fix(material/list): fix tabindex="-1" not being maintained when disabled (#25860)

When entire list is disabled, avoid adding list options to the tab order
in the following situations:
 - focusin event is triggered on an option. This can happen when the
   end user clicks on a list option.
 - ngOnInit happens when list is disabled
 - updating selection state

When list is disabled tabindex of every option should always be -1.
Tabindex was set to 0 mainly because `_resetActionOption` only considered when
list options where disabled, but didn't consider when the list itself is
disabled.

Fix issues by setting tabindex to -1 when disabled and making
`_handleFocusin` a noop when disabled.

Author: zarend

src/material/list/selection-list.spec.ts

@@ -806,8 +806,9 @@ describe('MDC-based MatSelectionList without forms', () => {
     });
 
     // when the entire list is disabled, its listitems should always have tabindex="-1"
-    it('should not put listitems in the tab order', () => {
+    it('should remove all listitems from the tab order when disabled state is enabled', () => {
       fixture.componentInstance.disabled = false;
+      fixture.detectChanges();
       let testListItem = listOption[2].injector.get<MatListOption>(MatListOption);
       testListItem.focus();
       fixture.detectChanges();
@@ -827,6 +828,26 @@ describe('MDC-based MatSelectionList without forms', () => {
         .withContext('Expected all list options to be excluded from the tab order')
         .toBe(0);
     });
+
+    it('should not allow focusin event to change the tabindex', () => {
+      fixture.componentInstance.disabled = true;
+      fixture.detectChanges();
+
+      expect(
+        listOption.filter(option => option.nativeElement.getAttribute('tabindex') !== '-1').length,
+      )
+        .withContext('Expected all list options to be excluded from the tab order')
+        .toBe(0);
+
+      listOption[1].triggerEventHandler('focusin', {target: listOption[1].nativeElement});
+      fixture.detectChanges();
+
+      expect(
+        listOption.filter(option => option.nativeElement.getAttribute('tabindex') !== '-1').length,
+      )
+        .withContext('Expected all list options to be excluded from the tab order')
+        .toBe(0);
+    });
   });
 
   describe('with checkbox position after', () => {

src/material/list/selection-list.ts

@@ -373,6 +373,10 @@ export class MatSelectionList
 
   /** Handles focusin events within the list. */
   private _handleFocusin = (event: FocusEvent) => {
+    if (this.disabled) {
+      return;
+    }
+
     const activeIndex = this._items
       .toArray()
       .findIndex(item => item._elementRef.nativeElement.contains(event.target as HTMLElement));
@@ -402,7 +406,7 @@ export class MatSelectionList
       .withHomeAndEnd()
       .withTypeAhead()
       .withWrap()
-      .skipPredicate(() => false);
+      .skipPredicate(() => this.disabled);
 
     // Set the initial focus.
     this._resetActiveOption();
@@ -429,8 +433,16 @@ export class MatSelectionList
     this._keyManager.updateActiveItem(index);
   }
 
-  /** Resets the active option to the first selected option. */
+  /**
+   * Resets the active option. When the list is disabled, remove all options from to the tab order.
+   * Otherwise, focus the first selected option.
+   */
   private _resetActiveOption() {
+    if (this.disabled) {
+      this._setActiveOption(-1);
+      return;
+    }
+
     const activeItem =
       this._items.find(item => item.selected && !item.disabled) || this._items.first;
     this._setActiveOption(activeItem ? this._items.toArray().indexOf(activeItem) : -1);