address comments

Author: mmalerba

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

@@ -1,7 +1,14 @@
 import {ArrayDataSource} from '@angular/cdk/collections';
 import {CdkVirtualForOf, CdkVirtualScrollViewport, ScrollingModule} from '@angular/cdk/scrolling';
 import {dispatchFakeEvent} from '@angular/cdk/testing';
-import {Component, Input, ViewChild, ViewContainerRef, ViewEncapsulation} from '@angular/core';
+import {
+  Component,
+  Input,
+  TrackByFunction,
+  ViewChild,
+  ViewContainerRef,
+  ViewEncapsulation
+} from '@angular/core';
 import {ComponentFixture, fakeAsync, flush, TestBed} from '@angular/core/testing';
 import {animationFrameScheduler, Subject} from 'rxjs';
 
@@ -727,7 +734,7 @@ class FixedSizeVirtualScroll {
   @Input() minBufferPx = 0;
   @Input() maxBufferPx = 0;
   @Input() items = Array(10).fill(0).map((_, i) => i);
-  @Input() trackBy;
+  @Input() trackBy: TrackByFunction<number>;
   @Input() templateCacheSize = 20;
 
   scrolledToIndex = 0;
@@ -777,7 +784,7 @@ class FixedSizeVirtualScrollWithRtlDirection {
   @Input() itemSize = 50;
   @Input() bufferSize = 0;
   @Input() items = Array(10).fill(0).map((_, i) => i);
-  @Input() trackBy;
+  @Input() trackBy: TrackByFunction<number>;
   @Input() templateCacheSize = 20;
 
   scrolledToIndex = 0;

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

@@ -285,7 +285,7 @@ export class CdkVirtualScrollViewport implements OnInit, OnDestroy {
     // For a horizontal viewport in a right-to-left language we need to calculate what `scrollRight`
     // would be.
     offset = this.orientation == 'horizontal' && this._dir && this._dir.value == 'rtl' ?
-        Math.max(0, this._totalContentSize - this._viewportSize - offset) : offset;
+        this._getRightOffsetAsLeftOffset(offset) : offset;
 
     if (supportsScrollBehavior()) {
       const offsetDirection = this.orientation === 'horizontal' ? 'left' : 'top';
@@ -315,7 +315,7 @@ export class CdkVirtualScrollViewport implements OnInit, OnDestroy {
       // For a horizontal viewport in a right-to-left language we need to calculate what
       // `scrollRight` would be.
       return this._dir && this._dir.value == 'rtl' ?
-          Math.max(0, this._totalContentSize - this._viewportSize - offset) : offset;
+          this._getRightOffsetAsLeftOffset(offset) : offset;
     }
     return this.elementRef.nativeElement.scrollTop;
   }
@@ -387,4 +387,9 @@ export class CdkVirtualScrollViewport implements OnInit, OnDestroy {
       fn();
     }
   }
+
+  /** Expresses an offset from the right as the equivalent offset from the left. */
+  private _getRightOffsetAsLeftOffset(offset: number): number {
+    return Math.max(0, this._totalContentSize - this._viewportSize - offset);
+  }
 }

src/demo-app/demo-app/demo-app.html

@@ -41,7 +41,7 @@ <h1>Angular Material Demos</h1>
       </div>
     </mat-toolbar>
 
-    <div #root="dir" dir="rtl" class="demo-content">
+    <div #root="dir" dir="ltr" class="demo-content">
       <router-outlet></router-outlet>
     </div>
   </div>