in 2.1.4, strictNullChecks make index types of nullable fields be never

[scottbessler]

TypeScript Version: 2.1.4

Code

function get<T, K extends keyof T, K2 extends keyof T[K]>(obj: T, propertyName: K, propertyName2: K2): T[K][K2] | undefined {
 const step1 = obj ? obj[propertyName] : undefined;
 return step1 ? step1[propertyName2] : undefined;
}

interface Org {
 admin?: User;
}
interface User {
 email?: string;
}

const o: Org = { admin: { email: 'foo' } };
const o2: Org = {};

console.log(get(o, 'admin', 'email'))
console.log(get(o2, 'admin', 'email'))

Expected behavior:

Expect to output:

foo
undefined

Actual behavior:
with strictNullChecks, fails to compile:

foo.ts(17,29): error TS2345: Argument of type '"email"' is not assignable to parameter of type 'never'.
foo.ts(18,30): error TS2345: Argument of type '"email"' is not assignable to parameter of type 'never'.

works without strictNullChecks:

foo
undefined

[mhegazy]

Duplicate of #12651, #12723, and #12744.

fixed by #12770

[ahejlsberg]

Actually, this isn't a duplicate, but more like a suggestion that we somehow permit indexed access types to work on types that include undefined and/or null. It would probably require a new type operator, e.g. T!, which removes undefined and null from the type of T. We could then say that when a truthy, undefined, or null check is applied to an expression of a generic type T, we produce the type T! in order to record the knowledge that the type is not nullable.

Anyway, I'm going to reopen and change to a suggestion.

[scottbessler]

Ah yeah i was wondering if this was expected behavior.

T! or somesuch would be great.

[RyanCavanaugh]

Closing due to low feedback volume.