Add NonEmptyObject type (#623)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

index.d.ts

@@ -6,6 +6,7 @@ export * from './source/observable-like';
 
 // Utilities
 export type {EmptyObject, IsEmptyObject} from './source/empty-object';
+export type {NonEmptyObject} from './source/non-empty-object';
 export type {UnknownRecord} from './source/unknown-record';
 export type {Except} from './source/except';
 export type {TaggedUnion} from './source/tagged-union';

readme.md

@@ -109,6 +109,7 @@ Click the type names for complete docs.
 
 - [`EmptyObject`](source/empty-object.d.ts) - Represents a strictly empty plain object, the `{}` value.
 - [`IsEmptyObject`](source/empty-object.d.ts) - Returns a `boolean` for whether the type is strictly equal to an empty plain object, the `{}` value.
+- [`NonEmptyObject`](source/non-empty-object.d.ts) - Represents an object with at least 1 non-optional key.
 - [`UnknownRecord`](source/unknown-record.d.ts) - Represents an object with `unknown` value. You probably want this instead of `{}`.
 - [`Except`](source/except.d.ts) - Create a type from an object type without certain keys. This is a stricter version of [`Omit`](https://www.typescriptlang.org/docs/handbook/utility-types.html#omittype-keys).
 - [`Writable`](source/writable.d.ts) - Create a type that strips `readonly` from all or some of an object's keys. The inverse of `Readonly<T>`.

source/non-empty-object.d.ts

@@ -0,0 +1,35 @@
+import type {HasRequiredKeys} from './has-required-keys';
+import type {RequireAtLeastOne} from './require-at-least-one';
+
+/**
+Represents an object with at least 1 non-optional key.
+
+This is useful when you need an object where all keys are optional, but there must be at least 1 key.
+
+@example
+```
+import type {NonEmptyObject} from 'type-fest';
+
+type User = {
+	name: string;
+	surname: string;
+	id: number;
+};
+
+type UpdateRequest<Entity extends object> = NonEmptyObject<Partial<Entity>>;
+
+const update1: UpdateRequest<User> = {
+	name: 'Alice',
+	surname: 'Acme',
+};
+
+// At least 1 key is required, therefore this will report a 2322 error:
+// Type '{}' is not assignable to type 'UpdateRequest<User>'
+const update2: UpdateRequest<User> = {};
+```
+
+@see Use `IsEmptyObject` to check whether an object is empty.
+
+@category Object
+*/
+export type NonEmptyObject<T extends object> = HasRequiredKeys<T> extends true ? T : RequireAtLeastOne<T, keyof T>;

test-d/non-empty-object.ts

@@ -0,0 +1,29 @@
+import {expectNever, expectType} from 'tsd';
+import type {NonEmptyObject, RequireAtLeastOne} from '../index';
+
+type TestType1 = {
+	a: string;
+	b: boolean;
+};
+
+type TestType2 = {
+	a?: string;
+	b?: boolean;
+};
+
+type TestType3 = {
+	a: string;
+	b?: boolean;
+};
+
+type TestType4 = {};
+
+declare const test1: NonEmptyObject<TestType1>;
+declare const test2: NonEmptyObject<TestType2>;
+declare const test3: NonEmptyObject<TestType3>;
+declare const test4: NonEmptyObject<TestType4>;
+
+expectType<TestType1>(test1);
+expectType<RequireAtLeastOne<TestType2>>(test2);
+expectType<TestType3>(test3);
+expectNever(test4);