Related: #12311

TypeScript Version: nightly
Code

type Boxed = {
    [k in string]: {value: any}
}

type Unboxed<T extends Boxed> = {
    [K in keyof T]: T[K]['value']
}

Expected behavior:
Should compile since Boxed has index signature. T with constraint Boxed should also be indexable, with T[K] constrained by Boxed's value type, in this case, {value: any}

Actual behavior:

Error, Property 'value' does not exist on type 'T[K]'