fix(table): add missing rowgroup roles (#15131)

The native cdk-table adds thead, tbody, and tfoot elements but was
omitting the "rowgroup" role from these. This is necessary since we also
specifically add roles to all of the other table elements.
This also marks thead and tfoot as `display: none` when there are no
corresponding rows.

src/cdk/table/table.spec.ts

@@ -505,6 +505,32 @@ describe('CdkTable', () => {
     ]);
   });
 
+  it('should apply correct roles for native table elements', () => {
+    const thisFixture = createComponent(NativeHtmlTableApp);
+    const thisTableElement: HTMLTableElement = thisFixture.nativeElement.querySelector('table');
+    thisFixture.detectChanges();
+
+    const rowGroups = Array.from(thisTableElement.querySelectorAll('thead, tbody, tfoot'));
+    expect(rowGroups.length).toBe(3, 'Expected table to have a thead, tbody, and tfoot');
+    for (const group of rowGroups) {
+      expect(group.getAttribute('role'))
+          .toBe('rowgroup', 'Expected thead, tbody, and tfoot to have role="rowgroup"');
+    }
+  });
+
+  it('should hide thead/tfoot when there are no header/footer rows', () => {
+    const thisFixture = createComponent(NativeTableWithNoHeaderOrFooterRows);
+    const thisTableElement: HTMLTableElement = thisFixture.nativeElement.querySelector('table');
+    thisFixture.detectChanges();
+
+    const rowGroups: HTMLElement[] = Array.from(thisTableElement.querySelectorAll('thead, tfoot'));
+    expect(rowGroups.length).toBe(2, 'Expected table to have a thead and tfoot');
+    for (const group of rowGroups) {
+      expect(group.style.display)
+          .toBe('none', 'Expected thead and tfoot to be `display: none`');
+    }
+  });
+
   it('should render cells even if row data is falsy', () => {
     setupTableTestApp(BooleanRowCdkTableApp);
     expectTableToMatchContent(tableElement, [
@@ -1591,27 +1617,27 @@ class MultipleHeaderFooterRowsCdkTableApp {
 
       <ng-container cdkColumnDef="index1Column">
         <cdk-header-cell *cdkHeaderCellDef> Column C</cdk-header-cell>
-        <cdk-cell *cdkCellDef="let row"> index_1_special_row</cdk-cell>
+        <cdk-cell *cdkCellDef> index_1_special_row</cdk-cell>
       </ng-container>
 
       <ng-container cdkColumnDef="c3Column">
         <cdk-header-cell *cdkHeaderCellDef> Column C</cdk-header-cell>
-        <cdk-cell *cdkCellDef="let row"> c3_special_row</cdk-cell>
+        <cdk-cell *cdkCellDef> c3_special_row</cdk-cell>
       </ng-container>
 
       <ng-container cdkColumnDef="index">
         <cdk-header-cell *cdkHeaderCellDef> Index</cdk-header-cell>
-        <cdk-cell *cdkCellDef="let row; let index = index"> {{index}}</cdk-cell>
+        <cdk-cell *cdkCellDef="let index = index"> {{index}}</cdk-cell>
       </ng-container>
 
       <ng-container cdkColumnDef="dataIndex">
         <cdk-header-cell *cdkHeaderCellDef> Data Index</cdk-header-cell>
-        <cdk-cell *cdkCellDef="let row; let dataIndex = dataIndex"> {{dataIndex}}</cdk-cell>
+        <cdk-cell *cdkCellDef="let dataIndex = dataIndex"> {{dataIndex}}</cdk-cell>
       </ng-container>
 
       <ng-container cdkColumnDef="renderIndex">
         <cdk-header-cell *cdkHeaderCellDef> Render Index</cdk-header-cell>
-        <cdk-cell *cdkCellDef="let row; let renderIndex = renderIndex"> {{renderIndex}}</cdk-cell>
+        <cdk-cell *cdkCellDef="let renderIndex = renderIndex"> {{renderIndex}}</cdk-cell>
       </ng-container>
 
       <cdk-header-row *cdkHeaderRowDef="columnsToRender"></cdk-header-row>
@@ -1662,12 +1688,12 @@ class WhenRowCdkTableApp {
 
       <ng-container cdkColumnDef="index1Column">
         <cdk-header-cell *cdkHeaderCellDef> Column C</cdk-header-cell>
-        <cdk-cell *cdkCellDef="let row"> index_1_special_row </cdk-cell>
+        <cdk-cell *cdkCellDef> index_1_special_row </cdk-cell>
       </ng-container>
 
       <ng-container cdkColumnDef="c3Column">
         <cdk-header-cell *cdkHeaderCellDef> Column C</cdk-header-cell>
-        <cdk-cell *cdkCellDef="let row"> c3_special_row </cdk-cell>
+        <cdk-cell *cdkCellDef> c3_special_row </cdk-cell>
       </ng-container>
 
       <cdk-header-row *cdkHeaderRowDef="columnsToRender"></cdk-header-row>
@@ -1705,12 +1731,12 @@ class WhenRowWithoutDefaultCdkTableApp {
 
       <ng-container cdkColumnDef="index1Column">
         <cdk-header-cell *cdkHeaderCellDef> Column C</cdk-header-cell>
-        <cdk-cell *cdkCellDef="let row"> index_1_special_row </cdk-cell>
+        <cdk-cell *cdkCellDef> index_1_special_row </cdk-cell>
       </ng-container>
 
       <ng-container cdkColumnDef="c3Column">
         <cdk-header-cell *cdkHeaderCellDef> Column C</cdk-header-cell>
-        <cdk-cell *cdkCellDef="let row"> c3_special_row </cdk-cell>
+        <cdk-cell *cdkCellDef> c3_special_row </cdk-cell>
       </ng-container>
 
       <cdk-header-row *cdkHeaderRowDef="columnsToRender"></cdk-header-row>
@@ -1790,7 +1816,7 @@ class TrackByCdkTableApp {
                     [sticky]="isStuck(stickyStartColumns, column)"
                     [stickyEnd]="isStuck(stickyEndColumns, column)">
         <cdk-header-cell *cdkHeaderCellDef> Header {{column}} </cdk-header-cell>
-        <cdk-cell *cdkCellDef="let row"> {{column}} </cdk-cell>
+        <cdk-cell *cdkCellDef>{{column}}</cdk-cell>
         <cdk-footer-cell *cdkFooterCellDef> Footer {{column}} </cdk-footer-cell>
       </ng-container>
 
@@ -2226,6 +2252,35 @@ class NativeHtmlTableApp {
   @ViewChild(CdkTable) table: CdkTable<TestData>;
 }
 
+@Component({
+  template: `
+    <table cdk-table [dataSource]="dataSource">
+      <ng-container cdkColumnDef="column_a">
+        <th cdk-header-cell *cdkHeaderCellDef> Column A</th>
+        <td cdk-cell *cdkCellDef="let row"> {{row.a}}</td>
+      </ng-container>
+
+      <ng-container cdkColumnDef="column_b">
+        <th cdk-header-cell *cdkHeaderCellDef> Column B</th>
+        <td cdk-cell *cdkCellDef="let row"> {{row.b}}</td>
+      </ng-container>
+
+      <ng-container cdkColumnDef="column_c">
+        <th cdk-header-cell *cdkHeaderCellDef> Column C</th>
+        <td cdk-cell *cdkCellDef="let row"> {{row.c}}</td>
+      </ng-container>
+
+      <tr cdk-row *cdkRowDef="let row; columns: columnsToRender" class="customRowClass"></tr>
+    </table>
+  `
+})
+class NativeTableWithNoHeaderOrFooterRows {
+  dataSource: FakeDataSource | undefined = new FakeDataSource();
+  columnsToRender = ['column_a', 'column_b', 'column_c'];
+
+  @ViewChild(CdkTable) table: CdkTable<TestData>;
+}
+
 @Component({
   template: `
     <table cdk-table [dataSource]="dataSource">

src/cdk/table/table.ts

@@ -579,11 +579,20 @@ export class CdkTable<T> implements AfterContentChecked, CollectionViewer, OnDes
    * sticky input changes. May be called manually for cases where the cell content changes outside
    * of these events.
    */
-  updateStickyHeaderRowStyles() {
+  updateStickyHeaderRowStyles(): void {
     const headerRows = this._getRenderedRows(this._headerRowOutlet);
-    this._stickyStyler.clearStickyPositioning(headerRows, ['top']);
+    const tableElement = this._elementRef.nativeElement as HTMLElement;
+
+    // Hide the thead element if there are no header rows. This is necessary to satisfy
+    // overzealous a11y checkers that fail because the `rowgroup` element does not contain
+    // required child `row`.
+    const thead = tableElement.querySelector('thead');
+    if (thead) {
+      thead.style.display = headerRows.length ? '' : 'none';
+    }
 
     const stickyStates = this._headerRowDefs.map(def => def.sticky);
+    this._stickyStyler.clearStickyPositioning(headerRows, ['top']);
     this._stickyStyler.stickRows(headerRows, stickyStates, 'top');
 
     // Reset the dirty state of the sticky input change since it has been used.
@@ -597,11 +606,20 @@ export class CdkTable<T> implements AfterContentChecked, CollectionViewer, OnDes
    * sticky input changes. May be called manually for cases where the cell content changes outside
    * of these events.
    */
-  updateStickyFooterRowStyles() {
+  updateStickyFooterRowStyles(): void {
     const footerRows = this._getRenderedRows(this._footerRowOutlet);
-    this._stickyStyler.clearStickyPositioning(footerRows, ['bottom']);
+    const tableElement = this._elementRef.nativeElement as HTMLElement;
+
+    // Hide the tfoot element if there are no footer rows. This is necessary to satisfy
+    // overzealous a11y checkers that fail because the `rowgroup` element does not contain
+    // required child `row`.
+    const tfoot = tableElement.querySelector('tfoot');
+    if (tfoot) {
+      tfoot.style.display = footerRows.length ? '' : 'none';
+    }
 
     const stickyStates = this._footerRowDefs.map(def => def.sticky);
+    this._stickyStyler.clearStickyPositioning(footerRows, ['bottom']);
     this._stickyStyler.stickRows(footerRows, stickyStates, 'bottom');
     this._stickyStyler.updateStickyFooterContainer(this._elementRef.nativeElement, stickyStates);
 
@@ -865,7 +883,7 @@ export class CdkTable<T> implements AfterContentChecked, CollectionViewer, OnDes
   }
 
   /** Gets the list of rows that have been rendered in the row outlet. */
-  _getRenderedRows(rowOutlet: RowOutlet) {
+  _getRenderedRows(rowOutlet: RowOutlet): HTMLElement[] {
     const renderedRows: HTMLElement[] = [];
 
     for (let i = 0; i < rowOutlet.viewContainer.length; i++) {
@@ -983,6 +1001,7 @@ export class CdkTable<T> implements AfterContentChecked, CollectionViewer, OnDes
 
     for (const section of sections) {
       const element = documentRef.createElement(section.tag);
+      element.setAttribute('role', 'rowgroup');
       element.appendChild(section.outlet.elementRef.nativeElement);
       documentFragment.appendChild(element);
     }