Add EmptyArray and IsEmptyArray

Fixes: sindresorhus#929

index.d.ts

@@ -9,6 +9,7 @@ export type {KeysOfUnion} from './source/keys-of-union';
 export type {DistributedOmit} from './source/distributed-omit';
 export type {DistributedPick} from './source/distributed-pick';
 export type {EmptyObject, IsEmptyObject} from './source/empty-object';
+export type {EmptyArray, IsEmptyArray} from './source/empty-array';
 export type {IfEmptyObject} from './source/if-empty-object';
 export type {NonEmptyObject} from './source/non-empty-object';
 export type {UnknownRecord} from './source/unknown-record';

source/empty-array.d.ts

@@ -0,0 +1,32 @@
+/**
+Represents a strictly empty array, the `[]` value.
+
+@example
+```
+import type {EmptyArray} from 'type-fest';
+
+const bar1: EmptyArray = []; // Pass
+const bar2: EmptyArray = {}; // Fail
+const bar3: EmptyArray = null; // Fail
+```
+
+@category Array
+*/
+export type EmptyArray = never[];
+
+/**
+Returns a `boolean` for whether the type is strictly equal to an empty array, the `[]` value.
+
+@example
+```
+import type {IsEmptyArray} from 'type-fest';
+
+type Pass = IsEmptyArray<[]>; //=> true
+type Fail = IsEmptyArray<{}>; //=> false
+type Fail = IsEmptyArray<null>; //=> false
+```
+
+@see EmptyArray
+@category Array
+*/
+export type IsEmptyArray<T> = T extends EmptyArray ? true : false;

test-d/empty-array.ts

@@ -0,0 +1,39 @@
+import {expectAssignable, expectNotAssignable, expectType} from 'tsd';
+import type {EmptyArray, IsEmptyArray} from '../index';
+
+declare let foo: EmptyArray;
+
+expectAssignable<EmptyArray>([]);
+expectNotAssignable<EmptyArray>([1]);
+expectNotAssignable<EmptyArray>([undefined]);
+expectNotAssignable<EmptyArray>({});
+
+foo = [];
+foo = [...[]]; // eslint-disable-line unicorn/no-useless-spread
+foo = [...new Set([])];
+foo.slice(1);
+foo.splice(1);
+const _length = foo.length;
+
+// @ts-expect-error
+foo.push(1);
+// @ts-expect-error
+foo.fill(1);
+// @ts-expect-error
+foo.unshift(1);
+// @ts-expect-error
+foo = [1];
+// @ts-expect-error
+foo = [...[1]]; // eslint-disable-line unicorn/no-useless-spread
+// @ts-expect-error
+foo = [...new Set([1])];
+// @ts-expect-error
+foo = null;
+// @ts-expect-error
+foo.bar = 42;
+// @ts-expect-error
+foo.bar = [];
+
+expectType<IsEmptyArray<[]>>(true);
+expectType<IsEmptyArray<[1]>>(false);
+expectType<IsEmptyArray<typeof foo>>(true);