ObjectEntry has poor behaviour for partial types

[cefn]

The ObjectEntry type is intended to help with consuming the pairs from Object.entries. It is currently implemented as...

export type ObjectEntry<T> = { [K in keyof T]: [K, T[K]] }[keyof T];

However its behaviour is not ideal in practice when consuming entries from a partial type (that has optional values) owing to...

• the use of keyof which is systematically too broad
• allowing through a partial value type, when optionality makes no sense for a entry which has been found in an object

In particular, undefined values and undefined entries are permitted through.

Expected behavior

ObjectEntry should reflect possible values from an object with optional properties (which is to say if there is an entry, it is populated, and that entries themselves cannot be undefined).

You can see an errored case of the current implementation, and a fixed implementation TypedEntryOf in the playground at https://www.typescriptlang.org/play?ts=5.3.2#code/C4TwDgpgBA8gRgKwgY2AUQHbAE4gDwAqAfFALxQDeUA2gNJQCWGUA1hCAPYBmUBAugC4atADS86fPlAC+1Npx78A3AFgAUOtCRe4CABNa7GF0IlyBKBAAewCBj0BnKAAUAhtmANXAGzxMuENhQAEokAPxQABTBljZ2jiEoHNh6fhgBQaJQAK4YLBgcAO4Y4VD0QhgQAG6BAJRQFdWBqmpa0AS6epg4IMamZJTCjMwdkAZGJsSCwmLBEACO2QzY+qYSUrKj+oa9k0R8LZq6Lt6ulcAAMhwcLNlgAxTqUFAAFhDe3hxhQgDkhcnePQ-FrPF4Mb5QH4AW3cDmB6mkhzUyA4GAcwCgnxudyEzlO5yu2Pu5EealB70+v3+2EBPxET1eDF+MOwcPpamkUFcThRaOASLaUDQVlcULA3ggWy6WFwxgGUu6spMbW4mOutzARBaAHptc8AHphdRHbTC0XiiDwJCoRUgAZWlDoGX4FU8LEarXqXUGo0aNRAA

Actual behavior

Undefined values creep in at multiple levels

Steps to reproduce

See provided playground

Suggested solution?

A preferred implementation is shown below...

type TypedKeyOf<T> = T extends Partial<infer R> ? (R extends Record<infer K, unknown> ? K : never) : never;
type TypedEntryOf<T> = { [K in TypedKeyOf<T>]: [K, Required<T>[K]] }[TypedKeyOf<T>];

What version of emery are you running?

Latest at the time of writing

Demo

type ObjectEntry<T> = { [K in keyof T]: [K, T[K]] }[keyof T];

type PlanetLookup = {
  hello?: 'world';
  hi?: 'mars';
};

const lookup: PlanetLookup = {
  hello: 'world',
  hi: 'mars',
} as const;

type ExampleObjectEntry = ObjectEntry<typeof lookup>;
//  ^? // ["hello", "world" | undefined] | ["hi", "mars" | undefined] | undefined