add tree path array

tree-path-array.ts

@@ -0,0 +1,33 @@
+import type { ExpectExtends, ExpectFalse, ExpectTrue } from '@type-challenges/utils'
+
+declare const example: {
+  foo: {
+    bar: {
+      a: string
+    }
+    baz: {
+      b: number
+      c: number
+    }
+  }
+}
+
+type cases = [
+  ExpectTrue<ExpectExtends<Path<typeof example['foo']['bar']>, ['a']>>,
+  ExpectTrue<ExpectExtends<Path<typeof example['foo']['baz']>, ['b'] | ['c'] >>,
+  ExpectTrue<ExpectExtends<Path<typeof example['foo']>, ['bar'] | ['baz'] | ['bar', 'a'] | ['baz', 'b'] | ['baz', 'c']>>,
+  ExpectFalse<ExpectExtends<Path<typeof example['foo']['bar']>, ['z']>>,
+];
+
+type Path<
+  T extends Record<PropertyKey, unknown>,
+  Keys extends keyof T = keyof T,
+> =
+Keys extends never
+  ? never
+  // This is the fancy part
+  : [Keys] | [Keys, ...(
+      T[Keys] extends Record<string, unknown>
+        ? Path<T[Keys]>
+        : never
+    )];