Homomorphic mapped types map unknown to {}

Imagine that you have this homomorphic mapped type in TypeScript.

type R<T> = { readonly [key in keyof T]: T[key] };

When you apply this to an object type or an array type, it maps them as expected.

// X1: { readonly x: string }
type X1 = R<{ x: string }>;

// X2: readonly string[]
type X2 = R<string[]>;

It also preserves primitive types.

// X3: string
type X3 = R<string>;

// X4: never
type X4 = R<never>;

// X5: undefined
type X5 = R<undefined>;

But it maps unknown to {}, and any to { readonly [x: string]: any } , which I didn’t expect.

// X6: {}
type X6 = R<unknown>;

// X7: { readonly [x: string]: any }
type X7 = R<any>;