Accessibility: Add `Skip to content` link (#68065)

* user essentials mob! 🔱

lastFile:public/app/core/components/AppChrome/AppChrome.tsx

* user essentials mob! 🔱

lastFile:public/app/core/components/AppChrome/AppChrome.test.tsx

* only show skiplink when page has app chrome

---------

Co-authored-by: Joao Silva <joao.silva@grafana.com>

public/app/core/components/AppChrome/AppChrome.test.tsx

@@ -1,4 +1,5 @@
-import { render, screen } from '@testing-library/react';
+import { render, screen, waitFor } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
 import { KBarProvider } from 'kbar';
 import React, { ReactNode } from 'react';
 import { TestProvider } from 'test/helpers/TestProvider';
@@ -109,4 +110,28 @@ describe('AppChrome', () => {
     expect(screen.getByRole('tab', { name: 'Tab Child1' })).toBeInTheDocument();
     expect(screen.getByRole('tab', { name: 'Tab pageNav child1' })).toBeInTheDocument();
   });
+
+  it('should create a skip link to skip to main content', async () => {
+    setup(<Page navId="child1">Children</Page>);
+    expect(await screen.findByRole('link', { name: 'Skip to main content' })).toBeInTheDocument();
+  });
+
+  it('should focus the skip link on initial tab before carrying on with normal tab order', async () => {
+    setup(<Page navId="child1">Children</Page>);
+    await userEvent.keyboard('{tab}');
+    const skipLink = await screen.findByRole('link', { name: 'Skip to main content' });
+    expect(skipLink).toHaveFocus();
+    await userEvent.keyboard('{tab}');
+    expect(await screen.findByRole('link', { name: 'Go to home' })).toHaveFocus();
+  });
+
+  it('should not render a skip link if the page is chromeless', async () => {
+    const { context } = setup(<Page navId="child1">Children</Page>);
+    context.chrome.update({
+      chromeless: true,
+    });
+    waitFor(() => {
+      expect(screen.queryByRole('link', { name: 'Skip to main content' })).not.toBeInTheDocument();
+    });
+  });
 });

public/app/core/components/AppChrome/AppChrome.tsx

@@ -3,7 +3,7 @@ import classNames from 'classnames';
 import React, { PropsWithChildren } from 'react';
 
 import { GrafanaTheme2, PageLayoutType } from '@grafana/data';
-import { useStyles2 } from '@grafana/ui';
+import { useStyles2, LinkButton } from '@grafana/ui';
 import { useGrafana } from 'app/core/context/GrafanaContext';
 import { CommandPalette } from 'app/features/commandPalette/CommandPalette';
 import { KioskMode } from 'app/types';
@@ -34,34 +34,39 @@ export function AppChrome({ children }: Props) {
   // doesn't get re-mounted when chromeless goes from true to false.
 
   return (
-    <main className={classNames('main-view', searchBarHidden && 'main-view--search-bar-hidden')}>
+    <div className={classNames('main-view', searchBarHidden && 'main-view--search-bar-hidden')}>
       {!state.chromeless && (
-        <div className={cx(styles.topNav)}>
-          {!searchBarHidden && <TopSearchBar />}
-          <NavToolbar
-            searchBarHidden={searchBarHidden}
-            sectionNav={state.sectionNav.node}
-            pageNav={state.pageNav}
-            actions={state.actions}
-            onToggleSearchBar={chrome.onToggleSearchBar}
-            onToggleMegaMenu={chrome.onToggleMegaMenu}
-            onToggleKioskMode={chrome.onToggleKioskMode}
-          />
-        </div>
+        <>
+          <LinkButton className={styles.skipLink} href="#pageContent">
+            Skip to main content
+          </LinkButton>
+          <div className={cx(styles.topNav)}>
+            {!searchBarHidden && <TopSearchBar />}
+            <NavToolbar
+              searchBarHidden={searchBarHidden}
+              sectionNav={state.sectionNav.node}
+              pageNav={state.pageNav}
+              actions={state.actions}
+              onToggleSearchBar={chrome.onToggleSearchBar}
+              onToggleMegaMenu={chrome.onToggleMegaMenu}
+              onToggleKioskMode={chrome.onToggleKioskMode}
+            />
+          </div>
+        </>
       )}
-      <div className={contentClass}>
+      <main className={contentClass} id="pageContent">
         <div className={styles.panes}>
           {state.layout === PageLayoutType.Standard && state.sectionNav && <SectionNav model={state.sectionNav} />}
           <div className={styles.pageContainer}>{children}</div>
         </div>
-      </div>
+      </main>
       {!state.chromeless && (
         <>
           <MegaMenu searchBarHidden={searchBarHidden} onClose={() => chrome.setMegaMenu(false)} />
           <CommandPalette />
         </>
       )}
-    </main>
+    </div>
   );
 }
 
@@ -112,5 +117,15 @@ const getStyles = (theme: GrafanaTheme2) => {
       flexGrow: 1,
       minHeight: 0,
     }),
+    skipLink: css({
+      position: 'absolute',
+      top: -1000,
+
+      ':focus': {
+        left: theme.spacing(1),
+        top: theme.spacing(1),
+        zIndex: theme.zIndex.portal,
+      },
+    }),
   };
 };