fix(merge): single array is not an array of sources (#6211)

* test(merge): add failing single-array test

* fix(merge): single array is not an array of sources

Author: cartant

spec/observables/merge-spec.ts

@@ -282,4 +282,10 @@ describe('merge(...observables, Scheduler, number)', () => {
 
     expect(e1Subscribed).to.be.false;
   });
+
+  it('should deem a single array argument to be an ObservableInput', () => {
+    const array = ['foo', 'bar'];
+    const expected = '(fb|)';
+    expectObservable(merge(array)).toBe(expected, { f: 'foo', b: 'bar' });
+  });
 });

src/internal/observable/merge.ts

@@ -2,7 +2,6 @@ import { Observable } from '../Observable';
 import { ObservableInput, ObservableInputTuple, SchedulerLike } from '../types';
 import { mergeAll } from '../operators/mergeAll';
 import { internalFromArray } from './fromArray';
-import { argsOrArgArray } from '../util/argsOrArgArray';
 import { innerFrom } from './from';
 import { EMPTY } from './empty';
 import { popNumber, popScheduler } from '../util/args';
@@ -88,7 +87,7 @@ export function merge<A extends readonly unknown[]>(
 export function merge(...args: (ObservableInput<unknown> | number | SchedulerLike)[]): Observable<unknown> {
   const scheduler = popScheduler(args);
   const concurrent = popNumber(args, Infinity);
-  const sources = argsOrArgArray(args) as ObservableInput<unknown>[];
+  const sources = args as ObservableInput<unknown>[];
   return !sources.length
     ? // No source provided
       EMPTY