Wrong checking return type from function

```typescript
type A = {
  a: boolean;
}
type B = (v: A) => A

const c: B = (a) => {
  return { a: true, asd: 235 }
}
```

Why I don't have error?

But if I will write such code, then I get error:
```typescript
const f = (v: A): A => {
  return { a: true, asd: 235 }
}
```