Fix: is-equal fails in some cases when intersecting wrapped types (F<[A]> & G<[A]>)

source/is-equal.d.ts

@@ -1,3 +1,5 @@
+import type {IsNever} from './is-never.d.ts';
+
 /**
 Returns a boolean for whether the two given types are equal.
 
@@ -25,7 +27,22 @@ type Includes<Value extends readonly any[], Item> =
 @category Utilities
 */
 export type IsEqual<A, B> =
+	_NonNeverId<A> extends [infer HeadA, ...infer TailA]
+		? _NonNeverId<B> extends [infer HeadB, ...infer TailB]
+			? IsEqual<HeadA, HeadB> extends true
+				? IsEqual<TailA, TailB>
+				: false
+			: _IsEqual<A, B>
+		: _IsEqual<A, B>;
+
+// This version fails the `equalWrappedTupleIntersectionToBeNeverAndNeverExpanded` test in `test-d/is-equal.ts`.
+type _IsEqual<A, B> =
 	(<G>() => G extends A & G | G ? 1 : 2) extends
 	(<G>() => G extends B & G | G ? 1 : 2)
 		? true
 		: false;
+
+type _NonNeverId<T> =
+	true extends IsNever<T>
+		? 0
+		: T;

test-d/is-equal.ts

@@ -19,6 +19,41 @@ expectType<false>(notEqualAnyAndNever);
 const notEqualArrayOfAnyAndArrayOfNever: IsEqual<[any], [never]> = false;
 expectType<false>(notEqualArrayOfAnyAndArrayOfNever);
 
+const equalNeverAndNever: IsEqual<never, never> = true;
+expectType<true>(equalNeverAndNever);
+
+const equalEmptyArrayAndEmptyArray: IsEqual<[], []> = true;
+expectType<true>(equalEmptyArrayAndEmptyArray);
+
+const equalReadonlyEmptyArrayAndReadonlyEmptyArray: IsEqual<readonly [], readonly []> = true;
+expectType<true>(equalReadonlyEmptyArrayAndReadonlyEmptyArray);
+
+const notEqualReadonlyEmptyArrayAndReadonlyEmptyArray: IsEqual<readonly [], []> = false;
+expectType<false>(notEqualReadonlyEmptyArrayAndReadonlyEmptyArray);
+
+const equalArrayNumberAndArrayNumber: IsEqual<number[], number[]> = true;
+expectType<true>(equalArrayNumberAndArrayNumber);
+
+const equalReadonlyArrayNumberAndReadonlyArrayNumber: IsEqual<readonly number[], readonly number[]> = true;
+expectType<true>(equalReadonlyArrayNumberAndReadonlyArrayNumber);
+
+const notEqualReadonlyArrayNumberAndReadonlyArrayNumber: IsEqual<readonly number[], number[]> = false;
+expectType<false>(notEqualReadonlyArrayNumberAndReadonlyArrayNumber);
+
+type LongTupleNumber = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50];
+const equalLongTupleNumberAndLongTupleNumber: IsEqual<LongTupleNumber, LongTupleNumber> = true;
+expectType<true>(equalLongTupleNumberAndLongTupleNumber);
+
+type ReadonlyLongTupleNumber = readonly [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50];
+const equalLongReadonlyTupleNumberAndLongReadonlyTupleNumber: IsEqual<ReadonlyLongTupleNumber, ReadonlyLongTupleNumber> = true;
+expectType<true>(equalLongReadonlyTupleNumberAndLongReadonlyTupleNumber);
+
+const notEqualLongTupleNumberAndLongTupleNumber: IsEqual<readonly [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50], [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50]> = false;
+expectType<false>(notEqualLongTupleNumberAndLongTupleNumber);
+
+const notEqualTupleUnionAndTuple: IsEqual<[0, 1] | [0, 2], [0, 2]> = false;
+expectType<false>(notEqualTupleUnionAndTuple);
+
 // Missing all generic parameters.
 // @ts-expect-error
 type A = IsEqual;
@@ -33,3 +68,21 @@ expectType<UnionType>(true);
 
 type IntersectionType = IsEqual<{a: 1} | {a: 1}, {a: 1}>; // eslint-disable-line @typescript-eslint/no-duplicate-type-constituents
 expectType<IntersectionType>(true);
+
+// Test for PR https://github.com/sindresorhus/type-fest/pull/1231
+type BranchOnWrappedTupleMatches<Tpl> = (Tpl extends [[0, 2]] ? ['A', true] : ['A', false]);
+type BranchOnWrappedTupleDoesNotMatch<Tpl> = (Tpl extends [[0, 1]] ? ['A', true] : ['A', false]);
+type BranchOnTupleMatches<Tpl> = (Tpl extends [0, 2] ? ['A', true] : ['A', false]);
+type BranchOnTupleDoesNotMatch<Tpl> = (Tpl extends [0, 1] ? ['A', true] : ['A', false]);
+
+const equalWrappedTupleIntersectionToBeNeverAndNever: IsEqual<(BranchOnWrappedTupleMatches<[[0, 2]]> & BranchOnWrappedTupleDoesNotMatch<[[0, 2]]>), never> = true;
+expectType<true>(equalWrappedTupleIntersectionToBeNeverAndNever);
+
+const equalWrappedTupleIntersectionToBeNeverAndNeverExpanded: [0, 2] extends infer Tpl ? IsEqual<(BranchOnWrappedTupleMatches<[Tpl]> & BranchOnWrappedTupleDoesNotMatch<[Tpl]>), never> : never = true;
+expectType<true>(equalWrappedTupleIntersectionToBeNeverAndNeverExpanded);
+
+const equalTupleIntersectionToBeNeverAndNever: IsEqual<(BranchOnTupleMatches<[0, 2]> & BranchOnTupleDoesNotMatch<[0, 2]>), never> = true;
+expectType<true>(equalTupleIntersectionToBeNeverAndNever);
+
+const equalTupleIntersectionToBeNeverAndNeverExpanded: [0, 2] extends infer Tpl ? IsEqual<(BranchOnTupleMatches<Tpl> & BranchOnTupleDoesNotMatch<Tpl>), never> : never = true;
+expectType<true>(equalTupleIntersectionToBeNeverAndNeverExpanded);