Port "Ensure correct DOM node order when performing focus actions"

tailwindlabs/headlessui#1038

This test didn't actually fail for me but w/e.

src/lib/components/tabs/tabs.test.ts

@@ -83,6 +83,45 @@ describe('Rendering', () => {
     assertTabs({ active: 0 })
   })
 
+  it('should guarantee the order of DOM nodes when performing actions', async () => {
+    render(svelte`
+      <script>
+        let hide = false;
+      </script>
+
+      <button on:click={() => hide = !hide}>toggle</button>
+      <TabGroup>
+        <TabList>
+          <Tab>Tab 1</Tab>
+          {#if !hide}
+            <Tab>Tab 2</Tab>
+          {/if}
+          <Tab>Tab 3</Tab>
+        </TabList>
+
+        <TabPanels>
+          <TabPanel>Content 1</TabPanel>
+          {#if !hide}
+            <TabPanel>Content 2</TabPanel>
+          {/if}
+          <TabPanel>Content 3</TabPanel>
+        </TabPanels>
+      </TabGroup>
+    `)
+
+    await click(getByText('toggle')) // Remove Tab 2
+    await click(getByText('toggle')) // Re-add Tab 2
+
+    await press(Keys.Tab)
+    assertTabs({ active: 0 })
+
+    await press(Keys.ArrowRight)
+    assertTabs({ active: 1 })
+
+    await press(Keys.ArrowRight)
+    assertTabs({ active: 2 })
+  })
+
   describe('`slot props`', () => {
     it('should expose the `selectedIndex` on the `TabGroup` component', async () => {
       render(svelte`

src/lib/test-utils/accessibility-assertions.ts

@@ -1359,12 +1359,8 @@ export function assertTabs(
     expect(list).toHaveAttribute("role", "tablist");
     expect(list).toHaveAttribute("aria-orientation", orientation);
 
-    let activeTab = tabs.find(
-      (tab) => tab.dataset.headlessuiIndex === "" + active
-    );
-    let activePanel = panels.find(
-      (panel) => panel.dataset.headlessuiIndex === "" + active
-    );
+    let activeTab = Array.from(list.querySelectorAll('[id^="headlessui-tabs-tab-"]'))[active]
+    let activePanel = panels.find(panel => panel.id === activeTab.getAttribute('aria-controls'))
 
     for (let tab of tabs) {
       expect(tab).toHaveAttribute("id");

src/lib/utils/focus-management.ts

@@ -100,7 +100,13 @@ export function focusElement(element: HTMLElement | null) {
 
 export function focusIn(container: HTMLElement | HTMLElement[], focus: Focus) {
   let elements = Array.isArray(container)
-    ? container
+    ? container.slice().sort((a, b) => {
+      let position = a.compareDocumentPosition(b)
+
+      if (position & Node.DOCUMENT_POSITION_FOLLOWING) return -1
+      if (position & Node.DOCUMENT_POSITION_PRECEDING) return 1
+      return 0
+    })
     : getFocusableElements(container);
   let active = document.activeElement as HTMLElement;