From 0da80a01d2a8cfce6d27bb0151f5228b84110bd8 Mon Sep 17 00:00:00 2001
From: Material Web Team <material-web-copybara@google.com>
Date: Wed, 17 May 2023 11:03:29 -0700
Subject: [PATCH] fix(tabs): adds a11y roles for tablist/tab

PiperOrigin-RevId: 532843567
---
 tabs/demo/stories.ts | 20 +++++++++++++++-----
 tabs/lib/_tab.scss   | 10 +++++++---
 tabs/lib/tab.ts      | 23 +++++++++++++++--------
 tabs/lib/tabs.ts     | 37 +++++++++++++++----------------------
 4 files changed, 52 insertions(+), 38 deletions(-)

diff --git a/tabs/demo/stories.ts b/tabs/demo/stories.ts
index 9b5dee09a1..3ae0fea3d7 100644
--- a/tabs/demo/stories.ts
+++ b/tabs/demo/stories.ts
@@ -49,7 +49,12 @@ const styles = css`
 
   md-tabs[variant~="vertical"].scrolling {
     block-size: 50vh;
-  }`;
+  }
+
+  .controls {
+    height: 48px;
+  }
+  `;
 
 const primary: MaterialStoryInit<StoryKnobs> = {
   name: 'Primary Tabs',
@@ -379,7 +384,7 @@ const dynamic: MaterialStoryInit<StoryKnobs> = {
     }
 
     return html`
-      <div>
+      <div class="controls">
         <md-standard-icon-button @click=${
         addTab}><md-icon>add</md-icon></md-standard-icon-button>
         <md-standard-icon-button @click=${
@@ -413,9 +418,14 @@ function getTabContentGenerator(knobs: StoryKnobs) {
   const contentKnob = knobs.content;
   const useIcon = contentKnob !== 'label';
   const useLabel = contentKnob !== 'icon';
-  return (icon: string, label: string) => html`
-        ${useIcon ? html`<md-icon slot="icon">${icon}</md-icon>` : nothing}
-        ${useLabel ? html`${label}` : nothing}`;
+  return (icon: string, label: string) => {
+    const iconTemplate =
+        html`<md-icon aria-hidden="true" slot="icon">${icon}</md-icon>`;
+    return html`
+      ${useIcon ? iconTemplate : nothing}
+      ${useLabel ? html`${label}` : nothing}
+    `;
+  };
 }
 
 /** Tabs stories. */
diff --git a/tabs/lib/_tab.scss b/tabs/lib/_tab.scss
index 11442600f3..e7cedb620c 100644
--- a/tabs/lib/_tab.scss
+++ b/tabs/lib/_tab.scss
@@ -54,8 +54,10 @@
 
     @include focus-ring.theme(
       (
-        shape: 8px,
-        offset: -7px,
+        // desired border-radius is 8px and it's internally calc'd as sum
+        // of shape + offset (-7 + 15)
+        shape: 15px,
+        offset: -7px
       )
     );
   }
@@ -114,7 +116,9 @@
     $_content-padding: 8px;
     // tabs are naturally sized up to their max height.
     max-height: calc(var(--_container-height) + 2 * $_content-padding);
-    padding: $_content-padding;
+    // min-height of touch target
+    min-height: 48px;
+    padding: $_content-padding calc(2 * $_content-padding);
     gap: 4px;
   }
 
diff --git a/tabs/lib/tab.ts b/tabs/lib/tab.ts
index d80cd5d86e..d0a5fd86fb 100644
--- a/tabs/lib/tab.ts
+++ b/tabs/lib/tab.ts
@@ -21,7 +21,7 @@ import {MdRipple} from '../../ripple/ripple.js';
 /**
  * An element that can select items.
  */
-export interface SelectionGroupElement extends HTMLElement {
+export interface Tabs extends HTMLElement {
   selected?: number;
   selectedItem?: Tab;
   previousSelectedItem?: Tab;
@@ -55,15 +55,20 @@ export class Tab extends LitElement {
   @property({reflect: true}) variant: Variant = 'primary';
 
   /**
-   * Whether or not the item is `disabled`.
+   * Whether or not the tab is `disabled`.
    */
   @property({type: Boolean, reflect: true}) disabled = false;
 
   /**
-   * Whether or not the item is `selected`.
+   * Whether or not the tab is `selected`.
    **/
   @property({type: Boolean, reflect: true}) selected = false;
 
+  /**
+   * Whether or not the tab is `focusable`.
+   */
+  @property({type: Boolean}) focusable = false;
+
   /**
    * Whether or not the icon renders inline with label or stacked vertically.
    */
@@ -102,7 +107,10 @@ export class Tab extends LitElement {
     };
     return html`
       <button
-        class="button md3-button"
+        class="button"
+        role="tab"
+        .tabIndex=${this.focusable && !this.disabled ? 0 : -1}
+        aria-selected=${this.selected ? 'true' : 'false'}
         ?disabled=${this.disabled}
         aria-label=${this.ariaLabel || nothing}
         ${ripple(this.getRipple)}
@@ -144,8 +152,8 @@ export class Tab extends LitElement {
     return html`<md-ripple ?disabled="${this.disabled}"></md-ripple>`;
   };
 
-  private get selectionGroup() {
-    return this.parentElement as SelectionGroupElement;
+  private get tabs() {
+    return this.parentElement as Tabs;
   }
 
   private animateSelected() {
@@ -166,8 +174,7 @@ export class Tab extends LitElement {
     const from: Keyframe = {};
     const isVertical = this.variant.includes('vertical');
     const fromRect =
-        (this.selectionGroup?.previousSelectedItem?.indicator
-             .getBoundingClientRect() ??
+        (this.tabs?.previousSelectedItem?.indicator.getBoundingClientRect() ??
          ({} as DOMRect));
     const fromPos = isVertical ? fromRect.top : fromRect.left;
     const fromExtent = isVertical ? fromRect.height : fromRect.width;
diff --git a/tabs/lib/tabs.ts b/tabs/lib/tabs.ts
index 148084d139..d325ab2c88 100644
--- a/tabs/lib/tabs.ts
+++ b/tabs/lib/tabs.ts
@@ -10,7 +10,7 @@ import {property, queryAssignedElements, state} from 'lit/decorators.js';
 import {Tab, Variant} from './tab.js';
 
 const NAVIGATION_KEYS = new Map([
-  ['default', new Set(['Home', 'End', 'Space'])],
+  ['default', new Set(['Home', 'End'])],
   ['horizontal', new Set(['ArrowLeft', 'ArrowRight'])],
   ['vertical', new Set(['ArrowUp', 'ArrowDown'])]
 ]);
@@ -110,6 +110,11 @@ export class Tabs extends LitElement {
     }
   }
 
+  override connectedCallback() {
+    super.connectedCallback();
+    this.setAttribute('role', 'tablist');
+  }
+
   // focus item on keydown and optionally select it
   private readonly handleKeydown = async (event: KeyboardEvent) => {
     const {key} = event;
@@ -124,31 +129,24 @@ export class Tabs extends LitElement {
     const focused = this.focusedItem ?? this.selectedItem;
     const itemCount = this.items.length;
     const isPrevKey = key === 'ArrowLeft' || key === 'ArrowUp';
-    const isNextKey = key === 'ArrowRight' || key === 'ArrowDown';
     if (key === 'Home') {
       indexToFocus = 0;
     } else if (key === 'End') {
       indexToFocus = itemCount - 1;
-    } else if (key === 'Space') {
-      indexToFocus = this.items.indexOf(focused);
-    } else if (isPrevKey || isNextKey) {
-      const d = (this.items.indexOf(focused) || 0) +
-          (isPrevKey     ? -1 :
-               isNextKey ? 1 :
-                           0);
-      indexToFocus = d < 0 ? itemCount - 1 : d % itemCount;
+    } else {
+      const focusedIndex = this.items.indexOf(focused) || 0;
+      indexToFocus = focusedIndex + (isPrevKey ? -1 : 1);
+      indexToFocus =
+          indexToFocus < 0 ? itemCount - 1 : indexToFocus % itemCount;
     }
     const itemToFocus =
         this.findFocusableItem(indexToFocus, key === 'End' || isPrevKey);
     indexToFocus = this.items.indexOf(itemToFocus!);
     if (itemToFocus !== null && itemToFocus !== focused) {
-      const shouldSelect = this.selectOnFocus || key === 'Space';
-      if (shouldSelect) {
-        this.selected = indexToFocus;
-      }
       this.updateFocusableItem(itemToFocus);
       itemToFocus.focus();
-      if (shouldSelect) {
+      if (this.selectOnFocus) {
+        this.selected = indexToFocus;
         await this.dispatchInteraction();
       }
     }
@@ -260,13 +258,8 @@ export class Tabs extends LitElement {
   }
 
   private updateFocusableItem(focusableItem: HTMLElement|null) {
-    const tabIndex = 'tabindex';
     for (const item of this.items) {
-      if (item === focusableItem) {
-        item.removeAttribute(tabIndex);
-      } else {
-        item.setAttribute(tabIndex, '-1');
-      }
+      item.focusable = item === focusableItem;
     }
   }
 
@@ -294,7 +287,7 @@ export class Tabs extends LitElement {
     }
   }
 
-  private handleSlotChange(e: Event) {
+  private handleSlotChange() {
     this.itemsDirty = true;
   }