Add UnwrapRequired type

index.d.ts

@@ -34,6 +34,7 @@ export type {OmitIndexSignature} from './source/omit-index-signature.d.ts';
 export type {PickIndexSignature} from './source/pick-index-signature.d.ts';
 export type {PartialDeep, PartialDeepOptions} from './source/partial-deep.d.ts';
 export type {UnwrapPartial} from './source/unwrap-partial.d.ts';
+export type {UnwrapRequired} from './source/unwrap-required.d.ts';
 export type {RequiredDeep} from './source/required-deep.d.ts';
 export type {PickDeep} from './source/pick-deep.d.ts';
 export type {OmitDeep} from './source/omit-deep.d.ts';

readme.md

@@ -135,6 +135,7 @@ Click the type names for complete docs.
 - [`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.
 - [`UndefinedOnPartialDeep`](source/undefined-on-partial-deep.d.ts) - Create a deep version of another type where all optional keys are set to also accept `undefined`.
 - [`UnwrapPartial`](source/unwrap-partial.d.ts) - Revert the `Partial` modifier on an object type.
+- [`UnwrapRequired`](source/unwrap-required.d.ts) - Revert the `Required` modifier on an object type.
 - [`ReadonlyDeep`](source/readonly-deep.d.ts) - Create a deeply immutable version of another type.
 - [`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.
 - [`Tagged`](source/tagged.d.ts) - Create a [tagged type](https://medium.com/@KevinBGreene/surviving-the-typescript-ecosystem-branding-and-type-tagging-6cf6e516523d) that can support [multiple tags](https://github.com/sindresorhus/type-fest/issues/665) and [per-tag metadata](https://medium.com/@ethanresnick/advanced-typescript-tagged-types-improved-with-type-level-metadata-5072fc125fcf).
@@ -534,6 +535,8 @@ There are many advanced types most users don't know about.
 			email: 'ex@mple.com',
 	});
 	```
+
+	`Required<T>` can be reverted with [`UnwrapRequired`](source/unwrap-required.d.ts).
 	</details>
 
 - [`Readonly<T>`](https://www.typescriptlang.org/docs/handbook/utility-types.html#readonlytype) - Make all properties in `T` readonly.

source/unwrap-required.d.ts

@@ -0,0 +1,30 @@
+/**
+Revert the `Required` modifier on an object type.
+
+Use-case: Infer the underlying type `T` when only `Required<T>` is available or the original type may not be directly accessible.
+
+@example
+```
+import type {UnwrapRequired} from 'type-fest';
+
+type ContactFormData = Required<{
+	email: string;
+	message?: string;
+}>;
+
+type DraftContactFormData = UnwrapRequired<ContactFormData>;
+//=> {email: string; message?: string}
+```
+
+Note 1: If the provided type isn’t of `Required<T>`, `UnwrapRequired` has no effect on the original type.
+
+Note 2: `Required<T>` is lossy for tuples with optional elements. `UnwrapRequired` cannot recover the original tuple type in these cases. Object types with optional properties are unaffected by this limitation (and work as expected with `UnwrapRequired`).
+
+@category Object
+*/
+export type UnwrapRequired<RequiredObjectType> =
+	RequiredObjectType extends Required<infer ObjectType>
+		? ObjectType
+		: RequiredObjectType;
+
+export {};

test-d/unwrap-required.ts

@@ -0,0 +1,58 @@
+import {expectType} from 'tsd';
+import type {UnwrapRequired} from '../index.d.ts';
+
+type TestType = {
+	a?: string;
+	b: number;
+};
+
+expectType<TestType>({} as UnwrapRequired<Required<TestType>>);
+
+// `UnwrapRequired` preserves optional properties
+type AnotherTestType = {
+	c?: boolean;
+	d?: 'literal';
+};
+
+type TestTypeWithOptionalProps = TestType & AnotherTestType;
+
+expectType<TestTypeWithOptionalProps>({} as UnwrapRequired<Required<TestTypeWithOptionalProps>>);
+
+// `UnwrapRequired` preserves nested `Required` properties
+type TestTypeWithRequiredProp = TestType & {
+	c: Required<AnotherTestType>;
+};
+
+expectType<TestTypeWithRequiredProp>({} as UnwrapRequired<Required<TestTypeWithRequiredProp>>);
+
+// `UnwrapRequired` preserves readonly properties
+type TestTypeWithReadonlyProps = {
+	readonly a?: string;
+	readonly b: number;
+	readonly c?: boolean;
+};
+
+expectType<TestTypeWithReadonlyProps>({} as UnwrapRequired<Required<TestTypeWithReadonlyProps>>);
+
+// `UnwrapRequired` works with methods
+type TestTypeWithMethod = {
+	a?: string;
+	c?(): void;
+};
+
+expectType<TestTypeWithMethod>({} as UnwrapRequired<Required<TestTypeWithMethod>>);
+
+// `UnwrapRequired` works with union types
+type RequiredUnionType = Required<TestType> | Required<AnotherTestType>;
+
+expectType<TestType | AnotherTestType>({} as UnwrapRequired<RequiredUnionType>);
+expectType<TestType | AnotherTestType>({} as UnwrapRequired<Required<TestType> | AnotherTestType>);
+
+// `UnwrapRequired` works with unknown types
+expectType<unknown>({} as UnwrapRequired<Required<unknown>>);
+expectType<any>({} as UnwrapRequired<Required<any>>);
+
+// `UnwrapRequired` has no effect on non-required types
+expectType<TestType>({} as UnwrapRequired<TestType>);
+expectType<{a: string; b: number}>({} as UnwrapRequired<{a: string; b: number}>);
+expectType<readonly string[]>({} as UnwrapRequired<readonly string[]>);