>>;
+			: Array<T[number] extends NotJsonable ? null : Jsonify<UndefinedToNull<T[number]>>>;
 
 type FilterJsonableKeys<T extends object> = {
 	[Key in keyof T]: T[Key] extends NotJsonable ? never : Key;
diff --git a/test-d/jsonify.ts b/test-d/jsonify.ts
index b8bc94d07..f505ca883 100644
--- a/test-d/jsonify.ts
+++ b/test-d/jsonify.ts
@@ -192,6 +192,12 @@ expectType<never>(plainSymbol);
 declare const arrayMemberUndefined: Jsonify<Array<typeof undefined>>;
 expectType<null[]>(arrayMemberUndefined);
 
+declare const arrayMemberUnionWithUndefined: Jsonify<Array<typeof undefined | typeof number>>;
+expectType<Array<null | number>>(arrayMemberUnionWithUndefined);
+
+declare const arrayMemberUnionWithUndefinedDeep: Jsonify<Array<Array<typeof undefined | typeof number>> | {foo: Array<typeof undefined | typeof number>}>;
+expectType<Array<Array<null | number>> | {foo: Array<null | number>}>(arrayMemberUnionWithUndefinedDeep);
+
 declare const arrayMemberFunction: Jsonify<Array<typeof function_>>;
 expectType<null[]>(arrayMemberFunction);