From 19e07eaea63210d1afc8045adab72f418341edc3 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Sun, 4 Mar 2018 16:49:06 -0800
Subject: [PATCH] Add tests

---
 .../types/conditional/inferTypes1.ts            | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/tests/cases/conformance/types/conditional/inferTypes1.ts b/tests/cases/conformance/types/conditional/inferTypes1.ts
index 1defacc08cc..8907cf79d91 100644
--- a/tests/cases/conformance/types/conditional/inferTypes1.ts
+++ b/tests/cases/conformance/types/conditional/inferTypes1.ts
@@ -90,6 +90,15 @@ type T76<T extends T[], U extends T> = { x: T };
 type T77<T> = T extends T76<infer X, infer Y> ? T76<X, Y> : never;
 type T78<T> = T extends T76<infer X, infer X> ? T76<X, X> : never;
 
+type Foo<T extends string, U extends T> = [T, U];
+type Bar<T> = T extends Foo<infer X, infer Y> ? Foo<X, Y> : never;
+
+type T90 = Bar<[string, string]>;  // [string, string]
+type T91 = Bar<[string, "a"]>;  // [string, "a"]
+type T92 = Bar<[string, "a"] & { x: string }>;  // [string, "a"]
+type T93 = Bar<["a", string]>;  // never
+type T94 = Bar<[number, number]>;  // never
+
 // Example from #21496
 
 type JsonifiedObject<T extends object> = { [K in keyof T]: Jsonified<T[K]> };
@@ -150,3 +159,11 @@ interface test {
 
 type T80 = MatchingKeys<test, void>;
 type T81 = VoidKeys<test>;
+
+// Repro from #22221
+
+type MustBeString<T extends string> = T;
+type EnsureIsString<T> = T extends MustBeString<infer U> ? U : never;
+
+type Test1 = EnsureIsString<"hello">;  // "hello"
+type Test2 = EnsureIsString<42>;  // never