Fix `<Tabs>` sync issue with inconsistent use of `icon` on `<TabItem>` components (#1811)

Co-authored-by: Chris Swithinbank <swithinbank@gmail.com>

4 files changed, 47 insertions, 2 deletions

diff --git a/.changeset/blue-otters-shave.md b/.changeset/blue-otters-shave.md
new file mode 100644
index 00000000..850356c4
--- /dev/null
+++ b/.changeset/blue-otters-shave.md
@@ -0,0 +1,5 @@
+---
+'@astrojs/starlight': patch
+---
+
+Fixes a `<Tabs>` sync issue when inconsistently using the `icon` prop or not on `<TabItem>` components.
diff --git a/packages/starlight/__e2e__/fixtures/basics/src/content/docs/tabs.mdx b/packages/starlight/__e2e__/fixtures/basics/src/content/docs/tabs.mdx
index 17e643a6..c01ba8c1 100644
--- a/packages/starlight/__e2e__/fixtures/basics/src/content/docs/tabs.mdx
+++ b/packages/starlight/__e2e__/fixtures/basics/src/content/docs/tabs.mdx
@@ -35,3 +35,20 @@ A set of tabs using the `style` sync key.
 	<TabItem label="css">css code</TabItem>
 	<TabItem label="tailwind">tailwind code</TabItem>
 </Tabs>
+
+Another set of tabs using the `pkg` sync key and using icons.
+
+<Tabs syncKey="pkg">
+	<TabItem label="npm" icon="seti:npm">
+		another npm command
+	</TabItem>
+	<TabItem label="pnpm" icon="pnpm">
+		another pnpm command
+	</TabItem>
+	<TabItem label="bun" icon="bun">
+		another bun command
+	</TabItem>
+	<TabItem label="yarn" icon="seti:yarn">
+		another yarn command
+	</TabItem>
+</Tabs>
diff --git a/packages/starlight/__e2e__/tabs.test.ts b/packages/starlight/__e2e__/tabs.test.ts
index e0a36ed5..f10f7972 100644
--- a/packages/starlight/__e2e__/tabs.test.ts
+++ b/packages/starlight/__e2e__/tabs.test.ts
@@ -116,6 +116,29 @@ test('preserves tabs position when alternating between tabs with different conte
 	expect((await tabs.boundingBox())?.y).toBe(initialBoundingBox?.y);
 });
 
+test('syncs tabs with the same sync key if they do not consistenly use icons', async ({
+	page,
+	starlight,
+}) => {
+	await starlight.goto('/tabs');
+
+	const tabs = page.locator('starlight-tabs');
+	const pkgTabsA = tabs.nth(0); // This set does not use icons for tab items.
+	const pkgTabsB = tabs.nth(4); // This set uses icons for tab items.
+
+	// Select the pnpm tab in the first set of synced tabs.
+	await pkgTabsA.getByRole('tab').filter({ hasText: 'pnpm' }).click();
+
+	await expectSelectedTab(pkgTabsA, 'pnpm', 'pnpm command');
+	await expectSelectedTab(pkgTabsB, 'pnpm', 'another pnpm command');
+
+	// Select the yarn tab in the second set of synced tabs.
+	await pkgTabsB.getByRole('tab').filter({ hasText: 'yarn' }).click();
+
+	await expectSelectedTab(pkgTabsB, 'yarn', 'another yarn command');
+	await expectSelectedTab(pkgTabsA, 'yarn', 'yarn command');
+});
+
 async function expectSelectedTab(tabs: Locator, label: string, panel: string) {
 	expect((await tabs.getByRole('tab', { selected: true }).textContent())?.trim()).toBe(label);
 	expect((await tabs.getByRole('tabpanel').textContent())?.trim()).toBe(panel);
diff --git a/packages/starlight/user-components/Tabs.astro b/packages/starlight/user-components/Tabs.astro
index 376fb19c..f93475c1 100644
--- a/packages/starlight/user-components/Tabs.astro
+++ b/packages/starlight/user-components/Tabs.astro
@@ -158,7 +158,7 @@ const { html, panels } = processPanels(panelHtml);
 			newTab.setAttribute('aria-selected', 'true');
 			if (shouldSync) {
 				newTab.focus();
-				StarlightTabs.#syncTabs(this, newTab.textContent);
+				StarlightTabs.#syncTabs(this, newTab.innerText);
 				window.scrollTo({
 					top: window.scrollY + (this.getBoundingClientRect().top - previousTabsOffset),
 				});
@@ -173,7 +173,7 @@ const { html, panels } = processPanels(panelHtml);
 
 			for (const receiver of syncedTabs) {
 				if (receiver === emitter) continue;
-				const labelIndex = receiver.tabs.findIndex((tab) => tab.textContent === label);
+				const labelIndex = receiver.tabs.findIndex((tab) => tab.innerText === label);
 				if (labelIndex === -1) continue;
 				receiver.switchTab(receiver.tabs[labelIndex], labelIndex, false);
 			}