fix(typescript): Update typings for race to support proper return typ…

…es (#4465)

* fix(typescript): Update typings for race to support proper return types

* fixup! fix(typescript): Update typings for race to support proper return types

spec-dtslint/observables/race-spec.ts

@@ -2,17 +2,68 @@ import { race, of } from 'rxjs';
 
 it('should infer correctly with 1 parameter', () => {
   const a = of(1);
-  const res = race(a); // $ExpectType Observable<number>
+  const o = race(a); // $ExpectType Observable<number>
 });
 
 it('should infer correctly with multiple parameters of the same type', () => {
   const a = of(1);
   const b = of(2);
-  const res = race(a, b); // $ExpectType Observable<number>
+  const o = race(a, b); // $ExpectType Observable<number>
 });
 
-it('should not support multiple parameters with different type', () => {
+it('should support 2 parameters with different types', () => {
   const a = of(1);
   const b = of('a');
-  const res = race(a, b); // $ExpectError
+  const o = race(a, b); // $ExpectType Observable<string> | Observable<number>
+});
+
+it('should support 3 parameters with different types', () => {
+  const a = of(1);
+  const b = of('a');
+  const c = of(true);
+  const o = race(a, b, c); // $ExpectType Observable<string> | Observable<number> | Observable<boolean>
+});
+
+it('should support 4 parameters with different types', () => {
+  const a = of(1);
+  const b = of('a');
+  const c = of(true);
+  const d = of([1, 2, 3]);
+  const o = race(a, b, c, d); // $ExpectType Observable<string> | Observable<number> | Observable<boolean> | Observable<number[]>
+});
+
+it('should support 5 parameters with different types', () => {
+  const a = of(1);
+  const b = of('a');
+  const c = of(true);
+  const d = of([1, 2, 3]);
+  const e = of(['blah']);
+  const o = race(a, b, c, d, e); // $ExpectType Observable<string> | Observable<number> | Observable<boolean> | Observable<number[]> | Observable<string[]>
+});
+
+it('should support 6 or more parameters of the same type', () => {
+  const a = of(1);
+  const o = race(a, a, a, a, a, a, a, a, a, a, a, a, a, a); // $ExpectType Observable<number>
+});
+
+it('should return {} for 6 or more arguments of different types', () => {
+  const a = of(1);
+  const b = of('a');
+  const c = of(true);
+  const d = of([1, 2, 3]);
+  const e = of(['blah']);
+  const f = of({ foo: 'bar' });
+  const o = race(a, b, c, d, e, f); // $ExpectType Observable<{}>
+});
+
+it('should handle an array of observables', () => {
+  const a = of(1);
+  const b = of(2);
+  const o = race([a, b]); // $ExpectType Observable<number>
+});
+
+it('should return {} for array of observables of different types', () => {
+  const a = of(1);
+  const b = of('test');
+  const o = race([a, b]); // $ExpectType Observable<{}>
 });

src/internal/observable/race.ts

@@ -9,9 +9,18 @@ import { OuterSubscriber } from '../OuterSubscriber';
 import { InnerSubscriber } from '../InnerSubscriber';
 import { subscribeToResult } from '../util/subscribeToResult';
 
-export function race<T>(observables: Array<Observable<T>>): Observable<T>;
-export function race<T>(observables: Array<Observable<any>>): Observable<T>;
-export function race<T>(...observables: Array<Observable<T> | Array<Observable<T>>>): Observable<T>;
+// tslint:disable:max-line-length
+export function race<A, B>(a: Observable<A>, b: Observable<B>): Observable<A> | Observable<B>;
+export function race<A, B, C>(a: Observable<A>, b: Observable<B>, c: Observable<C>): Observable<A> | Observable<B> | Observable<C>;
+export function race<A, B, C, D>(a: Observable<A>, b: Observable<B>, c: Observable<C>, d: Observable<D>): Observable<A> | Observable<B> | Observable<C> | Observable<D>;
+export function race<A, B, C, D, E>(a: Observable<A>, b: Observable<B>, c: Observable<C>, d: Observable<D>, e: Observable<E>): Observable<A> | Observable<B> | Observable<C> | Observable<D> | Observable<E>;
+// tslint:enable:max-line-length
+
+export function race<T>(observables: Observable<T>[]): Observable<T>;
+export function race(observables: Observable<any>[]): Observable<{}>;
+export function race<T>(...observables: Observable<T>[]): Observable<T>;
+export function race(...observables: Observable<any>[]): Observable<{}>;
+
 /**
  * Returns an Observable that mirrors the first source Observable to emit an item.
  *
@@ -38,14 +47,14 @@ export function race<T>(...observables: Array<Observable<T> | Array<Observable<T
  * @name race
  * @owner Observable
  */
-export function race<T>(...observables: Array<Observable<any> | Array<Observable<any>>>): Observable<T> {
+export function race<T>(...observables: (Observable<any>[] | Observable<any>)[]): Observable<T> {
   // if the only argument is an array, it was most likely called with
   // `race([obs1, obs2, ...])`
   if (observables.length === 1) {
     if (isArray(observables[0])) {
-      observables = <Array<Observable<any>>>observables[0];
+      observables = observables[0] as Observable<any>[];
     } else {
-      return <Observable<any>>observables[0];
+      return observables[0] as Observable<T>;
     }
   }
 

src/internal/operators/race.ts

@@ -23,14 +23,14 @@ export function race<T, R>(...observables: Array<Observable<any> | Array<Observa
  * @owner Observable
  * @deprecated Deprecated in favor of static {@link race}.
  */
-export function race<T>(...observables: Array<Observable<T> | Array<Observable<T>>>): MonoTypeOperatorFunction<T> {
+export function race<T>(...observables: (Observable<T> | Observable<T>[])[]): MonoTypeOperatorFunction<T> {
   return function raceOperatorFunction(source: Observable<T>) {
     // if the only argument is an array, it was most likely called with
     // `pair([obs1, obs2, ...])`
     if (observables.length === 1 && isArray(observables[0])) {
-      observables = <Array<Observable<T>>>observables[0];
+      observables = observables[0] as Observable<T>[];
     }
 
-    return source.lift.call(raceStatic<T>(source, ...observables));
+    return source.lift.call(raceStatic(source, ...(observables as Observable<T>[])));
   };
 }