is-equal: Fix handling with intersecting wrapped types (#1231)

Co-authored-by: Som Shekhar Mukherjee <iamssmkhrj@gmail.com>

Author: taiyakihitotsu

source/is-equal.d.ts

@@ -1,3 +1,4 @@
+import type {IsNever} from './is-never.d.ts';
 /**
 Returns a boolean for whether the two given types are equal.
 
@@ -25,6 +26,12 @@ type Includes<Value extends readonly any[], Item> =
 @category Utilities
 */
 export type IsEqual<A, B> =
+	[A, B] extends [infer A, infer B]
+		? _IsEqual<A, B>
+		: false;
+
+// 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

test-d/is-equal.ts

@@ -1,23 +1,51 @@
 import {expectType} from 'tsd';
 import type {IsEqual} from '../index.d.ts';
+import type {BuildTuple} from '../source/internal/index.d.ts';
 
-const notEqualNumberAndString: IsEqual<number, string> = false;
-expectType<false>(notEqualNumberAndString);
+expectType<false>({} as IsEqual<number, string>);
+expectType<true>({} as IsEqual<1, 1>);
+expectType<false>({} as IsEqual<'A', 'B'>);
+expectType<true>({} as IsEqual<'foo', 'foo'>);
+expectType<false>({} as IsEqual<true, false>);
+expectType<true>({} as IsEqual<false, false>);
 
-const equalNumbers: IsEqual<1, 1> = true;
-expectType<true>(equalNumbers);
+expectType<false>({} as IsEqual<any, number>);
+expectType<false>({} as IsEqual<'', never>);
+expectType<true>({} as IsEqual<any, any>);
+expectType<true>({} as IsEqual<never, never>);
+expectType<false>({} as IsEqual<any, never>);
+expectType<false>({} as IsEqual<never, any>);
+expectType<false>({} as IsEqual<any, unknown>);
+expectType<false>({} as IsEqual<[any], [never]>);
+expectType<true>({} as IsEqual<[any], [any]>);
+expectType<true>({} as IsEqual<[never], [never]>);
 
-const notEqualAnyAndNumber: IsEqual<any, number> = false;
-expectType<false>(notEqualAnyAndNumber);
+expectType<false>({} as IsEqual<1 | 2, 1>);
+expectType<false>({} as IsEqual<1 | 2, 2 | 3>);
+expectType<true>({} as IsEqual<1 | 2, 2 | 1>);
+expectType<false>({} as IsEqual<boolean, true>);
 
-const notEqualUnionAndNumber: IsEqual<1 | 2, 1> = false;
-expectType<false>(notEqualUnionAndNumber);
+expectType<true>({} as IsEqual<{a: 1}, {a: 1}>);
+expectType<false>({} as IsEqual<{a: 1}, {a?: 1}>);
+expectType<false>({} as IsEqual<{a: 1}, {readonly a: 1}>);
 
-const notEqualAnyAndNever: IsEqual<any, never> = false;
-expectType<false>(notEqualAnyAndNever);
+expectType<true>({} as IsEqual<[], []>);
+expectType<true>({} as IsEqual<readonly [], readonly []>);
+expectType<false>({} as IsEqual<readonly [], []>);
+expectType<true>({} as IsEqual<number[], number[]>);
+expectType<true>({} as IsEqual<readonly number[], readonly number[]>);
+expectType<false>({} as IsEqual<readonly number[], number[]>);
+expectType<true>({} as IsEqual<[string], [string]>);
+expectType<false>({} as IsEqual<[string], [string, number]>);
+expectType<false>({} as IsEqual<[0, 1] | [0, 2], [0, 2]>);
 
-const notEqualArrayOfAnyAndArrayOfNever: IsEqual<[any], [never]> = false;
-expectType<false>(notEqualArrayOfAnyAndArrayOfNever);
+type LongTupleNumber = BuildTuple<50, 0>;
+expectType<true>({} as IsEqual<LongTupleNumber, LongTupleNumber>);
+
+type ReadonlyLongTupleNumber = Readonly<BuildTuple<50, 0>>;
+expectType<true>({} as IsEqual<ReadonlyLongTupleNumber, ReadonlyLongTupleNumber>);
+
+expectType<false>({} as IsEqual<ReadonlyLongTupleNumber, LongTupleNumber>);
 
 // Missing all generic parameters.
 // @ts-expect-error
@@ -28,8 +56,29 @@ type A = IsEqual;
 type B = IsEqual<number>;
 
 // Test for issue https://github.com/sindresorhus/type-fest/issues/537
-type UnionType = IsEqual<{a: 1} & {a: 1}, {a: 1}>; // eslint-disable-line @typescript-eslint/no-duplicate-type-constituents
+type UnionType = IsEqual<{a: 1} | {a: 1}, {a: 1}>; // eslint-disable-line @typescript-eslint/no-duplicate-type-constituents
 expectType<UnionType>(true);
 
-type IntersectionType = IsEqual<{a: 1} | {a: 1}, {a: 1}>; // eslint-disable-line @typescript-eslint/no-duplicate-type-constituents
+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]] ? 'Foo' : 'Bar');
+type BranchOnWrappedTupleDoesNotMatch<Tpl> = (Tpl extends [[0, 1]] ? 'Foo' : 'Bar');
+type BranchOnTupleMatches<Tpl> = (Tpl extends [0, 2] ? 'Foo' : 'Bar');
+type BranchOnTupleDoesNotMatch<Tpl> = (Tpl extends [0, 1] ? 'Foo' : 'Bar');
+
+declare const equalWrappedTupleIntersectionToBeNeverAndNever: IsEqual<(BranchOnWrappedTupleMatches<[[0, 2]]> & BranchOnWrappedTupleDoesNotMatch<[[0, 2]]>), never>;
+expectType<true>(equalWrappedTupleIntersectionToBeNeverAndNever);
+
+declare const equalWrappedTupleIntersectionToBeNeverAndNeverExpanded: [0, 2] extends infer Tpl ? IsEqual<(BranchOnWrappedTupleMatches<[Tpl]> & BranchOnWrappedTupleDoesNotMatch<[Tpl]>), never> : never;
+expectType<true>(equalWrappedTupleIntersectionToBeNeverAndNeverExpanded);
+
+declare const equalTupleIntersectionToBeNeverAndNever: IsEqual<(BranchOnTupleMatches<[0, 2]> & BranchOnTupleDoesNotMatch<[0, 2]>), never>;
+expectType<true>(equalTupleIntersectionToBeNeverAndNever);
+
+declare const equalTupleIntersectionToBeNeverAndNeverExpanded: [0, 2] extends infer Tpl ? IsEqual<(BranchOnTupleMatches<Tpl> & BranchOnTupleDoesNotMatch<Tpl>), never> : never;
+expectType<true>(equalTupleIntersectionToBeNeverAndNeverExpanded);
+
+declare const equalTupleIntersectionAndTuple: IsEqual<[{a: 1}] & [{a: 1}], [{a: 1}]>; // eslint-disable-line @typescript-eslint/no-duplicate-type-constituents
+expectType<true>(equalTupleIntersectionAndTuple);