refactor(cdk/scrolling): add lightweight token for virtual scroll viewport

Adds a lightweight token for the virtual scroll viewport so it can be injected without a hard dependency.

Author: crisbeto

goldens/cdk/scrolling/index.api.md

@@ -26,6 +26,9 @@ export type _Bottom = {
     bottom?: number;
 };
 
+// @public
+export const CDK_VIRTUAL_SCROLL_VIEWPORT: InjectionToken<CdkVirtualScrollViewport>;
+
 // @public
 export class CdkFixedSizeVirtualScroll implements OnChanges {
     get itemSize(): number;

src/cdk/scrolling/virtual-for-of.ts

@@ -36,7 +36,7 @@ import {NumberInput, coerceNumberProperty} from '../coercion';
 import {Observable, Subject, of as observableOf, isObservable} from 'rxjs';
 import {pairwise, shareReplay, startWith, switchMap, takeUntil} from 'rxjs/operators';
 import {CdkVirtualScrollRepeater} from './virtual-scroll-repeater';
-import {CdkVirtualScrollViewport} from './virtual-scroll-viewport';
+import {CDK_VIRTUAL_SCROLL_VIEWPORT} from './virtual-scroll-viewport';
 
 /** The context for an item rendered by `CdkVirtualForOf` */
 export type CdkVirtualForOfContext<T> = {
@@ -87,7 +87,7 @@ export class CdkVirtualForOf<T>
   private _template = inject<TemplateRef<CdkVirtualForOfContext<T>>>(TemplateRef);
   private _differs = inject(IterableDiffers);
   private _viewRepeater = new _RecycleViewRepeaterStrategy<T, T, CdkVirtualForOfContext<T>>();
-  private _viewport = inject(CdkVirtualScrollViewport, {skipSelf: true});
+  private _viewport = inject(CDK_VIRTUAL_SCROLL_VIEWPORT, {skipSelf: true});
 
   /** Emits when the rendered view of the data changes. */
   readonly viewChange = new Subject<ListRange>();

src/cdk/scrolling/virtual-scroll-viewport.ts

@@ -19,6 +19,7 @@ import {
   effect,
   ElementRef,
   inject,
+  InjectionToken,
   Injector,
   Input,
   OnDestroy,
@@ -57,6 +58,14 @@ function rangesEqual(r1: ListRange, r2: ListRange): boolean {
 const SCROLL_SCHEDULER =
   typeof requestAnimationFrame !== 'undefined' ? animationFrameScheduler : asapScheduler;
 
+/**
+ * Lightweight token that can be used to inject the `CdkVirtualScrollViewport`
+ * without introducing a hard dependency on it.
+ */
+export const CDK_VIRTUAL_SCROLL_VIEWPORT = new InjectionToken<CdkVirtualScrollViewport>(
+  'CDK_VIRTUAL_SCROLL_VIEWPORT',
+);
+
 /** A viewport that virtualizes its scrolling with the help of `CdkVirtualForOf`. */
 @Component({
   selector: 'cdk-virtual-scroll-viewport',
@@ -75,6 +84,7 @@ const SCROLL_SCHEDULER =
       useFactory: () =>
         inject(VIRTUAL_SCROLLABLE, {optional: true}) || inject(CdkVirtualScrollViewport),
     },
+    {provide: CDK_VIRTUAL_SCROLL_VIEWPORT, useExisting: CdkVirtualScrollViewport},
   ],
 })
 export class CdkVirtualScrollViewport extends CdkVirtualScrollable implements OnInit, OnDestroy {