fix(material/datepicker): correct structure for grid role

Previously, the grid in mat-datepicker was not strictly following the structure expected for the grid role. Additionally, this change adds an `<abbr>` element to the column headers such that VoiceOver can correctly read column headers.

Fixes #21357

Author: jelbourn

src/material/datepicker/calendar-body.ts

@@ -58,8 +58,6 @@ export interface MatCalendarUserEvent<D> {
   styleUrls: ['calendar-body.css'],
   host: {
     'class': 'mat-calendar-body',
-    'role': 'grid',
-    'aria-readonly': 'true'
   },
   exportAs: 'matCalendarBody',
   encapsulation: ViewEncapsulation.None,

src/material/datepicker/calendar.scss

@@ -122,3 +122,7 @@ $calendar-next-icon-transform: translateX(-2px) rotate(45deg);
     height: $calendar-header-divider-width;
   }
 }
+
+.mat-calendar-abbr {
+  text-decoration: none;
+}

src/material/datepicker/month-view.html

@@ -1,11 +1,17 @@
-<table class="mat-calendar-table" role="presentation">
-  <thead class="mat-calendar-table-header">
-    <tr>
-      <th scope="col" *ngFor="let day of _weekdays" [attr.aria-label]="day.long">{{day.narrow}}</th>
+<table class="mat-calendar-table" role="grid">
+  <thead role="rowgroup" class="mat-calendar-table-header">
+    <tr role="row">
+      <!-- For the day-of-the-week column header, we use an `<abbr>` element because VoiceOver
+           ignores the `aria-label`. ChromeVox, however, does not read the full name
+           for the `<abbr>`, so we still set `aria-label` on the header element. -->
+      <th role="columnheader" scope="col" *ngFor="let day of _weekdays" [attr.aria-label]="day.long">
+        <abbr class="mat-calendar-abbr" [attr.title]="day.long">{{day.narrow}}</abbr>
+      </th>
     </tr>
-    <tr><th class="mat-calendar-table-header-divider" colspan="7" aria-hidden="true"></th></tr>
+    <tr><th aria-hidden="true" class="mat-calendar-table-header-divider" colspan="7"></th></tr>
   </thead>
   <tbody mat-calendar-body
+         role="rowgroup"
          [label]="_monthLabel"
          [rows]="_weeks"
          [todayValue]="_todayDate!"

src/material/datepicker/month-view.spec.ts

@@ -114,7 +114,7 @@ describe('MatMonthView', () => {
       describe('a11y', () => {
         it('should set the correct role on the internal table node', () => {
           const table = monthViewNativeElement.querySelector('table')!;
-          expect(table.getAttribute('role')).toBe('presentation');
+          expect(table.getAttribute('role')).toBe('grid');
         });
 
         it('should set the correct scope on the table headers', () => {

src/material/datepicker/multi-year-view.html

@@ -1,5 +1,5 @@
-<table class="mat-calendar-table" role="presentation">
-  <thead class="mat-calendar-table-header">
+<table class="mat-calendar-table" role="grid">
+  <thead aria-hidden="true" class="mat-calendar-table-header">
     <tr><th class="mat-calendar-table-header-divider" colspan="4"></th></tr>
   </thead>
   <tbody mat-calendar-body

src/material/datepicker/multi-year-view.spec.ts

@@ -104,7 +104,7 @@ describe('MatMultiYearView', () => {
     describe('a11y', () => {
       it('should set the correct role on the internal table node', () => {
         const table = multiYearViewNativeElement.querySelector('table')!;
-        expect(table.getAttribute('role')).toBe('presentation');
+        expect(table.getAttribute('role')).toBe('grid');
       });
 
       describe('calendar body', () => {

src/material/datepicker/year-view.html

@@ -1,8 +1,9 @@
-<table class="mat-calendar-table" role="presentation">
-  <thead class="mat-calendar-table-header">
+<table class="mat-calendar-table" role="grid">
+  <thead aria-hidden="true" class="mat-calendar-table-header">
     <tr><th class="mat-calendar-table-header-divider" colspan="4"></th></tr>
   </thead>
   <tbody mat-calendar-body
+         role="rowgroup"
          [label]="_yearLabel"
          [rows]="_months"
          [todayValue]="_todayMonth!"

src/material/datepicker/year-view.spec.ts

@@ -118,7 +118,7 @@ describe('MatYearView', () => {
     describe('a11y', () => {
       it('should set the correct role on the internal table node', () => {
         const table = yearViewNativeElement.querySelector('table')!;
-        expect(table.getAttribute('role')).toBe('presentation');
+        expect(table.getAttribute('role')).toBe('grid');
       });
 
       describe('calendar body', () => {