From 587380ce8eb8204861edd9d2e6f5d983d7c4656e Mon Sep 17 00:00:00 2001
From: CJ Quines <cjquines0@gmail.com>
Date: Fri, 7 Jun 2024 07:06:00 -0400
Subject: [PATCH] `IsLiteral`: Return `false` for tagged types (#886)

---
 source/is-literal.d.ts | 10 ++++++----
 test-d/is-literal.ts   |  6 ++++++
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/source/is-literal.d.ts b/source/is-literal.d.ts
index 6f471dd22..262d4a61d 100644
--- a/source/is-literal.d.ts
+++ b/source/is-literal.d.ts
@@ -22,10 +22,12 @@ LiteralCheck<1, string>
 */
 type LiteralCheck<T, LiteralType extends Primitive> = (
 	IsNever<T> extends false // Must be wider than `never`
-		? [T] extends [LiteralType] // Must be narrower than `LiteralType`
-			? [LiteralType] extends [T] // Cannot be wider than `LiteralType`
-				? false
-				: true
+		? [T] extends [LiteralType & infer U] // Remove any branding
+			? [U] extends [LiteralType] // Must be narrower than `LiteralType`
+				? [LiteralType] extends [U] // Cannot be wider than `LiteralType`
+					? false
+					: true
+				: false
 			: false
 		: false
 );
diff --git a/test-d/is-literal.ts b/test-d/is-literal.ts
index b37337368..fc67fd0bf 100644
--- a/test-d/is-literal.ts
+++ b/test-d/is-literal.ts
@@ -5,6 +5,7 @@ import type {
 	IsNumericLiteral,
 	IsBooleanLiteral,
 	IsSymbolLiteral,
+	Tagged,
 } from '../index';
 
 const stringLiteral = '';
@@ -65,3 +66,8 @@ type A2 = IsNumericLiteral;
 type A3 = IsBooleanLiteral;
 // @ts-expect-error
 type A4 = IsSymbolLiteral;
+
+// Tagged types should be false
+expectType<IsStringLiteral<Tagged<string, 'Tag'>>>(false);
+expectType<IsNumericLiteral<Tagged<number, 'Tag'>>>(false);
+expectType<IsBooleanLiteral<Tagged<boolean, 'Tag'>>>(false);