fix: execute sole static script tag (#11095)

- take into account that template could consist of a single script tag, for which querySelectorAll('script') would yield false negatives
- add test to ensure that we don't execute script tags inside `@html` tags next to static script tags

fixes #11082

Author: dummdidumm

.changeset/cuddly-points-tickle.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: execute sole static script tag

packages/svelte/src/internal/client/dom/template.js

@@ -3,6 +3,7 @@ import { clone_node, empty } from './operations.js';
 import { create_fragment_from_html } from './reconciler.js';
 import { current_effect } from '../runtime.js';
 import { TEMPLATE_FRAGMENT, TEMPLATE_USE_IMPORT_NODE } from '../../../constants.js';
+import { effect } from '../reactivity/effects.js';
 
 /**
  * @param {string} content
@@ -120,14 +121,29 @@ export function svg_template_with_script(content, flags) {
  * @param {Element | DocumentFragment} node
  */
 function run_scripts(node) {
-	for (const script of node.querySelectorAll('script')) {
+	// scripts were SSR'd, in which case they will run
+	if (hydrating) return;
+
+	const scripts =
+		/** @type {HTMLElement} */ (node).tagName === 'SCRIPT'
+			? [/** @type {HTMLScriptElement} */ (node)]
+			: node.querySelectorAll('script');
+	for (const script of scripts) {
 		var clone = document.createElement('script');
 		for (var attribute of script.attributes) {
 			clone.setAttribute(attribute.name, attribute.value);
 		}
 
 		clone.textContent = script.textContent;
-		script.replaceWith(clone);
+		// If node === script tag, replaceWith will do nothing because there's no parent yet,
+		// waiting until that's the case using an effect solves this.
+		// Don't do it in other circumstances or we could accidentally execute scripts
+		// in an adjacent @html tag that was instantiated in the meantime.
+		if (script === node) {
+			effect(() => script.replaceWith(clone));
+		} else {
+			script.replaceWith(clone);
+		}
 	}
 }
 

packages/svelte/tests/runtime-browser/driver-ssr.js

@@ -6,5 +6,5 @@ import config from '__CONFIG__';
 import { render } from 'svelte/server';
 
 export default function () {
-	return render(SvelteComponent, { props: config.props || {} }).html;
+	return render(SvelteComponent, { props: config.props || {} });
 }

packages/svelte/tests/runtime-legacy/samples/head-script/_config.js renamed to packages/svelte/tests/runtime-browser/samples/head-script/_config.js

@@ -1,7 +1,7 @@
-import { test } from '../../test';
+import { test } from '../../assert';
 
 export default test({
-	test({ assert, component, window }) {
+	test({ assert, window }) {
 		document.dispatchEvent(new Event('DOMContentLoaded'));
 		assert.equal(window.document.querySelector('button')?.textContent, 'Hello world');
 	}

packages/svelte/tests/runtime-legacy/samples/head-script/main.svelte renamed to packages/svelte/tests/runtime-browser/samples/head-script/main.svelte

@@ -0,0 +1,17 @@
+import { test } from '../../assert';
+
+export default test({
+	// Test that @html does not execute scripts when instantiated in the client.
+	// Needs to be in this test suite because JSDOM does not quite get this right.
+	mode: ['client'],
+	test({ window, assert }) {
+		// In here to give effects etc time to execute
+		assert.htmlEqual(
+			window.document.body.innerHTML,
+			`<main>
+				<div><script></script></div><script>document.body.innerHTML = 'this should not be executed'</script>
+				<script></script><script>document.body.innerHTML = 'this neither'</script>
+			</main>`
+		);
+	}
+});

packages/svelte/tests/runtime-browser/samples/html-tag-script-2/_config.js

@@ -0,0 +1,7 @@
+<div>
+    <script></script>
+</div>
+{@html `<script>document.body.innerHTML = 'this should not be executed'</script>`}
+{#if true}
+    <script></script>{@html `<script>document.body.innerHTML = 'this neither'</script>`}
+{/if}

packages/svelte/tests/runtime-browser/samples/html-tag-script-2/main.svelte

@@ -3,6 +3,12 @@ import { test } from '../../assert';
 export default test({
 	// Test that @html does not execute scripts when instantiated in the client.
 	// Needs to be in this test suite because JSDOM does not quite get this right.
-	html: `<div></div><script>document.body.innerHTML = 'this should not be executed'</script>`,
-	mode: ['client']
+	mode: ['client'],
+	test({ window, assert }) {
+		// In here to give effects etc time to execute
+		assert.htmlEqual(
+			window.document.body.innerHTML,
+			`<main><div></div><script>document.body.innerHTML = 'this should not be executed'</script></main>`
+		);
+	}
 });

packages/svelte/tests/runtime-browser/samples/html-tag-script/_config.js

@@ -0,0 +1,11 @@
+import { test } from '../../assert';
+
+export default test({
+	// Test that template with sole script tag does execute when instantiated in the client.
+	// Needs to be in this test suite because JSDOM does not quite get this right.
+	mode: ['client'],
+	test({ window, assert }) {
+		// In here to give effects etc time to execute
+		assert.htmlEqual(window.document.body.innerHTML, 'this should be executed');
+	}
+});

packages/svelte/tests/runtime-browser/samples/sole-script-tag/_config.js

@@ -0,0 +1,4 @@
+<div></div>
+{#if true}
+    <script>document.body.innerHTML = 'this should be executed'</script>
+{/if}