fix(table): update implicit when using trackby (#7893)

* fix(table): update implicit when using trackby

* imports

* syntax change

src/cdk/table/table.spec.ts

@@ -391,6 +391,24 @@ describe('CdkTable', () => {
       expect(changedRows[1].getAttribute('initialIndex')).toBe('1');
       expect(changedRows[2].getAttribute('initialIndex')).toBe(null);
     });
+
+    it('should change row implicit data even when trackBy finds no changes', () => {
+      createTestComponentWithTrackyByTable('index');
+      const firstRow = getRows(tableElement)[0];
+      expect(firstRow.textContent!.trim()).toBe('a_1 b_1');
+      expect(firstRow.getAttribute('initialIndex')).toBe('0');
+      mutateData();
+
+      // Change each item reference to show that the trackby is checking the index.
+      // Otherwise this would cause them all to be removed/added.
+      trackByComponent.dataSource.data = trackByComponent.dataSource.data
+          .map(item => ({a: item.a, b: item.b, c: item.c}));
+
+      // Expect the rows were given the right implicit data even though the rows were not moved.
+      trackByFixture.detectChanges();
+      expect(firstRow.textContent!.trim()).toBe('a_2 b_2');
+      expect(firstRow.getAttribute('initialIndex')).toBe('0');
+    });
   });
 
   it('should match the right table content with dynamic data', () => {

src/cdk/table/table.ts

@@ -37,7 +37,8 @@ import {Subscription} from 'rxjs/Subscription';
 import {Subject} from 'rxjs/Subject';
 import {CdkCellDef, CdkColumnDef, CdkHeaderCellDef} from './cell';
 import {
-  getTableDuplicateColumnNameError, getTableMissingMatchingRowDefError,
+  getTableDuplicateColumnNameError,
+  getTableMissingMatchingRowDefError,
   getTableMultipleDefaultRowDefsError,
   getTableUnknownColumnError
 } from './table-errors';
@@ -68,6 +69,12 @@ export const CDK_TABLE_TEMPLATE = `
   <ng-container headerRowPlaceholder></ng-container>
   <ng-container rowPlaceholder></ng-container>`;
 
+/**
+ * Class used to conveniently type the embedded view ref for rows with a context.
+ * @docs-private
+ */
+abstract class RowViewRef<T> extends EmbeddedViewRef<CdkCellOutletRowContext<T>> { }
+
 /**
  * A data table that connects with a data source to retrieve data of type `T` and renders
  * a header row and data rows. Updates the rows when new data is provided by the data source.
@@ -292,25 +299,36 @@ export class CdkTable<T> implements CollectionViewer {
     this._changeDetectorRef.markForCheck();
   }
 
-  /** Check for changes made in the data and render each change (row added/removed/moved). */
+  /**
+   * Check for changes made in the data and render each change (row added/removed/moved) and update
+   * row contexts.
+   */
   private _renderRowChanges() {
     const changes = this._dataDiffer.diff(this._data);
     if (!changes) { return; }
 
     const viewContainer = this._rowPlaceholder.viewContainer;
     changes.forEachOperation(
-        (item: IterableChangeRecord<any>, adjustedPreviousIndex: number, currentIndex: number) => {
-          if (item.previousIndex == null) {
-            this._insertRow(this._data[currentIndex], currentIndex);
+        (record: IterableChangeRecord<T>, adjustedPreviousIndex: number, currentIndex: number) => {
+          if (record.previousIndex == null) {
+            this._insertRow(record.item, currentIndex);
           } else if (currentIndex == null) {
             viewContainer.remove(adjustedPreviousIndex);
           } else {
-            const view = viewContainer.get(adjustedPreviousIndex);
+            const view = <RowViewRef<T>>viewContainer.get(adjustedPreviousIndex);
             viewContainer.move(view!, currentIndex);
           }
         });
 
-    this._updateRowContext();
+    // Update the meta context of a row's context data (index, count, first, last, ...)
+    this._updateRowIndexContext();
+
+    // Update rows that did not get added/removed/moved but may have had their identity changed,
+    // e.g. if trackBy matched data on some property but the actual data reference changed.
+    changes.forEachIdentityChange((record: IterableChangeRecord<T>) => {
+      const rowView = <RowViewRef<T>>viewContainer.get(record.currentIndex!);
+      rowView.context.$implicit = record.item;
+    });
   }
 
   /**
@@ -353,14 +371,13 @@ export class CdkTable<T> implements CollectionViewer {
   }
 
   /**
-   * Updates the context for each row to reflect any data changes that may have caused
-   * rows to be added, removed, or moved. The view container contains the same context
-   * that was provided to each of its cells.
+   * Updates the index-related context for each row to reflect any changes in the index of the rows,
+   * e.g. first/last/even/odd.
    */
-  private _updateRowContext() {
+  private _updateRowIndexContext() {
     const viewContainer = this._rowPlaceholder.viewContainer;
     for (let index = 0, count = viewContainer.length; index < count; index++) {
-      const viewRef = viewContainer.get(index) as EmbeddedViewRef<CdkCellOutletRowContext<T>>;
+      const viewRef = viewContainer.get(index) as RowViewRef<T>;
       viewRef.context.index = index;
       viewRef.context.count = count;
       viewRef.context.first = index === 0;
@@ -404,4 +421,3 @@ export class CdkTable<T> implements CollectionViewer {
     });
   }
 }
-