fix(types): support passing union types to from

Author: benlesh

spec-dtslint/observables/from-spec.ts

@@ -0,0 +1,45 @@
+import { from, of, asyncScheduler } from 'rxjs';
+
+it('should accept an array', () => {
+  const o = from([1, 2, 3, 4]); // $ExpectType Observable<number>
+});
+
+it('should accept a Promise', () => {
+  const o = from(Promise.resolve('test')); // $ExpectType Observable<string>
+});
+
+it('should accept an Iterable', () => {
+  const iterable = (function*() {
+    yield 42;
+  }());
+
+  const o = from(iterable); // $ExpectType Observable<number>
+});
+
+it('should accept an Observable', () => {
+  const o = from(of('test')); // $ExpectType Observable<string>
+});
+
+it('should accept union types', () => {
+  const o = from(Math.random() > 0.5 ? of(123) : of('test')); // $ExpectType Observable<string | number>
+});
+
+it('should accept Observable<Observable<number>>', () => {
+  const o = from(of(of(123))); // $ExpectType Observable<Observable<number>>
+});
+
+it('should accept Observable<number[]>', () => {
+  const o = from(of([1, 2, 3])); // $ExpectType Observable<number[]>
+});
+
+it('should accept an array of Observables', () => {
+  const o = from([of(1), of(2), of(3)]); // $ExpectType Observable<Observable<number>>
+});
+
+it('should accept an array of Inputs', () => {
+  const iterable = (function*() {
+    yield 42;
+  }());
+
+  const o = from([of(1), ['test'], iterable]); // $ExpectType Observable<Observable<number> | IterableIterator<number> | string[]>
+});

src/internal/observable/from.ts

@@ -8,10 +8,9 @@ import { fromPromise } from './fromPromise';
 import { fromIterable } from './fromIterable';
 import { fromObservable } from './fromObservable';
 import { subscribeTo } from '../util/subscribeTo';
-import { ObservableInput, SchedulerLike } from '../types';
+import { ObservableInput, SchedulerLike, ObservedValueOf } from '../types';
 
-export function from<T>(input: ObservableInput<T>, scheduler?: SchedulerLike): Observable<T>;
-export function from<T>(input: ObservableInput<ObservableInput<T>>, scheduler?: SchedulerLike): Observable<Observable<T>>;
+export function from<O extends ObservableInput<any>>(input: O, scheduler?: SchedulerLike): Observable<ObservedValueOf<O>>;
 
 /**
  * Creates an Observable from an Array, an array-like object, a Promise, an iterable object, or an Observable-like object.