fix: support undefined as optional keys in loader data

Author: itsMapleLeaf

packages/remix-react/__tests__/hook-types-test.tsx

@@ -100,4 +100,14 @@ describe("type serializer", () => {
     type response = UseDataFunctionReturn<Loader>;
     isEqual<response, { arg: string }>(true);
   });
+
+  it("makes keys optional if the value is undefined", () => {
+    type AppData = {
+      arg1: string;
+      arg2: number | undefined;
+      arg3: undefined;
+    };
+    type response = UseDataFunctionReturn<AppData>;
+    isEqual<response, { arg1: string; arg2?: number }>(true);
+  });
 });

packages/remix-react/components.tsx

@@ -1336,6 +1336,7 @@ type JsonPrimitives =
   | Boolean
   | null;
 type NonJsonPrimitives = undefined | Function | symbol;
+
 type SerializeType<T> = T extends JsonPrimitives
   ? T
   : T extends NonJsonPrimitives
@@ -1353,13 +1354,21 @@ type SerializeType<T> = T extends JsonPrimitives
   : T extends (infer U)[]
   ? (U extends NonJsonPrimitives ? null : SerializeType<U>)[]
   : T extends object
-  ? {
-      [k in keyof T as T[k] extends NonJsonPrimitives
-        ? never
-        : k]: SerializeType<T[k]>;
-    }
+  ? SerializeObject<UndefinedOptionals<T>>
   : never;
 
+type SerializeObject<T> = {
+  [k in keyof T as T[k] extends NonJsonPrimitives ? never : k]: SerializeType<
+    T[k]
+  >;
+};
+
+type UndefinedOptionals<T> = {
+  [k in keyof T as undefined extends T[k] ? never : k]: NonNullable<T[k]>;
+} & {
+  [k in keyof T as undefined extends T[k] ? k : never]?: NonNullable<T[k]>;
+};
+
 export type UseDataFunctionReturn<T extends DataOrFunction> = T extends (
   ...args: any[]
 ) => infer Output