Merge pull request #122 from jsr-core/fix-test-equal

test[Equal]: fix false positive

Author: lambdalisue

_testutil.ts

@@ -1,4 +1,5 @@
 import { assertEquals } from "@std/assert";
+import type { IsExact } from "@std/testing/types";
 import type { Predicate } from "./type.ts";
 
 const examples = {
@@ -51,9 +52,14 @@ export async function testWithExamples<T>(
 
 // It seems 'IsExact' in deno_std is false positive so use `Equal` in type-challenges
 // https://github.com/type-challenges/type-challenges/blob/e77262dba62e9254451f661cb4fe5517ffd1d933/utils/index.d.ts#L7-L9
-export type Equal<X, Y> = (<T>() => T extends X ? 1 : 2) extends
+/** @deprecated use {@linkcode Equal} */
+export type TypeChallengesEqual<X, Y> = (<T>() => T extends X ? 1 : 2) extends
   (<T>() => T extends Y ? 1 : 2) ? true : false;
 
+// `Equal` in type-challenges is false positive so combine `IsExact` + `Equal`.
+export type Equal<X, Y> = TypeChallengesEqual<X, Y> extends true ? IsExact<X, Y>
+  : false;
+
 export function stringify(x: unknown): string {
   if (x instanceof Date) return `Date(${x.valueOf()})`;
   if (x instanceof Promise) return "Promise";

_testutil_test.ts

@@ -0,0 +1,43 @@
+// deno-lint-ignore-file no-explicit-any
+import { assertType, type IsExact } from "@std/testing/types";
+
+import type { Equal, TypeChallengesEqual } from "./_testutil.ts";
+
+declare class Foo<T> {
+  declare private _: T;
+}
+
+Deno.test("IsExact gives false positive", () => {
+  // all of the following should be false
+  assertType<IsExact<() => void, (x?: number) => void>>(true);
+  assertType<IsExact<Foo<{ x: 1; a?: 1 }>, Foo<{ x: 1; b?: 1 }>>>(true);
+  assertType<IsExact<() => any, () => number>>(true);
+  assertType<IsExact<Foo<any>, Foo<number>>>(true);
+  assertType<IsExact<{ a: 1 }, { readonly a: 1 }>>(true);
+});
+
+Deno.test("TypeChallengesEqual gives false positive", () => {
+  // all of the following should be false
+  assertType<TypeChallengesEqual<[...any[]], [...any[], any]>>(true);
+  assertType<TypeChallengesEqual<[any, ...any[]], [any, ...any[], any]>>(true);
+});
+
+Deno.test("Equal", async (t) => {
+  await t.step(
+    "should be correct in cases where IsExact gives false positive",
+    () => {
+      assertType<Equal<() => void, (x?: number) => void>>(false);
+      assertType<Equal<Foo<{ x: 1; a?: 1 }>, Foo<{ x: 1; b?: 1 }>>>(false);
+      assertType<Equal<() => any, () => number>>(false);
+      assertType<Equal<Foo<any>, Foo<number>>>(false);
+      assertType<Equal<{ a: 1 }, { readonly a: 1 }>>(false);
+    },
+  );
+  await t.step(
+    "should be correct in cases where TypeChallengesEqual gives false positive",
+    () => {
+      assertType<Equal<[...any[]], [...any[], any]>>(false);
+      assertType<Equal<[any, ...any[]], [any, ...any[], any]>>(false);
+    },
+  );
+});