fix(angular): remove the tabindex set by routerLink from Ionic components (#29744)

Issue number: resolves #20632

---------

## What is the current behavior?
When using the `routerLink` directive in Angular, it automatically adds
`tabindex="0"` to the element. This creates issues with Ionic components
that render native button or anchor elements, as they have their own
focus management. As a result, when navigating between list items with
`routerLink` using the `Tab` key, you need to press the `Tab` key twice
to move to the next item. This problem is illustrated in the following
demo:

[![Open in
StackBlitz](https://developer.stackblitz.com/img/open_in_stackblitz.svg)](https://stackblitz.com/edit/angular-blfa7h?file=src%2Fapp%2Fexample.component.html)

Related Angular issue: https://github.com/angular/angular/issues/28345

## What is the new behavior?
Updated our `RouterLinkDelegateDirective` to check if the element using
`routerLink` is one of the following Ionic components:
`ion-back-button`, `ion-breadcrumb`, `ion-button`, `ion-card`,
`ion-fab-button`, `ion-item`, `ion-item-option`, `ion-menu-button`,
`ion-segment-button`, or `ion-tab-button`. If so, it removes the
`tabindex` attribute from the element. This allows these Ionic
components to let the native button or anchor element handle the focus.

This solution is demonstrated in the following demo:

[![Open in
StackBlitz](https://developer.stackblitz.com/img/open_in_stackblitz.svg)](https://stackblitz.com/edit/angular-blfa7h-svmguh?file=src%2Fapp%2Fexample.component.html)

> [!NOTE]
> I did not include the `ion-router-link` component in the list to
remove `tabindex` because [the router link
documentation](https://ionicframework.com/docs/api/router-link) does not
recommend using it with Angular:
>> Note: this component should only be used with vanilla and Stencil
JavaScript projects. For Angular projects, use an `<a>` and `routerLink`
with the Angular router.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

## Other information

Dev build: `8.2.7-dev.11722448707.1e8c66e6`

packages/angular/common/src/directives/navigation/router-link-delegate.ts

@@ -31,12 +31,45 @@ export class RouterLinkDelegateDirective implements OnInit, OnChanges {
 
   ngOnInit(): void {
     this.updateTargetUrlAndHref();
+    this.updateTabindex();
   }
 
   ngOnChanges(): void {
     this.updateTargetUrlAndHref();
   }
 
+  /**
+   * The `tabindex` is set to `0` by default on the host element when
+   * the `routerLink` directive is used. This causes issues with Ionic
+   * components that wrap an `a` or `button` element, such as `ion-item`.
+   * See issue https://github.com/angular/angular/issues/28345
+   *
+   * This method removes the `tabindex` attribute from the host element
+   * to allow the Ionic component to manage the focus state correctly.
+   */
+  private updateTabindex() {
+    // Ionic components that render a native anchor or button element
+    const ionicComponents = [
+      'ION-BACK-BUTTON',
+      'ION-BREADCRUMB',
+      'ION-BUTTON',
+      'ION-CARD',
+      'ION-FAB-BUTTON',
+      'ION-ITEM',
+      'ION-ITEM-OPTION',
+      'ION-MENU-BUTTON',
+      'ION-SEGMENT-BUTTON',
+      'ION-TAB-BUTTON',
+    ];
+    const hostElement = this.elementRef.nativeElement;
+
+    if (ionicComponents.includes(hostElement.tagName)) {
+      if (hostElement.getAttribute('tabindex') === '0') {
+        hostElement.removeAttribute('tabindex');
+      }
+    }
+  }
+
   private updateTargetUrlAndHref() {
     if (this.routerLink?.urlTree) {
       const href = this.locationStrategy.prepareExternalUrl(this.router.serializeUrl(this.routerLink.urlTree));

packages/angular/test/base/e2e/src/lazy/router-link.spec.ts

@@ -123,6 +123,21 @@ describe('Router Link', () => {
       testBack();
     });
   });
+
+  // Angular sets the `tabindex` to `"0"` on any element that uses
+  // the `routerLink` directive. Ionic removes the `tabindex` from
+  // components that wrap an `a` or `button` element, so we are
+  // checking here that it is only removed from Ionic components.
+  // https://github.com/ionic-team/ionic-framework/issues/20632
+  describe('tabindex', () => {
+    it('should have tabindex="0" with a native span', () => {
+      cy.get('#span').should('have.attr', 'tabindex', '0');
+    });
+
+    it('should not have tabindex set with an ionic button', () => {
+      cy.get('#routerLink').should('not.have.attr', 'tabindex');
+    });
+  });
 });
 
 function testForward() {

packages/angular/test/base/e2e/src/standalone/router-link.spec.ts

@@ -2,7 +2,7 @@ describe('RouterLink', () => {
   beforeEach(() => {
     cy.visit('/standalone/router-link');
   });
-  
+
   it('should mount the root component', () => {
     cy.ionPageVisible('app-router-link');
 
@@ -21,4 +21,17 @@ describe('RouterLink', () => {
 
     cy.url().should('include', '/standalone/popover');
   });
+
+  // Angular sets the `tabindex` to `"0"` on any element that uses
+  // the `routerLink` directive. Ionic removes the `tabindex` from
+  // components that wrap an `a` or `button` element, so we are
+  // checking here that it is only removed from Ionic components.
+  // https://github.com/ionic-team/ionic-framework/issues/20632
+  it('should have tabindex="0" with a native span', () => {
+    cy.get('span').should('have.attr', 'tabindex', '0');
+  });
+
+  it('should not have tabindex set with an ionic button', () => {
+    cy.get('ion-button').should('not.have.attr', 'tabindex');
+  });
 });

packages/angular/test/base/src/app/lazy/router-link/router-link.component.html

@@ -36,4 +36,5 @@
   <p><button id="queryParamsFragment" routerLink="/lazy/router-link-page2/MyPageID==" [queryParams]="{ token: 'A&=#Y' }"
       fragment="myDiv1">Query Params and Fragment</button></p>
 
+  <p><span routerLink="/lazy/router-link-page" id="span">span[routerLink]</span></p>
 </ion-content>

packages/angular/test/base/src/app/standalone/router-link/router-link.component.html

@@ -4,3 +4,9 @@
 <button routerLink="/standalone/popover" routerDirection="root">
   I'm a button
 </button>
+<span routerLink="/standalone/popover" routerDirection="root">
+  I'm a span
+</span>
+<ion-button routerLink="/standalone/popover" routerDirection="root">
+  I'm an ion-button
+</ion-button>