fix(listbox): align setCheckedIndex behavior for multi and single choice

packages/combobox/src/LionCombobox.js

@@ -648,7 +648,6 @@ export class LionCombobox extends OverlayMixin(LionListbox) {
         this.opened = false;
         this.__shouldAutocompleteNextUpdate = true;
         this._setTextboxValue('');
-        // this.checkedIndex = -1;
         break;
       case 'Enter':
         if (!this.formElements[this.activeIndex]) {

packages/combobox/test/lion-combobox.test.js

@@ -208,6 +208,42 @@ describe('lion-combobox', () => {
       await el.updateComplete;
       expect(el._inputNode.value).to.equal('20');
     });
+
+    it('sets modelValue to empty string if no option is selected', async () => {
+      const el = /** @type {LionCombobox} */ (await fixture(html`
+        <lion-combobox name="foo" .modelValue="${'Artichoke'}">
+          <lion-option .choiceValue="${'Artichoke'}">Artichoke</lion-option>
+          <lion-option .choiceValue="${'Chard'}">Chard</lion-option>
+          <lion-option .choiceValue="${'Chicory'}">Chicory</lion-option>
+          <lion-option .choiceValue="${'Victoria Plum'}">Victoria Plum</lion-option>
+        </lion-combobox>
+      `));
+
+      expect(el.modelValue).to.equal('Artichoke');
+      expect(el.formElements[0].checked).to.be.true;
+      el.checkedIndex = -1;
+      await el.updateComplete;
+      expect(el.modelValue).to.equal('');
+      expect(el.formElements[0].checked).to.be.false;
+    });
+
+    it('sets modelValue to empty array if no option is selected for multiple choice', async () => {
+      const el = /** @type {LionCombobox} */ (await fixture(html`
+        <lion-combobox name="foo" multiple-choice .modelValue="${['Artichoke']}">
+          <lion-option .choiceValue="${'Artichoke'}">Artichoke</lion-option>
+          <lion-option .choiceValue="${'Chard'}">Chard</lion-option>
+          <lion-option .choiceValue="${'Chicory'}">Chicory</lion-option>
+          <lion-option .choiceValue="${'Victoria Plum'}">Victoria Plum</lion-option>
+        </lion-combobox>
+      `));
+
+      expect(el.modelValue).to.eql(['Artichoke']);
+      expect(el.formElements[0].checked).to.be.true;
+      el.checkedIndex = [];
+      await el.updateComplete;
+      expect(el.modelValue).to.eql([]);
+      expect(el.formElements[0].checked).to.be.false;
+    });
   });
 
   describe('Listbox visibility', () => {

packages/listbox/src/ListboxMixin.js

@@ -223,7 +223,7 @@ const ListboxMixinImplementation = superclass =>
      * @deprecated
      * This setter exists for backwards compatibility of single choice groups.
      * A setter api would be confusing for a multipleChoice group. Use `setCheckedIndex` instead.
-     * @param {number} index
+     * @param {number|number[]} index
      */
     set checkedIndex(index) {
       this.setCheckedIndex(index);
@@ -338,23 +338,29 @@ const ListboxMixinImplementation = superclass =>
     }
 
     /**
-     * When `multipleChoice` is false, will toggle, else will check provided index
-     * @param {number} index
-     * @param {'set'|'unset'|'toggle'} multiMode
+     * If an array is passed for multiple-choice, it will check the indexes in array, and uncheck the rest
+     * If a number is passed, the item with the passed index is checked without unchecking others
+     * For single choice, __onChildCheckedChanged we ensure that we uncheck siblings
+     * @param {number|number[]} index
      */
-    setCheckedIndex(index, multiMode = 'toggle') {
-      if (this.formElements[index]) {
-        if (!this.multipleChoice) {
-          this.formElements[index].checked = true;
-          // In __onChildCheckedChanged, which also responds to programmatic (model)value changes
-          // of children, we do the rest (uncheck siblings)
-        } else if (multiMode === 'toggle') {
-          this.formElements[index].checked = !this.formElements[index].checked;
-        } else {
-          this.formElements[index].checked = multiMode === 'set';
+    setCheckedIndex(index) {
+      if (this.multipleChoice && Array.isArray(index)) {
+        this._uncheckChildren(this.formElements.filter(i => i === index));
+        index.forEach(i => {
+          if (this.formElements[i]) {
+            this.formElements[i].checked = true;
+          }
+        });
+        return;
+      }
+
+      if (typeof index === 'number') {
+        if (index === -1) {
+          this._uncheckChildren();
+        }
+        if (this.formElements[index]) {
+          this.formElements[index].checked = true;
         }
-      } else if (!this.multipleChoice) {
-        this._uncheckChildren();
       }
     }
 

packages/listbox/test-suites/ListboxMixin.suite.js

@@ -413,8 +413,8 @@ export function runListboxMixinSuite(customConfig = {}) {
             <${optionTag} .choiceValue=${'30'} checked>Item 3</${optionTag}>
           </${tag}>
         `);
-        el.setCheckedIndex(2);
-        expect(el.modelValue).to.deep.equal(['20']);
+        el.setCheckedIndex(0);
+        expect(el.modelValue).to.deep.equal(['10', '20', '30']);
         el.reset();
         expect(el.modelValue).to.deep.equal(['20', '30']);
       });

packages/listbox/types/ListboxMixinTypes.d.ts

@@ -39,7 +39,7 @@ export declare class ListboxHost {
 
   public formElements: LionOption[];
 
-  public setCheckedIndex(index: number): void;
+  public setCheckedIndex(index: number | number[]): void;
 
   /** Reset interaction states and modelValue */
   public reset(): void;