Inlining definition of NonNullable<T> results in different behavior #23046
Description
Apologies if this was submitted already, I could not find anything similar by searching.
TypeScript Version: 2.8.1
Search Terms: Existential types, undefined, Exclude, Required, NonNullable, in keyof
Code
type OnlyPresentV1<T> = {
[P in keyof T]: NonNullable<T[P]>
};
// should pass, and it does
const Test_1: OnlyPresentV1<{test: string}> = {test: "asd"};
// should fail, and it does
const Test_2: OnlyPresentV1<{test: string}> = {test: undefined};
// should pass, and it does
const Test_3: OnlyPresentV1<{test: string | undefined}> = {test: "asd"};
// should fail, and it does
const Test_4: OnlyPresentV1<{test: string | undefined}> = {test: undefined};
type OnlyPresentV2<T> = {
[P in keyof T]: T[P] extends null | undefined ? never : T[P]
};
// should pass, and it does
const Test_5: OnlyPresentV2<{test: string}> = {test: "asd"};
// should fail, and it does
const Test_6: OnlyPresentV2<{test: string}> = {test: undefined};
// should pass, and it does
const Test_7: OnlyPresentV2<{test: string | undefined}> = {test: "asd"};
// should fail, but it doesn't!
const Test_8: OnlyPresentV2<{test: string | undefined}> = {test: undefined};Expected behavior:
I noted down what my expectations are above each case.
I expected that inlining the definition of NonNullable would be the same as using the type.
Actual behavior:
Behavior is different, but definitions are essentially the same?
Playground Link: https://goo.gl/fWzwzA (shortend it because it was really long) Enabled all strictness checks I could
Related Issues: Could not find any