[combo-box / dropdown] Improve accessibility (#11421)

### Related Ticket(s)

Closes #11268
[Jira ticket](https://jsw.ibm.com/browse/ADCMS-4401)

### Description

Fixes accessibility issues with Combo-box, and by extension Dropdown.

Used both React package (which uses [Downshift](https://www.downshift-js.com/)), and [ARIA APG](https://www.w3.org/WAI/ARIA/apg/patterns/combobox/) as references. Tested with VoiceOver on Mac OS.

### Testing

* Use both dropdown and combo-box components. Ensure there are no regressions for sighted users
* Using a screenreader, test both dropdown and combo-box components. Should work well. See [Select-Only Combobox Example](https://www.w3.org/WAI/ARIA/apg/patterns/combobox/examples/combobox-select-only/) and [Editable Combobox With List Autocomplete Example](https://www.w3.org/WAI/ARIA/apg/patterns/combobox/examples/combobox-autocomplete-list/) are great reference examples.
* Regression test the Multi select component (it extends the Dropdown component)

### Changelog

**Changed**

- Improved dropdown and combo-box accessibility.

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packages/carbon-web-components/src/components/combo-box/combo-box.ts

@@ -1,7 +1,7 @@
 /**
  * @license
  *
- * Copyright IBM Corp. 2019, 2023
+ * Copyright IBM Corp. 2019, 2024
  *
  * This source code is licensed under the Apache-2.0 license found in the
  * LICENSE file in the root directory of this source tree.
@@ -17,6 +17,8 @@ import CDSDropdown, { DROPDOWN_KEYBOARD_ACTION } from '../dropdown/dropdown';
 import CDSComboBoxItem from './combo-box-item';
 import styles from './combo-box.scss';
 import { carbonElement as customElement } from '../../globals/decorators/carbon-element';
+import { ifDefined } from 'lit/directives/if-defined';
+import ifNonEmpty from '../../globals/directives/if-non-empty';
 
 export { DROPDOWN_DIRECTION, DROPDOWN_SIZE } from '../dropdown/dropdown';
 
@@ -200,11 +202,12 @@ class CDSComboBox extends CDSDropdown {
       ),
       (item) => {
         (item as CDSComboBoxItem).selected = false;
+        item.setAttribute('aria-selected', 'false');
       }
     );
     if (itemToSelect) {
       itemToSelect.selected = true;
-      this._assistiveStatusText = this.selectedItemAssistiveText;
+      itemToSelect.setAttribute('aria-selected', 'true');
     }
     this._handleUserInitiatedToggle(false);
   }
@@ -214,8 +217,10 @@ class CDSComboBox extends CDSDropdown {
       disabled,
       inputLabel,
       label,
+      open,
       readOnly,
       value,
+      _activeDescendant: activeDescendant,
       _filterInputValue: filterInputValue,
       _handleInput: handleInput,
     } = this;
@@ -225,17 +230,29 @@ class CDSComboBox extends CDSDropdown {
       [`${prefix}--text-input--empty`]: !value,
     });
 
+    let activeDescendantFallback: string | undefined;
+    if (open && !activeDescendant) {
+      const constructor = this.constructor as typeof CDSDropdown;
+      const items = this.querySelectorAll(constructor.selectorItem);
+      activeDescendantFallback = items[0]?.id;
+    }
+
     return html`
       <input
-        id="trigger-label"
+        id="trigger-button"
         class="${inputClasses}"
         ?disabled=${disabled}
         placeholder="${label}"
         .value=${filterInputValue}
         role="combobox"
-        aria-label="${inputLabel}"
+        aria-label="${ifNonEmpty(inputLabel)}"
         aria-controls="menu-body"
+        aria-haspopup="listbox"
         aria-autocomplete="list"
+        aria-expanded="${String(open)}"
+        aria-activedescendant="${ifDefined(
+          open ? activeDescendant ?? activeDescendantFallback : ''
+        )}"
         ?readonly=${readOnly}
         @input=${handleInput} />
     `;
@@ -268,7 +285,7 @@ class CDSComboBox extends CDSDropdown {
    * The `aria-label` attribute for the icon to clear selection.
    */
   @property({ attribute: 'clear-selection-label' })
-  clearSelectionLabel = '';
+  clearSelectionLabel = 'Clear selection';
 
   /**
    * The `aria-label` attribute for the `<input>` for filtering.

packages/carbon-web-components/src/components/dropdown/dropdown-item.ts

@@ -1,7 +1,7 @@
 /**
  * @license
  *
- * Copyright IBM Corp. 2019, 2023
+ * Copyright IBM Corp. 2019, 2024
  *
  * This source code is licensed under the Apache-2.0 license found in the
  * LICENSE file in the root directory of this source tree.
@@ -58,6 +58,21 @@ class CDSDropdownItem extends LitElement {
   @property()
   value = '';
 
+  connectedCallback() {
+    super.connectedCallback();
+    if (!this.hasAttribute('role')) {
+      this.setAttribute('role', 'option');
+    }
+    if (!this.hasAttribute('id')) {
+      this.setAttribute(
+        'id',
+        `${prefix}-dropdown-item-${(this.constructor as typeof CDSDropdownItem)
+          .id++}`
+      );
+    }
+    this.setAttribute('aria-selected', String(this.selected));
+  }
+
   render() {
     const { selected } = this;
     return html`
@@ -73,6 +88,13 @@ class CDSDropdownItem extends LitElement {
     `;
   }
 
+  /**
+   * Store an identifier for use in composing this item's id.
+   *
+   * Auto-increments anytime a new dropdown-item appears.
+   */
+  static id = 0;
+
   static styles = styles;
 }
 

packages/carbon-web-components/src/components/dropdown/dropdown-story.ts

@@ -1,7 +1,7 @@
 /**
  * @license
  *
- * Copyright IBM Corp. 2019, 2023
+ * Copyright IBM Corp. 2019, 2024
  *
  * This source code is licensed under the Apache-2.0 license found in the
  * LICENSE file in the root directory of this source tree.
@@ -143,6 +143,7 @@ export const WithLayer = () => {
 
 export const Playground = (args) => {
   const {
+    ariaLabel,
     open,
     direction,
     disabled,
@@ -162,6 +163,7 @@ export const Playground = (args) => {
 
   return html`
     <cds-dropdown
+      aria-label=${ifDefined(ariaLabel)}
       ?open=${open}
       ?disabled="${disabled}"
       ?hide-label=${hideLabel}
@@ -191,6 +193,7 @@ export const Playground = (args) => {
 Playground.parameters = {
   knobs: {
     [`${prefix}-dropdown`]: () => ({
+      ariaLabel: textNullable('aria-label (aria-label)', ''),
       open: boolean('Open (open)', false),
       direction: select('Direction', directionOptions, null),
       disabled: boolean('Disabled (disabled)', false),

packages/carbon-web-components/src/components/dropdown/dropdown.ts

@@ -10,7 +10,7 @@
 import { classMap } from 'lit/directives/class-map.js';
 import { ifDefined } from 'lit/directives/if-defined.js';
 import { LitElement, html, TemplateResult } from 'lit';
-import { property, query } from 'lit/decorators.js';
+import { property, query, state } from 'lit/decorators.js';
 import { prefix } from '../../globals/settings';
 import ChevronDown16 from '@carbon/icons/lib/chevron--down/16';
 import WarningFilled16 from '@carbon/icons/lib/warning--filled/16';
@@ -71,10 +71,8 @@ class CDSDropdown extends ValidityMixin(
    */
   protected _hasSlug = false;
 
-  /**
-   * The latest status of this dropdown, for screen reader to accounce.
-   */
-  protected _assistiveStatusText?: string;
+  @state()
+  protected _activeDescendant?: string;
 
   /**
    * The content of the selected item.
@@ -123,16 +121,18 @@ class CDSDropdown extends ValidityMixin(
   protected _selectionDidChange(itemToSelect?: CDSDropdownItem) {
     if (itemToSelect) {
       this.value = itemToSelect.value;
+      this._activeDescendant = itemToSelect.id;
       forEach(
         this.querySelectorAll(
           (this.constructor as typeof CDSDropdown).selectorItemSelected
         ),
         (item) => {
           (item as CDSDropdownItem).selected = false;
+          item.setAttribute('aria-selected', 'false');
         }
       );
       itemToSelect.selected = true;
-      this._assistiveStatusText = this.selectedItemAssistiveText;
+      itemToSelect.setAttribute('aria-selected', 'true');
       this._handleUserInitiatedToggle(false);
     }
   }
@@ -322,23 +322,7 @@ class CDSDropdown extends ValidityMixin(
     if (!disabled) {
       if (this.dispatchEvent(new CustomEvent(eventBeforeToggle, init))) {
         this.open = force;
-        if (this.open) {
-          this._assistiveStatusText = this.selectingItemsAssistiveText;
-        } else {
-          const {
-            selectedItemAssistiveText,
-            label,
-            _assistiveStatusText: assistiveStatusText,
-            _selectedItemContent: selectedItemContent,
-          } = this;
-          const selectedItemText =
-            (selectedItemContent && selectedItemContent.textContent) || label;
-          if (
-            selectedItemText &&
-            assistiveStatusText !== selectedItemAssistiveText
-          ) {
-            this._assistiveStatusText = selectedItemText;
-          }
+        if (!this.open) {
           forEach(
             this.querySelectorAll(
               (this.constructor as typeof CDSDropdown).selectorItemHighlighted
@@ -401,11 +385,10 @@ class CDSDropdown extends ValidityMixin(
     // IE falls back to the old behavior.
     nextItem.scrollIntoView({ block: 'nearest' });
 
-    const nextItemText = nextItem.textContent;
-    if (nextItemText) {
-      this._assistiveStatusText = nextItemText;
+    const nextItemId = nextItem.id;
+    if (nextItemId) {
+      this._activeDescendant = nextItemId;
     }
-    this.requestUpdate();
   }
 
   /* eslint-disable class-methods-use-this */
@@ -453,8 +436,10 @@ class CDSDropdown extends ValidityMixin(
 
     return html`
       <label
+        id="dropdown-label"
         part="title-text"
         class="${labelClasses}"
+        for="trigger-button"
         ?hidden="${!hasTitleText}">
         <slot name="title-text" @slotchange="${handleSlotchangeLabelText}"
           >${titleText}</slot
@@ -564,19 +549,6 @@ class CDSDropdown extends ValidityMixin(
   @property({ attribute: 'required-validity-message' })
   requiredValidityMessage = 'Please fill out this field.';
 
-  /**
-   * An assistive text for screen reader to announce, telling the open state.
-   */
-  @property({ attribute: 'selecting-items-assistive-text' })
-  selectingItemsAssistiveText =
-    'Selecting items. Use up and down arrow keys to navigate.';
-
-  /**
-   * An assistive text for screen reader to announce, telling that an item is selected.
-   */
-  @property({ attribute: 'selected-item-assistive-text' })
-  selectedItemAssistiveText = 'Selected an item.';
-
   /**
    * Dropdown size.
    */
@@ -724,7 +696,7 @@ class CDSDropdown extends ValidityMixin(
       type,
       warn,
       warnText,
-      _assistiveStatusText: assistiveStatusText,
+      _activeDescendant: activeDescendant,
       _shouldTriggerBeFocusable: shouldTriggerBeFocusable,
       _handleClickInner: handleClickInner,
       _handleKeydownInner: handleKeydownInner,
@@ -735,6 +707,13 @@ class CDSDropdown extends ValidityMixin(
     } = this;
     const inline = type === DROPDOWN_TYPE.INLINE;
 
+    let activeDescendantFallback: string | undefined;
+    if (open && !activeDescendant) {
+      const constructor = this.constructor as typeof CDSDropdown;
+      const items = this.querySelectorAll(constructor.selectorItem);
+      activeDescendantFallback = items[0]?.id;
+    }
+
     const helperClasses = classMap({
       [`${prefix}--form__helper-text`]: true,
       [`${prefix}--form__helper-text--disabled`]: disabled,
@@ -764,38 +743,56 @@ class CDSDropdown extends ValidityMixin(
             'aria-label': toggleLabel,
           });
     const helperMessage = invalid ? invalidText : warn ? warnText : helperText;
-    const menuBody = !open
-      ? undefined
-      : html`
-          <div
-            aria-label="${ariaLabel}"
-            id="menu-body"
-            part="menu-body"
-            class="${prefix}--list-box__menu"
-            role="listbox"
-            tabindex="-1">
-            <slot></slot>
-          </div>
-        `;
+    const menuBody = html`
+      <div
+        aria-labelledby="${ifDefined(ariaLabel ? undefined : 'dropdown-label')}"
+        aria-label="${ifDefined(ariaLabel ? ariaLabel : undefined)}"
+        id="menu-body"
+        part="menu-body"
+        class="${prefix}--list-box__menu"
+        role="listbox"
+        tabindex="-1"
+        ?hidden=${!open}>
+        <slot></slot>
+      </div>
+    `;
     return html`
       ${this._renderTitleLabel()}
       <div
-        role="listbox"
         class="${classes}"
         ?data-invalid=${invalid}
         @click=${handleClickInner}
         @keydown=${handleKeydownInner}
         @keypress=${handleKeypressInner}>
         <div
-          part="trigger-button"
-          role="${ifDefined(!shouldTriggerBeFocusable ? undefined : 'button')}"
+          id="${ifDefined(
+            !shouldTriggerBeFocusable ? undefined : 'trigger-button'
+          )}"
           class="${prefix}--list-box__field"
+          part="trigger-button"
           tabindex="${ifDefined(!shouldTriggerBeFocusable ? undefined : '0')}"
-          aria-labelledby="trigger-label"
-          aria-expanded="${String(open)}"
-          aria-haspopup="listbox"
-          aria-owns="menu-body"
-          aria-controls="menu-body">
+          role="${ifDefined(
+            !shouldTriggerBeFocusable ? undefined : 'combobox'
+          )}"
+          aria-labelledby="${ifDefined(
+            !shouldTriggerBeFocusable ? undefined : 'dropdown-label'
+          )}"
+          aria-expanded="${ifDefined(
+            !shouldTriggerBeFocusable ? undefined : String(open)
+          )}"
+          aria-haspopup="${ifDefined(
+            !shouldTriggerBeFocusable ? undefined : 'listbox'
+          )}"
+          aria-controls="${ifDefined(
+            !shouldTriggerBeFocusable ? undefined : 'menu-body'
+          )}"
+          aria-activedescendant="${ifDefined(
+            !shouldTriggerBeFocusable
+              ? undefined
+              : open
+              ? activeDescendant ?? activeDescendantFallback
+              : ''
+          )}">
           ${this._renderPrecedingLabel()}${this._renderLabel()}${validityIcon}${warningIcon}${this._renderFollowingLabel()}
           <div id="trigger-caret" class="${iconContainerClasses}">
             ${ChevronDown16({ 'aria-label': toggleLabel })}
@@ -812,13 +809,6 @@ class CDSDropdown extends ValidityMixin(
           >${helperMessage}</slot
         >
       </div>
-      <div
-        class="${prefix}--assistive-text"
-        role="status"
-        aria-live="assertive"
-        aria-relevant="additions text">
-        ${assistiveStatusText}
-      </div>
     `;
   }
 
@@ -889,6 +879,7 @@ class CDSDropdown extends ValidityMixin(
     ...LitElement.shadowRootOptions,
     delegatesFocus: true,
   };
+
   static styles = styles;
 
   /**