From fb623cb9bbeb78bc0b5e2cd402dec0e67b0b3a72 Mon Sep 17 00:00:00 2001
From: Ron Buckton <ron.buckton@microsoft.com>
Date: Tue, 4 Jun 2019 11:02:36 -0700
Subject: [PATCH] Fix 'co' for strict generators (#35937)

---
 types/co/index.d.ts | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/types/co/index.d.ts b/types/co/index.d.ts
index ab53fc0857..98a2a1cfa1 100644
--- a/types/co/index.d.ts
+++ b/types/co/index.d.ts
@@ -4,7 +4,12 @@
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 3.1
 
-type ExtractType<T> = T extends IterableIterator<infer R> ? R : never;
+type ExtractType<T> =
+    T extends { [Symbol.iterator](): { next(): { done: true, value: infer U } } } ? U :
+    T extends { [Symbol.iterator](): { next(): { done: false } } } ? never :
+    T extends { [Symbol.iterator](): { next(): { value: infer U } } } ? U :
+    T extends { [Symbol.iterator](): any } ? unknown :
+    never;
 
 interface Co {
     <F extends (...args: any[]) => Iterator<any>>(fn: F, ...args: Parameters<F>): Promise<ExtractType<ReturnType<F>>>;