type-fest/source/require-at-least-one.d.ts

A collection of essential TypeScript types

import type {Except} from './except.d.ts';
import type {If} from './if.d.ts';
import type {IfNotAnyOrNever} from './internal/index.d.ts';
import type {IsAny} from './is-any.d.ts';
import type {IsNever} from './is-never.d.ts';

/**
Create a type that requires at least one of the given keys. The remaining keys are kept as is.

@example
```
import type {RequireAtLeastOne} from 'type-fest';

type Responder = {
	text?: () => string;
	json?: () => string;
	secure?: boolean;
};

const responder: RequireAtLeastOne<Responder, 'text' | 'json'> = {
	json: () => '{"message": "ok"}',
	secure: true
};
```

@category Object
*/
export type RequireAtLeastOne<
	ObjectType,
	KeysType extends keyof ObjectType = keyof ObjectType,
> =
	IfNotAnyOrNever<ObjectType,
		If<IsNever<KeysType>,
			never,
			_RequireAtLeastOne<ObjectType, If<IsAny<KeysType>, keyof ObjectType, KeysType>>
		>>;

type _RequireAtLeastOne<
	ObjectType,
	KeysType extends keyof ObjectType,
> = {
	// For each `Key` in `KeysType` make a mapped type:
	[Key in KeysType]-?: Required<Pick<ObjectType, Key>> & // 1. Make `Key`'s type required
	// 2. Make all other keys in `KeysType` optional
		Partial<Pick<ObjectType, Exclude<KeysType, Key>>>;
}[KeysType] &
// 3. Add the remaining keys not in `KeysType`
Except<ObjectType, KeysType>;