fix(sidenav): scrollable instance not exposed when explicitly specifying content element (#11706)

This is a resubmit of #11517 which got in by accident.

* Fixes the `MatSidenavContainer.scrollable` being undefined if the consumer has set the `mat-sidenav-content` themselves. The issue comes from the fact that we only query for scrollables inside the drawer's own view, but not inside the projected content.
* Fixes the example in the sidenav docs accessing the scrollable too early.

Fixes #10884.

BREAKING CHANGE: the constructor signature of the `MatDrawerContent` and `MatSidenavContent` has changed.

src/lib/sidenav/drawer-container.html

@@ -5,6 +5,6 @@
 
 <ng-content select="mat-drawer-content">
 </ng-content>
-<mat-drawer-content *ngIf="!_content" cdkScrollable>
+<mat-drawer-content *ngIf="!_content">
   <ng-content></ng-content>
 </mat-drawer-content>

src/lib/sidenav/drawer.spec.ts

@@ -16,6 +16,7 @@ import {A11yModule} from '@angular/cdk/a11y';
 import {PlatformModule} from '@angular/cdk/platform';
 import {ESCAPE} from '@angular/cdk/keycodes';
 import {dispatchKeyboardEvent} from '@angular/cdk/testing';
+import {CdkScrollable} from '@angular/cdk/scrolling';
 
 
 describe('MatDrawer', () => {
@@ -497,6 +498,7 @@ describe('MatDrawerContainer', () => {
         DrawerContainerStateChangesTestApp,
         AutosizeDrawer,
         BasicTestApp,
+        DrawerContainerWithContent,
       ],
     });
 
@@ -719,6 +721,27 @@ describe('MatDrawerContainer', () => {
       expect(fixture.componentInstance.drawer.opened).toBe(false);
     }));
 
+    it('should expose a scrollable when the consumer has not specified drawer content',
+      fakeAsync(() => {
+        const fixture = TestBed.createComponent(DrawerContainerTwoDrawerTestApp);
+
+        fixture.detectChanges();
+
+        expect(fixture.componentInstance.drawerContainer.scrollable instanceof CdkScrollable)
+            .toBe(true);
+      }));
+
+    it('should expose a scrollable when the consumer has specified drawer content',
+      fakeAsync(() => {
+        const fixture = TestBed.createComponent(DrawerContainerWithContent);
+
+        fixture.detectChanges();
+
+        expect(fixture.componentInstance.drawerContainer.scrollable instanceof CdkScrollable)
+            .toBe(true);
+      }));
+
+
 });
 
 
@@ -901,3 +924,16 @@ class AutosizeDrawer {
   @ViewChild(MatDrawer) drawer: MatDrawer;
   fillerWidth = 0;
 }
+
+
+@Component({
+  template: `
+    <mat-drawer-container>
+      <mat-drawer>Drawer</mat-drawer>
+      <mat-drawer-content>Content</mat-drawer-content>
+    </mat-drawer-container>
+  `,
+})
+class DrawerContainerWithContent {
+  @ViewChild(MatDrawerContainer) drawerContainer: MatDrawerContainer;
+}

src/lib/sidenav/drawer.ts

@@ -11,7 +11,7 @@ import {Directionality} from '@angular/cdk/bidi';
 import {coerceBooleanProperty} from '@angular/cdk/coercion';
 import {ESCAPE} from '@angular/cdk/keycodes';
 import {Platform} from '@angular/cdk/platform';
-import {CdkScrollable} from '@angular/cdk/scrolling';
+import {CdkScrollable, ScrollDispatcher} from '@angular/cdk/scrolling';
 import {DOCUMENT} from '@angular/common';
 import {
   AfterContentChecked,
@@ -75,10 +75,14 @@ export function MAT_DRAWER_DEFAULT_AUTOSIZE_FACTORY(): boolean {
   changeDetection: ChangeDetectionStrategy.OnPush,
   encapsulation: ViewEncapsulation.None,
 })
-export class MatDrawerContent implements AfterContentInit {
+export class MatDrawerContent extends CdkScrollable implements AfterContentInit {
   constructor(
       private _changeDetectorRef: ChangeDetectorRef,
-      @Inject(forwardRef(() => MatDrawerContainer)) public _container: MatDrawerContainer) {
+      @Inject(forwardRef(() => MatDrawerContainer)) public _container: MatDrawerContainer,
+      elementRef: ElementRef<HTMLElement>,
+      scrollDispatcher: ScrollDispatcher,
+      ngZone: NgZone) {
+    super(elementRef, scrollDispatcher, ngZone);
   }
 
   ngAfterContentInit() {
@@ -401,6 +405,7 @@ export class MatDrawer implements AfterContentInit, AfterContentChecked, OnDestr
 export class MatDrawerContainer implements AfterContentInit, DoCheck, OnDestroy {
   @ContentChildren(MatDrawer) _drawers: QueryList<MatDrawer>;
   @ContentChild(MatDrawerContent) _content: MatDrawerContent;
+  @ViewChild(MatDrawerContent) _userContent: MatDrawerContent;
 
   /** The drawer child with the `start` position. */
   get start(): MatDrawer | null { return this._start; }
@@ -471,7 +476,9 @@ export class MatDrawerContainer implements AfterContentInit, DoCheck, OnDestroy
   readonly _contentMarginChanges = new Subject<{left: number|null, right: number|null}>();
 
   /** Reference to the CdkScrollable instance that wraps the scrollable content. */
-  @ViewChild(CdkScrollable) scrollable: CdkScrollable;
+  get scrollable(): CdkScrollable {
+    return this._userContent || this._content;
+  }
 
   constructor(@Optional() private _dir: Directionality,
               private _element: ElementRef,

src/lib/sidenav/sidenav.md

@@ -109,8 +109,8 @@ The `<mat-sidenav>` can render in one of three different ways based on the `mode
 
 | Mode   | Description                                                                             |
 |--------|-----------------------------------------------------------------------------------------|
-| `over` | Sidenav floats over the primary content, which is covered by a backdrop               |
-| `push` | Sidenav pushes the primary content out of its way, also covering it with a backdrop   |
+| `over` | Sidenav floats over the primary content, which is covered by a backdrop                 |
+| `push` | Sidenav pushes the primary content out of its way, also covering it with a backdrop     |
 | `side` | Sidenav appears side-by-side with the main content, shrinking the main content's width to make space for the sidenav. |
 
 If no `mode` is specified, `over` is used by default.
@@ -186,10 +186,10 @@ To react to scrolling inside the `<mat-sidenav-container>`, you can get a hold o
 `CdkScrollable` instance through the `MatSidenavContainer`.
 
 ```ts
-class YourComponent {
+class YourComponent implements AfterViewInit {
   @ViewChild(MatSidenavContainer) sidenavContainer: MatSidenavContainer;
 
-  constructor() {
+  ngAfterViewInit() {
     this.sidenavContainer.scrollable.elementScrolled().subscribe(() => /* react to scrolling */);
   }
 }

src/lib/sidenav/sidenav.ts

@@ -17,10 +17,13 @@ import {
   Input,
   ViewEncapsulation,
   QueryList,
+  ElementRef,
+  NgZone,
 } from '@angular/core';
 import {MatDrawer, MatDrawerContainer, MatDrawerContent} from './drawer';
 import {matDrawerAnimations} from './drawer-animations';
 import {coerceBooleanProperty, coerceNumberProperty} from '@angular/cdk/coercion';
+import {ScrollDispatcher} from '@angular/cdk/scrolling';
 
 
 @Component({
@@ -38,8 +41,11 @@ import {coerceBooleanProperty, coerceNumberProperty} from '@angular/cdk/coercion
 export class MatSidenavContent extends MatDrawerContent {
   constructor(
       changeDetectorRef: ChangeDetectorRef,
-      @Inject(forwardRef(() => MatSidenavContainer)) container: MatSidenavContainer) {
-    super(changeDetectorRef, container);
+      @Inject(forwardRef(() => MatSidenavContainer)) container: MatSidenavContainer,
+      elementRef: ElementRef<HTMLElement>,
+      scrollDispatcher: ScrollDispatcher,
+      ngZone: NgZone) {
+    super(changeDetectorRef, container, elementRef, scrollDispatcher, ngZone);
   }
 }