refactor(forkJoin): readd resultSelector as deprecated

spec/observables/forkJoin-spec.ts

@@ -19,6 +19,54 @@ describe('forkJoin', () => {
       expectObservable(e1).toBe(expected, {x: ['d', '3']});
     });
 
+  it('should support the deprecated resultSelector with an Array of ObservableInputs', () => {
+    const results: Array<number|string> = [];
+    forkJoin(
+      [
+        of(1, 2, 3),
+        of(4, 5, 6),
+        of(7, 8, 9),
+      ],
+      (a: number, b: number, c: number) => a + b + c,
+    )
+    .subscribe({
+      next(value) {
+        results.push(value);
+      },
+      error(err) {
+        throw err;
+      },
+      complete() {
+        results.push('done');
+      }
+    });
+
+    expect(results).to.deep.equal([18, 'done']);
+  });
+
+  it('should support the deprecated resultSelector with a spread of ObservableInputs', () => {
+    const results: Array<number|string> = [];
+    forkJoin(
+      of(1, 2, 3),
+      of(4, 5, 6),
+      of(7, 8, 9),
+      (a: number, b: number, c: number) => a + b + c,
+    )
+    .subscribe({
+      next(value) {
+        results.push(value);
+      },
+      error(err) {
+        throw err;
+      },
+      complete() {
+        results.push('done');
+      }
+    });
+
+    expect(results).to.deep.equal([18, 'done']);
+  });
+
   it('should join the last values of the provided observables into an array', () => {
     const e1 = forkJoin(
                hot('--a--b--c--d--|'),

src/internal/observable/forkJoin.ts

@@ -6,6 +6,7 @@ import { subscribeToResult } from '../util/subscribeToResult';
 import { OuterSubscriber } from '../OuterSubscriber';
 import { InnerSubscriber } from '../InnerSubscriber';
 import { Subscriber } from '../Subscriber';
+import { map } from '../operators/map';
 
 /* tslint:disable:max-line-length */
 // forkJoin([a$, b$, c$]);
@@ -24,7 +25,10 @@ export function forkJoin<T, T2, T3>(v1: ObservableInput<T>, v2: ObservableInput<
 export function forkJoin<T, T2, T3, T4>(v1: ObservableInput<T>, v2: ObservableInput<T2>, v3: ObservableInput<T3>, v4: ObservableInput<T4>): Observable<[T, T2, T3, T4]>;
 export function forkJoin<T, T2, T3, T4, T5>(v1: ObservableInput<T>, v2: ObservableInput<T2>, v3: ObservableInput<T3>, v4: ObservableInput<T4>, v5: ObservableInput<T5>): Observable<[T, T2, T3, T4, T5]>;
 export function forkJoin<T, T2, T3, T4, T5, T6>(v1: ObservableInput<T>, v2: ObservableInput<T2>, v3: ObservableInput<T3>, v4: ObservableInput<T4>, v5: ObservableInput<T5>, v6: ObservableInput<T6>): Observable<[T, T2, T3, T4, T5, T6]>;
-export function forkJoin<T>(...sources: Array<ObservableInput<T>>): Observable<T[]>;
+
+/** @deprecated resultSelector is deprecated, pipe to map instead */
+export function forkJoin(...args: Array<ObservableInput<any>|Function>): Observable<any>;
+export function forkJoin<T>(...sources: ObservableInput<T>[]): Observable<T[]>;
 /* tslint:enable:max-line-length */
 
 /**
@@ -64,7 +68,7 @@ export function forkJoin<T>(...sources: Array<ObservableInput<T>>): Observable<T
  * when output Observable is supposed to emit a result.
  *
  * @example <caption>Use forkJoin with operator emitting immediately</caption>
- * import { forkJoin, of } from 'rxjs/create';
+ * import { forkJoin, of } from 'rxjs';
  *
  * const observable = forkJoin(
  *   of(1, 2, 3, 4),
@@ -82,7 +86,7 @@ export function forkJoin<T>(...sources: Array<ObservableInput<T>>): Observable<T
  *
  *
  * @example <caption>Use forkJoin with operator emitting after some time</caption>
- * import { forkJoin, interval } from 'rxjs/create';
+ * import { forkJoin, interval } from 'rxjs';
  * import { take } from 'rxjs/operators';
  *
  * const observable = forkJoin(
@@ -101,7 +105,7 @@ export function forkJoin<T>(...sources: Array<ObservableInput<T>>): Observable<T
  *
  *
  * @example <caption>Use forkJoin with project function</caption>
- * import { jorkJoin, interval } from 'rxjs/create';
+ * import { jorkJoin, interval } from 'rxjs';
  * import { take } from 'rxjs/operators';
  *
  * const observable = forkJoin(
@@ -128,12 +132,17 @@ export function forkJoin<T>(...sources: Array<ObservableInput<T>>): Observable<T
  * that will appear in resulting Observable instead of default array.
  * @return {Observable} Observable emitting either an array of last values emitted by passed Observables
  * or value from project function.
- * @static true
- * @name forkJoin
- * @owner Observable
  */
-export function forkJoin<T>(...sources: Array<ObservableInput<T> |
-                                Array<ObservableInput<T>>>): Observable<T[]> {
+export function forkJoin<T>(
+  ...sources: Array<ObservableInput<T> | ObservableInput<T>[] | Function>
+): Observable<T[]> {
+
+  let resultSelector: Function;
+  if (typeof sources[sources.length - 1] === 'function') {
+    // DEPRECATED PATH
+    resultSelector = sources.pop() as Function;
+  }
+
   // if the first and only other argument is an array
   // assume it's been called with `forkJoin([obs1, obs2, obs3])`
   if (sources.length === 1 && isArray(sources[0])) {
@@ -144,6 +153,13 @@ export function forkJoin<T>(...sources: Array<ObservableInput<T> |
     return EMPTY;
   }
 
+  if (resultSelector) {
+    // DEPRECATED PATH
+    return forkJoin(sources).pipe(
+      map(args => resultSelector(...args))
+    );
+  }
+
   return new Observable(subscriber => {
     return new ForkJoinSubscriber(subscriber, sources as Array<ObservableInput<T>>);
   });