From 08a1cb16889fd8bada9682f78d8a745aacb25bff Mon Sep 17 00:00:00 2001
From: gerjanvangeest <gerjanvangeest@users.noreply.github.com>
Date: Wed, 22 May 2024 09:24:20 +0200
Subject: [PATCH] fix(tabs): make tab panels focusable (#2281)

---
 .changeset/ninety-needles-drop.md             |  5 ++
 packages/ui/components/tabs/src/LionTabs.js   | 10 +++
 .../ui/components/tabs/test/lion-tabs.test.js | 87 +++++++++++--------
 3 files changed, 64 insertions(+), 38 deletions(-)
 create mode 100644 .changeset/ninety-needles-drop.md

diff --git a/.changeset/ninety-needles-drop.md b/.changeset/ninety-needles-drop.md
new file mode 100644
index 000000000..e65095b40
--- /dev/null
+++ b/.changeset/ninety-needles-drop.md
@@ -0,0 +1,5 @@
+---
+'@lion/ui': patch
+---
+
+[tabs] make tab panels focusable
diff --git a/packages/ui/components/tabs/src/LionTabs.js b/packages/ui/components/tabs/src/LionTabs.js
index bb9849acc..821c072b9 100644
--- a/packages/ui/components/tabs/src/LionTabs.js
+++ b/packages/ui/components/tabs/src/LionTabs.js
@@ -19,6 +19,16 @@ function setupPanel({ el, uid }) {
   el.setAttribute('id', `panel-${uid}`);
   el.setAttribute('role', 'tabpanel');
   el.setAttribute('aria-labelledby', `button-${uid}`);
+  /**
+   * Facilitates navigation to panel content for assistive technology users.
+   *
+   * Focusable tab panel elements are recommended if any panels in a set contain
+   * content where the first element in the panel is not focusable.
+   * https://www.w3.org/WAI/ARIA/apg/patterns/tabs/examples/tabs-automatic/
+   */
+  if (!el.hasAttribute('tabindex')) {
+    el.setAttribute('tabindex', '0');
+  }
 }
 
 /**
diff --git a/packages/ui/components/tabs/test/lion-tabs.test.js b/packages/ui/components/tabs/test/lion-tabs.test.js
index 6511a0566..d7a4a929e 100644
--- a/packages/ui/components/tabs/test/lion-tabs.test.js
+++ b/packages/ui/components/tabs/test/lion-tabs.test.js
@@ -452,45 +452,26 @@ describe('<lion-tabs>', () => {
   });
 
   describe('Accessibility', () => {
-    it('does not make panels focusable', async () => {
-      const el = /** @type {LionTabs} */ (
-        await fixture(html`
-          <lion-tabs>
-            <button slot="tab">tab 1</button>
-            <div slot="panel">panel 1</div>
-            <button slot="tab">tab 2</button>
-            <div slot="panel">panel 2</div>
-          </lion-tabs>
-        `)
-      );
-      expect(Array.from(el.children).find(child => child.slot === 'panel')).to.not.have.attribute(
-        'tabindex',
-      );
-      expect(Array.from(el.children).find(child => child.slot === 'panel')).to.not.have.attribute(
-        'tabindex',
-      );
-    });
-
-    it('makes selected tab focusable (other tabs are unfocusable)', async () => {
-      const el = /** @type {LionTabs} */ (
-        await fixture(html`
-          <lion-tabs>
-            <button slot="tab">tab 1</button>
-            <div slot="panel">panel 1</div>
-            <button slot="tab">tab 2</button>
-            <div slot="panel">panel 2</div>
-            <button slot="tab">tab 3</button>
-            <div slot="panel">panel 3</div>
-          </lion-tabs>
-        `)
-      );
-      const tabs = el.querySelectorAll('[slot=tab]');
-      expect(tabs[0]).to.have.attribute('tabindex', '0');
-      expect(tabs[1]).to.have.attribute('tabindex', '-1');
-      expect(tabs[2]).to.have.attribute('tabindex', '-1');
-    });
-
     describe('Tabs', () => {
+      it('makes selected tab focusable (other tabs are unfocusable)', async () => {
+        const el = /** @type {LionTabs} */ (
+          await fixture(html`
+            <lion-tabs>
+              <button slot="tab">tab 1</button>
+              <div slot="panel">panel 1</div>
+              <button slot="tab">tab 2</button>
+              <div slot="panel">panel 2</div>
+              <button slot="tab">tab 3</button>
+              <div slot="panel">panel 3</div>
+            </lion-tabs>
+          `)
+        );
+        const tabs = el.querySelectorAll('[slot=tab]');
+        expect(tabs[0]).to.have.attribute('tabindex', '0');
+        expect(tabs[1]).to.have.attribute('tabindex', '-1');
+        expect(tabs[2]).to.have.attribute('tabindex', '-1');
+      });
+
       it('links ids of content items to tab via [aria-controls]', async () => {
         const el = /** @type {LionTabs} */ (
           await fixture(html`
@@ -562,6 +543,36 @@ describe('<lion-tabs>', () => {
         expect(panels[0]).to.have.attribute('aria-labelledby', tabs[0].id);
         expect(panels[1]).to.have.attribute('aria-labelledby', tabs[1].id);
       });
+
+      it('makes panel focusable', async () => {
+        const el = /** @type {LionTabs} */ (
+          await fixture(html`
+            <lion-tabs>
+              <button slot="tab">tab 1</button>
+              <div slot="panel">panel 1</div>
+              <button slot="tab">tab 2</button>
+              <div slot="panel">panel 2</div>
+            </lion-tabs>
+          `)
+        );
+        const panels = el.querySelectorAll('[slot=panel]');
+        expect(panels[0]).to.have.attribute('tabindex', '0');
+      });
+
+      it('does not override the tabindex already set on the panel', async () => {
+        const el = /** @type {LionTabs} */ (
+          await fixture(html`
+            <lion-tabs>
+              <button slot="tab">tab 1</button>
+              <div slot="panel" tabindex="-1">panel 1</div>
+              <button slot="tab">tab 2</button>
+              <div slot="panel">panel 2</div>
+            </lion-tabs>
+          `)
+        );
+        const panels = el.querySelectorAll('[slot=panel]');
+        expect(panels[0]).to.have.attribute('tabindex', '-1');
+      });
     });
   });