From ad951b13b95e1f1a99291ff03cea59032e5a64dc Mon Sep 17 00:00:00 2001
From: Josep M Sobrepere <josepot@gmail.com>
Date: Thu, 15 Oct 2020 23:49:17 +0200
Subject: [PATCH] feat(filter): improve type inference for filter(Boolean)

---
 api_guard/dist/types/operators/index.d.ts | 2 +-
 spec-dtslint/operators/filter-spec.ts     | 2 +-
 src/internal/operators/filter.ts          | 3 +--
 3 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/api_guard/dist/types/operators/index.d.ts b/api_guard/dist/types/operators/index.d.ts
index b707aab65ff..66f43cdba6c 100644
--- a/api_guard/dist/types/operators/index.d.ts
+++ b/api_guard/dist/types/operators/index.d.ts
@@ -109,7 +109,7 @@ export declare function expand<T, R>(project: (value: T, index: number) => Obser
 export declare function expand<T, R>(project: (value: T, index: number) => ObservableInput<R>, concurrent: number | undefined, scheduler: SchedulerLike): OperatorFunction<T, R>;
 
 export declare function filter<T, S extends T>(predicate: (value: T, index: number) => value is S, thisArg?: any): OperatorFunction<T, S>;
-export declare function filter<T>(predicate: BooleanConstructor): OperatorFunction<T | null | undefined, NonNullable<T>>;
+export declare function filter<T>(predicate: BooleanConstructor): OperatorFunction<T, T extends null | undefined | false | 0 | 0n | '' ? never : T>;
 export declare function filter<T>(predicate: (value: T, index: number) => boolean, thisArg?: any): MonoTypeOperatorFunction<T>;
 
 export declare function finalize<T>(callback: () => void): MonoTypeOperatorFunction<T>;
diff --git a/spec-dtslint/operators/filter-spec.ts b/spec-dtslint/operators/filter-spec.ts
index 5bbcc76668f..d2320585ebf 100644
--- a/spec-dtslint/operators/filter-spec.ts
+++ b/spec-dtslint/operators/filter-spec.ts
@@ -51,7 +51,7 @@ it('should support Boolean as a predicate', () => {
 // https://github.com/ReactiveX/rxjs/issues/4959#issuecomment-520629091
 it('should support inference from a return type with Boolean as a predicate', () => {
   interface I {
-    a: string | null;
+    a: string | null | undefined | false | 0 | 0n | '';
   }
 
   const i$: Observable<I> = of();
diff --git a/src/internal/operators/filter.ts b/src/internal/operators/filter.ts
index 050dc7b0278..a5f44357cdb 100644
--- a/src/internal/operators/filter.ts
+++ b/src/internal/operators/filter.ts
@@ -5,8 +5,7 @@ import { OperatorSubscriber } from './OperatorSubscriber';
 
 /* tslint:disable:max-line-length */
 export function filter<T, S extends T>(predicate: (value: T, index: number) => value is S, thisArg?: any): OperatorFunction<T, S>;
-// NOTE(benlesh): T|null|undefined solves the issue discussed here: https://github.com/ReactiveX/rxjs/issues/4959#issuecomment-520629091
-export function filter<T>(predicate: BooleanConstructor): OperatorFunction<T | null | undefined, NonNullable<T>>;
+export function filter<T>(predicate: BooleanConstructor): OperatorFunction<T, T extends null | undefined | false | 0 | 0n | '' ? never : T>;
 export function filter<T>(predicate: (value: T, index: number) => boolean, thisArg?: any): MonoTypeOperatorFunction<T>;
 /* tslint:enable:max-line-length */