feat: add 0089-hard-required-keys

Author: coderhyy

type-challenges/0089-hard-required-keys/template.ts

@@ -0,0 +1,3 @@
+type RequiredKeys<T> = keyof {
+  [K in keyof T as T[K] extends Required<T>[K] ? K : never]: T[K];
+};

type-challenges/0089-hard-required-keys/test-cases.ts

@@ -0,0 +1,13 @@
+import type { Equal, Expect } from "@type-challenges/utils";
+
+type cases = [
+  Expect<Equal<RequiredKeys<{ a: number; b?: string }>, "a">>,
+  Expect<Equal<RequiredKeys<{ a: undefined; b?: undefined }>, "a">>,
+  Expect<
+    Equal<
+      RequiredKeys<{ a: undefined; b?: undefined; c: string; d: null }>,
+      "a" | "c" | "d"
+    >
+  >,
+  Expect<Equal<RequiredKeys<{}>, never>>
+];