dialog: support nesting/stacking & improve ergonomics

- stacked/nested dialogs work properly
- dialog api expanded to include `hasError` and `focus`
- `onopenchange` prop added, `onopen` and `onclose` deprecated
- improve accessibility with additional aria props

src/lib/Dialog.svelte

@@ -5,6 +5,8 @@
 	export interface DialogAPI {
 		/** shows an error message at the top of the dialog */
 		error: (message: RawError | null) => void;
+		/** Returns if the dialog is displaying an error */
+		hasError: () => boolean;
 		/** closes the dialog */
 		close: () => void;
 		/** opens the dialog */
@@ -39,6 +41,8 @@
 		 * changes made via this API will NOT propagate to consuming components.
 		 */
 		title: (title: string) => void;
+		/** Focuses the dialog */
+		focus: () => void;
 	}
 
 	type DialogControlButton = {
@@ -79,6 +83,9 @@
 	};
 
 	export { dialogCancelButton, dialogOkButton, dialogCloseButton };
+
+	/** stack of currently open dialogs by identifier */
+	let dialogStack: DialogAPI[] = $state([]);
 </script>
 
 <script lang="ts">
@@ -91,7 +98,7 @@
 	import { X } from 'phosphor-svelte';
 	import { ErrorMessage, type RawError } from './error';
 	import ErrorBox from './ErrorBox.svelte';
-	import { mergeOverrideObject } from './util';
+	import { generateIdentifier, mergeOverrideObject } from './util';
 
 	interface Props {
 		/** Bindable open state of the dialog */
@@ -112,10 +119,18 @@
 		controlsAlign?: 'start' | 'center' | 'end';
 		/** Top-right close control */
 		close?: Snippet | Omit<DialogControlButton, 'label'> | null;
-		/** Callback when the dialog is opened */
+		/**
+		 * Callback when the dialog is opened
+		 * @deprecated use onopenchange instead and check the open parameter
+		 */
 		onopen?: (dialog: DialogAPI) => void;
-		/** Callback when the dialog is closed */
+		/**
+		 * Callback when the dialog is closed
+		 * @deprecated use onopenchange instead and check the open parameter
+		 */
 		onclose?: (dialog: DialogAPI) => void;
+		/** Callback when the dialog open state changes */
+		onopenchange?: ({ open, dialog }: { open: boolean; dialog: DialogAPI }) => void;
 		/** If default controls are used, controls loading state of submit button */
 		loading?: boolean;
 		/** If default controls are used, freezes all interactions */
@@ -136,34 +151,68 @@
 		close = {},
 		onopen,
 		onclose,
+		onopenchange,
 		loading = $bindable(false),
 		frozen = $bindable(false),
 		disabled = $bindable(false)
 	}: Props = $props();
 
-	let controls = $derived(
+	const controls = $derived(
 		typeof rawControls === 'function'
 			? rawControls
 			: mergeOverrideObject(defaultDialogControls, rawControls)
 	);
 
+	const identifier = generateIdentifier('dialog');
+
+	let lastOpen = $state(open);
+	let dialogPage = $state<HTMLDivElement | null>(null);
 	let dialogContainer = $state<HTMLDivElement | null>(null);
 	let error = $state<ErrorMessage | null>(null);
+	let stackIndex = $state(-1);
 
-	// disable window scroll when dialog is open
+	/** handles open change */
-	$effect(() => {
+	const handleOpenChange = (localOpen: boolean) => {
-		if (open) {
+		if (localOpen) {
-			document.body.style.overflow = 'hidden';
+			document.body.style.overflow = 'hidden'; // prevent scrolling
-			untrack(() => onopen?.(dialogAPI));
+			// focus the dialog BEFORE callbacks for accessibility & flexibility
+			dialogPage?.focus();
+			// run callbacks
+			onopen?.(dialogAPI);
+			onopenchange?.({ open: true, dialog: dialogAPI });
+			//update stack
+			dialogStack.push(dialogAPI); // add to stack of open dialogs
+			stackIndex = dialogStack.length - 1; // track index in stack for this dialog
 		} else {
-			document.body.style.overflow = '';
+			// update stack
-			untrack(() => onclose?.(dialogAPI));
+			dialogStack.pop(); // remove from stack of open dialogs
+			stackIndex = -1; // reset stack index for this dialog
+			// update focus & handle scroll locking for accessibility
+			if (dialogStack.length > 0) {
+				dialogStack[dialogStack.length - 1].focus();
+			} else {
+				document.body.style.overflow = ''; // re-enable scrolling since no dialogs are open
+			}
+			// run callbacks
+			onclose?.(dialogAPI);
+			onopenchange?.({ open: false, dialog: dialogAPI });
+		}
+	};
+
+	// deduplicate open changes
+	$effect(() => {
+		if (open !== untrack(() => lastOpen)) {
+			lastOpen = open;
+			untrack(() => {
+				handleOpenChange(open);
+			});
 		}
 	});
 
 	/** DialogAPI instance to control this dialog */
 	export const dialogAPI: DialogAPI = {
 		error: (message) => (error = ErrorMessage.from(message)),
+		hasError: () => error !== null,
 		close: () => (open = false),
 		open: () => (open = true),
 		isOpen: () => open,
@@ -177,7 +226,8 @@
 		unfreeze: () => (frozen = false),
 		isFrozen: () => frozen,
 		canContinue: () => !loading && !disabled && !frozen,
-		title: (newTitle) => (title = newTitle)
+		title: (newTitle) => (title = newTitle),
+		focus: () => dialogPage?.focus()
 	};
 
 	/** Returns the current state of the dialog */
@@ -199,11 +249,14 @@
 
 {#snippet dialog()}
 	<div
+		bind:this={dialogPage}
 		class={[
-			'fixed inset-0 z-50 flex items-center-safe justify-center bg-black/50 backdrop-blur-sm',
+			'fixed inset-0 flex items-center-safe justify-center bg-black/50 backdrop-blur-sm',
 			'overflow-auto p-8',
 			classValue
 		]}
+		style={// increase z-index and decrease opacity for each nested dialog
+		`z-index: ${1000 + stackIndex}`}
 		transition:fade={{ duration: 150 }}
 		onclick={(e) => {
 			const target = e.target as HTMLElement;
@@ -212,10 +265,15 @@
 		}}
 		onkeydown={(e) => {
 			if (e.key === 'Escape' && !frozen) {
+				if (stackIndex === dialogStack.length - 1) {
+					// only close if this dialog is the topmost dialog
 					open = false;
 				}
+			}
 		}}
 		role="dialog"
+		aria-labelledby="{identifier}-title"
+		aria-describedby="{identifier}-description"
 		tabindex="-1"
 	>
 		<div
@@ -235,7 +293,10 @@
 		>
 			<div class="flex items-center justify-between">
 				<!-- Dialog title -->
-				<h2 class="pointer-events-none mb-2 text-lg font-medium text-black select-none">
+				<h2
+					class="pointer-events-none mb-2 text-lg font-medium text-black select-none"
+					id="{identifier}-title"
+				>
 					{@render stringOrSnippet(title)}
 				</h2>
 
@@ -254,7 +315,7 @@
 			{/if}
 
 			{#if description}
-				<p class="mb-3 leading-normal text-zinc-600">
+				<p class="mb-3 leading-normal text-zinc-600" id="{identifier}-description">
 					{@render stringOrSnippet(description)}
 				</p>
 			{/if}

src/routes/+page.svelte

@@ -35,8 +35,7 @@
 	import { createLazyComponent, type ComboboxOption, type Option } from '$lib';
 	import Tabs from '$lib/Tabs.svelte';
 	import { Time } from '@internationalized/date';
-	import { onMount, type Component } from 'svelte';
+	import { onMount } from 'svelte';
-	import ErrorBox from '$lib/ErrorBox.svelte';
 	import TextareaInput from '$lib/TextareaInput.svelte';
 	import DurationInput, { formatDuration } from '$lib/DurationInput.svelte';
 	import Banner from '$lib/Banner.svelte';
@@ -60,6 +59,7 @@
 	let dateInputValue = $state<CalendarDate | null>(null);
 	let checkboxValue = $state<CheckboxState>('indeterminate');
 	let dialogOpen = $state(false);
+	let nestedDialogOpen = $state(false);
 	let scrollableDialogOpen = $state(false);
 	let toggleOptions: Option[] = $state([
 		'item one',
@@ -218,7 +218,7 @@
 			label="Lazy combobox"
 			placeholder="Choose..."
 			options={lazyOptions}
-			lazy={'always'}
+			lazy="always"
 			onlazy={async () => {
 				await new Promise((resolve) => setTimeout(resolve, 2500));
 				lazyOptions = [
@@ -555,6 +555,13 @@
 	}}
 >
 	<p>This is a dialog content area.</p>
+
+	<Button onclick={() => (nestedDialogOpen = true)}>Open Nested Dialog</Button>
+</Dialog>
+
+<!-- Nested Dialog Demo -->
+<Dialog bind:open={nestedDialogOpen} title="Nested Dialog" size="sm">
+	<p>This is a nested dialog content area.</p>
 </Dialog>
 
 <!-- Scrollable Dialog Demo -->