Render a tab panel's id and its hidden state on the server

Every panel was visible until Alpine booted — four role="tabpanel" regions at
once for a screen reader, and aria-controls pointing at ids that did not exist
yet. The panel now carries its id, its aria-labelledby and, unless it is the
chosen one, display:none from the server. A slot renders before the component
around it, so the panel reads <x-tabs>'s attributes off the component stack and
repeats its id and initial-tab lines; both files say so.
Plan: docs/plans/material-3-alignment.md, step 14 (navigation N-05).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

resources/views/components/tab.blade.php

@@ -1,17 +1,43 @@
 {{-- One tab's panel, inside `<x-tabs>`, which draws the bar from its own `tabs` list. Shown while
      its `name` is the chosen one; every panel is rendered, so switching never waits on the server.
-     `class` lands on the panel (it has `pt-6` above its content by default). --}}
+     `class` lands on the panel (it has `pt-6` above its content by default).
+
+     The id and the `hidden` panels come from the server, not from Alpine: until Alpine boots, every
+     panel would otherwise be on screen at once — four `role="tabpanel"` regions for a screen reader
+     to walk — and the tab buttons' `aria-controls` would point at nothing. `<x-tabs>` renders this
+     slot before its own view, so it cannot hand the panel anything; the panel reads the attributes
+     written on `<x-tabs>` off the component stack (Blade's `@aware` mechanism) and repeats the two
+     lines tabs.blade.php runs on them. The two must agree, so change them together. --}}
 
 @props([
     'name',
 ])
 
+@php
+    $aware = fn (string $key, $default = null) => $__env->getConsumableComponentData($key, $default);
+
+    $tabs = $aware('tabs', []);
+    // `wire:model` is a key, not a prop, and its modifiers are part of the key: the spellings that
+    // make sense on a tab set. An exotic one only means the panel falls back to the first tab.
+    $model = collect(['wire:model', 'wire:model.live', 'wire:model.blur', 'wire:model.change', 'wire:model.lazy'])
+        ->map(fn (string $key) => $aware($key))
+        ->first(fn ($value): bool => filled($value));
+
+    $tabsId = $aware('id') ?? 'tabs-'.substr(md5($model.'|'.implode('|', array_column($tabs, 'name'))), 0, 8);
+
+    $initial = $aware('selected') ?? (collect($tabs)->first(fn (array $tab): bool => ! ($tab['disabled'] ?? false))['name'] ?? null);
+    if ($model !== null && ($component = \Livewire\Livewire::current()) !== null && filled(data_get($component, $model))) {
+        $initial = data_get($component, $model);
+    }
+@endphp
+
 <div
     x-show="selected === @js($name)"
     role="tabpanel"
-    x-bind:id="tabsId + '-' + @js($name) + '-panel'"
+    id="{{ $tabsId }}-{{ $name }}-panel"
-    x-bind:aria-labelledby="tabsId + '-' + @js($name)"
+    aria-labelledby="{{ $tabsId }}-{{ $name }}"
     tabindex="0"
+    @if ((string) $name !== (string) $initial) style="display: none" @endif
     {{ $attributes->class(['pt-6 outline-none']) }}
 >
     {{ $slot }}

resources/views/components/tabs.blade.php

@@ -3,7 +3,8 @@
      The bar is rendered on the server from `tabs`, a list of `['name' => …, 'label' => …]` with an
      optional `icon`, `badge` and `disabled` — so it arrives with the page, never a moment after it.
      The panels are `<x-tab name="…">` in the slot; every panel is rendered, so switching never waits
-     on the server.
+     on the server, and each arrives with its id and with every panel but the chosen one already
+     hidden, so nothing flashes and no screen reader meets four panels at once.
 
      The chosen tab is the Livewire property in `wire:model` (entangled; `wire:model.live` tells the
      server at once), or, without it, `selected` (the first tab by default) and `x-model`. The bar is
@@ -24,6 +25,8 @@
 @php
     $model = $attributes->wire('model')->value() ?: null;
     $variant = $variant === 'secondary' ? 'secondary' : 'primary';
+    // tab.blade.php repeats these two lines off the component stack, because a slot renders before
+    // the component around it: change them together, or a panel's id stops matching aria-controls.
     $id = $attributes->get('id') ?? 'tabs-'.substr(md5($model.'|'.implode('|', array_column($tabs, 'name'))), 0, 8);
 
     $initial = $selected ?? (collect($tabs)->first(fn (array $tab): bool => ! ($tab['disabled'] ?? false))['name'] ?? null);

tests/Feature/Components/TabsTest.php

@@ -21,10 +21,27 @@ it('renders the tablist on the server with the first enabled tab chosen', functi
         ->toContain('data-tab-indicator')
         ->toContain('--tabs-indicator: share-indicator')
         ->toContain('x-modelable="selected"')
-        ->toContain('role="tabpanel"')
+        // The panel's id is the server's, so aria-controls never dangles (N-05).
+        ->toMatch('/role="tabpanel"\s+id="share-people-panel"\s+aria-labelledby="share-people"/')
         ->toContain('>3</span>');
 });
 
+it('renders every panel but the chosen one hidden, before Alpine boots', function () {
+    $html = (string) $this->blade(<<<'BLADE'
+        <x-tabs :tabs="[['name' => 'files', 'label' => 'Files'], ['name' => 'people', 'label' => 'People']]" selected="people">
+            <x-tab name="files">Three files.</x-tab>
+            <x-tab name="people">Anna and Ben.</x-tab>
+        </x-tabs>
+        BLADE);
+
+    expect($html)
+        ->toMatch('/id="[^"]+-files-panel"[^>]*style="display: none"/')
+        ->toMatch('/id="[^"]+-people-panel"(?![^>]*style="display: none")/')
+        // The tab button and its panel agree on the id the slot worked out for itself.
+        ->toMatch('/aria-controls="(tabs-[0-9a-f]{8})-people-panel"/')
+        ->toMatch('/id="(tabs-[0-9a-f]{8})-people-panel"/');
+});
+
 it('takes a variant, stacks icons and scrolls on request', function () {
     expect((string) $this->blade('<x-tabs variant="secondary" stacked scrollable :tabs="[[\'name\' => \'a\', \'label\' => \'A\']]" />'))
         ->toContain('data-variant="secondary"')
@@ -42,14 +59,17 @@ it('entangles the chosen tab with Livewire and renders the one the property name
 
         public function render(): string
         {
-            return '<div><x-tabs wire:model.live="tab" :tabs="[[\'name\' => \'files\', \'label\' => \'Files\'], [\'name\' => \'people\', \'label\' => \'People\']]" /></div>';
+            return '<div><x-tabs wire:model.live="tab" :tabs="[[\'name\' => \'files\', \'label\' => \'Files\'], [\'name\' => \'people\', \'label\' => \'People\']]"><x-tab name="files">Three files.</x-tab><x-tab name="people">Anna and Ben.</x-tab></x-tabs></div>';
         }
     });
 
     expect(Livewire::test('tabs-probe')->html())
         ->toContain(".entangle('tab').live")
         ->not->toContain('x-modelable')
-        ->toMatch('/data-tab="people"\s+aria-controls="[^"]+"\s+aria-selected="true"/');
+        ->toMatch('/data-tab="people"\s+aria-controls="[^"]+"\s+aria-selected="true"/')
+        // The panel the property names is the one drawn, before Alpine entangles anything (N-05).
+        ->toMatch('/id="[^"]+-files-panel"[^>]*style="display: none"/')
+        ->toMatch('/id="[^"]+-people-panel"(?![^>]*style="display: none")/');
 });
 
 it('draws section navigation as secondary tabs and a picker', function () {