Add PartialOnUndefinedDeep type

index.d.ts

@@ -15,6 +15,7 @@ export {RequireExactlyOne} from './source/require-exactly-one';
 export {RequireAllOrNone} from './source/require-all-or-none';
 export {RemoveIndexSignature} from './source/remove-index-signature';
 export {PartialDeep} from './source/partial-deep';
+export {PartialOnUndefinedDeep} from './source/partial-on-undefined-deep';
 export {ReadonlyDeep} from './source/readonly-deep';
 export {LiteralUnion} from './source/literal-union';
 export {Promisable} from './source/promisable';

readme.md

@@ -169,6 +169,7 @@ Click the type names for complete docs.
 - [`RequireAllOrNone`](source/require-all-or-none.d.ts) - Create a type that requires all of the given keys or none of the given keys.
 - [`RemoveIndexSignature`](source/remove-index-signature.d.ts) - Create a type that only has explicitly defined properties, absent of any index signatures.
 - [`PartialDeep`](source/partial-deep.d.ts) - Create a deeply optional version of another type. Use [`Partial<T>`](https://www.typescriptlang.org/docs/handbook/utility-types.html#partialtype) if you only need one level deep.
+- [`PartialOnUndefinedDeep`](source/partial-on-undefined-deep.d.ts) - Create a deep version of another type where all keys accepting `undefined` type are set to optional.
 - [`ReadonlyDeep`](source/readonly-deep.d.ts) - Create a deeply immutable version of an `object`/`Map`/`Set`/`Array` type. Use [`Readonly<T>`](https://www.typescriptlang.org/docs/handbook/utility-types.html#readonlytype) if you only need one level deep.
 - [`LiteralUnion`](source/literal-union.d.ts) - Create a union type by combining primitive types and literal types without sacrificing auto-completion in IDEs for the literal type part of the union. Workaround for [Microsoft/TypeScript#29729](https://github.com/Microsoft/TypeScript/issues/29729).
 - [`Opaque`](source/opaque.d.ts) - Create an [opaque type](https://codemix.com/opaque-types-in-javascript/).

source/partial-on-undefined-deep.d.ts

@@ -0,0 +1,72 @@
+import type {BuiltIns} from './internal';
+import type {Merge} from './merge';
+
+/**
+@see PartialOnUndefinedDeep
+*/
+export interface PartialOnUndefinedDeepOptions {
+	/**
+	Whether to affect the individual elements of arrays and tuples
+
+	@default false
+	*/
+	readonly recurseIntoArrays?: boolean;
+}
+
+/**
+Create a deep version of another type where all keys accepting `undefined` type are set to optional.
+
+This utility type is recursive, transforming at any level deep.
+By default, this type does not affects array and tuple types unless you explicitly pass `{recurseIntoArrays: true}` as the second type argument.
+
+Use-cases:
+- Make all properties of a type that can be undefined optional to not have to specify keys with undefined value
+
+https://github.com/sindresorhus/type-fest/issues/399
+@example
+```
+import type {PartialOnUndefinedDeep} from 'type-fest';
+
+interface Settings {
+	optionA: string;
+	optionB: number | undefined;
+	subOption: {
+		subOptionA: boolean;
+		subOptionB: boolean | undefined;
+	}
+};
+
+const testSettings: PartialOnUndefinedDeep<Settings> = {
+	optionA: 'foo',
+	// 👉 optionB is now optional and can be omitted
+	subOption: {
+		subOptionA: true,
+		// 👉 subOptionB is now optional as well and can be omitted
+	},
+};
+```
+
+@category Object
+*/
+export type PartialOnUndefinedDeep<T, Options extends PartialOnUndefinedDeepOptions = {}> = T extends Record<any, any> | undefined
+	? {[KeyType in keyof T as undefined extends T[KeyType] ? KeyType : never]?: PartialOnUndefinedDeepValue<T[KeyType], Options>} extends infer U // Make a partial type with all value types accepting undefined (and set them optional)
+		? Merge<{[KeyType in keyof T as KeyType extends keyof U ? never : KeyType]: PartialOnUndefinedDeepValue<T[KeyType], Options>}, U> // Join all remaining keys not treated in U
+		: never // Should not happen
+	: T;
+
+/**
+Utility type to get the value type by key and recursively call `PartialOnUndefinedDeep` to transform sub-objects.
+*/
+type PartialOnUndefinedDeepValue<T, Options extends PartialOnUndefinedDeepOptions> = T extends BuiltIns | ((...arguments: any[]) => unknown)
+	? T
+	: T extends ReadonlyArray<infer U> // Test if type is array or tuple
+	? Options['recurseIntoArrays'] extends true // Check if option is activated
+		? U[] extends T // Check if array not tuple
+		? readonly U[] extends T
+			? ReadonlyArray<PartialOnUndefinedDeep<U, Options>> // Readonly array treatment
+			: Array<PartialOnUndefinedDeep<U, Options>> // Mutable array treatment
+		: PartialOnUndefinedDeep<{[Key in keyof T]: PartialOnUndefinedDeep<T[Key], Options>}, Options> // Tuple treatment
+		: T
+	: T extends Record<any, any> | undefined
+	? PartialOnUndefinedDeep<T, Options>
+	: unknown;

test-d/partial-on-undefined-deep.ts

@@ -0,0 +1,78 @@
+import {expectAssignable} from 'tsd';
+import type {PartialOnUndefinedDeep} from '../index';
+
+type TestingType = {
+	function: (() => void) | undefined;
+	object: {objectKey: 1} | undefined;
+	objectDeep: {
+		subObject: string | undefined;
+	};
+	string: string | undefined;
+	union: 'test1' | 'test2' | undefined;
+	number: number | undefined;
+	boolean: boolean | undefined;
+	date: Date | undefined;
+	regexp: RegExp | undefined;
+	symbol: symbol | undefined;
+	null: null | undefined;
+	record: Record<string, any> | undefined;
+	map: Map<string, string> | undefined;
+	set: Set<string> | undefined;
+	array1: any[] | undefined;
+	array2: Array<{propertyA: string; propertyB: number | undefined}> | undefined;
+	readonly1: readonly any[] | undefined;
+	readonly2: ReadonlyArray<{propertyA: string; propertyB: number | undefined}> | undefined;
+	tuple: ['test1', {propertyA: string; propertyB: number | undefined}] | undefined;
+};
+
+// Default behavior, without recursion into arrays/tuples
+declare const foo: PartialOnUndefinedDeep<TestingType>;
+expectAssignable<{
+	function?: TestingType['function'];
+	object?: TestingType['object'];
+	objectDeep: {
+		subObject?: TestingType['objectDeep']['subObject'];
+	};
+	string?: TestingType['string'];
+	union?: TestingType['union'];
+	number?: TestingType['number'];
+	boolean?: TestingType['boolean'];
+	date?: TestingType['date'];
+	regexp?: TestingType['regexp'];
+	symbol?: TestingType['symbol'];
+	null?: TestingType['null'];
+	record?: TestingType['record'];
+	map?: TestingType['map'];
+	set?: TestingType['set'];
+	array1?: TestingType['array1'];
+	array2?: TestingType['array2'];
+	readonly1?: TestingType['readonly1'];
+	readonly2?: TestingType['readonly2'];
+	tuple?: TestingType['tuple'];
+}>(foo);
+
+// With recursion into arrays/tuples activated
+declare const bar: PartialOnUndefinedDeep<TestingType, {recurseIntoArrays: true}>;
+expectAssignable<{
+	function?: TestingType['function'];
+	object?: TestingType['object'];
+	objectDeep: {
+		subObject?: TestingType['objectDeep']['subObject'];
+	};
+	string?: TestingType['string'];
+	union?: TestingType['union'];
+	number?: TestingType['number'];
+	boolean?: TestingType['boolean'];
+	date?: TestingType['date'];
+	regexp?: TestingType['regexp'];
+	symbol?: TestingType['symbol'];
+	null?: TestingType['null'];
+	record?: TestingType['record'];
+	map?: TestingType['map'];
+	set?: TestingType['set'];
+	array1?: TestingType['array1'];
+	array2?: Array<{propertyA: string; propertyB?: number | undefined}> | undefined;
+	readonly1?: TestingType['readonly1'];
+	readonly2?: ReadonlyArray<{propertyA: string; propertyB?: number | undefined}> | undefined;
+	tuple?: ['test1', {propertyA: string; propertyB?: number | undefined}] | undefined;
+}>(bar);