From df774a6dd0338b2f92bdac7c9b2e4e710643f1a7 Mon Sep 17 00:00:00 2001
From: John Chadwick <jchw@google.com>
Date: Fri, 11 Oct 2019 13:18:33 -0700
Subject: [PATCH 1/2] fix(toPromise): correct toPromise return type

---
 src/internal/Observable.ts | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/internal/Observable.ts b/src/internal/Observable.ts
index 3decd66e47..54ec2a9267 100644
--- a/src/internal/Observable.ts
+++ b/src/internal/Observable.ts
@@ -347,9 +347,9 @@ export class Observable<T> implements Subscribable<T> {
   }
 
   /* tslint:disable:max-line-length */
-  toPromise<T>(this: Observable<T>): Promise<T>;
-  toPromise<T>(this: Observable<T>, PromiseCtor: typeof Promise): Promise<T>;
-  toPromise<T>(this: Observable<T>, PromiseCtor: PromiseConstructorLike): Promise<T>;
+  toPromise<T>(this: Observable<T>): Promise<T | undefined>;
+  toPromise<T>(this: Observable<T>, PromiseCtor: typeof Promise): Promise<T | undefined>;
+  toPromise<T>(this: Observable<T>, PromiseCtor: PromiseConstructorLike): Promise<T | undefined>;
   /* tslint:enable:max-line-length */
 
   /**
@@ -362,13 +362,13 @@ export class Observable<T> implements Subscribable<T> {
    * @return A Promise that resolves with the last value emit, or
    * rejects on an error.
    */
-  toPromise(promiseCtor?: PromiseConstructorLike): Promise<T> {
+  toPromise(promiseCtor?: PromiseConstructorLike): Promise<T | undefined> {
     promiseCtor = getPromiseCtor(promiseCtor);
 
     return new promiseCtor((resolve, reject) => {
-      let value: any;
+      let value: T | undefined;
       this.subscribe((x: T) => value = x, (err: any) => reject(err), () => resolve(value));
-    }) as Promise<T>;
+    }) as Promise<T | undefined>;
   }
 }
 

From ab17ff935abccaf688b71cf600bd3c9ff2964f24 Mon Sep 17 00:00:00 2001
From: John Chadwick <jchw@google.com>
Date: Mon, 14 Oct 2019 10:42:27 -0700
Subject: [PATCH 2/2] fix(toPromise): add test for toPromise type

---
 spec-dtslint/Observable-spec.ts | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/spec-dtslint/Observable-spec.ts b/spec-dtslint/Observable-spec.ts
index ee7c1b1053..3033f6f1bf 100644
--- a/spec-dtslint/Observable-spec.ts
+++ b/spec-dtslint/Observable-spec.ts
@@ -126,4 +126,8 @@ describe('pipe', () => {
     const customOperator = () => <T>(a: Observable<T>) => a;
     const o = of('foo').pipe(customOperator()); // $ExpectType Observable<string>
   });
+
+  it('should have proper return type for toPromise', () => {
+    const o = of('foo').toPromise(); // $ExpectType Promise<string | undefined>
+  });
 });