html tags

packages/svelte/src/compiler/phases/1-parse/state/tag.js

@@ -613,7 +613,10 @@ function special(parser) {
 			type: 'HtmlTag',
 			start,
 			end: parser.index,
-			expression
+			expression,
+			metadata: {
+				expression: create_expression_metadata()
+			}
 		});
 
 		return;

packages/svelte/src/compiler/phases/2-analyze/visitors/HtmlTag.js

@@ -15,5 +15,8 @@ export function HtmlTag(node, context) {
 	// unfortunately this is necessary in order to fix invalid HTML
 	mark_subtree_dynamic(context.path);
 
-	context.next();
+	context.next({
+		...context.state,
+		expression: node.metadata.expression
+	});
 }

packages/svelte/src/compiler/phases/3-transform/client/visitors/HtmlTag.js

@@ -11,17 +11,38 @@ import * as b from '../../../../utils/builders.js';
 export function HtmlTag(node, context) {
 	context.state.template.push('<!>');
 
+	const { is_async } = node.metadata.expression;
+
+	const expression = /** @type {Expression} */ (context.visit(node.expression));
+	const html = is_async ? b.call('$.get', b.id('$$html')) : expression;
+
+	const is_svg = context.state.metadata.namespace === 'svg';
+	const is_mathml = context.state.metadata.namespace === 'mathml';
+
+	const statement = b.stmt(
+		b.call(
+			'$.html',
+			context.state.node,
+			b.thunk(html),
+			is_svg && b.true,
+			is_mathml && b.true,
+			is_ignored(node, 'hydration_html_changed') && b.true
+		)
+	);
+
 	// push into init, so that bindings run afterwards, which might trigger another run and override hydration
+	if (node.metadata.expression.is_async) {
 		context.state.init.push(
 			b.stmt(
 				b.call(
-				'$.html',
+					'$.async',
 					context.state.node,
-				b.thunk(/** @type {Expression} */ (context.visit(node.expression))),
-				b.literal(context.state.metadata.namespace === 'svg'),
-				b.literal(context.state.metadata.namespace === 'mathml'),
-				is_ignored(node, 'hydration_html_changed') && b.true
+					b.array([b.thunk(expression, true)]),
+					b.arrow([context.state.node, b.id('$$html')], b.block([statement]))
 				)
 			)
 		);
+	} else {
+		context.state.init.push(statement);
+	}
 }

packages/svelte/src/compiler/types/template.d.ts

@@ -135,6 +135,10 @@ export namespace AST {
 	export interface HtmlTag extends BaseNode {
 		type: 'HtmlTag';
 		expression: Expression;
+		/** @internal */
+		metadata: {
+			expression: ExpressionMetadata;
+		};
 	}
 
 	/** An HTML comment */

packages/svelte/src/internal/client/dom/blocks/html.js

@@ -39,7 +39,7 @@ function check_hash(element, server_hash, value) {
  * @param {boolean} [skip_warning]
  * @returns {void}
  */
-export function html(node, get_value, svg, mathml, skip_warning) {
+export function html(node, get_value, svg = false, mathml = false, skip_warning = false) {
 	var anchor = node;
 
 	var value = '';

packages/svelte/tests/runtime-runes/samples/async-html-tag/_config.js

@@ -0,0 +1,35 @@
+import { flushSync, tick } from 'svelte';
+import { deferred } from '../../../../src/internal/shared/utils.js';
+import { test } from '../../test';
+
+/** @type {ReturnType<typeof deferred>} */
+let d;
+
+export default test({
+	html: `<p>pending</p>`,
+
+	get props() {
+		d = deferred();
+
+		return {
+			promise: d.promise
+		};
+	},
+
+	async test({ assert, target, component }) {
+		d.resolve('hello');
+		await Promise.resolve();
+		await Promise.resolve();
+		await tick();
+		flushSync();
+		assert.htmlEqual(target.innerHTML, '<h1>hello</h1>');
+
+		component.promise = (d = deferred()).promise;
+		await tick();
+		assert.htmlEqual(target.innerHTML, '<p>pending</p>');
+
+		d.resolve('wheee');
+		await tick();
+		assert.htmlEqual(target.innerHTML, '<h1>wheee</h1>');
+	}
+});

packages/svelte/tests/runtime-runes/samples/async-html-tag/main.svelte

@@ -0,0 +1,11 @@
+<script>
+	let { promise } = $props();
+</script>
+
+<svelte:boundary>
+	<h1>{@html await promise}</h1>
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>

packages/svelte/tests/snapshot/samples/skip-static-subtree/_expected/client/index.svelte.js

@@ -13,7 +13,7 @@ export default function Skip_static_subtree($$anchor, $$props) {
 
 	var node = $.sibling(h1, 10);
 
-	$.html(node, () => $$props.content, false, false);
+	$.html(node, () => $$props.content);
 	$.next(14);
 	$.reset(main);