Open a submenu from a menu item

Plan step 22, actions.md § Missing (Submenus): M3's Expressive vertical
menu specifies submenus and the Left/Right keys that open and close them,
and the library had neither.

`<x-menu-item submenu>` puts its slot in a second popover on the item's
end, flipping to the start where there is no room. `materialSubmenu`
reuses the menu button pattern one level in: the item is its own trigger,
so the anchor move and the button lookup are overridden away; Right,
Enter and Space open it, Left and Escape close it and return the focus,
and a fine pointer resting on the item opens it after a moment. `items()`
now stops at the popover it belongs to, so the arrows never walk between
a menu and an open submenu. The menu publishes its container as custom
properties so a vibrant menu's submenus are vibrant too.

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

resources/boost/skills/livewire-material-development/SKILL.md

@@ -261,7 +261,18 @@ M3's plain tooltip, standalone around any trigger: `<x-tooltip text="Copy link"
 </x-menu>
 ```
 
-`<x-menu>`: `trigger` slot (its first button or link becomes the menu button, and the menu hangs on that button — a `position: fixed` trigger such as `<x-button fab>` carries it along, and a menu with no room flips to the other side, end or both), `label`, `position` (`bottom-start` default, `bottom-end`, `top-start`, `top-end`), `vibrant`. `<x-menu-item>`: `label`, `icon`, `icon-class` (classes for the leading icon; a colour there paints it, a selected item's too, but not a disabled one's — `icon-class="text-sport-run"`), `icon-right`, `description`, `shortcut`, `link`, `external`, `selected` (makes it a `menuitemcheckbox`, ticked at its end unless it has an `icon-right`), `current` (for a menu of places: marks the page you are on with `aria-current="page"` in secondary-container, never a checked choice), `badge` (`true` for a dot, or a count, at the end of the row), `disabled`, `keep-open`. Choosing an item closes the menu unless `keep-open`; a second press on the menu button closes it too. An open menu stays open while the Livewire component around it renders, a `keep-open` item's own `wire:click` included. Keyboard: arrows, Home, End, a letter, Escape (focus returns to the trigger), Tab; a `disabled` item keeps its place in that order, as M3 asks, but cannot be activated. A menu longer than the window scrolls.
+`<x-menu>`: `trigger` slot (its first button or link becomes the menu button, and the menu hangs on that button — a `position: fixed` trigger such as `<x-button fab>` carries it along, and a menu with no room flips to the other side, end or both), `label`, `position` (`bottom-start` default, `bottom-end`, `top-start`, `top-end`), `vibrant`. `<x-menu-item>`: `label`, `icon`, `icon-class` (classes for the leading icon; a colour there paints it, a selected item's too, but not a disabled one's — `icon-class="text-sport-run"`), `icon-right`, `description`, `shortcut`, `link`, `external`, `selected` (makes it a `menuitemcheckbox`, ticked at its end unless it has an `icon-right`), `current` (for a menu of places: marks the page you are on with `aria-current="page"` in secondary-container, never a checked choice), `badge` (`true` for a dot, or a count, at the end of the row), `disabled`, `keep-open`, `submenu`. Choosing an item closes the menu unless `keep-open`; a second press on the menu button closes it too. An open menu stays open while the Livewire component around it renders, a `keep-open` item's own `wire:click` included. Keyboard: arrows, Home, End, a letter, Escape (focus returns to the trigger), Tab; a `disabled` item keeps its place in that order, as M3 asks, but cannot be activated. A menu longer than the window scrolls.
+
+`submenu` makes an item a menu of its own — the slot holds the nested `<x-menu-item>`s instead of a label, and they open beside it, on its end, flipping to its start where the window has no room:
+
+```blade
+<x-menu-item label="Export as" icon="download" submenu>
+    <x-menu-item label="ZIP" icon="folder_zip" wire:click="exportZip" />
+    <x-menu-item label="PDF" icon="picture_as_pdf" wire:click="exportPdf" />
+</x-menu-item>
+```
+
+The item says so with `aria-haspopup="menu"`, `aria-expanded` and a chevron; Right, Enter or Space open it on its first item, Left or Escape close it and come back, and on a fine pointer resting on the item opens it. Choosing anything inside closes the whole menu. Arrows stay inside the list they are in. M3 calls submenus a large-screen pattern — on a phone give the menu `sheet-at-compact`, or keep the list flat.
 
 ### `<x-button-group>`
 

resources/css/components/menu.css

@@ -1,7 +1,7 @@
 /*
- * The exposed dropdown menu — the list a field drops open.
+ * The menus: the exposed dropdown a field drops open, and what `<x-menu>` cannot say in utilities.
  *
- * Two lists wear it, so a form reads as one family:
+ * Two lists wear the dropdown, so a form reads as one family:
  *
  *   - `<x-select>`'s: the native <select>, opted into the browser's customizable select
  *     (`appearance: base-select`). `::picker(select)` is the menu and each <option> a row, while the
@@ -20,6 +20,29 @@
  * paints option colours into its native list would otherwise show a half-painted one.
  */
 
+/*
+ * `<x-menu>` and the submenus inside it.
+ *
+ * A submenu is a popover of its own nested in the menu's, so it cannot take the container colour
+ * from a class the item knows nothing about: the menu declares the pair as custom properties,
+ * which a nested popover inherits down the DOM whatever the top layer does with its painting. The
+ * fallbacks are the standard menu's, for a submenu in some other list (a FAB menu's).
+ */
+[data-menu] {
+    --material-menu-surface: var(--md-sys-color-surface-container-low);
+    --material-menu-ink: var(--md-sys-color-on-surface);
+}
+
+[data-menu][data-vibrant] {
+    --material-menu-surface: var(--md-sys-color-tertiary-container);
+    --material-menu-ink: var(--md-sys-color-on-tertiary-container);
+}
+
+[data-submenu] {
+    background: var(--material-menu-surface, var(--md-sys-color-surface-container-low));
+    color: var(--material-menu-ink, var(--md-sys-color-on-surface));
+}
+
 .field-menu {
     max-block-size: 18rem;
     overflow-y: auto;

resources/js/menu.js

@@ -1,5 +1,6 @@
 /**
  * `materialMenu`: the behaviour of `<x-menu>` — WAI-ARIA's menu button pattern on a popover.
+ * `materialSubmenu`: the same pattern one level in, for `<x-menu-item submenu>`.
  *
  * The menu button is the trigger's first button or link. Its ARIA attributes are written by
  * script, which a Livewire morph removes along with anything else the server did not render,
@@ -12,6 +13,13 @@
  * so the menu opened there. Script moves the name onto the menu button, beside any name the button
  * carries itself (a button's tooltip anchors on it too), and moves it again after every morph,
  * which puts the server's attributes, and a fresh name, back.
+ *
+ * A submenu's popover sits inside its parent's, so the browser keeps the two open together — a
+ * nested `popover="auto"` light-dismisses only down to its DOM ancestor — and closes the inner one
+ * when the outer goes. Its trigger *is* the item, which the server names itself, so the two pieces
+ * that exist only for a wrapper (moving the anchor name, and finding the button inside the trigger
+ * slot) are overridden away. `items()` stops at the popover it belongs to, so the arrow keys in a
+ * menu never walk into an open submenu's rows, nor a submenu's back out into its parent's.
  */
 const ITEMS = '[role="menuitem"], [role="menuitemcheckbox"], [role="menuitemradio"]'
 
@@ -21,8 +29,13 @@ const ITEMS = '[role="menuitem"], [role="menuitemcheckbox"], [role="menuitemradi
 // click.
 const REOPEN_GUARD_MS = 250
 
-document.addEventListener('alpine:init', () => {
+// A submenu opens after the pointer has rested on its item for a moment, and closes a moment after
-    window.Alpine.data('materialMenu', () => ({
+// it leaves the pair — long enough to cross the gap between them. APG's menu pattern asks for both
+// delays. A coarse pointer has no hover to speak of, so there it opens on the press instead.
+const HOVER_OPEN_MS = 180
+const HOVER_CLOSE_MS = 320
+
+const menu = () => ({
     closedAt: -Infinity,
     anchored: null,
     returnFocus: true,
@@ -160,7 +173,12 @@ document.addEventListener('alpine:init', () => {
         }
 
         this.control()?.setAttribute('aria-expanded', 'true')
+
+        // `false` opens without taking the focus: a submenu the pointer rested on belongs to the
+        // pointer, and taking the focus out from under the keyboard would be the wrong answer.
+        if (focus !== false) {
             this.focusItem(focus)
+        }
     },
 
     close() {
@@ -180,12 +198,15 @@ document.addEventListener('alpine:init', () => {
     },
 
     /**
-         * Every item, disabled ones included: M3 keeps a disabled item focusable ("disabled items
+     * Every item of *this* menu, disabled ones included: M3 keeps a disabled item focusable
-         * can still receive focus, just aren't selectable") so a person reading the menu with the
+     * ("disabled items can still receive focus, just aren't selectable") so a person reading the
-         * keyboard learns that it exists. activate() is where the refusal lives.
+     * menu with the keyboard learns that it exists. activate() is where the refusal lives.
+     *
+     * An open submenu is a popover of its own nested in this one, and its rows are its: the
+     * nearest popover around a row says which menu the arrow keys should find it in.
      */
     items() {
-            return [...this.$refs.menu.querySelectorAll(ITEMS)]
+        return [...this.$refs.menu.querySelectorAll(ITEMS)].filter((item) => item.closest('[popover]') === this.$refs.menu)
     },
 
     /** The menu scrolls when it is too long for the window, so the item taken has to be shown. */
@@ -260,5 +281,80 @@ document.addEventListener('alpine:init', () => {
     destroy() {
         this.listeners.forEach((remove) => remove())
     },
-    }))
+})
+
+document.addEventListener('alpine:init', () => {
+    window.Alpine.data('materialMenu', menu)
+
+    window.Alpine.data('materialSubmenu', () => {
+        const base = menu()
+
+        return {
+            ...base,
+            hoverTimer: null,
+
+            /** The item is the menu button, and the server named it: nothing has to be moved. */
+            control() {
+                return this.$refs.trigger
+            },
+
+            anchor() {},
+
+            navigate(event) {
+                // APG: Left closes a submenu and puts the focus back on the item that opened it.
+                // Escape does the same through the browser's own light dismiss, which the `toggle`
+                // listener follows with the focus.
+                if (event.key === 'ArrowLeft') {
+                    event.preventDefault()
+                    this.returnFocus = true
+                    this.close()
+                    this.control()?.focus()
+
+                    return
+                }
+
+                base.navigate.call(this, event)
+            },
+
+            /** Hover opens a submenu only where hovering means something, and never on a first tap. */
+            fine(event) {
+                return (event === undefined || event.pointerType !== 'touch') && window.matchMedia('(hover: hover) and (pointer: fine)').matches
+            },
+
+            hover(event) {
+                if (!this.fine(event)) {
+                    return
+                }
+
+                clearTimeout(this.hoverTimer)
+                this.hoverTimer = setTimeout(() => this.open(false), HOVER_OPEN_MS)
+            },
+
+            /**
+             * The submenu is a DOM child of the item's wrapper, so crossing into it is not a leave;
+             * a pointer that really left closes it, unless the keyboard has since taken it over.
+             */
+            unhover() {
+                clearTimeout(this.hoverTimer)
+
+                if (!this.fine()) {
+                    return
+                }
+
+                this.hoverTimer = setTimeout(() => {
+                    if (this.$el.contains(document.activeElement)) {
+                        return
+                    }
+
+                    this.returnFocus = false
+                    this.close()
+                }, HOVER_CLOSE_MS)
+            },
+
+            destroy() {
+                clearTimeout(this.hoverTimer)
+                base.destroy.call(this)
+            },
+        }
+    })
 })

resources/views/components/menu-item.blade.php

@@ -13,6 +13,14 @@
      is there. `keep-open` leaves the menu open when it is activated — for a choice the person may
      want to change twice.
 
+     `submenu` turns the item into a menu of its own: the slot holds `<x-menu-item>`s instead of a
+     label, and they open in a second popover beside this one, on the item's end, flipping to its
+     start where the window has no room. The item says so — `aria-haspopup="menu"`,
+     `aria-expanded`, and a chevron at its end — and keeps the APG menu keyboard: Right, Enter or
+     Space open it on its first item, Left or Escape close it and come back here, and on a fine
+     pointer resting on the item opens it. Choosing anything inside closes the whole menu, as it
+     would from the outer list.
+
      `icon-class` is for an icon whose colour means something of its own, a sport's glyph in the
      sport's colour (`icon-class="text-sport-run"`). A colour there paints the icon, a selected
      item's too: the icon's own colour then carries no specificity, because which of two colour
@@ -41,12 +49,18 @@
     'badge' => null,
     'disabled' => false,
     'keepOpen' => false,
+    'submenu' => false,
 ])
 
 @php
     $isLink = filled($link);
     $tag = $isLink ? 'a' : 'button';
 
+    // A submenu's own popover, named like the menu's: a new id and a new anchor name with every
+    // render, matched through a morph by the key rather than by either of them.
+    $key = $submenu ? \Illuminate\Support\Str::lower(\Illuminate\Support\Str::random(10)) : null;
+    $anchor = $submenu ? "--material-submenu-{$key}" : null;
+
     $attributes = $attributes
         ->class([
             'group/item state-layer flex w-full min-h-12 cursor-pointer items-center gap-3 px-4 text-start outline-none',
@@ -64,12 +78,19 @@
             'aria-current' => $current ? 'page' : null,
             'aria-disabled' => $disabled ? 'true' : null,
             'tabindex' => '-1',
+            'x-ref' => $submenu ? 'trigger' : null,
+            'style' => $submenu ? "anchor-name: {$anchor}" : null,
+            'aria-haspopup' => $submenu ? 'menu' : null,
+            'aria-expanded' => $submenu ? 'false' : null,
+            'aria-controls' => $submenu ? "material-submenu-{$key}" : null,
+            'x-on:click' => $submenu ? "toggle('first')" : null,
             'type' => $isLink ? null : 'button',
             'href' => $isLink ? $link : null,
             'target' => $isLink && $external ? '_blank' : null,
             'rel' => $isLink && $external ? 'noopener' : null,
             'wire:navigate' => $isLink && ! $external && ! $noWireNavigate && ! $attributes->has('wire:navigate') ? true : null,
-            'data-keep-open' => $keepOpen ? true : null,
+            // Opening a submenu is not choosing anything: the outer menu stays where it was.
+            'data-keep-open' => $keepOpen || $submenu ? true : null,
         ], fn ($value): bool => $value !== null));
 
     $iconInk = match (true) {
@@ -88,13 +109,21 @@
     };
 @endphp
 
+@if ($submenu)
+    <div x-data="materialSubmenu"
+        x-on:keydown.right.prevent.stop="open('first')"
+        x-on:pointerenter="hover($event)"
+        x-on:pointerleave="unhover()"
+    >
+@endif
+
 <{{ $tag }} {{ $attributes }}>
     @if ($icon)
         <x-livewire-material::icon :name="$icon" optical="20" :filled="$selected === true || $current" :class="$leadingIcon" />
     @endif
 
     <span class="min-w-0 flex-1">
-        <span class="block truncate type-body-lg">{{ $label ?? $slot }}</span>
+        <span class="block truncate type-body-lg">{{ $submenu ? $label : ($label ?? $slot) }}</span>
 
         @if ($description)
             <span @class(['block type-body-md', $iconInk])>{{ $description }}</span>
@@ -110,8 +139,31 @@
 
     @if ($iconRight)
         <x-livewire-material::icon :name="$iconRight" optical="20" :class="'size-5 '.$iconInk" />
+    @elseif ($submenu)
+        {{-- M3's submenu marker: it points the way the list opens, and turns over in an RTL page. --}}
+        <x-livewire-material::icon name="chevron_right" optical="20" :class="'size-5 rtl:-scale-x-100 '.$iconInk" />
     @elseif ($selected === true)
         {{-- The third cue M3 recommends, so a chosen item is not told by colour and shape alone. --}}
         <x-livewire-material::icon name="check" optical="20" :class="'size-5 '.$iconInk" />
     @endif
 </{{ $tag }}>
+
+@if ($submenu)
+        <div
+            x-ref="menu"
+            {{ new \Illuminate\View\ComponentAttributeBag(['wire:key' => 'material-submenu-'.substr(md5((string) $label), 0, 10)]) }}
+            id="material-submenu-{{ $key }}"
+            popover="auto"
+            role="menu"
+            data-submenu
+            aria-label="{{ $label }}"
+            tabindex="-1"
+            style="position-anchor: {{ $anchor }}"
+            x-on:keydown.stop="navigate($event)"
+            x-on:click="activate($event)"
+            class="m-0 mx-1 min-w-28 max-w-70 max-h-[min(18rem,calc(100dvh-2rem))] origin-top overflow-y-auto border-0 p-1 rounded-corner-lg shadow-elevation-2 popover-transition [inset:auto] [position-area:inline-end_span-block-end] [position-try-fallbacks:flip-inline]"
+        >
+            {{ $slot }}
+        </div>
+    </div>
+@endif

resources/views/components/menu.blade.php

@@ -69,6 +69,8 @@
         id="material-menu-{{ $key }}"
         popover="auto"
         role="menu"
+        data-menu
+        @if ($vibrant) data-vibrant @endif
         @if ($label) aria-label="{{ $label }}" @endif
         tabindex="-1"
         style="position-anchor: {{ $anchor }}"

resources/views/showcase/sections/menus.blade.php

@@ -36,6 +36,30 @@
                 <x-menu-item label="Upload a folder" icon="drive_folder_upload" />
             </x-menu>
             BLADE,
+        'Submenus' => <<<'BLADE'
+            <x-menu label="Share actions">
+                <x-slot:trigger>
+                    <x-button label="Share" icon="share" variant="tonal" />
+                </x-slot:trigger>
+
+                <x-menu-item label="Copy link" icon="content_copy" shortcut="⌘C" />
+                <x-menu-item label="Send to" icon="send" submenu>
+                    <x-menu-item label="A person" icon="person" />
+                    <x-menu-item label="A team" icon="group" />
+                    <x-menu-item label="Somewhere else" icon="more_horiz" submenu>
+                        <x-menu-item label="Slack" icon="chat" />
+                        <x-menu-item label="Email" icon="mail" />
+                    </x-menu-item>
+                </x-menu-item>
+                <x-menu-item label="Export as" icon="download" submenu>
+                    <x-menu-item label="ZIP" icon="folder_zip" />
+                    <x-menu-item label="PDF" icon="picture_as_pdf" />
+                    <x-menu-item label="CSV" icon="table" disabled />
+                </x-menu-item>
+                <x-menu-separator />
+                <x-menu-item label="Delete" icon="delete" />
+            </x-menu>
+            BLADE,
         'Icons in their own colour' => <<<'BLADE'
             <x-menu label="New plan">
                 <x-slot:trigger>
@@ -56,7 +80,8 @@
 
     <p class="max-w-3xl type-body-md text-on-surface-variant">
         <code>&lt;x-menu&gt;</code> with <code>&lt;x-menu-item&gt;</code>, <code>&lt;x-menu-group&gt;</code> and <code>&lt;x-menu-separator&gt;</code>.
-        Open one with the keyboard too: arrows, Home, End, a letter, Escape.
+        Open one with the keyboard too: arrows, Home, End, a letter, Escape. A <code>submenu</code> item opens a second list beside it
+        &mdash; Right to enter it, Left to come back.
     </p>
 
     @foreach ($examples as $title => $code)

tests/Feature/Components/MenuTest.php

@@ -117,3 +117,51 @@ it('adds icon-class to the leading icon, over its own colour but not over disabl
         ->and((string) $this->blade('<x-menu-item label="Next" icon-right="chevron_right" icon-class="text-sport-run" />'))
         ->not->toContain('text-sport-run');
 });
+
+it('opens a submenu beside the item that holds it', function () {
+    $html = (string) $this->blade(<<<'BLADE'
+        <x-menu-item label="Send to" icon="send" submenu>
+            <x-menu-item label="A person" icon="person" />
+        </x-menu-item>
+        BLADE);
+
+    preg_match('/anchor-name: (--material-submenu-([a-z0-9]+))/', $html, $anchor);
+
+    expect($anchor)->not->toBeEmpty()
+        ->and($html)
+        ->toContain('x-data="materialSubmenu"')
+        ->toContain('x-on:keydown.right.prevent.stop="open(\'first\')"')
+        ->toContain('x-on:pointerenter="hover($event)"')
+        ->toContain('aria-haspopup="menu"')
+        ->toContain('aria-expanded="false"')
+        ->toContain("aria-controls=\"material-submenu-{$anchor[2]}\"")
+        ->toContain("id=\"material-submenu-{$anchor[2]}\"")
+        ->toContain("position-anchor: {$anchor[1]}")
+        ->toContain('data-submenu')
+        ->toContain('aria-label="Send to"')
+        ->toContain('[position-area:inline-end_span-block-end]')
+        ->toContain('[position-try-fallbacks:flip-inline]')
+        // Opening a submenu chooses nothing, so the menu around it stays where it was.
+        ->toContain('data-keep-open')
+        ->toContain('A person');
+});
+
+it('marks a submenu item with a chevron instead of a tick', function () {
+    $chevron = trim((string) file_get_contents(__DIR__.'/../../../resources/svg/symbols/outlined-20/chevron_right.svg'));
+    $chevron = substr($chevron, (int) strpos($chevron, '><') + 1);
+
+    expect((string) $this->blade('<x-menu-item label="Export as" submenu><x-menu-item label="ZIP" /></x-menu-item>'))
+        ->toContain($chevron)
+        ->toContain('rtl:-scale-x-100')
+        ->and((string) $this->blade('<x-menu-item label="Export as" icon-right="download" submenu><x-menu-item label="ZIP" /></x-menu-item>'))
+        ->not->toContain($chevron);
+});
+
+it('tells a vibrant menu apart, so the submenus inside it take the same container', function () {
+    expect((string) $this->blade('<x-menu vibrant><x-slot:trigger><button>x</button></x-slot:trigger></x-menu>'))
+        ->toContain('data-menu')
+        ->toContain('data-vibrant')
+        ->and((string) $this->blade('<x-menu><x-slot:trigger><button>x</button></x-slot:trigger></x-menu>'))
+        ->toContain('data-menu')
+        ->not->toContain('data-vibrant');
+});