Jsonify: Fix handling of tuples (#638)

Co-authored-by: Pedro Cattori <pcattori@gmail.com>

source/jsonify.d.ts

@@ -1,16 +1,26 @@
 import type {JsonPrimitive, JsonValue} from './basic';
 import type {EmptyObject} from './empty-object';
 import type {UndefinedToOptional} from './internal';
+import type {IsAny} from './is-any';
+import type {IsNever} from './is-never';
 import type {NegativeInfinity, PositiveInfinity} from './numeric';
 import type {TypedArray} from './typed-array';
-import type {IsAny} from './is-any';
 
 // Note: The return value has to be `any` and not `unknown` so it can match `void`.
 type NotJsonable = ((...arguments_: any[]) => any) | undefined | symbol;
 
-type JsonifyTuple<T extends [unknown, ...unknown[]]> = {
-	[Key in keyof T]: T[Key] extends NotJsonable ? null : Jsonify<T[Key]>;
-};
+type FilterNonNever<T extends unknown[]> = T extends [infer F, ...infer R]
+	? IsNever<F> extends true
+		? FilterNonNever<R>
+		: [F, ...FilterNonNever<R>]
+	: IsNever<T[number]> extends true
+		? []
+		: T;
+
+// Handles tuples and arrays
+type JsonifyList<T extends unknown[]> = T extends [infer F, ...infer R]
+	? FilterNonNever<[Jsonify<F>, ...JsonifyList<R>]>
+	: Array<Jsonify<T[number]>>;
 
 type FilterJsonableKeys<T extends object> = {
 	[Key in keyof T]: T[Key] extends NotJsonable ? never : Key;
@@ -107,7 +117,7 @@ export type Jsonify<T> = IsAny<T> extends true
 										: T extends []
 											? []
 											: T extends [unknown, ...unknown[]]
-												? JsonifyTuple<T>
+												? JsonifyList<T>
 												: T extends ReadonlyArray<infer U>
 													? Array<U extends NotJsonable ? null : Jsonify<U>>
 													: T extends object

test-d/jsonify.ts

@@ -222,6 +222,9 @@ expectType<[string, string]>(tupleJson);
 declare const tupleRestJson: Jsonify<[string, ...Date[]]>;
 expectType<[string, ...string[]]>(tupleRestJson);
 
+declare const tupleStringJson: Jsonify<string[] & ['some value']>;
+expectType<['some value']>(tupleStringJson);
+
 // BigInt fails JSON.stringify
 declare const bigInt: Jsonify<bigint>;
 expectType<never>(bigInt);