fix(afs): allow stateChanges and auditLog to emit blank arrays at first

This allows a developer to detirmine that the collection being observed is empty
and keeps the subscription from holding up isStable.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@angular/fire",
-  "version": "6.1.2",
+  "version": "6.1.3",
   "description": "The official Angular library for Firebase.",
   "private": true,
   "scripts": {

src/auth/auth.spec.ts

@@ -118,20 +118,21 @@ describe('AngularFireAuth', () => {
 
 });
 
-const FIREBASE_APP_NAME_TOO = (Math.random() + 1).toString(36).substring(7);
-
 describe('AngularFireAuth with different app', () => {
   let app: FirebaseApp;
   let afAuth: AngularFireAuth;
+  let firebaseAppName: string;
 
   beforeEach(() => {
+    firebaseAppName = rando();
+
     TestBed.configureTestingModule({
       imports: [
         AngularFireModule.initializeApp(COMMON_CONFIG, rando()),
         AngularFireAuthModule
       ],
       providers: [
-        { provide: FIREBASE_APP_NAME, useValue: FIREBASE_APP_NAME_TOO },
+        { provide: FIREBASE_APP_NAME, useValue: firebaseAppName },
         { provide: FIREBASE_OPTIONS, useValue: COMMON_CONFIG }
       ]
     });
@@ -156,7 +157,7 @@ describe('AngularFireAuth with different app', () => {
 
     it('should have an initialized Firebase app instance member', async () => {
       const app = await afAuth.app;
-      expect(app.name).toEqual(FIREBASE_APP_NAME_TOO);
+      expect(app.name).toEqual(firebaseAppName);
     });
   });
 

src/firestore/collection/collection.spec.ts

@@ -399,7 +399,7 @@ describe('AngularFirestoreCollection', () => {
       const ITEMS = 10;
       const { ref, stocks, names } = await collectionHarness(afs, ITEMS);
 
-      const sub = stocks.stateChanges(['modified']).subscribe(data => {
+      const sub = stocks.stateChanges(['modified']).pipe(skip(1), take(1)).subscribe(data => {
         sub.unsubscribe();
         expect(data.length).toEqual(1);
         expect(data[0].payload.doc.data().price).toEqual(2);
@@ -436,7 +436,7 @@ describe('AngularFirestoreCollection', () => {
       const ITEMS = 10;
       const { ref, stocks, names } = await collectionHarness(afs, ITEMS);
 
-      const sub = stocks.stateChanges(['removed']).subscribe(data => {
+      const sub = stocks.stateChanges(['removed']).pipe(skip(1), take(1)).subscribe(data => {
         sub.unsubscribe();
         expect(data.length).toEqual(1);
         expect(data[0].type).toEqual('removed');
@@ -446,6 +446,21 @@ describe('AngularFirestoreCollection', () => {
 
       delayDelete(stocks, names[0], 400);
     });
+
+    it('stateChanges() should emit on empty collection', async (done) => {
+      afs.collection('EMPTY_COLLECTION').stateChanges().pipe(take(1)).subscribe(data => {
+        expect(data.length).toEqual(0);
+        done();
+      });
+    });
+
+    it('stateChanges() w/filter should emit on empty collection', async (done) => {
+      afs.collection('EMPTY_COLLECTION').stateChanges(['added']).pipe(take(1)).subscribe(data => {
+        expect(data.length).toEqual(0);
+        done();
+      });
+    });
+
   });
 
   describe('auditTrail()', () => {
@@ -471,7 +486,7 @@ describe('AngularFirestoreCollection', () => {
       const ITEMS = 10;
       const { ref, stocks, names } = await collectionHarness(afs, ITEMS);
 
-      const sub = stocks.auditTrail(['removed']).subscribe(data => {
+      const sub = stocks.auditTrail(['removed']).pipe(skip(1), take(1)).subscribe(data => {
         sub.unsubscribe();
         expect(data.length).toEqual(1);
         expect(data[0].type).toEqual('removed');

src/firestore/collection/collection.ts

@@ -1,6 +1,6 @@
 import { from, Observable } from 'rxjs';
 import { fromCollectionRef } from '../observable/fromRef';
-import { filter, map, observeOn, scan } from 'rxjs/operators';
+import { filter, map, observeOn, pairwise, scan, startWith } from 'rxjs/operators';
 import firebase from 'firebase/app';
 
 import { CollectionReference, DocumentChangeAction, DocumentChangeType, DocumentData, DocumentReference, Query } from '../interfaces';
@@ -59,15 +59,19 @@ export class AngularFirestoreCollection<T = DocumentData> {
    * your own data structure.
    */
   stateChanges(events?: DocumentChangeType[]): Observable<DocumentChangeAction<T>[]> {
-    if (!events || events.length === 0) {
-      return docChanges<T>(this.query, this.afs.schedulers.outsideAngular).pipe(
-        filter(changes =>  changes.length > 0),
-        this.afs.keepUnstableUntilFirst
+    let source = docChanges<T>(this.query, this.afs.schedulers.outsideAngular);
+    if (events && events.length > 0) {
+      source = source.pipe(
+        map(actions => actions.filter(change => events.indexOf(change.type) > -1))
       );
     }
-    return docChanges<T>(this.query, this.afs.schedulers.outsideAngular).pipe(
-      map(actions => actions.filter(change => events.indexOf(change.type) > -1)),
-      filter(changes =>  changes.length > 0),
+    return source.pipe(
+      // We want to filter out empty arrays, but always emit at first, so the developer knows
+      // that the collection has been resolve; even if it's empty
+      startWith(undefined),
+      pairwise(),
+      filter(([prior, current]) => current.length > 0 || !prior),
+      map(([prior, current]) => current),
       this.afs.keepUnstableUntilFirst
     );
   }

src/firestore/utils.spec.ts

@@ -54,4 +54,4 @@ export function delayDelete<T>(collection: AngularFirestoreCollection<T>|firebas
   }, delay);
 }
 
-export const rando = () => (Math.random() + 1).toString(36).substring(7);
+export const rando = () => (Math.random() + 1).toString(36).split('.')[1];